Question

Distinguish between:

(a) afferent neurons and efferent neurons

(b) impulse conduction in a myelinated nerve fibre and unmyelinated nerve fibre

(c) aqueous humor and vitreous humor

(d) blind spot and yellow spot

(f) cranial nerves and spinal nerves.

Answer 1

(a) Afferent neurons and efferent neurons

Afferent neurons	Efferent neurons
Afferent neuron conducts nerve impulses toward the brain or the spinal cord.	Efferent neuron conducts nerve impulses from the brain or spinal cord to the effector organs such as muscles or glands.

(b) Impulse conduction in a myelinated nerve fibre and an unmyelinated nerve fibre

	Impulse conduction in a myelinated nerve fibre		Impulse conduction in an unmyelinated nerve fibre
1.	In a myelinated nerve fibre, the action potential is conducted from one node to another.	1.	In an unmyelinated nerve fibre, the action potential is not conducted from node to node. It is carried along the whole length of the nerve fibre.
2.	The conduction of impulses is faster.	2.	The conduction of impulses is slower.

(c) Aqueous humour and vitreous humour

Aqueous humour	Vitreous humour
It is a thin, watery fluid present between the cornea and the lens.	It is a transparent gel present between the lens and the retina.

(d) Blind spot and yellow spot

	Blind spot		Yellow spot
1.	Blind spot is a spot on the retina present at the point of origin of the optic nerve.	1.	Yellow spot is a small area on the retina present at the posterior pole of the eye, lateral to the blind spot.
2.	Photoreceptor cells are absent from this region.	2.	Only cones are present in this region.
3.	They are insensitive to light as both rods and cones are absent.	3.	They are sensitive to bright light as cones are present.

(f) Cranial nerves and spinal nerves

	Cranial nerves		Spinal nerves
1.	Cranial nerves arise from the brain.	1.	Spinal nerves arise from the spinal cord.
2.	There are 12 pairs of cranial nerves.	2.	There are 31 pairs of spinal nerves.