Page 340 - Atlas of Histology with Functional Correlations

that occur between axons and dendrites are classified as axodendritic, between

an axon and the neuron cell body as axosomatic, and between axons as
axoaxonic. A typical synapse in the CNS consists of a presynaptic component
with a presynaptic membrane, a synaptic cleft, and a postsynaptic
membrane. The synaptic cleft separates the presynaptic and postsynaptic
membranes.

SUPPORTING CELLS IN THE CENTRAL

NERVOUS SYSTEM: NEUROGLIA

Neuroglia are the highly branched, supportive, nonneuronal cells in the CNS

that surround the neurons, their axons, and dendrites. These cells do not become
stimulated or conduct impulses and are morphologically and functionally
different from the neurons. Neuroglial cells can be distinguished by their much
smaller size and dark-staining nuclei. The CNS contains approximately 10-fold

more neuroglial cells than neurons. The four types of neuroglial cells are
astrocytes, oligodendrocytes, microglia, and ependymal cells.

Supplemental micrographic images are available at
www.thePoint.com/Eroschenko13e under Nervous Tissue.

FIGURE 9.3 | Spinal Cord: Midthoracic Region

(Transverse Section)

The transverse section of a spinal cord cut in the midthoracic region and stained
with hematoxylin and eosin is illustrated. Although a basic structural pattern is
seen throughout the spinal cord, the shape and structure of the cord vary at
different levels (cervical, thoracic, lumbar, and sacral).

The thoracic region of the spinal cord differs from the cervical region

illustrated in Figure 9.5. The thoracic spinal cord exhibits slender posterior gray
horns (6) and smaller anterior gray horns (10, 20) with fewer motor neurons
(10, 20). The lateral gray horns (8, 19) are well developed in the thoracic
region and contain the motor neurons (8, 19) of the sympathetic division of the

ANS.

The remaining structures in the midthoracic region of the spinal cord

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