Question

11). Explain why myelinated nerve fibers conduct signals much faster than unmyelinated nerve fibers.

12). What is meant by the anterior (ventral) & posterior (dorsal) roots of a spinal nerve? Which of these is sensory & which is motor?

13. Contrast the composition and locations of gray matter & white matter in the brain.

20. ). If the oculomotor nerve or the trochlear nerve or the abducens nerve each was damaged, the effect would be similar in all three cases. What would that effect be? Explain.

Answer 1

11) The myelinated nerve fibers conduct signals much faster than unmyelinated nerve fibers because of the saltatory conduction, which is the propagation of action potential from one node of Ranvier to the next node along the myelinated axons, which thereby increase the conduction velocity of the action potential. The nerve impulse jumps over the myelin areas and it travels much faster along a myelinated neuron than along an unmyelinated neuron. So, nerve fibers with myelin conducts signals much faster than nerve fibers without myelin.

12) The posterior (dorsal) root of a spinal nerve consists of dorsal root ganglion, which contains the cell bodies of sensory neurons and hence it is a sensory root. The anterior (ventral) root of a spinal nerve consists of axons of the lower motor neurons in the ventral horn of spinal cord and hence it is a motor unit. In general, the posterior (dorsal) root carry afferent sensory axons and the anterior (ventral) root carry efferent motor axons.

13) Contrasting the composition and location of gray and white matter in the brain:

• The gray matter is the grayish nerve tissue in the central nervous system (CNS) and is composed of dendrites and nerve cell bodies (soma). The gray matter is located on the surface of brain, brain stem and cerebellum and throughout the spinal cord.
• The white matter is the whitish nerve tissue in the central nervous system (CNS) and is composed of axons or the myelinated nerve fibers. The white matter is located in the inner layer of the cortex of brain.

14) If the oculomotor nerve (CN III), trochlear nerve (IV) and abducens nerve (CN VI) are damaged, the effect would be the same for the damage of these three nerves and that effect is "dysconjugate gaze", which results in double vision with characteristic patterns of diplopia. The damage of these three cranial nerves results in failure of eyes to turn together in the same direction.

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