Tap to Read ➤

Structure and Functions of the Sympathetic Nervous System

Dr. Sumaiya Khan Oct 9, 2018
Here is some information about the sympathetic nervous system and its related functions.
The human body nervous system is divided into the central and the peripheral nervous system. The autonomic system (a part of the peripheral system) is further divided into three parts - the enteric system, the sympathetic system and the parasympathetic system.
The sympathetic nervous system is involved in controlling the functioning of the body below the level of consciousness.


Sympathetic nerves originate in the vertebral column beginning in the first thoracic segment of the spinal cord, extending till the second or third lumbar segments. In order to reach the various target organs, the axons of the nerves travel along long distances in the body.
Information travels through this system in a bidirectional flow, i.e., messages can simultaneously trigger different changes in the body. This is important, because the main function of this system is to bring about instant changes in the body, which readies it for facing a stressful situation.


The sympathetic system is responsible for mobilizing the body's responses under stressful situations. It is supposed to initialize the 'flight or fight' response of the body. It is a part of the nervous system, which is responsible for mediating the neuronal and hormonal stress response. It acts on many organs of the body:
  • It acts on the eyes by increasing the diameter of the pupil by dilation.
  • It acts on the heart to increase the heart rate, by increasing the force of contraction of the heart muscles. This system is directly related to blood pressure, as an increase in the heart rate and force of contraction eventually leads to a rise in blood pressure.
  • It acts on the lungs by causing dilation of the bronchioles, so as to increase the airway passage that is available.
  • It acts on the digestive system by preventing and inhibiting the movement of food.
  • It acts on the kidneys to increase the secretion of renin.
  • It acts on the penis to promote ejaculation.
Thus, the system's response is such that it equips the body to handle a situation of stress. It primarily activates large amounts of secretion of adrenaline from the adrenal glands. It is also active at a basal level, so as to maintain a state of homeostasis in the body.


There are many diseases that can affect the functioning of the sympathetic system. These conditions tend to slowly cause degeneration of the nerves, thereby affecting their transmission system. One of the long term effects of alcohol includes degeneration of the peripheral nervous system.
Initial consumption of alcohol causes alcoholic cardiomyopathy, which is said to occur due to an increase in the sympathetic output. One of the illnesses that affects the central and autonomic nervous system is Parkinson's disease.
In this ailment, besides impairment of motor skills, there also is alteration in the functioning of the autonomic system, leading to secondary symptoms like orthostatic hypotension, oily skin, excessive sweating, urinary incontinence, altered sexual functions, etc.