Supportive cells

^ Supporting cells of the CNS (neuroglial cells); outnumber neurons 10:1

• Astrocytes

♦ Stellate morphology

■ Fibrous astrocytes in white matter

■ Protoplasmic astrocytes in gray matter

Astrocytes Reflex Arc

figure 8.2. The reflex arc.

Spinal cord Ventral root figure 8.2. The reflex arc.

■ Physical support

■ Transport nutrients

■ Maintain ionic homeostasis

■ Take up neurotransmitters

■ Form glial scars (gliosis)

• Oligodendrocytes

♦ Present in white and gray matter

♦ Interfascicular oligodendrocytes are located in the white matter of the CNS, where they produce the myelin sheath.

• Ependymal cells. Line ventricles

♦ Not a true neuroglial cell; derived from mesoderm whereas neu-roglial cells, as well as neurons, are derived from ectoderm

♦ Highly phagocytic cells

^ Supporting cells of the PNS. Schwann cells

• Satellite Schwann cells surround cell bodies in ganglia

• Ensheathing Schwann cells

♦ Surround unmyelinated axons. Numerous axons indent the Schwann cell cytoplasm and are ensheathed only by a single wrapping of plasma membrane.

♦ Produce the myelin sheath around axons

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