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Autonomic Nervous System - Anatomy & Physiology (view source)
Revision as of 16:56, 9 March 2011
, 16:56, 9 March 2011→Autonomic Nervous System: Basic Principles
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Both the SNS and PNS employ different forms of neurotransmitters to facilitate their signals. Preganglionic parasympathetic and sympathetic fibres utilise acetylcholine (ACh) as their neurotransmitter molecule, which are termed ''cholinergic'' neurones. Postganglionic PNS fibres also release ACh whilst nearly all postganglionic SNS fibres release norepinephrine as their neurotransmitter (there are exceptions to this rule but in general these are the expected neurotransmitters). Neurones releasing norepinephrine are called ''adrenergic''.
Both the SNS and PNS employ different forms of neurotransmitters to facilitate their signals. Preganglionic parasympathetic and sympathetic fibres utilise acetylcholine (ACh) as their neurotransmitter molecule, which are termed ''cholinergic'' neurones. Postganglionic PNS fibres also release ACh whilst nearly all postganglionic SNS fibres release norepinephrine as their neurotransmitter (there are exceptions to this rule but in general these are the expected neurotransmitters). Neurones releasing norepinephrine are called ''adrenergic''.
===SNS and PNS Integration===
Most organs in the body are under some form of autonomic control and therefore receive nerve fibres from both the SNS and PNS. There are some exceptions to this rule, for example, most blood vessels only receive an SNS supply. In organs where there is dual nerve fibre supply, the two divisions of the ANS almost always have opposing effects. Using the heart as an example, increased activity in the SNS leads to increased cardiac acitivity such as heart rate whilst stimulation of PNS fibres leads to reduced cardiac activity.
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The ANS integrating centres are located in the spinal cord, medulla oblongata and the hypothalamus. The hypothalamus functions as the principle coordinating centre for the ANS and also has the ability to affect other ANS coordination centres within other parts of the CNS. For example, there is a close association between the hypothalamus and the ''limbic system'' (emotion centre). There is also considerable connectivity between the hypothalamus and the cerebral cortex. Therefore autonomic functionality is not independent of thoughts or emotions; fear and anger have the ability to activate the SNS whilst anticipation of food stimulates the PNS resulting in increased salivation and intestinal peristalsis. It should be noted that although the ANS and higher processes such as the cerebral cortex are connected, the connection is indirect. Sensory cells within the ANS do not convey information directly to the cerebral cortex and therefore the animal is not normally aware of the impact that their thoughts and emotions are having on their organs.
==Sympathetic Nervous System==
==Sympathetic Nervous System==