ANS

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The autonomic nervous system (ANS or visceral nervous system or involuntary nervous system) is the part of the peripheral nervous system that acts as a control system, functioning largely below the level of consciousness, and controls visceral functions.[1] The ANS affects heart rate, digestion, respiratory rate, salivation, perspiration, pupillary dilation, micturition (urination), and sexual arousal. Most autonomous functions are involuntary but a number of ANS actions can work alongside some degree of conscious control. Everyday examples include breathing, swallowing, and sexual arousal, and in some cases functions such as heart rate.

Within the brain, the ANS is located in the medulla oblongata in the lower brainstem. The medulla's major ANS functions include respiration (the respiratory control centre, or "rcc"), cardiac regulation (the cardiac control centre, or "ccc"), vasomotor activity (the vasomotor centre or "vmc"), and certain reflex actions (such as coughing, sneezing, vomiting and swallowing). These then subdivide into other areas and are also linked to ANS subsystems and nervous systems external to the brain. The hypothalamus, just above the brain stem, acts as an integrator for autonomic functions, receiving ANS regulatory input from the limbic system to do so.[2]

The ANS is classically divided into two subsystems: the parasympathetic nervous system (PSNS) and sympathetic nervous system (SNS),[1][3]

which operate independently in some functions and interact

co-operatively in others. In many cases, the two have "opposite" actions

where one activates a physiological response and the other inhibits it.

An older simplification of the sympathetic and parasympathetic nervous

systems as "excitory" and "inhibitory" was overturned due to the many

exceptions found. A more modern characterisation is that the sympathetic

nervous system is a "quick response mobilising system" and the

parasympathetic is a "more slowly activated dampening system", but even this has exceptions, such as in sexual arousal and orgasm, wherein both play a role.[2] The enteric nervous system is also sometimes considered part of the autonomic nervous system,[2] and sometimes considered an independent system.

In general, ANS functions can be divided into sensory (afferent) and motor (efferent) subsystems. Within both, there are inhibitory and excitatory synapses

between neurons. Relatively recently, a third subsystem of neurons that

have been named 'non-adrenergic and non-cholinergic' neurons (because

they use nitric oxide as a neurotransmitter) have been described and

found to be integral in autonomic function, in particular inhttp://en.wikipedia.org/wiki/Autonomic_nervous_system the gut and

the lungs.[4]

Contents

1 Anatomy

1.1 Sympathetic division

1.2 Parasympathetic division

1.3 Sensory neurons

1.4 Motor neurons

2 Function

2.1 Sympathetic nervous system

2.2 Parasympathetic nervous system

3 Neurotransmitters and pharmacology

3.1 Circulatory system

3.1.1 Heart

3.1.2 Blood vessels

3.1.3 Other

3.2 Respiratory system

3.3 Visual System

3.4 Digestive system

3.5 Endocrine system

3.6 Urinary system

3.7 Reproductive system

3.8 Integumentary system

4 References

5 External links

ANS - Overview

Contents