Chapter 10: The Nervous System and The Eye

Question 1

What is sensitivity?

Answer 1

The ability of an organism to detect and respond to changes in the environment

Question 2

What is the role of the nervous system in humans?

Answer 2

• Allows organisms to detect changes in their surroundings and respond to it
• Enables the coordination of the different parts of the body

Question 3

What does the Central Nervous System consist of?

Answer 3

Brain
Spinal cord

Question 4

What does the Peripheral Nervous System consist of?

Answer 4

Cranial nerves
Spinal nerves
Sense organs (receptors)

Question 5

What are the 5 sense organs and the stimuli to which they respond?

Answer 5

1. Eye
- Light, stimulates photoreceptors on retina
2. Ear
- Sound waves, detected by eardrum in the form of vibrations
3. Tongue
- Four tastes, stimulate receptors on taste buds
4. Nose
- Odours, stimulate olfactory receptors lining the nasal cavity
5. Skin
- Sensations of pain, pressure, heat and cold, stimulate nerve endings in skin

Question 6

What are the differences between a sensory and a motor neurone?

Answer 6

Sensory neurone: Short axon
Motor neurone: Long axon

Sensory neurone: Long dendron
Motor neurone: Short dendron

Sensory neurone: Circular cell body
Motor neurone: Irregularly-shaped cell body

Sensory neurone: Transmits nerve impulses from the receptors to the central nervous system
Motor neurone: Transmits nerve impulses from the central nervous system to the effectors

Question 7

What is a reflex action?

Answer 7

• An immediate response to a specific stimulus without conscious control
• Involuntary, not under the control of a person’s will

Question 8

What are the processes which occur within the body after touching a hot object?

Answer 8

• Heat stimulates the receptors in the skin
• Nerve impulses are produced
  -transmitted along the sensory neurone
  -across a synapse to the relay neurone in the spinal cord
  -to the motor neurone across a synapse
• At the same time, nerve impulses are transmitted to the brain
• The motor neurone transmits the nerve impulses to the effector
• The effector muscle contracts, resulting in the withdrawal of the hand from the hot object

Question 9

Which part of the nervous system perceives pain?

Answer 9

The brain

Question 10

What is the reflex arc?

Answer 10

A reflex arc is the shortest pathway which nerve impulses travel from the receptor to the effector in a reflex action

Question 11

What is a synapse?

Answer 11

A junction between two neurones/
A junction between a neurone and an effector

Question 12

Where do relay neurones lie?

Answer 12

Within the grey matter of the spinal cord and brain

Question 13

How does the nervous system process a sensation?

Answer 13

• Receptors in skin are stimulated
• Nerve impulses are produced and transmitted by a sensory neurone
• to a relay neurone in the CNS
• The brain receives the nerve impulses
• The brain interprets the impulses
• The sensation is felt

Question 14

How does the nervous system process a voluntary action?

Answer 14

• Nerve impulses are produced in the brain
• Nerve impulses are transmitted to a relay neurone in the CNS
• and transmitted to a motor neurone
• Effector muscles receive nerve impulses from the motor neurone
• Muscle contracts
• The action is carried out

Question 15

How does the nervous system process a reflex action?

Answer 15

• Receptors are stimulated
• Nerve impulses are produced and transmitted by a sensory neurone
• to a relay neurone in the CNS
• and to a motor neurone
• Effector muscles receive the nerve impulses from the motor neurone
• Muscle contracts
• The action is carried out

Question 16

Comparison between a voluntary action, an involuntary action and a reflex action?

Answer 16

Voluntary: Controlled by our will
Involuntary: Not controlled by our will
Reflex: A sudden action in response to something

Voluntary: Does not require a stimulus
Involuntary: Does not require a stimulus
Reflex: Requires a stimulus

Voluntary: Regulated by brain
Involuntary: Regulated by brain
Reflex: Regulated by brain or spinal cord

Voluntary: Produced by choice
Involuntary: Occurs throughout our lifetime
Reflex: Produced during an emergency

Voluntary: Choice-dependent speed
Involuntary: May be slow or quick
Reflex: Always quick

Question 17

What are the three layers of the wall of the eyeball?

Answer 17

• Sclera
• Choroid
• Retina

Question 18

What is the function of the sclera?

Answer 18

• Continuous with the cornea
• Attached to eye muscles
• Facilitate movement of eyeball

Question 19

What is the function of the choroid?

Answer 19

• Prevents internal refraction of light
• Contains blood vessels
  -carry oxygen and nutrients to the eyeball
  -remove metabolic waste products from

Question 20

What is the function of the retina?

Answer 20

• Contains photoreceptors (rods and cones)
  -Rods-> more sensitive to light, enable us to see in dim light (but only in black and white)
  -Cones-> enable us to see colours in bright light
  -Photoreceptors: detect light changes, convert light waves into nerve impulses
• Connected to nerve fibres in optic nerve

Question 21

What is the function of the fovea?

Answer 21

• Where images are focused
• Contains cones but not rods
• Enables a person to have detailed colour vision in bright light

Question 22

What is the blind spot?

Answer 22

• Region where optic nerve leaves the eye
• Does not contain photoreceptors

Question 23

What is the function of the optic nerve?

Answer 23

• Transmits nerve impulses to the brain when photoreceptors are stimulated

Question 24

What is the function of the lens?

Answer 24

• Transparent, circular, biconvex structure
• Shape or thickness changed in order to refract light onto the retina

Question 25

What is the function of the cornea?

Answer 25

- Refracts light rays into the eye

Question 26

What is the function of the eyelid?

Answer 26

- Protects the cornea from mechanical damage - Squinting prevents excessive entry of light which may damage the retina - Blinking spreads tears over the eyes so that dust can be wiped off

Question 27

What is the function of the tear gland?

Answer 27

- Secretes tears to: -wash away dust particles -moisten cornea for absorption of dissolved oxygen -lubricate the conjunctiva, reducing friction when the eyelids move

Question 28

What is the function of the conjunctiva?

Answer 28

- Secretes mucus to keep the front of the eyeball moist

Question 29

What is the function of the iris?

Answer 29

- Circular sheet of 2 sets of involuntary antagonistic muscles (circular and radial muscles) - Contains pigment which gives the eye its colour

Question 30

What is the function of the eyelash?

Answer 30

- Shields eye from dust particles

Question 31

What processes occur within the eye in bright light?

Answer 31

- More light enters the eye - **Photoreceptors on the retina** are stimulated - Nerve impulses are transmitted to the brain through **sensory neurone** in the **optic nerve** - The **relay neurone** in the brain transmits nerve impulses via the **motor neurone** to the **iris** of the eye -**Circular muscles** of the iris **contract** -**Radial muscles** of the iris **relax** - Size of pupil **decreases** and pupil **constricts** - **Less light** enters the eye

Question 32

What processes occur within the eye in dim light?

Answer 32

- Less light enters the eye - **Photoreceptors on the retina** are stimulated - Nerve impulses are transmitted to the brain through **sensory neurone** in the **optic nerve** - The **relay neurone** in the brain transmits nerve impulses via the **motor neurone** to the **iris** of the eye -**Circular muscles** of the iris **relax** -**Radial muscles** of the iris **contract** - Size of pupil **increases** and pupil **dilates** - **More light** enters the eye

Question 33

What are the properties of the image formed on the retina?

Answer 33

1. Vertically inverted 2. Laterally inverted 3. Smaller in size than actual object

Question 34

What is the pathway for the formation of an upright image at the brain?

Answer 34

1. Inverted image formed on the retina 2. Photoreceptors are stimulated 3. Nerve impulses generated are transmitted through the optic nerve 4. Nerve impulses reach the optic centre of the brain 5. The brain interprets the information and forms an upright image

Question 35

What is focusing?

Answer 35

- The adjustment of the lens of the eye so that clear images of objects at different distances are formed on the retina

Question 36

What happens within the eye when looking at nearby objects?

Answer 36

- Light rays from a **near** object are **divergent** - A **greater angle of refraction** is needed to focus on the object - **Ciliary muscles** _contract_ - **Suspensory ligaments** _slacken_ - **Lens** becomes **thicker** and **more convex** - **Focal length decreases** - Light rays are focused sharply on the retina - Photoreceptors on the retina are stimulated - Nerve impulses are transmitted to the brain via the optic nerve - The brain interprets the impulses - Person sees the near object

Question 37

What happens within the eye when looking at distant objects?

Answer 37

- Light rays from a distant object are **parallel** - A **smaller angle of refraction** is needed to focus on the object - **Ciliary muscles** _relax_ - **Suspensory ligaments** _become taut_ - **Lens** is **pulled thinner** and **less convex** - **Focal length increases** - Light rays are focused sharply on the retina - Photoreceptors on the retina are stimulated - Nerve impulses are transmitted to the brain via the optic nerve - The brain interprets the impulses - Person sees the distant object

Question 38

Why does the shape of the eyeball being too long cause myopia?

Answer 38

When the eyeball is too long, light rays converge in front of the fovea and cause an unclear image to be formed on the retina.

Question 39

What are some causes of myopia? (8 pts.)

Answer 39

- Eyeball too long - Lens too strong - Lens too convex - Lens not elastic enough - Lens not flexible enough - Ciliary muscles are unable to relax - Cornea is too curved - Cornea is too convex