Page 239 - Anatomy and Physiology of Farm Animals, 8th Edition

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Motor cortex
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Brainstem motor nuclei
Figure 11-11. The motor cortex is populated by UMNs whose distribution creates a functional map
of the contralateral side of the body. The left side of the cerebrum (depicted here) therefore controls
voluntary movement predominantly on the right side of the body. The body map is distorted, with
regions (like the face) with fine motor control occupying a relatively larger region than areas (like the
trunk) with more power and less precision. UMNs of the motor cortex produce most voluntary move­
ments through the intermediaries of motor nuclei in the brainstem.

(associated with cranial nerves) and spinal of practiced movements are virtually auto­
cord (associated with spinal nerves). This matic and can be done with very little con­
is in contrast to voluntary movements in scious direction. Repeatedly practicing a
primates (including humans) in whom the movement with the goal of making it more
motor cortex has many axons that directly accurate and automatic has often been
influence LMNs. The UMNs that arise in called “muscle memory,” but inasmuch as it
the brainstem of domestic animals trans­ is the nervous system that is learning (and
mit motor instructions from the motor not the muscle tissue), it is more accurately
cortex to LMNs to carry out voluntary referred to as “motor memory” or “proce­
movements. dural memory.” The cerebellum along with
Accuracy and efficiency of movement the basal nuclei (see Chapter 10) appear to
is greatly enhanced by the participation of the have special importance in the sort of
cerebellum. As one of its main functions, the memory that makes practiced movements
cerebellum receives sensory information skilled and automatic.
about movement, compares it to the intended
motor plan, then modifies the output of
UMNs so that the actual movement is more Physiology of the Autonomic
accurate and smooth. The cerebellum does Nervous System
not initiate movements, but it is essential
for normal coordination of voluntary move­ Regulation of Autonomic Nervous
ments. Cerebellar dysfunction does not System Activity
produce weakness or paralysis, but instead
results in exaggerated, crude, and poorly The ANS exists to maintain a relatively
timed movements. stable internal body environment and to
It is clear that repetition of patterns of enable the body to respond to stressors. It
movements increases the ease with which accomplishes this through autonomic
those movements can be repeated; this reflexes. The motor output of autonomic
amounts to a kind of learning and memory. reflexes, the visceral motor system, is divided
After such motor learning occurs, a series into sympathetic and parasympathetic