Human Nervous System

Question 1

What are dendrons and axons?

Answer 1

Dendrons are nerve fibres that transmit nerve impulses towards the cell body.

Axons are nerve fibres that carry the nerve impulse away from the cell body.

Question 2

What is the myelin sheath?

Answer 2

The myelin sheath are layers of plasma membranes of the Schwann cell, made up of lipids, that insulate the nerve fibres and provides nourishment of the cell.

The outermost membrane that surrounds the myelin sheath is known as the neurilemma.

Question 3

What are Nodes of Ranvier?

Answer 3

Nodes of Ranvier are regions where the Myelin sheath are absent.

-They speed up transmission by allowing nerve impulses to jump from node to node.

Question 4

What is synapse?

Answer 4

Syanpse is the junction between two neurons where impulses are transmitted from an axon to a dendron through neurotransmitters.

Question 5

What do grey and white matter contain, and where are each of them found?

Answer 5

Grey matter: Cell bodies of neurons
Found in: outer layers of the brain
-central parts of the spinal cord

White matter: Mainly nerve fibres of neurons
Found in: Central parts of the brain
Outer layers of the spinal cord

Question 6

Describe pupil reflex of iris.

Answer 6

• Changes in light intensity stimulate the retina (receptor)
• Nervous impulses are sent to the brain via optic nerve (sensory neuron)
• The brain intepret these impulses and sends impulses via motor neurons to the circular and radial muscles in the iris (effector)

In bright light:

• circular muscles contract, radial muscles relax
• pupil constricts, reducing the amount of light that enters the eye

In dim light:

• circular muscles relax, radial muscles contract
• pupil dilates, increasing the amount of light that enters the eye

Question 7

Describe how the eye focuses on nearby object.

Answer 7

Cilliary muscles contract, relaxing their pull on suspensory ligaments.

• Suspensory ligaments slacken/become taut, relaxing their pull on the lens
• Lens becomes thickers/thinner and more/less convex, decreasing the focal length
• Light rays are sharply focused on the retina stimulating the photoreceptors
• Nerve impulses produced are transmitted to the brain via the optic nerve
• The brain inteprets the nearby object and the person sees the object