Amyelin sheath is

a. large band of neural fibers connecting the two hemispheres of the brain.
b. fatty tissue layer encasing the axon of a nerve cell.
c. bushy extension of a neuron that conducts impulses toward the cell body.
d. nerve network within the brainstem that controls physical arousal.

B. Fatty tissue layer encasing the axon of a nerve cell

Explanation: Myelin is an insulating layer that forms around a nerves including those of brain and spinal cord,its is made up if protein and fatty substances.The myelin sheath aids in the quick and efficient transfer of electrical impulses along a nerve cells. Damage to it can slow down the impulse,for example multiple sclerosis diseases.

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