Chapter 10: Nervous System and the Eye

Describe the pathway of neurones??

sense organ (receptor) → sensory neurone → relay neurone → motor neurone → muscle fibres

How does the nervous system process pain?

receptor in skin → sensory neurone → relay neurone in spinal cord → brain

What is the pathway of nerve impulses when a person performs a voluntary action?

brain → relay neurone in spinal cord → motor neurone → effector

Describe what happens when your hand touches a hot object.

Heat from the object stimulates the receptors in the skin and produce nerve impulses. Nerve impulses are transmitted by the sensory neurone to the spinal cord. In the spinal cord, nerve impulses are transmitted to the relay neurone and then to the motor neurone. The motor neurone transmits nerve impulses from the spinal cord to the muscles in the hand. The muscles contract and causes his hand to withdraw rapidly. At the same time, impulses are transmitted by the sensory neurone to the brain to interpret pain.

Explain how coordination by hormones differs from coordination by nerves.

Nervous coordination involves nerve impulses transmitting rapidly along neruones to specific effectors, so the response is fast and usually short lived. Hormonal coordination involves hormoes being released by endocrine glands into the blood plasma, which is slower and longer lasting. Endocrine control are chemicals while nerve impulses are electrical messages.

Explain how the image of the time on his wristwatch is produced when he looks down on it.

1. The object distance changed from far to near.

2. The ciliary muscles contract, relaxing pull on the suspensory ligaments.

3. The suspensory ligaments slacken, relaxing their pull on the lens.

4. The lens become thicker and more convex.

5. Light rays from the wristwatch are sharply focused on the fovea, stimulating photoreceptors

6. Nerve impulses are transmitted by optic nerve to the brain. The brain interprets impulses and the person can see the wristwatch.

Explain how the image of the aeroplane is produced when he looks up at it.

1. The object distance changed from near to far.

2. The ciliary muscles relax and pull on the suspensory ligaments.

3. The suspensory ligaments become taut, pulling the edge of the lens.

4. The lens become thinner and less convex.

5. Light rays from the wristwatch are sharply focused on the fovea, stimulating photoreceptors

6. Nerve impulses are transmitted by optic nerve to the brain. The brain interprets impulses and the person can see the aeroplane.

Describe the changes of the pupil when light intensity increases

1. When light intensity increases, the circular muscles of the iris contract while the radial muscles of the iris relax

2. The pupil constricts and reduces the amount of light entering the eye

Describe the changes of the pupil when light intensity decreases

1. When light intensity decreases, the circular muscles of the iris relax while the radial muscles of the iris contract

2. The pupil dilates and increases the amount of light entering the eye

Describe the reflex arc involved in the pupil reflex

1. Light rays stimulate photoreceptors in the retina

2. Sensory neurone in the optic nerve transmit nerve impulses to relay neurones in the brain

3. Nerve impulses are transmitted from relay neurones to motor neurones in the brain

4. Motor neurones transmits nerve impulses from the brain to the iris muslces to carry out pupil reflex