SNS and PNS

Topics: Nervous system, Acetylcholine, Parasympathetic nervous system Pages: 3 (896 words) Published: May 4, 2014

The autonomic nervous system (ANS) consists of three main anatomical divisions: sympathetic, parasympathetic and enteric nervous systems. The sympathetic (SNS) and parasympathetic (PNS) systems provide a link between the central nervous system and peripheral organs.

The sympathetic nervous system originates in the spinal cord. Specifically, the cell bodies of the first neuron (the preganglionic neuron) are located in the thoracic and lumbar spinal cord. Axons from these neurons project to a chain of ganglia located near the spinal cord. In most cases, this neuron makes a synapse with another neuron (post-ganglionic neuron) in the ganglion. A few preganglionic neurons go to other ganglia outside of the sympathetic chain and synapse there. The post-ganglionic neuron then projects to the "target" - either a muscle or a gland. The sympathetic nervous system operates through a series of interconnected neurons. The synapse in the sympathetic ganglion uses acetylcholine (Ach) as a neurotransmitter; the synapse of the post-ganglionic neuron with the target organ uses the neurotransmitter called Noradrenaline (NA). However, there is one exception: the sympathetic post-ganglionic neuron that terminates on the sweat glands uses acetylcholine.

The cell bodies of the parasympathetic nervous system are located in the spinal cord (sacral region) and in the medulla. In the medulla, the cranial nerves III, VII, IX and X form the preganglionic parasympathetic fibres. The preganglionic fibre from the medulla or spinal cord projects to ganglia very close to the target organ and makes a synapse. This synapse uses the neurotransmitter called acetylcholine. From this ganglion, the post-ganglionic neuron projects to the target organ and uses acetylcholine again at its terminal.

The two main neurotransmitters that operate in the autonomic system are acetylcholine and noradrenaline.

This diagram taken from Rang and Dale Pharmacology shows the type of postsynaptic...
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