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Another major difference between the two ANS (autonomic nervous systems) is divergence. Whereas in the parasympathetic division there is a divergence factor of roughly 1:4, in the sympathetic division there can be a divergence of up to 1:20. This is due to the number of synapses formed by the preganglionic fibers with ganglionic neurons.
There are two kinds of neurons involved in the transmission of any signal through the sympathetic system: pre-ganglionic and post-ganglionic. The shorter preganglionic neurons originate in the thoracolumbar division of the spinal cord specifically at T1 to L2~L3, and travel to a ganglion, often one of the paravertebral ganglia, where they synapse with a postganglionic neuron.
It is this ability to move superiorly and inferiorly along the chain that results in the mass response to the sympathetic nervous system. A preganglionic fibre may synapse to 15–20 postganglionic fibres. The postganglionic neurons extend across most of the body. [4]
Their axons continue away from the CNS to synapse at an autonomic ganglion. The parasympathetic ganglion where these preganglionic neurons synapse will be close to the organ of innervation. This differs from the sympathetic nervous system, where synapses between pre- and post-ganglionic efferent nerves in general occur at ganglia that are ...
The preganglionic neuron can travel superiorly or inferiorly to a sympathetic paravertebral ganglion of a higher or lower level where it can synapse with a postganglionic sympathetic neuron. From here, the postganglionic sympathetic neuron can travel back out the grey ramus communicans of that level to the mixed spinal nerve and on to an ...
Acetylcholine is the preganglionic neurotransmitter for both divisions of the ANS, as well as the postganglionic neurotransmitter of parasympathetic neurons. Nerves that release acetylcholine are said to be cholinergic. In the parasympathetic system, ganglionic neurons use acetylcholine as a neurotransmitter to stimulate muscarinic receptors.
The bodies of its preganglionic sympathetic afferent neurons are located in the lateral horn of the spinal cord. Their axons enter the SCG to synapse with postganglionic neurons whose axons then exit the rostral end of the SCG and proceed to innervate their target organs in the head.
Cranial nerve ganglia contain the cell bodies of cranial nerve neurons. Autonomic ganglia contain the cell bodies of autonomic nerves. In the autonomic nervous system, fibers from the central nervous system to the ganglia are known as preganglionic fibers, while those from the ganglia to the effector organ are called postganglionic fibers.