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A2 Biology Module 1 - Physiology, Coordination and Control, and Ecosystems > Chapter 5 - The Eye and Muscle > Flashcards

Chapter 5 - The Eye and Muscle Flashcards

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1
Q
  • The mammalian eye

The mammalian eye is …

A

A complex sense organ.

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2
Q
  • The mammalian eye

The mammalian eye is a complex sense organ. Only a very small section of the eye contains …

A

The photoreceptors that are sensitive to light.

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3
Q
  • The mammalian eye

The mammalian eye is a complex sense organ. Only a very small section of the eye contains the photoreceptors that are sensitive to light. The rest of the eye contains …

A

Structures that ensure that the receptors in the retina at the back of the eye receive focused light rays at the correct intensity to form an image.

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4
Q

Draw a diagram showing the structure of the mammalian eye in cross-section

A

Textbook page 69

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5
Q

What is the conjunctiva?

A

Thin transparent membrane covering the cornea

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6
Q

What is the function of the conjunctiva?

A

Protects the cornea from damage

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7
Q

What is the sclera?

A

Tough opaque connective tissue covering the eye - replaced by transparent cornea at front

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8
Q

What is the function of the sclera?

A

Protects against damage; site of attachment of eye muscles

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9
Q

What is the cornea?

A

Front transparent part of sclera

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10
Q

What is the function of the cornea?

A

Transparent and most refraction (bending) of light occurs here

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11
Q

What is the aqueous humour?

A

Transparent watery fluid between cornea and lens

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12
Q

What is the function of the aqueous humour?

A

Maintains the shape of the front part of the eye

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13
Q

What is the iris?

A

Muscular layer with both circular and radial muscle; contains pigment that absorbs light

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14
Q

What is the function of the iris?

A

Adjusts the size of the pupil to control the amount of light entering the eye

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15
Q

What is the pupil?

A

Gap within the iris

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16
Q

What is the function of the pupil?

A

The area through which light reaches the lens and enters the centre of the eye

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17
Q

What is the ciliary body?

A

Contains a muscular ring of (ciliary) muscle around the eye; suspenseful ligaments extend from the ciliary body and hold the lens in place

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18
Q

What is the function of the ciliary body?

A

Adjusts the shape of the lens to focus light rays

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19
Q

What are the suspensory ligaments?

A

Ligaments that connect the ciliary body to the lens

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20
Q

What is the function of the suspensory ligaments?

A

Transfers tension in the wall of the eyeball to make the lens thinner; important when focusing on distant objects

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21
Q

What is the lens?

A

Transparent biconcave structure with refractive properties

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22
Q

What is the function of the lens?

A

Refracts light and focuses light rays on the retina

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23
Q

What is the vitreous humour?

A

Transparent, jelly-like material between the lens and the back of the eye

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24
Q

What is the function of the vitreous humour?

A

Maintains the shape of the rear part of the eye and supports the lens

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25
Q

What is the retina?

A

Inner layer of the eyeball containing the light sensitive receptor cells (rods and cones)

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26
Q

What is the function of the retina?

A

When stimulated the rods and cones initiate impulses in associated neurones

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27
Q

What is the fovea?

A

Region in the centre of the retina that is particularly rich in cones and does not contain rods

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28
Q

What is the function of the fovea?

A

Part of eye that gives the clearest daylight colour vision

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29
Q

What is the choroid?

A

A layer of pigmented cells between the retina and the sclera

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30
Q

What is the function of the choroid?

A

Contains blood vessels that supply the retina; prevents reflection of light back through the eye

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31
Q

What is the optic nerve?

A

Bundle of sensory nerve fibres that leave the retina

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32
Q

What is the function of the optic nerve?

A

Transmits impulses from the retina to the brain

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33
Q

What is the blind spot?

A

Part of the retina where the sensory neurones that unite to form the optic nerve leave the eye

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34
Q

What is the function of the blind spot?

A

Contains no light sensitive cells so is not sensitive to light

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35
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some …

A

Bending (refraction) of light automatically takes place.

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36
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place …

A

In the cornea

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37
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes …

A

Through the lens

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38
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be …

A

Focused on the retina

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39
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of …

A

Their angle as they enter the eye

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40
Q

Draw a diagram showing how the eye focuses on distant objects

A

Textbook page 71, first diagram

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41
Q

Draw a diagram showing how the eye focuses on near objects

A

Textbook page 71, second diagram

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42
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye.

The ciliary body contains …

A

A ring of muscle (ciliary muscle)

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43
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye.

The ciliary body contains a ring of muscle (ciliary muscle) running …

A

Around the inside of the eyeball and surrounding the lens

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44
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye.

The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to …

A

The ciliary body

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45
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye.

The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by …

A

Suspensory ligaments

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46
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye.

The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble …

A

Small pieces of nylon thread

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47
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye.

The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, …

A

Tension in the wall of the eyeball is transferred through the suspensory ligaments to the lens

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48
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye.

The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, …

A

The ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut).

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49
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye.

The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, …

A

The suspensory ligaments pull the lens into a thinner shape that has less refractive power.

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50
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye.

The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power.

The opposite happens to make the lens …

A

Fatter when a greater degree of refraction is required.

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51
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye.

The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power.

The opposite happens to make the lens fatter when a greater degree of refraction is required. The ciliary muscle …

A

Contracts

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52
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye.

The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power.

The opposite happens to make the lens fatter when a greater degree of refraction is required. The ciliary muscle contracts to form …

A

A tighter circle

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53
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye.

The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power.

The opposite happens to make the lens fatter when a greater degree of refraction is required. The ciliary muscle contracts to form a tighter circle with a …

A

Smaller diameter

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54
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye.

The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power.

The opposite happens to make the lens fatter when a greater degree of refraction is required. The ciliary muscle contracts to form a tighter circle with a smaller diameter. The suspensory ligaments are …

A

Not pulled taught so relax

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55
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye.

The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power.

The opposite happens to make the lens fatter when a greater degree of refraction is required. The ciliary muscle contracts to form a tighter circle with a smaller diameter. The suspensory ligaments are not pulled taught so relax and with less pressure on …

A

The lens

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56
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye.

The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power.

The opposite happens to make the lens fatter when a greater degree of refraction is required. The ciliary muscle contracts to form a tighter circle with a smaller diameter. The suspensory ligaments are not pulled taught so relax and with less pressure on the lens it is able to …

A

Spring back to its ‘normal’ thicker shape.

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57
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye.

The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power.

The opposite happens to make the lens fatter when a greater degree of refraction is required. The ciliary muscle contracts to form a tighter circle with a smaller diameter. The suspensory ligaments are not pulled taught so relax and with less pressure on the lens it is able to spring back to its ‘normal’ thicker shape.

The adjustment of lens thickness to ensure that …

A

The light rays are focused on the retina

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58
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye.

The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power.

The opposite happens to make the lens fatter when a greater degree of refraction is required. The ciliary muscle contracts to form a tighter circle with a smaller diameter. The suspensory ligaments are not pulled taught so relax and with less pressure on the lens it is able to spring back to its ‘normal’ thicker shape.

The adjustment of lens thickness to ensure that the light rays are focused on the retina, irrespective of …

A

The angle of light rays reaching the eye

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59
Q
  • Function of the eye

Obtaining a focused image - As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Further bending takes place as the light passes through the lens. By adjusting the thickness of the lens, lights rays can be focused on the retina, irrespective of their angle as they enter the eye.

The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens. The lens is attached to the ciliary body by suspensory ligaments that resemble small pieces of nylon thread. If the ciliary body relaxes, tension in the wall of the eyeball is transferred through the suspensory to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taut). When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power.

The opposite happens to make the lens fatter when a greater degree of refraction is required. The ciliary muscle contracts to form a tighter circle with a smaller diameter. The suspensory ligaments are not pulled taught so relax and with less pressure on the lens it is able to spring back to its ‘normal’ thicker shape.

The adjustment of lens thickness to ensure that the light rays are focused on the retina, irrespective of the angle of light rays reaching the eye, is called …

A

Accommodation

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60
Q

What happens as light rays enter and pass through the cornea?

A

Some bending (refraction) of light automatically takes place.

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61
Q

Where in the eye does most refraction of light take place?

A

In the cornea

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62
Q

As light rays enter and pass through the cornea, some bending (refraction) of light automatically takes place. In reality, most of the refraction takes place in the cornea. Where in the eye does further refraction take place?

A

As light passes through the lens

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63
Q

In simple terms, how can light be focused on the retina?

A

By adjusting the thickness of the lens, light rays can be focused on the retina, irrespective of their angle as they enter the eye.

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64
Q

Comment on the angle of light rays as they enter the eye from a distant object

A

Light rays arrive parallel

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65
Q

Comment on the angle of light rays as they enter the eye from a near object

A

Light rays diverge from a close-up object

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66
Q

Why is the lens thin when focusing light rays from a distant object?

A

Lens is thin as little additional refraction is necessary to focus light on the retina

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67
Q

Why is the lens thick when focusing light rays from a near object?

A

Lens is thicker as further refraction is necessary to focus light on the retina

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68
Q

What does the ciliary body contain?

A

The ciliary body contains a ring of muscle (ciliary muscle) running around the inside of the eyeball and surrounding the lens.

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69
Q

How is the lens attached to the ciliary body?

A

The lens is attached to the ciliary body by suspensory ligaments.

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70
Q

What do suspensory ligaments resemble?

A

Small pieces of nylon thread

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71
Q

What happens if the ciliary body relaxes?

A
  • If the ciliary body relaxes, the tension in the wall of the eyeball is transferred through the suspensory ligaments to the lens (in effect, the ciliary body springs out to form a bigger diameter pulling the suspensory ligaments taught).
  • When this happens, the suspensory ligaments pull the lens into a thinner shape that has less refractive power.
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72
Q

What happens if the ciliary body contracts?

A
  • The ciliary muscle contracts to form a tighter circle with a smaller diameter.
  • The suspensory ligaments are not pulled taught so relax and with less pressure on the lens it is able to spring back to its ‘normal’ thicker shape.
  • This makes the lens fatter when a greater degree of refraction is required.
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73
Q

What is accommodation?

A

The adjustment of lens thickness to ensure that the light rays are focused on the retina, irrespective of the angle of light rays reaching the eye.

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74
Q

Comment on the state of the ciliary muscles, suspensory ligaments and the lens when the eye is:

a) Focusing on a distant object
b) Focusing on a near object

A

a) Ciliary muscles relaxed
Suspensory ligaments stretched
Lens pulled thin

b) Ciliary muscles contracted
Suspensory ligaments slack
Thick lens

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75
Q

Draw a diagram showing the state of the lens, ciliary muscles and suspensory ligaments within the mammalian eye as it is focusing on a distant object.
Furthermore, draw a diagram showing only the lens, ciliary muscles and suspensory ligaments in cross-section during this accommodation.

A

Textbook page 72, first diagram

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76
Q

Draw a diagram showing the state of the lens, ciliary muscles and suspensory ligaments within the mammalian eye as it is focusing on a near object.
Furthermore, draw a diagram showing only the lens, ciliary muscles and suspensory ligaments in cross-section during this accommodation.

A

Textbook page 72, second diagram

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77
Q

Describe the structural composition of ligaments and how it relates to their role in the mammalian eye

A
  • Ligaments are tough and flexible but they do not stretch.
  • Not being stretchable is important as this ensures that the suspensory ligaments pull the lens thin when the ciliary muscle contracts.
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78
Q

Controlling the amount of light that enters the eye - It is important that …

A

The correct intensity of light enters the eye

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79
Q

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches …

A

The retina

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80
Q

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will …

A

Prevent an image being formed

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81
Q

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light …

A

Can damage the sensitive light receptor cells in the retina

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82
Q

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows …

A

As much light as possible to enter the eye

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83
Q

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure …

A

That there is sufficient light to stimulate the photoreceptors in the retina

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84
Q

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure that there is sufficient light to stimulate the photoreceptors in the retina. In bright light the pupil is …

A

Reduced to a small size

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85
Q

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure that there is sufficient light to stimulate the photoreceptors in the retina. In bright light the pupil is reduced to a small size to …

A

Restrict the amount of light entering

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86
Q

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure that there is sufficient light to stimulate the photoreceptors in the retina. In bright light the pupil is reduced to a small size to restrict the amount of light entering. The size of the pupil is a direct consequence of …

A

The size of the iris

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87
Q

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure that there is sufficient light to stimulate the photoreceptors in the retina. In bright light the pupil is reduced to a small size to restrict the amount of light entering. The size of the pupil is a direct consequence of the size of the iris.

The muscles of the iris can …

A

Contract or relax

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88
Q

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure that there is sufficient light to stimulate the photoreceptors in the retina. In bright light the pupil is reduced to a small size to restrict the amount of light entering. The size of the pupil is a direct consequence of the size of the iris.

The muscles of the iris can contract or relax to …

A

Change the size of the pupil

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89
Q

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure that there is sufficient light to stimulate the photoreceptors in the retina. In bright light the pupil is reduced to a small size to restrict the amount of light entering. The size of the pupil is a direct consequence of the size of the iris.

The muscles of the iris can contract or relax to change the size of the pupil. The iris consists of ____ types of muscle.

A

Two

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90
Q

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure that there is sufficient light to stimulate the photoreceptors in the retina. In bright light the pupil is reduced to a small size to restrict the amount of light entering. The size of the pupil is a direct consequence of the size of the iris.

The muscles of the iris can contract or relax to change the size of the pupil. The iris consists of two types of muscle - …

A

Radial and circular

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91
Q

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure that there is sufficient light to stimulate the photoreceptors in the retina. In bright light the pupil is reduced to a small size to restrict the amount of light entering. The size of the pupil is a direct consequence of the size of the iris.

The muscles of the iris can contract or relax to change the size of the pupil. The iris consists of two types of muscle - radial and circular. Radial muscles are like …

A

The spokes of a wheel moving out from the edge of the pupil through the iris

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92
Q

Controlling the amount of light that enters the eye - It is important that the correct intensity of light enters the eye and reaches the retina. Too little or too much light will prevent an image being formed. In addition, too much light can damage the sensitive light receptor cells in the retina. In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure that there is sufficient light to stimulate the photoreceptors in the retina. In bright light the pupil is reduced to a small size to restrict the amount of light entering. The size of the pupil is a direct consequence of the size of the iris.

The muscles of the iris can contract or relax to change the size of the pupil. The iris consists of two types of muscle - radial and circular. Radial muscles are like the spokes of a wheel moving out from the edge of the pupil through the iris, and circular muscles form …

A

Rings within the iris around the pupil

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93
Q

In low light intensities the radial muscles …

A

Contract

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94
Q

In low light intensities the radial muscles contract (and the circular muscles …

A

Relax

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95
Q

In low light intensities the radial muscles contract (and the circular muscles relax) - this makes the pupil …

A

Larger (dilated)

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96
Q

In bright light the circular muscles …

A

Contract

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97
Q

In bright light the circular muscles contract (and the radial muscles …

A

Relax

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98
Q

In bright light the circular muscles contract (and the radial muscles relax) - this makes the pupil …

A

Smaller (constricted)

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99
Q

Draw a cross-section of the iris and pupil in dim light. Your diagram should include the state of the radial and circular muscles in the iris.

A

Textbook page 72. Diagram on the bottom left.

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100
Q

Draw a cross-section of the iris and pupil in bright light. Your diagram should include the state of the radial and circular muscles in the iris.

A

Textbook page 72. Diagram on the bottom right.

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101
Q

Accommodation and the control of the amount of light entering the eye are both examples of …

A

Reflex action

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102
Q

Accommodation and the control of the amount of light entering the eye are both examples of reflex action. They are …

A

Automatic responses, not under voluntary control

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103
Q

Give two examples of reflex actions

A

Accommodation

The control of the amount of light entering the eye

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104
Q

What is a reflex action?

A

An automatic response, not under voluntary control.

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105
Q

Why is it important that the correct intensity of light enters the eye and reaches the retina?

A
  • Too little or too much light will prevent an image being formed.
  • In addition, too much light can damage the sensitive light receptor cells in the retina.
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106
Q

Why is the pupil dilated in low light intensities?

A

In low light intensities a large pupil diameter allows as much light as possible to enter the eye to ensure that there is sufficient light to stimulate the photoreceptors in the retina.

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107
Q

Why is the pupil constricted in bright light?

A

In bright light the pupil is reduced to a small size to restrict the amount of light entering.

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108
Q

The size of the pupil is a direct consequence of what?

A

The size of the iris

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109
Q

How many types of muscle does the iris consist of?

A

Two

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110
Q

How do the muscles of the iris change the size of the pupil?

A

The muscles of the iris can contract or relax to change the size of the pupil.

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111
Q

What two types of muscle does the iris consist of?

A

Radial and circular

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112
Q

How is the size of the pupil adjusted when the eye is exposed to a low light intensity?

A

In low light intensities the radial muscles contract (and the circular muscles relax) - this makes the pupil larger.

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113
Q

How is the size of the pupil adjusted when the eye is exposed to bright light?

A

In bright light the circular muscles contract (and the radial muscles relax) - this makes the pupil smaller.

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114
Q
  • The retina in detail

The retina contains …

A

Millions of light sensitive cells and the neurones with which they synapse.

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115
Q
  • The retina in detail

The retina contains millions of light sensitive cells and the neurones with which they synapse. Rod and cone cells are …

A

Specialised photoreceptors (photosensitive cells)

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116
Q
  • The retina in detail

The retina contains millions of light sensitive cells and the neurones with which they synapse. Rod and cone cells are specialised photoreceptors (photosensitive cells) in that …

A

Light energy brings about change in the level of polarisation of their membranes

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117
Q
  • The retina in detail

The retina contains millions of light sensitive cells and the neurones with which they synapse. Rod and cone cells are specialised photoreceptors (photosensitive cells) in that light energy brings about change in the level of polarisation of their membranes - they act as …

A

Transducers converting a light stimulus to a nerve impulse in their associated neurones.

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118
Q
  • The retina in detail

Rod cells - In rods the light sensitive pigment …

A

Rhodopsin

119
Q
  • The retina in detail

Rod cells - In rods the light sensitive pigment rhodopsin is …

A

Packed into an array of membranes in the outer part of the rod cell.

120
Q
  • The retina in detail

Rod cells - In rods the light sensitive pigment rhodopsin is packed into an array of membranes in the outer part of the rod cell. Rhodopsin is formed from …

A

A protein opsin, combined with a light absorbing compound called retinal which is derived from vitamin A.

121
Q
  • The retina in detail

Rod cells - In rods the light sensitive pigment rhodopsin is packed into an array of membranes in the outer part of the rod cell. Rhodopsin is formed from a protein opsin, combined with a light absorbing compound called retinal which is derived from vitamin A. When stimulated by light, the rhodopsin …

A

Breaks down into its retinal and opsin components

122
Q
  • The retina in detail

Rod cells - In rods the light sensitive pigment rhodopsin is packed into an array of membranes in the outer part of the rod cell. Rhodopsin is formed from a protein opsin, combined with a light absorbing compound called retinal which is derived from vitamin A. When stimulated by light, the rhodopsin breaks down into its retinal and opsin components. This …

A

Changes the membrane potential of the rod cell

123
Q
  • The retina in detail

Rod cells - In rods the light sensitive pigment rhodopsin is packed into an array of membranes in the outer part of the rod cell. Rhodopsin is formed from a protein opsin, combined with a light absorbing compound called retinal which is derived from vitamin A. When stimulated by light, the rhodopsin breaks down into its retinal and opsin components. This changes the membrane potential of the rod cell and creates …

A

A generator potential

124
Q
  • The retina in detail

Rod cells - In rods the light sensitive pigment rhodopsin is packed into an array of membranes in the outer part of the rod cell. Rhodopsin is formed from a protein opsin, combined with a light absorbing compound called retinal which is derived from vitamin A. When stimulated by light, the rhodopsin breaks down into its retinal and opsin components. This changes the membrane potential of the rod cell and creates a generator potential. If …

A

A threshold level is achieved

125
Q
  • The retina in detail

Rod cells - In rods the light sensitive pigment rhodopsin is packed into an array of membranes in the outer part of the rod cell. Rhodopsin is formed from a protein opsin, combined with a light absorbing compound called retinal which is derived from vitamin A. When stimulated by light, the rhodopsin breaks down into its retinal and opsin components. This changes the membrane potential of the rod cell and creates a generator potential. If a threshold level is achieved, this can …

A

Cause the adjacent linking neurone (bipolar neurone) to become depolarised to the extent that it will conduct an action potential.

126
Q

What is a generator potential?

A
  • A generator potential is the degree of depolarisation a stimulated receptor can produce.
  • Only if the generator potential reaches a threshold level will it produce an action potential in the neurone.
127
Q
  • The retina in detail

The inner segment of the rod contains …

A

The cell’s nucleus and mitochondria

128
Q
  • The retina in detail

The inner segment of the rod contains the cell’s nucleus and mitochondria, the latter important in …

A

Producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation.

129
Q
  • The retina in detail

The inner segment of the rod contains the cell’s nucleus and mitochondria, the latter important in producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation.

Rods are adapted for …

A

Vision in low light intensities

130
Q
  • The retina in detail

The inner segment of the rod contains the cell’s nucleus and mitochondria, the latter important in producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation.

Rods are adapted for vision in low light intensities. They have …

A

High sensitivity

131
Q
  • The retina in detail

The inner segment of the rod contains the cell’s nucleus and mitochondria, the latter important in producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation.

Rods are adapted for vision in low light intensities. They have high sensitivity as …

A

The rhodopsin will break down readily in low light levels

132
Q
  • The retina in detail

The inner segment of the rod contains the cell’s nucleus and mitochondria, the latter important in producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation.

Rods are adapted for vision in low light intensities. They have high sensitivity as the rhodopsin will break down readily in low light levels requiring …

A

Only a small amount of light energy

133
Q
  • The retina in detail

The inner segment of the rod contains the cell’s nucleus and mitochondria, the latter important in producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation.

Rods are adapted for vision in low light intensities. They have high sensitivity as the rhodopsin will break down readily in low light levels requiring only a small amount of light energy. However, this can lead to …

A

The phenomenon of dark adaptation

134
Q
  • The retina in detail

The inner segment of the rod contains the cell’s nucleus and mitochondria, the latter important in producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation.

Rods are adapted for vision in low light intensities. They have high sensitivity as the rhodopsin will break down readily in low light levels requiring only a small amount of light energy. However, this can lead to the phenomenon of dark adaptation. In bright light …

A

Virtually all the rhodopsin is broken down (bleached)

135
Q
  • The retina in detail

The inner segment of the rod contains the cell’s nucleus and mitochondria, the latter important in producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation.

Rods are adapted for vision in low light intensities. They have high sensitivity as the rhodopsin will break down readily in low light levels requiring only a small amount of light energy. However, this can lead to the phenomenon of dark adaptation. In bright light virtually all the rhodopsin is broken down (bleached) and it …

A

Takes time for it to be re-synthesised

136
Q
  • The retina in detail

The inner segment of the rod contains the cell’s nucleus and mitochondria, the latter important in producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation.

Rods are adapted for vision in low light intensities. They have high sensitivity as the rhodopsin will break down readily in low light levels requiring only a small amount of light energy. However, this can lead to the phenomenon of dark adaptation. In bright light virtually all the rhodopsin is broken down (bleached) and it takes time for it to be re-synthesised. This explains why …

A

If we move from a well lit area into a dark room, our vision in the low light environment is very poor initially but gradually improves.

137
Q
  • The retina in detail

The inner segment of the rod contains the cell’s nucleus and mitochondria, the latter important in producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation.

Rods are adapted for vision in low light intensities. They have high sensitivity as the rhodopsin will break down readily in low light levels requiring only a small amount of light energy. However, this can lead to the phenomenon of dark adaptation. In bright light virtually all the rhodopsin is broken down (bleached) and it takes time for it to be re-synthesised. This explains why if we move from a well lit area into a dark room, our vision in the low light environment is very poor initially but gradually improves. In effect, …

A

Our eyes have changed from being light-adapted (when in bright light) to being dark-adapted

138
Q
  • The retina in detail

The inner segment of the rod contains the cell’s nucleus and mitochondria, the latter important in producing the ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation.

Rods are adapted for vision in low light intensities. They have high sensitivity as the rhodopsin will break down readily in low light levels requiring only a small amount of light energy. However, this can lead to the phenomenon of dark adaptation. In bright light virtually all the rhodopsin is broken down (bleached) and it takes time for it to be re-synthesised. This explains why if we move from a well lit area into a dark room, our vision in the low light environment is very poor initially but gradually improves. In effect, our eyes have changed from being light-adapted (when in bright light) to being dark-adapted, ie …

A

Adapted for functioning in low light intensities.

139
Q

Give a definition of transduction

A

Transduction is the process of changing energy from one form to another.

140
Q

What does the retina contain?

A

The retina contains millions of light sensitive cells and the neurones with which they synapse.

141
Q

What are rods and cones?

A

Rods and cones are specialised photoreceptors (photosensitive cells)

142
Q

What makes rods and cones specialised photoreceptors (photosensitive cells)?

A

Light energy brings about change in the level of polarisation of their membranes - they act as transducers converting a stimulus to a nerve impulse in their associated neurones.

143
Q

Name the light sensitive pigment found in rods

A

Rhodopsin

144
Q

Describe the arrangement of rhodopsin in rods

A

In rods the light sensitive pigment rhodopsin is packed into an array of membranes in the outer part of the rod cell.

145
Q

What is rhodopsin made up of?

A

Rhodopsin is formed from a protein opsin, combined with a light absorbing compound called retinal which is derived from vitamin A.

146
Q

What happens to rhodopsin when it is stimulated by light?

A

The rhodopsin breaks down into its retinal and opsin components.

147
Q

When will rhodopsin break down?

A

When stimulated by light, the rhodopsin breaks down into its retinal and opsin components.

148
Q

What happens to the rod cell when a light stimulus breaks down rhodopsin into its retinal and opsin components?

A
  • This changes the membrane potential of the rod cell and creates a generator potential.
  • If a threshold level is achieved, this can cause the adjacent linking neurone (bipolar neurone) to become depolarised to the extent that it will conduct an action potential.
149
Q

What does the inner segment of the rod cell contain?

A

The cell nucleus and numerous mitochondria

150
Q

What is the role of the mitochondria found in the inner segment of rod cells?

A

Produce ATP needed for the re-synthesis of rhodopsin from retinal and opsin following light stimulation.

151
Q

What are rod cells adapted for?

A

Vision in low light intensities

152
Q

Why do rods have high sensitivity?

A

As the rhodopsin will break down readily in low light levels requiring only a small amount of light energy.

153
Q

Describe how the phenomenon of dark adaptation arises

A
  • Rods are adapted for vision in low light intensities.
  • They have high sensitivity as the rhodopsin will break down readily in low lights levels requiring only a small amount of light energy.
  • In bright light virtually all the rhodopsin is broken down (bleached) and it takes time for it to be re-synthesised.
  • This explains why if we move from a well lit area into a dark room, our vision in the low light environment is very poor initially but gradually improves.
  • In effect, our eyes have changed from being light-adapted (when in bright light) to being dark-adapted, ie adapted for functioning in low light intensities.
154
Q

Name the pigment found in cone cells

A

Iodopsin

155
Q

Where in the cone cell is iodopsin situated?

A

In the membranes of the outer segment

156
Q

How does iodopsin compare with rhodopsin?

A

Iodopsin is less readily broken down and will only produce a generator potential in bright light.

157
Q
  • Cone cells

The same general principles apply …

A

To the functioning of cone cells

158
Q
  • Cone cells

The same general principles apply to the functioning of cone cells. However, in cones …

A

A different pigment, iodopsin, is situated in the membranes of the outer segment.

159
Q
  • Cone cells

The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is …

A

Less readily broken down and will only produce a generator potential in bright light.

160
Q
  • Cone cells

The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light.

While rods are …

A

Not sensitive to colour and provide monochromatic vision

161
Q
  • Cone cells

The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light.

While rods are not sensitive to colour and provide monochromatic vision, cones provide …

A

Colour vision

162
Q
  • Cone cells

The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light.

While rods are not sensitive to colour and provide monochromatic vision, cones provide colour vision.

Iodopsin exists in …

A

Three different forms

163
Q
  • Cone cells

The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light.

While rods are not sensitive to colour and provide monochromatic vision, cones provide colour vision.

Iodopsin exists in three different forms with each form being …

A

Sensitive to different wavelengths of light

164
Q
  • Cone cells

The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light.

While rods are not sensitive to colour and provide monochromatic vision, cones provide colour vision.

Iodopsin exists in three different forms with each form being sensitive to different wavelengths of light. The absorption peaks of …

A

The three different types of cone

165
Q
  • Cone cells

The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light.

While rods are not sensitive to colour and provide monochromatic vision, cones provide colour vision.

Iodopsin exists in three different forms with each form being sensitive to different wavelengths of light. The absorption peaks of the three different types of cone (each with …

A

A different type of iodopsin)

166
Q
  • Cone cells

The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light.

While rods are not sensitive to colour and provide monochromatic vision, cones provide colour vision.

Iodopsin exists in three different forms with each form being sensitive to different wavelengths of light. The absorption peaks of the three different types of cone (each with a different type of iodopsin) correspond to …

A

The colours blue, green and red

167
Q
  • Cone cells

The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light.

While rods are not sensitive to colour and provide monochromatic vision, cones provide colour vision.

Iodopsin exists in three different forms with each form being sensitive to different wavelengths of light. The absorption peaks of the three different types of cone (each with a different type of iodopsin) correspond to the colours blue, green and red (the …

A

Trichromatic theory of colour vision).

168
Q
  • Cone cells

The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light.

While rods are not sensitive to colour and provide monochromatic vision, cones provide colour vision.

Iodopsin exists in three different forms with each form being sensitive to different wavelengths of light. The absorption peaks of the three different types of cone (each with a different type of iodopsin) correspond to the colours blue, green and red (the trichromatic theory of colour vision). Pure blue light will …

A

Only break down the ‘blue’ iodopsin

169
Q
  • Cone cells

The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light.

While rods are not sensitive to colour and provide monochromatic vision, cones provide colour vision.

Iodopsin exists in three different forms with each form being sensitive to different wavelengths of light. The absorption peaks of the three different types of cone (each with a different type of iodopsin) correspond to the colours blue, green and red (the trichromatic theory of colour vision). Pure blue light will only break down the ‘blue’ iodopsin but of course …

A

Most light is not pure blue, green or red

170
Q
  • Cone cells

The same general principles apply to the functioning of cone cells. However, in cones a different pigment, iodopsin, is situated in the membranes of the outer segment. The iodopsin is less readily broken down and will only produce a generator potential in bright light.

While rods are not sensitive to colour and provide monochromatic vision, cones provide colour vision.

Iodopsin exists in three different forms with each form being sensitive to different wavelengths of light. The absorption peaks of the three different types of cone (each with a different type of iodopsin) correspond to the colours blue, green and red (the trichromatic theory of colour vision). Pure blue light will only break down the ‘blue’ iodopsin but of course most light is not pure blue, green or red. In effect, …

A

It is the degree of stimulation of each type of cone that determines colour vision.

171
Q

Draw a diagram of a rod cell. Your diagram should indicate the direction of the light rays entering the retina and reaching the cell.

A

Diagram on textbook page 73

Light ray moving from inner segment towards outer segment (direction)

172
Q

What is the role of cone cells?

A

While rods are not sensitive to colour and provide monochromatic vision, cones provide colour vision.

173
Q

How many different forms of iodopsin are there?

A

Iodopsin exists in three different forms

174
Q

How are the three different forms of iodopsin different from each other?

A
  • Each form is sensitive to different wavelengths of light.

* The absorption peaks of the three types of iodopsin correspond to the colours blue, green and red.

175
Q

What wavelength of light will break down ‘blue’ iodopsin?

A

Blue light

176
Q

What determines colour vision?

A

The degree of stimulation of each type of cone

177
Q
  • The arrangement of rods and cones in the retina

It is not only the …

A

Differences in structure and sensitivities of rod and cone cells

178
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are …

A

Important in their functioning.

179
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their …

A

Distribution across the retina

180
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and …

A

The different ways in which they are arranged with linking neurone cells

181
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are …

A

Also crucial.

182
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form …

A

A layer immediately inside the choroid.

183
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of _______ ________ lies immediately inside the photosensitive cells

A

Bipolar neurones

184
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is …

A

Another layer of sensory cells (ganglion cells).

185
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is …

A

The axons of the ganglion cells that group together to make up the optic nerve

186
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that …

A

Carries impulses from the retina to the brain

187
Q

Draw a diagram of a cross-section through the retina and choroid showing photoreceptor cells and their associated neurones

A

Textbook page 74

188
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain.

The diagram also shows that …

A

Each cone cell can synapse individually with its own bipolar neurone

189
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain.

The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie …

A

Each provides its own discrete image in vision.

190
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain.

The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of …

A

High visual acuity

191
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain.

The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - …

A

The ability of cones to provide highly precise (colour) vision of high resolution

192
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain.

The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling …

A

The brain to distinguish between two points that are very close together

193
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain.

The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show …

A

Retinal convergence

194
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain.

The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves …

A

A number of rods having a common bipolar neurone

195
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain.

The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and …

A

A number of bipolar cells having a common ganglion cell).

196
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain.

The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows …

A

The generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone

197
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain.

The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone.

Allied to the ability of …

A

Rhodopsin

198
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain.

The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone.

Allied to the ability of rhodopsin (in …

A

Rods

199
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain.

The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone.

Allied to the ability of rhodopsin (in rods) to …

A

Break down more easily than iodopsin

200
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain.

The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone.

Allied to the ability of rhodopsin (in rods) to break down more easily than iodopsin (in …

A

Cones

201
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain.

The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone.

Allied to the ability of rhodopsin (in rods) to break down more easily than iodopsin (in cones), retinal convergence is the basis of …

A

The sensitivity that rods show.

202
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain.

The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone.

Allied to the ability of rhodopsin (in rods) to break down more easily than iodopsin (in cones), retinal convergence is the basis of the sensitivity that rods show. The light energy reaching any one rod is …

A

Not enough to stimulate the bipolar cell sufficiently

203
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain.

The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone.

Allied to the ability of rhodopsin (in rods) to break down more easily than iodopsin (in cones), retinal convergence is the basis of the sensitivity that rods show. The light energy reaching any one rod is not enough to stimulate the bipolar cell sufficiently but …

A

Stimulation of a group of rods provides enough generator potential to produce an impulse in the bipolar neurone.

204
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain.

The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone.

Allied to the ability of rhodopsin (in rods) to break down more easily than iodopsin (in cones), retinal convergence is the basis of the sensitivity that rods show. The light energy reaching any one rod is not enough to stimulate the bipolar cell sufficiently but stimulation of a group of rods provides enough generator potential to produce an impulse in the bipolar neurone. This of course also explains …

A

Another feature of rods

205
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain.

The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone.

Allied to the ability of rhodopsin (in rods) to break down more easily than iodopsin (in cones), retinal convergence is the basis of the sensitivity that rods show. The light energy reaching any one rod is not enough to stimulate the bipolar cell sufficiently but stimulation of a group of rods provides enough generator potential to produce an impulse in the bipolar neurone. This of course also explains another feature of rods - …

A

Their lack of visual acuity or high resolution

206
Q
  • The arrangement of rods and cones in the retina

It is not only the differences in structure and sensitivities of rod and cone cells that are important in their functioning. Their distribution across the retina and the different ways in which they are arranged with linking neurone cells are also crucial.

As the diagram below shows, the rods and cones form a layer immediately inside the choroid. A layer of bipolar neurones lies immediately inside the photosensitive cells and beyond the bipolar neurones there is another layer of sensory cells (ganglion cells). It is the axons of the ganglion cells that group together to make up the optic nerve that carries impulses from the retina to the brain.

The diagram also shows that each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision. This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together. However, the rods show retinal convergence. This involves a number of rods having a common bipolar neurone (and a number of bipolar cells having a common ganglion cell). Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone.

Allied to the ability of rhodopsin (in rods) to break down more easily than iodopsin (in cones), retinal convergence is the basis of the sensitivity that rods show. The light energy reaching any one rod is not enough to stimulate the bipolar cell sufficiently but stimulation of a group of rods provides enough generator potential to produce an impulse in the bipolar neurone. This of course also explains another feature of rods - their lack of visual acuity or high resolution as …

A

The individual rods in each ‘convergence unit’ only provide as much detail as one cone cell.

207
Q

What factors are important in the functioning of rod and cone cells?

A
  1. The differences in the structure and sensitivities of rod and cone cells.
  2. The distribution of rod and cone cells across the retina along with the different ways in which they are arranged with linking neurone cells.
208
Q

Comment on the position of the rod and cone cells relative to the choroid layer

A

The rods and cones form a layer immediately inside the choroid.

209
Q

Comment on the position of the layer of bipolar neurones relative to the photosensitive cells

A

The layer of bipolar neurones lies immediately inside the photosensitive cells

210
Q

Comment on the position of the ganglion cells relative to the layer of bipolar neurones

A

The layer of sensory cells (ganglion cells) lies immediately inside the layer of bipolar neurones.

211
Q

What is the optic nerve composed of?

A

The axons of ganglion cells group together to form the optic nerve.

212
Q

How many cone cells can synapse with a bipolar neurone?

A

One

213
Q

How many rod cells can synapse with a bipolar neurone?

A

Many

214
Q

The different properties of rods and cones, and their retinal arrangement, explains why we can see detailed colour vision during daytime (…

A

The light intensity is sufficient to break down iodopsin

215
Q

The different properties of rods and cones, and their retinal arrangement, explains why we can see detailed colour vision during daytime (the light intensity is sufficient to break down iodopsin) but can only see less detailed black and white image during the night (…

A

Light intensity sufficient to break down rhodopsin but not iodopsin

216
Q

Describe the structure of a ‘convergence unit’

A

Single ganglion cell which synapses with two or more bipolar neurones which individually synapse with many rod cells.

217
Q

What is the structural basis of high visual acuity in the mammalian eye?

A

Each cone cells can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision.

218
Q

What is high visual acuity?

A

The ability of cones to provide highly precise (colour) vision of high resolution

219
Q

How can the brain distinguish between two points that are very close together?

A
  • Each cone cell can synapse individually with its own bipolar neurone, ie each provides its own discrete image in vision.
  • This is the basis of high visual acuity - the ability of cones to provide highly precise (colour) vision of high resolution - enabling the brain to distinguish between two points that are very close together.
220
Q

The arrangement of rod cells within the mammalian eye displays what phenomenon?

A

Retinal convergence

221
Q

What is retinal convergence?

A

A number of rod cells have a common bipolar neurone (and a number of bipolar cells have a common ganglion cell).

222
Q

What does retinal convergence facilitate in the mammalian eye?

A

Retinal convergence allows the generator potentials from individual rods to combine together (summation) and reach the threshold required for producing an action potential in a bipolar neurone, therefore facilitating the sensitivity that rods show.

223
Q

What factors contribute to the sensitivity that rod cells show?

A

Allied to the ability of rhodopsin (in rods) to break down more easily than iodopsin (in cones), retinal convergence is the basis of the sensitivity that rods show.

224
Q

Comment on the stimulation of rod cells when light enters the eye with reference to retinal convergence

A

The light energy reaching any one rod is not enough to stimulate the bipolar cell sufficiently but stimulation of a group of rods provides enough generator potential to produce an impulse in the bipolar neurone.

225
Q

Why do rods display a lack of visual acuity?

A

Rod cells display a lack of visual acuity (or high resolution) as the individual rods in each ‘convergence unit’ only provide as much detail as one cone cell.

226
Q

Do not confuse sensitivity with visual acuity.

What is sensitivity?

What is visual acuity?

A

Sensitivity is the ability to operate in very low light intensities.

Visual acuity is the ability to provide precision vision.

227
Q

What can be noted about the arrangement of photosensitive cells and neurones in the retina?

A

Light rays have to pass through layers of neurones before reaching the light sensitive cells.

228
Q

If you look again at the arrangement of photosensitive cells and neurones in the retina, you will note that the light rays have to pass through layers of neurones before reaching the light sensitive cells. Why is this the case?

A

This ‘inverted’ arrangement appears to be less efficient than if it was the opposite way round with the photosensitive cells being on the inside and the neurone ‘cabling’ behind. Perhaps, but the arrangement in mammals is a consequence of the evolutionary development of the eye.

229
Q

Draw a graph showing the distribution and abundance of rod and cone cells across the retina of the human left eye

A

Textbook page 75

230
Q

The graph on page 75 of the textbook shows how the cones and rods are distributed across the retina. What phenomena does this distribution explain?

A

The distribution explains phenomena such as the blind spot and why we can distinguish shapes but not colour at the periphery of our vision, ie when the light rays are focused on the edge of the retina

231
Q

Comment on the distribution of rods across the retina of the human left eye

A

There are more rods at the right side of the retina (closer to centre of head) compared to the left. This facilitates peripheral vision on the left side of the head - the converse arrangement exists in the right eye.

232
Q

The presence of two eyes in mammals provides what type of vision?

A

Binocular or stereoscopic vision

233
Q

What is the advantage of the two eyes creating a single image?

A

If the two eyes create a single image it allows accurate judgement of distance. Stereoscopic vision, the ability to form three-dimensional images, is also possible.

234
Q

Comment on the position of the eyes in humans and other primates

A

In humans and other primates, and also in most predatory species, the eyes are positioned on the front of the head.

235
Q

In humans and other primates, and also in most predatory species, the eyes are positioned on the front of the head. What is the advantage of this?

A

This facilitates excellent judgement of distance and 3-D vision.

236
Q

Comment on the position of the eyes in prey species

A

Many prey species, such as rabbits, have their eyes positioned on the side of their heads rather than at the front.

237
Q

Many prey species, such as rabbits, have their eyes positioned on the side of their heads rather than at the front. What is the advantage of this?

A

This provides a wider field of view, a greater priority for prey aiding the detection of potential predators than 3-D vision.

238
Q

What are muscles?

A

Muscles are specialised effectors that bring about movement through contraction.

239
Q

What is the main type of muscle in the body?

A

Skeletal muscle

240
Q

What is skeletal muscle?

A

Muscle that is attached (via tendons) to the skeleton. Skeletal muscle is voluntary muscle in that it is under conscious control.

241
Q

Comment on the size of skeletal muscle

A

Skeletal (voluntary) muscle can vary considerably in size, for example, compare the triceps and biceps muscles with the muscles controlling the eyeball. However, the basic structure of all skeletal muscle is the same.

242
Q

Describe the structure of skeletal muscle

A
  • Skeletal muscle consists of many muscle fibres bunched together.
  • Each fibre is surrounded by a cell surface membrane (sarcolemma).
  • Each fibre is multinucleate with the nuclei typically arranged just inside the sarcolemma.
  • The fibre, which is effectively a very specialised ‘cell’, contains the cell organelles typically found in any cell, but is particularly rich in mitochondria.
  • At intervals, the sarcolemma folds deeply inwards to form transverse tubules or T-tubules.
  • The bulk of the muscle fibre is filled with highly specialised contractile units called myofibrils.
  • Muscle fibres are very large structures and can be up to many centimetres long.
243
Q

Draw a simple diagram showing the macrostructure of a skeletal muscle

A

Textbook page 76

244
Q

How many proteins make up the myofibril?

A

The myofibril consists largely of two types of protein

245
Q

The myofibril consists largely of two types of protein. What are these two proteins?

A

Myosin

Actin

246
Q

Briefly describe the ultrastructure of a myofibril

A
  • The myofibril consists largely of two types of protein, myosin and actin.
  • Myosin forms thick filaments around 15 nm in diameter and actin forms thin filaments about 7 nm in diameter.
247
Q

Comment briefly on the distribution of myosin and actin filaments in a myofibril

A
  • Myosin filaments lie in the central region of each contractile unit and are linked together by a thin disc (the M-line) that runs perpendicular to the orientation of the myosin filaments.
  • Actin filaments slot between the outer edges of the myosin filaments and they are also held together by a thin disc called the Z-line.
248
Q

What is a sarcomere?

A

A section of myofibril between two Z-lines (ie the basic contractile unit)

249
Q

How do the myosin filaments affect the appearance of skeletal muscle in electron micrographs?

A

The thicker myosin filaments form denser or darker striations or bands.

250
Q

How do the actin filaments affect the appearance of skeletal muscle in electron micrographs?

A

The thinner actin filaments form less dense or lighter regions between the myosin filaments.

251
Q

Why does skeletal (voluntary) muscle display a striated (banded) pattern?

A

The thicker myosin filaments form denser or darker striations or bands and the thinner actin filaments form less dense or lighter regions between them. It is this alternating pattern of myosin and actin that forms the striated (banded) pattern of voluntary (striated) muscle as seen in electron micrographs.

252
Q

What is the name given to the part of the myofibril containing myosin?

A

A-band (anisotropic band)

253
Q

What is the A-band?

A

The part of the myofibril containing myosin is referred to as the A-band (or anisotropic band). The A-band includes those areas where the thinner actin penetrates between the myosin filaments.

254
Q

What is the name given to the part of the myofibril that contains actin only?

A

The I-band (isotropic band)

255
Q

What is the I-band?

A

The I-band (isotropic band) is the part of the myofibril that contains actin only.

256
Q

What is the H-zone?

A

The H-zone is the zone in the centre of the A-band where there is myosin only (the area beyond the ends of the actin filaments).

257
Q

Draw a diagram showing a cross-section of a myofibril through an I-band

A

Textbook page 77. Diagram A.

258
Q

Draw a diagram showing a cross-section of a myofibril through an A-band area where the thinner actin penetrates between the myosin filaments

A

Textbook page 77. Diagram B.

259
Q

Draw a diagram showing a cross-section of a myofibril through a H-zone

A

Textbook page 77. Diagram C.

260
Q

Draw a diagram of multiple sarcomeres in sequence. Include labels.

A

Textbook page 77. Top diagram.

261
Q

Comment on the relationship between the overlapping actin and myosin within each myofibril

A

The relationship between the overlapping actin and myosin is very regular with each myosin filament being surrounded by six actin filaments in a regular hexagonal pattern.

262
Q

The relationship between the overlapping actin and myosin is very regular with each myosin filament being surrounded by six actin filaments in a regular hexagonal pattern. Draw a diagram illustrating this.

A

Textbook page 77

263
Q

Label the structures evident in the TEM of a striated muscle showing series of myofibrils running left to right on page 77 of the textbook.

A

Textbook page 77

264
Q

What is the basic principle of muscle contraction?

A

The basic principle of muscle contraction is that the myosin and actin filaments slide past each other so reducing the overall length of the sarcomere (and muscle).

265
Q

What is the process of muscle contraction called?

A

The sliding filament mechanism

266
Q

Describe the structure of the myosin and actin filaments

A

Myosin filaments are thick (around 15 nm in diameter).
Although mainly a long fibrous molecule, the myosin also has small bulbous heads that protrude at intervals.

The thinner actin filaments (around 7 nm in diameter) have small binding sites into which the bulbous heads of the myosin fit.

267
Q

Draw a diagram illustrating the structure of a myosin filament

A

Textbook page 78

268
Q

Draw a diagram illustrating the structure of an actin filament

A

Textbook page 78

269
Q

Comment on the state of the myosin head binding sites on the actin filaments when the muscle is not contracting

A

When not contracting, the actin binding sites are blocked by another ancillary protein (tropomyosin) to prevent binding.

270
Q

Describe the process of muscle contraction

A
  1. An action potential stimulates the muscle fibre as it travels through its extensive system of T-tubules.
  2. The action potential causes the calcium ion channels in the sarcoplasmic reticulum (the name given to the specialised endoplasmic reticulum of muscle cells) to open.
  3. This causes the calcium ions (Ca2+) that have been stored in the sarcoplasmic reticulum to diffuse into the sarcoplasm (the cytoplasm of muscle cells) down a concentration gradient.
  4. The calcium ions cause ancillary protein (tropomyosin) that normally covers the binding sites on the actin filaments to be moved, so enabling the myosin bulbous heads to link with the actin binding sites (forming actomyosin bridges).
  5. Once attached, the myosin heads change their angle (rotate or ‘rock’ back to an angle about 45°) and pull the actin filaments over the adjacent myosin filaments (by about 10 nm).
  6. An ATP molecule attaches to each myosin head and the energy released from its hydrolysis enables the myosin head to detach from the stationary actin binding site and return to its original position.
  7. The detached myosin heads repeat the process so that the cycle of attachment, rotation and release is repeated in a type of ratchet mechanism, with each cycle occurring about five times each second.
  8. The cycle continues as long as the muscle fibre receives nervous stimulation (and has calcium ions present).
271
Q

Draw a flow diagram illustrating the sliding filament mechanism of muscle contraction

A

Textbook page 79

272
Q

Describe how the arrangement of the myosin and actin filaments in each sarcomere change as contraction takes place

A
  • The sarcomere shortens (distance between the Z-lines decreases).
  • The H-zone becomes shorter.
  • The I-band becomes shorter.
  • The A-band remains the same length.
273
Q

Draw a diagram showing a sarcomere in a relaxed and contracted state

A

Textbook page 79

274
Q

Why is overall muscle contraction considerable despite each sarcomere being microscopic in size?

A
  • With each sarcomere being microscopic in size (approx 2.5 micrometers) it is obvious that the contraction caused by each sarcomere shortening is almost negligible.
  • However, with many sarcomeres lined end to end in a muscle fibre, and all contracting at the same time, the overall muscle contraction can be considerable.
275
Q

What contributes to the power of muscle contraction?

A

The power of muscle contraction is due to the many parallel myofibrils lined side by side in a muscle fibre (and many fibres in a single muscle) all contracting at the same time.

276
Q

What contributes to the strength of muscle contraction?

A
  • The strength of muscle contraction depends on a number of factors including for how long the muscle is stimulated but also how many muscle fibres are actually stimulated and contracting.
  • Although one motor neurone may control contraction in an entire muscle, not all the fibres may be contracted at the one time.
277
Q

What are the different types of muscle in the body?

A

Skeletal muscle, although the most obvious in terms of size and extent, is not the only type of muscle in the body. Smooth and cardiac muscle also contract and bring about movement but are different in appearance, nervous control, distribution and function to skeletal muscle.

278
Q

Describe the appearance of skeletal muscle

A
  • Striated (banded)

* Multinucleate fibres

279
Q

Describe the appearance of smooth muscle

A
  • Discrete uninucleate cells are spindle-shaped
  • Not striated
  • There is a single central nucleus in each cell
  • Cells are elongated and taper towards their ends
280
Q

Describe the appearance of cardiac muscle

A

• Striated but branched with intercalated discs (seen as discrete lines) between cells

281
Q

Describe the distribution of skeletal muscle

A

• Attached to bone throughout the body (most of the muscle in the body)

282
Q

Describe the distribution of smooth muscle

A
  • Lining gut and blood vessels

* Iris and ciliary body in eye

283
Q

Describe the distribution of cardiac muscle

A

• Wall of heart

284
Q

Describe the nervous control of skeletal muscle

A

• Voluntary (conscious) control

285
Q

Describe the nervous control of smooth muscle

A

• Involuntary or automatic (for example, reflex action)

286
Q

Describe the nervous control of cardiac muscle

A

• Myogenic and involuntary control

287
Q

Draw a simple diagram of skeletal muscle

A

Textbook page 80

288
Q

Draw a simple diagram of smooth muscle

A

Textbook page 80

289
Q

Draw a simple diagram of cardiac muscle

A

Textbook page 80

290
Q

Practical work

- For this topic, what should an A-level biology student be familiar with in terms of practical work?

A

They must be familiar with prepared slides, photomicrographs and electron micrographs of muscle and muscle components in addition to the different types muscle present in the body.

291
Q

Why can cardiac muscle be difficult to distinguish from skeletal muscle in electron micrograph images?

A

Cardiac muscle can be difficult to distinguish from skeletal muscle - it is clear in this electron micrograph that the characteristic striated appearance of skeletal muscle is also present in cardiac muscle.

However, there are crucial differences. In cardiac muscle:

  • Cells branch
  • Intercalated discs run across the myofibrils - these are important in synchronising electrical conduction and contraction in heart muscle
  • The cells are uninucleate
292
Q

Label the structures evident in the electron micrographs of cardiac muscle on page 81 of the textbook

A

Cells branch
Mitochondrion
Intercalated discs

293
Q

Why is smooth muscle not always very obvious in photographs?

A

Although smooth muscle consists of discrete cells, each with a central nucleus, this is not always very obvious in photographs as many smooth muscle cells are bunched together and intertwined to form smooth muscle tissue as shown in the diagram on page 81 of the textbook.

294
Q

You should also be familiar with preparations of the eye as prepared slides and EM photographs.

A

Take time to google images now

A2 Biology Module 1 - Physiology, Coordination and Control, and Ecosystems (9 decks)

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