Anatomy of the Vessels and Nerves of the Trunk (Angioneurology) - Chornokulskyi S. T. 2011

Autonomic (Vegetative) Nervous System

The Autonomic Nervous system — A.N.S. (from autos — self, nomos — law) — is that part of the unified nervous system specialized in the following Functions:

1. Adaptive-trophic — maintaining Homeostasis by regulating METABOLISM at the organ, tissue, and cellular levels in response to environmental conditions;

2. Contractile with respect to the non-striated (smooth) musculature of the body;

3. Secretory — stimulation or inhibition of the secretion of all glands;

4. REGULATION OF CARDIAC Muscle activity.

Based on morphological, neurochemical, and functional features, the autonomic nervous system is divided into sympathetic, parasympathetic, and metasympathetic divisions (partes sympathica, parasympathica, metasympathica). Debates are still ongoing regarding the metasympathica division: whether it is an independent complex of microganglionic structures forming nerve plexuses in the walls of Organs with noticeable motor activity (Heart, intestine, Ureters), or an intramural nervous system acting as a component of the parasympathetic division.

Morphological Features of the Autonomic Nervous System

1. The nuclei of the autonomic nervous system (A.N.S.) are located in the Brain AND SPINAL cord in localized clusters (focal distribution), which is also characteristic of the nerves originating from them.

2. The Cell bodies of the efferent Neurons of the A.N.S. are housed in ganglia across three Relay stages and lie outside the Central Nervous System (C.N.S.). Nerve fibers reaching a ganglion are preganglionic, whereas those extending from the ganglion to the effector organ after synapsing are postganglionic.

3. The efferent peripheral pathway of the A.N.S. reflex arc is two-neuron: the 1st neuron is located in the focal nuclei of the C.N.S., and the 2nd neuron is in the ganglia. For the Sympathetic division of the A.N.S., this occurs in the first- and second-order ganglia, while for the parasympathetic division, it occurs in the third-order ganglia (terminal — pre- and intramural).

4. The cell bodies of the afferent neurons of the A.N.S. reflex arc are located in the sensory ganglia of Cranial and Spinal Nerves (ganglia sensoria nervi craniales et spinales).

5. The innervation territory of the A.N.S. is larger than that of the somatic nervous system. The higher (suprasegmental) centers of the autonomic nervous system are shared by both its sympathetic and parasympathetic divisions.