Chapter 6 - Impulse Transmission Through Autonomic Ganglia

Summary

Synaptic transmission from preganglionic to postganglionic neurons in autonomic ganglia is cholinergic nicotinic. Most autonomic ganglia transmit the central message with high accuracy to the postganglionic neurons. This concurs with the idea that the target tissues are predominantly under the control of the central nervous system. A small number of sympathetic preganglionic neurons connect to a large number of postganglionic neurons. This divergence is primarily for distribution. Additionally, postganglionic neurons receive convergent synaptic input from several preganglionic neurons. Neurons in sympathetic paravertebral and parasympathetic ganglia and some neurons in prevertebral ganglia receive one or two suprathreshold preganglionic synaptic inputs, the rest being subthreshold. Discharges in these postganglionic neurons are generated by strong synaptic inputs but not by summation of weak synaptic inputs. Some neurons with non-vascular functions in sympathetic prevertebral ganglia receive, in addition to preganglionic inputs, cholinergic synaptic inputs from peripheral intestinofugal neurons. In many sympathetic neurons of the prevertebral ganglia, and in some parasympathetic ganglia, the central synaptic input is weak or even may play a subordinate role. Nicotinic synaptic transmission in vasoconstrictor neurons in sympathetic ganglia can be enhanced by muscarinic and non-cholinergic mechanisms.