Definition of the Autonomic Nervous System

What is Autonomic Nervous System: Function, Definition & Divisions

The autonomic nervous system is composed of nerve fibers originating from the brain and from the spinal cord and to the organs concerned. In this system, there are several pathways and each pathway forms a complex synapse and also forms a ganglion. The nerves at the base of the ganglion are called preganglionic nerves and those at the end of the ganglion are called postganglionic nerves.

The autonomic nervous system is the part of the peripheral nervous system that acts largely independently of conscious (intentional) control and consists of nerves in cardiac muscle, smooth muscle, exocrine and endocrine glands.

The autonomic nervous system is responsible for maintenance functions (metabolism, cardiovascular activity, temperature regulation, digestion) that have a reputation for being out of conscious control. The other major division of the peripheral nervous system, the somatic nervous system, consists of the cranial and spinal nerves which innervate the skeletal muscle tissue and are more under voluntary control (Anissimov 2006; Towle 1989).

The autonomic nervous system functions to maintain a state of the body in a controlled condition without conscious control. The autonomic nervous system works automatically without commands from the conscious nervous system. The autonomic nervous system is also called the involuntary nervous system because it works outside of consciousness. Tissue structures controlled by the autonomic nervous system are the heart muscle, blood vessels, iris, thoracic, abdominal and glandular organs. In general, the autonomic nervous system is divided into two parts, namely the sympathetic nervous system and the parasympathetic nervous system.

The nervous system is broadly divided into the central nervous system (CNS) and the peripheral nervous system (PNS). The PNS has 2 divisions, namely the sensory nervous system and motor nerves, then the sensory nerves are divided into sensory somatic nerves and sensory visceral nerves while motor nerves are divided into somatic motor nerves and autonomic motor nerves. The following is an illustration of the organization of the nervous system.


Based on the image above, the CNS receives sensory information from somatic and visceral afferent nerves. Furthermore, sensory information will be integrated in the central nervous system which consists of the cerebrum, brain stem and spinal cord. Furthermore, the CNS will react via efferent nerves, namely somatic motor nerves and visceral motor nerves (autonomic nerves). The autonomic nerves are divided into 2, namely the sympathetic and parasympathetic nerves.

The autonomic nervous system ( autonomic-auto=self; nom=govern ) works subconsciously. There are 3 things that distinguish between somatic and autonomic motor nerves, namely:

Effector: Somatic motor nerves will stimulate skeletal muscles, while autonomic nerves will innervate visceral organs such as heart muscle, intestines, etc.

Efferent pathways and ganglion: Somatic nerve cell bodies are located in the CNS to form the nucleus (nerve nucleus) and their axons to skeletal muscles and these axons have thick and myelinated characteristics that conduct nerve impulses rapidly.

Neurotransmitters: all somatic motor nerves will release the neurotransmitter acetylcholine (ACh) which has an excitatory effect that causes skeletal muscles to contract while autonomic nerves will release postganglionic neurotransmitters in the form of norepinephrine at the postganglionic axon synapse of the sympathetic nerve and acetylcholine at the postganglionic axon synapse of the parasympathetic nerve which can cause excitation. or inhibition of the target organ depending on the receptor it has.

Autonomous Nerve Anatomy

Anatomically the sympathetic nerves and parasympathetic nerves are distinguished based on the following:

1. Location: The parasympathetic nerves originate from the brain and the craniosacral portion of the spinal cord, while the sympathetic nerves originate from the thoracolumbar spinal cord as shown in the image below.


2. Length of neurons: In contrast, sympathetic nerves have shorter preganglionic neurons and longer postganglionic neurons.

Length of neurons

In contrast, the parasympathetic nerves have long preganglionic neurons and shorter postganglionic neurons.

3. Location of ganglion: The parasympathetic ganglion is located in the visceral organs innervated while the sympathetic ganglion is located adjacent to the spinal cord.

Location of ganglion

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