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Y4 Biology > 1. Eye > Flashcards

1. Eye Flashcards

1
Q

Eyelids

Function

A

Function:

  • Protect the cornea from mechanical damage
  • Prevent excess light from entering the eye and damaging the retina by squinting
  • Helps spread tears over the cornea and conjunctiva
  • Wipes dust particles off the cornea by blinking
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2
Q

Eyelashes

Function

A

Function:

  • Help to shield eye from dust particles
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3
Q

Tear Glands

Function

A

Function:

  • Secrete tears to wash away dust particles
  • Keep cornea moist for atmospheric oxygen to dissolve so that oxygen can diffuse into the cornea
  • Lubricate the conjunctiva, helping to reduce friction when the eyelids move
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4
Q

Conjunctiva

Structure & Function

A

Structure:

  • Thin, transparent membrane covering the sclera

Function:

  • Secretes mucus to keep the front of the eyeball moist
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5
Q

Sclera

Structure & Function

A

Structure:

  • Tough, white outer covering of the eyeball
  • Continuous with cornea

Function:

  • Protects eyeball from mechanical damage
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6
Q

Choroid

Structure & Function

A

Structure:

  • Middle layer of the eyeball between the sclera and retina

Function:

  • Contains black pigments to prevent internal reflection of light
  • Contains blood vessels that bring oxygen and nutrients to the eyeball and remove metabolic waste products
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7
Q

Retina

Structure & Function

A

Structure:

  • The intermost layer of the eyeball
  • Contains photoreceptors (rods and cones)

Function:

  • Light-sensitive layer where images are formed
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8
Q

Cornea

Structure & Function

A

Structure:

  • Transparent layer in front of eye (beneath the conjunctiva)
  • Continuous with sclera

Function:

  • Refracts light towards lens
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9
Q

Iris

Structure & Function

A

Structure:

  • Consists of 2 sets of involuntary muscles, the circular muscles and radial muscles
  • Surrounds the pupil
  • In front of the lens

Function:

  • Adjusts the amount of light entering the eye by changing the size of the pupil
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10
Q

Pupil

Structure & Function

A

Structure:

  • Hole in the centre of iris
  • Appears black because the choroid is visible through it

Function:

  • Allows light to enter the eye
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11
Q

Lens

Structure & Function

A

Structure:

  • Transparent, biconvex, elastic crystalline body

Function:

  • Changes curvature or thickness to refract light onto the retina
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12
Q

Suspensory Ligaments

Structure & Function

A

Structure:

  • Connective tissue
  • Attached to the edge of the lens and the ciliary body

Function:

  • Transfer the effect of the ciliary muscles to the lens
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13
Q

Ciliary Body

Structure & Function

A

Structure:

  • Consists of ciliary muscles

Function:

  • Controls the curvature or thickness of the lens
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14
Q

Aqueous Humour

Structure & Function

A

Structure:

  • Transparent, watery fluid
  • In front of the lens

Function:

  • Refracts light onto the lens
  • Serves as a medium for the diffusion of oxygen and nutrients
  • Keeps eyeball firm
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15
Q

Vitreous Humour

Structure & Function

A

Structure:

  • Transparent, jelly-like fluid

Function:

  • Refracts light onto retina
  • Keeps the eyeball firm
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16
Q

Fovea (Yellow Spot)

Structure & Function

A

Structure:

  • Greatest concentration of cones but no rods

Function:

  • Part of the retina that best resolves images, where images are focused onto it
  • Gives detailed colour vision in bright light
17
Q

Blind spot

Structure & Function

A

Structure:

  • Found over the optic nerve
  • No photoreceptors

Function:

  • Area on the retina where neurones leave the eye
18
Q

Optic Nerve

Structure & Function

A

Structure:

  • Composed of sensory neurones

Function:

  • Trasmists nerve impulses from photoreceptors to brain
19
Q

Cones

Properties

A
  • Cones enable us to see colours in bright light
  • There are 3 types of cones: red, green and blue cones
  • Each cone contains different pigments which absorbs light of different wavelengths
  • Most concentrated at the yellow spot/fovea
  • Cones do not work well in dim light
20
Q

Rods

Properties

A
  • Rods are more sensitive to light than cones
  • Rods enable us to see in dim light, but only in black and white
  • Contain the light sensitive pigment, visual purple (rhodopsin)
  • Rods lie outside the fovea in the more peripheral parts of the retina
21
Q

Rhodopsin (Visual Purple)

Properties

A
  • Found in rods
  • Visual purple is bleached when the eye is exposed to bright light, It takes a while for visual purple to reform when you walk from a bright place to a dimly lit room
  • Requires Vitamin A for the formation of visual purple
22
Q

Accommodation

Definition

A

Accomodation is the adjustment of the lens to change curvature or thickness so that clear images at different distances are formed on the retina.

Accomodation is achieved by the following structures:

  • Ciliary muscles to alter the shape of the lens
  • Suspensory ligaments which transfer the effect of the ciliary muscles to the lens
  • Elasticity of the lens
23
Q

Describe the changes in the eye when focusing on a near object

Process

A
  1. Ciliary muscles contract, reducing the pull on the suspensory ligaments
  2. Suspensory ligaments slacken
  3. Lens becomes thicker and more convex
  4. Focal length decreases
  5. Light rays from the near object are brought to focus on the retina
  6. Photoreceptors are stimulated. Nerve impulses are produced and transmitted to the brain via the optic nerve.
24
Q

Describe the changes in the eye when focusing on a distant object

Process

A
  1. Ciliary muscles relax, pulling on the suspensory ligaments
  2. Suspensory ligaments become taut
  3. Lens becomes thinner and longer
  4. Focal length increases
  5. Light rays from the distant object are brought to focus on the retina
  6. Photoreceptors are stimulated. Nerve impulses are produced and transmitted to the brain via the optic nerve.
25
Q

Simple reflexes in the Eye

Function + Types

A

Simple reflex actions have protective functions.

  1. Pupil reflex - strong light causes pupils to become smaller to protect retina
  2. Blink reflex - any object seen coming towards the eyes cause the eyelids to close
  3. Tearing reflex - dust sensed by the conjunctiva causes an increase in tear flow to wash it away

These are cranial reflex actions, where the reflex centre is in the brain.

26
Q

Describe pupil reflex in bright light

Process

A
  1. Photoreceptors in the retina detect an increase in the light intensity.
  2. Nerve impulses are sent along the sensory neurone in the optic nerve to the brain.
  3. The brain returns nerve impulses along the motor neurone to the radial and circular muscles of the iris.
  4. The radial iris muscles relax while the circular iris muscles contract.
  5. The diameter of the pupil decreases, allowing less light to enter the eye.
27
Q

Describe pupil reflex in dim light

Process

A
  1. Photoreceptors in the retina detect a decrease in the light intensity.
  2. Nerve impulses are sent along the sensory neurone in the optic nerve to the brain.
  3. The brain returns nerve impulses along the motor neurone to the radial and circular muscles of the iris.
  4. The radial iris muscles contract while the circular iris muscles relax.
  5. The diameter of the pupil increases, allowing more light to enter the eye.

Y4 Biology (10 decks)

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