Sympathetic ganglia, location

As in the sympathetic division, parasympathetic preganglionic neurons synapse in the periphery with a postganglionic fiber. This synapse usually takes place in a terminal ganglion that is located directly in the organ or tissue supplied by the postganglionic neuron. Consequently, the parasympathetic ganglia are usually embedded directly in the innervated organ or tissue. 

The enteric nervous system (see Chapter 6 Introduction to Autonomic Pharmacology) is composed of interconnected networks of ganglion cells and nerve fibers mainly located in the submucosa (submucosal plexus) and between the circular and longitudinal muscle layers (myenteric plexus). These networks give rise to nerve fibers that connect with the mucosa and deep muscle. Although extrinsic sympathetic and parasympathetic nerves project onto the submucosal and myenteric plexuses, the enteric nervous system can independently regulate gastrointestinal motility and secretion. Afferent fibers present in the mucosa and muscularis connect to cell bodies in the plexuses that mediate local reflexes. 

Nicotinic mechanism The mechanism of nicotinic action has been clearly defined. The ACh receptor is located on a channel protein that is selective for sodium and potassium. When the receptor is activated, the channel opens and depolarization of the cell (an excitatory postsynaptic potential EPSP) occurs as a direct result of the influx of sodium. These ACh receptors are present on ganglion cells (both sympathetic and parasympathetic) and the neuromuscular end plate. If large enough, the EPSP evokes a propagated action potential in the surrounding membrane. 

Ganglionic transmission Acetylcholine transmits both sympathetic and parasympathetic impulses from the "preganglionic" neurons in the brain and spinal cord to nicotinic ganglionic (N ) receptors on "postganglionic" neurons of the autonomic nervous system. This occurs in sympathetic ganglia, which are located along the spinal cord, and in parasympa-... 

The morphology of a neuron is characterized by a prominent round nucleus cell body, an axon (a long cell process), and dendrites (numerous short cell processes). The nervous system contains a network of neurons that communicate with each other by means of the synapse. The cell bodies of peripheral neurons originate in the spinal cord, specifically the dorsal root ganglion and autonomic ganghon, while the axons extend from the centrally located cell bodies and terminate in neuromuscular endings (motor neurons), end organs, or receptors (sensory or sympathetic fibers). 

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