Page 208 - Anatomy and Physiology of Farm Animals, 8th Edition

Anatomy of the Nervous System / 193

Table 10-1. Gray Versus White Matter Locations
VetBooks.ir CNS Gray Matter (Neuronal Cell Bodies) White Matter (Axons)

Tracts/fasciculi/funiculi
Cerebral cortex
Cerebellar cortex
Nuclei
Spinal cord gray
PNS Ganglia Nerves

(A) (B) (C) (D)

Figure 10-3. Morphological types of neurons. Classification is based on number of processes extend-
ing from the cell body. Unipolar neurons (A) are not found in adult vertebrate nervous systems; the uni-
polar neuron here is depicted with a growth cone at the tip of its axon, illustrating its developmental
nature. Bipolar (B) and pseudounipolar (C) neurons are characteristic of sensory systems. Most neurons
in the nervous system are multipolar (D) and can assume a variety of shapes.

is the synapse. The neuron belonging processes (Fig. 10‐3). Unipolar neurons
to the axon is the presynaptic neuron, have one process; true unipolar neurons
and the one receiving information from are seen only during development. Bipolar
the axon is the postsynaptic neuron. neurons have one dendrite and one axon;
Information flow is largely unidirectional, these are common in sensory systems.
with the presynaptic neuron sending infor- Many sensory neurons have their single
mation to the postsynaptic neuron. dendrite and axon fused so as to give the
Synapses may occur between the axon of appearance and function of a single pro-
one neuron and the cell body, dendrites, cess; this configuration is pseudounipo-
and/or axon of the postsynaptic neuron. lar. Multipolar neurons have a number of
Typically, each neuron synapses with many dendrites in addition to their single axon.
other neurons through the extensive Most neurons are multipolar in nature.
branching of its telodendrion and of its Nervous tissue consists of not only neu-
axon; branches of the main axon are axon rons but also supportive cells, which out-
collaterals. number the neurons by as much as 10 to
Neurons may be classified morphologi- one. These supportive cells are the neuro-
cally according to their number of nerve glia, or sometimes simply glia. The different