The autonomic nervous system is made up of nerves supplying the viscera (and blood vessels) along with the parts of the brain and spinal cord related to them. It is subdivided into two divisions, sympathetic and parasympathetic. Both these divisions contain efferent as well as afferentfibres. The efferent fibres supply smooth muscle throughout the body. The influence may be either to cause contraction or relaxation. In a given situation, the sympathetic and parasympathetic nerves generally produce opposite effects. For example, sympathetic stimulation causes dilatation of the pupil, whereas parasympathetic stimulation causes constriction. In hollow viscera like the stomach or urinary bladder, parasympathetic stimulation produces movement and inhibits the sphincters. An opposite sympathetic effect is usually described. In the case of blood vessels, the influence on smooth muscle may result in vasoconstriction or in vasodilatation.
In addition to supplying smooth muscle autonomic nerves innervate glands. Such nerves are described as secretomotor. The secretomotor nerves to almost all glands are parasympathetic. The only exception are the sweat glands which have a sympathetic supply.
The autonomic nervous system includes the following.
These are the structures in the limbic region which have been considered. The hypothalamus, parts of the thalamus, and the prefrontal cortex are also involved in autonomic functions.
These are located in the reticular formation and in the general visceral nuclei of cranial nerves.
These are located in the intermediolateral grey column.
This is made up of all autonomic nerves and ganglia throughout the body. Many of these are intimately related to cranial and spinal nerves.
For details of peripheral autonomic pathways see the author’s TEXTBOOK OF HUMAN ANATOMY. The description that follows aims at providing a simple account of neuronal arrangements within the system and the autonomic innervation of important organs.
Before we can consider the arrangement of neurons it is necessary to take a brief look at some aspects of gross anatomy.