myelin sheath

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Diagram comparing action potential conduction in myelinated and unmyelinated axons, showing a neuron with labeled cell body, myelin sheath, nodes of Ranvier, and the flow of electrical signals along each type of axon.

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myelin sheath

anatomy

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July 1, 2026

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Diagram comparing action potential conduction in myelinated and unmyelinated axons, showing a neuron with labeled cell body, myelin sheath, nodes of Ranvier, and the flow of electrical signals along each type of axon. — neuron; conduction of the action potential In a myelinated axon, the myelin sheath prevents the local current (small black arrows) from flowing across the membrane. This forces the current to travel down the nerve fibre to the unmyelinated nodes of Ranvier, which have a high concentration of ion channels. Upon stimulation, these ion channels propagate the action potential (large green arrows) to the next node. Thus, the action potential jumps along the fibre as it is regenerated at each node, a process called saltatory conduction. In an unmyelinated axon, the action potential is propagated along the entire membrane, fading as it diffuses back through the membrane to the original depolarized region.

The myelin sheath is a white, insulating layer that surrounds the axon of many neurons. It is composed of fatty materials, protein, and water. In the peripheral nervous system, Schwann cells produce the myelin sheath, while in the central nervous system, oligodendrocytes create it.1

This sheath is not continuous; it has gaps called nodes of Ranvier. This structure is crucial for nerve function because it allows nerve impulses to travel much faster. The impulses essentially jump from one node to the next, a process known as saltatory conduction. The myelin sheath's primary role is to increase the speed at which nerve impulses can travel along an axon. Damage to the myelin sheath, as seen in demyelinating neuropathies, can block nerve impulse conduction.123

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muscle disease
Lower motor neuron disease
…caused by degeneration of the myelin sheaths, the insulation around the axons. These are known as demyelinating neuropathies. Symptoms are similar to neuropathies with axonal degeneration, but since the axons remain intact, the muscles rarely atrophy. Recovery from demyelinating neuropathies can be rapid. Diphtheria and autoimmune diseases such as Guillain-Barré…
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…caused by degeneration of the myelin sheaths, the insulation around the axons. These are known as demyelinating neuropathies. Symptoms are similar to neuropathies with axonal degeneration, but since the axons remain intact, the muscles rarely atrophy. Recovery from demyelinating neuropathies can be rapid. Diphtheria and autoimmune diseases such as Guillain-Barré…
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multiple sclerosis
… characterized by destruction of the myelin sheath surrounding the nerve fibres of the brain, spinal cord, and optic nerves, as a result of which, the transmission of nerve impulses becomes impaired, particularly in pathways involving vision, sensation, and movement.
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… characterized by destruction of the myelin sheath surrounding the nerve fibres of the brain, spinal cord, and optic nerves, as a result of which, the transmission of nerve impulses becomes impaired, particularly in pathways involving vision, sensation, and movement.
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nutritional disease
Vitamin B12
Additionally, vitamin B₁₂ maintains the myelin sheath that protects nerve fibres; therefore, an untreated deficiency of the vitamin can result in nerve degeneration and eventually paralysis. Large amounts of folic acid (over 1,000 μg per day) may conceal, and possibly even exacerbate, an underlying vitamin B₁₂ deficiency. Symptoms of vitamin…
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Additionally, vitamin B₁₂ maintains the myelin sheath that protects nerve fibres; therefore, an untreated deficiency of the vitamin can result in nerve degeneration and eventually paralysis. Large amounts of folic acid (over 1,000 μg per day) may conceal, and possibly even exacerbate, an underlying vitamin B₁₂ deficiency. Symptoms of vitamin…
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node of Ranvier
…in the insulating sheath (myelin) on the axon of certain neurons that serves to facilitate the rapid conduction of nerve impulses. These interruptions in the myelin covering were first discovered in 1878 by French histologist and pathologist Louis-Antoine Ranvier, who described the nodes as constrictions.
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…in the insulating sheath (myelin) on the axon of certain neurons that serves to facilitate the rapid conduction of nerve impulses. These interruptions in the myelin covering were first discovered in 1878 by French histologist and pathologist Louis-Antoine Ranvier, who described the nodes as constrictions.
Read More