The autonomic nervous system regulates certain body processes, such as blood pressure and the rate of breathing. This system works automatically (autonomously), without a person's conscious effort.
Disorders of the autonomic nervous system can affect any body part or process. Autonomic disorders may result from other disorders that damage autonomic nerves (such as diabetes), or they may occur on their own. Autonomic disorders may be reversible or progressive.
Anatomy: The autonomic nervous system is the part of the nervous system that supplies the internal organs, including the blood vessels, stomach, intestine, liver, kidneys, bladder, genitals, lungs, pupils, heart, and sweat, salivary, and digestive glands.
The autonomic nervous system has two main divisions:
Sympathetic
Parasympathetic
After the autonomic nervous system receives information about the body and external environment, it responds by stimulating body processes, usually through the sympathetic division, or inhibiting them, usually through the parasympathetic division.
An autonomic nerve pathway involves two nerve cells. One cell is located in the brain stem or spinal cord. It is connected by nerve fibers to the other cell, which is located in a cluster of nerve cells (called an autonomic ganglion). Nerve fibers from these ganglia connect with internal organs. Most of the ganglia for the sympathetic division are located just outside the spinal cord on both sides of it. The ganglia for the parasympathetic division are located near or in the organs they connect with.
Function:
The autonomic nervous system controls blood pressure, heart and breathing rates, body temperature, digestion, metabolism (thus affecting body weight), the balance of water and electrolytes (such as sodium and calcium), the production of body fluids (saliva, sweat, and tears), urination, defecation, sexual response, and other processes.
Many organs are controlled primarily by either the sympathetic or the parasympathetic division. Sometimes the two divisions have opposite effects on the same organ. For example, the sympathetic division increases blood pressure, and the parasympathetic division decreases it. Overall, the two divisions work together to ensure that the body responds appropriately to different situations.
Autonomic Nervous System
Generally, the sympathetic division prepares the body for stressful or emergency situations—fight or flight. Thus, it increases heart rate and the force of heart contractions and widens (dilates) the airways to make breathing easier. It causes the body to release stored energy. Muscular strength is increased. This division also causes palms to sweat, pupils to dilate, and hair to stand on end. It slows body processes that are less important in emergencies, such as digestion and urination.
The parasympathetic division controls body process during ordinary situations. Generally, it conserves and restores. It slows the heart rate and decreases blood pressure. It stimulates the digestive tract to process food and eliminate wastes. Energy from the processed food is used to restore and build tissues.
Both the sympathetic and parasympathetic divisions are involved in sexual activity, as are the parts of the nervous system that control voluntary actions and transmit sensation from the skin (somatic nervous system).
Increases the following:
Heart rate and force of heart contractions
Release of energy stored in the liver
The speed at which energy is used to perform body functions while a person is at rest (basal metabolic rate)
Muscle strength
Widens the airways to make breathing easier
Causes sweaty palms
Decreases functions that are less important in an emergency (such as digestion and urination)
Controls the release of semen (ejaculation)
Parasympathetic
Stimulates the digestive tract to process food and eliminate wastes (in bowel movements)
Slows the heart rate
Reduces blood pressure
Controls erections
Two chemical messengers (neurotransmitters), acetylcholine and norepinephrine, are used to communicate within the autonomic nervous system. Nerve fibers that secrete acetylcholine are called cholinergic fibers. Fibers that secrete norepinephrine are called adrenergic fibers. Generally, acetylcholine has parasympathetic (inhibiting) effects and norepinephrine has sympathetic (stimulating) effects. However, acetylcholine has some sympathetic effects. For example, it sometimes stimulates sweating or makes the hair stand on end.
Symptoms
In men, difficulty initiating and maintaining an erection (erectile dysfunction) can be an early symptom of an autonomic disorder.
Autonomic disorders commonly cause dizziness or light-headedness due to an excessive decrease in blood pressure when a person stands (orthostatic hypotension).
People may sweat less or not at all and thus become intolerant of heat. The eyes and mouth may be dry.
After eating, a person with an autonomic disorder may feel prematurely full or even vomit because the stomach empties very slowly (called gastroparesis). Some people pass urine involuntarily (urinary incontinence), often because the bladder is overactive. Other people have difficulty emptying the bladder (urine retention) because the bladder is underactive. Constipation may occur, or control of bowel movements may be lost.
The pupils may not dilate and narrow (constrict) as light changes.
Diagnosis
Doctors can check for signs of autonomic disorders during the physical examination. They measure blood pressure and heart rate while a person is lying down or sitting and after the person stands. …………..
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Topic: Autonomic nervous system (explained) (Read 3192 times)