Special Histology and Embryology: Practical Manual - V. K. Napkhanyuk 2001

Nervous System
Autonomic Nervous System
Nerve Trunks and Nerve Ganglia

Nerve trunks, or nerves (nervus), consist of myelinated and unmyelinated fibers along with Connective Tissue sheaths. A cross-section of a nerve reveals a plexus of axonal cylinders of nerve fibers surrounded by glial sheaths. The nerve trunk contains thin layers of connective tissue between the nerve fibers, which, depending on their Location, are divided into the endoneurium, surrounding an individual nerve fiber; the perineurium, surrounding a bundle of nerve fibers; and the epineurium, enclosing the entire nerve.

A nerve ganglion (ganglion nervorum) is an accumulation of Nerve Cells located outside the Central Nervous system (micrograph 1).

Nerve ganglia can be sensory or autonomic. Externally, they are surrounded by a connective tissue capsule, from which trabeculae extend into the interior of the ganglion. The neurocytes of a ganglion may be pseudounipolar (spinal ganglion) or multipolar (autonomic nerve ganglia). In addition to neurocytes, the ganglion also contains nerve fibers and gliocytes. Sympathetic nerve ganglia (nerve ganglia) are typically located outside the organ, while parasympathetic ones are situated within the organ wall (intramurally). Neurons of spinal ganglia are sensory, whereas those of autonomic ganglia are efferent.

Nerve endings (terminationes nervorum) are classified into receptors, effectors, and interneuronal synapses.

Receptors (receptores) are specialized sensory endings of nerve Cell dendrites adapted to perceive stimuli acting upon the Organism: exteroceptors perceive external stimuli, while interteroceptors perceive stimuli from Internal Organs and tissues, which in turn are subdivided into thermoreceptors, baroreceptors, mechanoreceptors, and nociceptors.

Depending on their Structure, there are free nerve endings, and non-free nerve endings, which can be either encapsulated or unencapsulated.

Effectors (effectores) are formed by the terminals of neurocyte axons and are of two types: motor and secretory.

Interneuronal synapses (synapsis interneuronalis) represent a specialized form of Intercellular junctions characteristic of Nervous Tissue, consisting of two parts: 1) the presynaptic component, formed by the terminal branch of the axon of the neuron transmitting the impulse; and 2) the postsynaptic component, which contains a specialized protein—the neurotransmitter receptor. Functionally, synapses are distinguished into excitatory and inhibitory.

Morphologically, the following types of synapses are distinguished: axodendritic; axosomatic; axoaxonic.