Preganglionic Neurons Are Influenced by Many Regions of the Brain

Much as the lower motor neuron of the somatic system is influenced by the upper motor neuron (see Chapter 9), the

FIGURE 13-5 Autonomic control areas of the brainstem and diencephalon.

preganglionic autonomic neuron is also influenced by CNS axons descending from the brainstem, hypothalamus, and even the cerebral cortex. Many brainstem nuclei are known to influence preganglionic neurons in order to control particular visceral functions; Figure 13-5 illustrates several such regions. In turn, each of these brainstem regions can be influenced by the hypothalamus and cerebral cortex of the forebrain, creating a complex system of upper motor neurons within the CNS that helps coordinate autonomic reflexes and directly influences action potential frequency within pre­ganglionic neurons. As more is learned about these central systems controlling the ANS, their role in such conditions as hypertension and various gastrointestinal diseases may become clearer.