Ganglia are clusters of neuronal cell bodies located outside the central nervous system (CNS); nerve fibers lead to and from them. Sensory ganglia lie just outside the CNS and contain the cell bodies of sensory nerves that carry impulses into the CNS. Autonomic ganglia are pe-ripheral motor ganglia of the autonomic nervous system (ANS) and contain the cell bodies of postsynaptic neurons that conduct nerve im-pulses to smooth muscle, cardiac muscle, and glands. Synapses between presynaptic neurons (all of which have their cell bodies in the CNS) and postsynaptic neurons occur in autonomic ganglia. Sympathetic ganglia constitute a major subclass of autonomic ganglia; parasym-pathetic ganglia and enteric ganglia constitute the other subclasses. Sympathetic ganglia are located in the sympathetic chain (paravertebral ganglia) and on the anterior surface of the aorta (prevertebral ganglia). They send long postsynaptic axons to the viscera. Parasympathetic ganglia (terminal ganglia) are located in, or close to, the or-gans innervated by their postsynaptic neurons. The enteric ganglia are located in the submucosal plexus and the myenteric plexus of the ali-mentary canal. They receive parasympathetic presynaptic input as well as intrinsic input from other enteric ganglia and innervate smooth muscle of the gut wall.
Sympathetic ganglion, human, silver and H&E stains ×160.
A sympathetic ganglion stained with silver and counter-stained with H&E is illustrated here. Shown to advantage are several discrete bundles of nerve fibers (NF) and numerous large circular structures, namely, the cell bodies (CB) of the postsynaptic neurons. Random patterns of nerve fibers are also seen. Moreover, careful examination of the cell bodies shows that some display several processes joined to them. Thus, these are multipolar neurons (one contained within the rectangle is shown at higher magnification). Generally, the connective tissue is not conspicuous in a silver preparation, although it can be identified by virtue of its location about the larger blood vessels (BV), particularly in the upper part of this figure.
PLATE 27 • SYM PATH ETIC AN D DORSAL ROOT GANG LIA KEY A, axon BV, blood vessels CB, cell body of neuron CT, connective tissue L, lipofuscin N, nucleus of nerve cell NF, nerve fibers NL, nucleolus P, processes of nerve cell body Sat C, satellite cells arrowheads, neurilemma asterisks, clusters of satellite cells
Sympathetic ganglion, human, silver and H&E stains ×500.
The cell bodies of the sympathetic ganglion are typically large, and the one labeled here shows several processes (P). In addition, the cell body contains a large, pale-staining spherical nucleus (N); this, in turn, contains a spherical, intensely staining nucleolus (NL). These features, namely, a large pale-staining nucleus (indicating much-extended chromatin) and a large nucleolus, reflect a cell active in protein synthesis. Also shown in the cell body are accumulations of lipofuscin (L), a yellow pigment that is darkened by the silver. Because of the large size of the cell body, the nucleus is not always included in the section; in that case, the cell body appears as a rounded cytoplasmic mass.
Dorsal root ganglion, cat, H&E ×160.
Dorsal root ganglia differ from autonomic ganglia in a number of ways. Whereas the latter contain multipolar neurons and have synaptic connections, dorsal root ganglia contain pseudounipolar sensory neurons and have no synaptic connections in the ganglion.