Nervous system 3

Groups of myelinated axons appear

white

Myelin gives the cell membranes of Schwann cells a

Higher proportion of lipid than other cell membranes. This coating is called a Myelin sheath.

Myelinated axons conduct

Impulses rapidly compared to unmyelinated axons.

Oligodendrocytes (CNS)

Type of neuroglia in the CNS that produces myelin

Axons that do not have these sheaths are

Unmyelinated axons.

Tight covering form Schwann cell membranes

Wind and wrap around axons.

Unmyelinated nerve tissue appears

gray

Schwann cells also enclose

But do not wind around, the smallest axons of peripheral neurons. Consequently, these axons do not have myelin sheaths.

In the brain and spinal cord, myelinated axons

Do mot have Neurilemmae.

The White matter in the brain and spinal cord gets

Its color from masses of myelinated axons.

Myelin

Lipid material that forms a sheatlike covering around some axons

Neurilemma

Living cellular layer formed from Schwann cells on the exterior of some axons.

Gray matter in the CNS contains

Many unmyelinated axons and neuron cell bodies. Discusses multiple sclerosis, a condition in which neurons in the brain and spinal cord lose their myelin.

Schwann cell layers are composed

Myelin , which consists Of several types of lipids and proteins.

Axins that have myelin sheaths Are called

Myelinated ( medullated ) axons

The parts of the Schwann cells that contain most of the cytoplasm and the nuclei remain outside the myelin sheath and comprise a

Neurilemma or Neurilemmal sheath , which surrounds the myelin sheath.

Narrow gaps in the myelin sheath between Schwann cells are called

Nodes of Ranvier

In the CNS , myelin is produced by a type of neuroglia called

Oligodendrocyte , rather than by a Schwann cell

In the PNS , Neuroglia called

Schwann cells - encase the large axons of peripheral neurons in lipid- rich sheaths.

Myelin begins to form on Axon during

The fourteenth week of prenatal development. At the time of birth, many axons are not completely myelinated. All myelinated axons have begun to develop sheaths by the time a child starts to walk, and myelinated continues into adolescence.

Schwann cells (PNS)

Type of neuroglia that surrounds an axon of a peripheral neuron, forming the neurilemma and myelin.