The presynaptic nerve cell bodies of the parasympathetic system are located in two sites: the gray matter of the brainstem (cranial parasympathetic out ow) and in the gray matter of the sacral segments of the spinal cord (sacral parasympathetic out ow).
DISTRIBUTION OF SYMPATHETIC NERVE FIBERS
The cell bodies of presynaptic neurons of the sympathetic system are located in the intermediolateral cell column and extend between the rst thoracic and the second lumbar segments of the spinal cord.
VISCERAL AFFERENT AND VISCERAL EFFERENT (MOTOR) INNERVATION
Schematic illustration. Visceral afferent bers have important relationships to the central nervous system (CNS), both anatomically and functionally. We are usually unaware of the sensory input of these bers, which provides information about the condition of the body’s internal environment. This information is integrated in the CNS, often triggering visceral or somatic re exes or both. Visceral re exes regulate blood pressure and chemistry by altering such functions as heart and respiratory rates and vascular resistance. Visceral sensation that reaches a conscious level is generally categorized as pain that is usually poorly localized and may be perceived as hunger or nausea. However, adequatestimulation may elicit true pain. Most visceral/ re ex (unconscious) sensation and some pain travel in visceral afferent bers that accompany the parasympathetic bers retrograde. Most visceral pain impulses (from the heart and most organs of the peritoneal cavity) travel along visceral afferent bers accompanying sympathetic bers. Visceral efferen t (motor) in n ervation . The efferent nerve bers and ganglia of the ANS are organized into two systems or divisions.
1. Symp athet ic (thoracolumbar) d ivision. In general, the effects of sympathetic stimulation are catabolic (preparing the body for “ ight or ght”).
2. Parasympathet ic (craniosacral) division. In general, the effects of parasympathetic stimulation are anabolic (promoting normal function and conserving energy). Conduction of impulses from the CNS to the effector organ involves a series of two neurons in both sympathetic and parasympathetic systems. The cell body of the presynaptic (preganglionic) neuron ( rst neuron) is located in the gray matter of the CNS. Its ber (axon) synapses on the cell body of a postsynaptic (postganglionic) neuron, the second neuron in the series. The cell bodies of such second neurons are located in autonomic ganglia outside the CNS, and the postsynaptic bers terminate on the effector
VISCERAL AFFERENT AND VISCERAL EFFERENT (MOTOR) INNERVATION (continued )
Courses taken by sympathetic motor bers. Presynaptic bers all follow the same course until they reach the sympathetic trunks. In the sympathetic trunks, they follow one of four possible courses. Fibers involved in providing sympathetic innervation to the body wall and limbs or viscera above the level of the diaphragm follow paths 1 to 3. They synapse in the paravertebral ganglia of the sympathetic trunks. Fibers involved in innervating abdominopelvic viscera follow path 4 to prevertebral ganglion via abdominopelvic splanchnic nerves. Postsynaptic bers usually do not ascend or descend within the sympathetic trunks, exiting at the level of synapse.
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