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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.
The first neuron in this pathway is referred to as the preganglionic or presynaptic neuron. Its cell body sits in the central nervous system and its axon usually extends to synapse with the dendrites of a postganglionic neuron somewhere else in the body. The axons of presynaptic parasympathetic neurons are usually long, extending from the CNS ...
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.
The motor root carries presynaptic parasympathetic nerve fibers that terminate in the ganglion and synapse with the postsynaptic fibers that, in turn, project to target organs. The sympathetic root carries postsynaptic sympathetic fibers ( GVE ) that traverse the ganglion without synapsing.
Preganglionic sympathetic fibers originate from neurons in the intermediolateral column of the thoracic spinal cord, at the level of thoracic spinal nerve 1 (T1) and thoracic spinal nerve 2 (T2). They form synapses in the superior cervical ganglion. The ratio of incoming to outgoing fibers (the “convergence”) in this ganglion is ...
The autonomic nervous system is unique in that it requires a sequential two-neuron efferent pathway; the preganglionic neuron must first synapse onto a postganglionic neuron before innervating the target organ. The preganglionic, or first, neuron will begin at the "outflow" and will synapse at the postganglionic, or second, neuron's cell body.
The white ramus communicans (pl.: rami communicantes) from Latin ramus (branch) and communicans (communicating) is the preganglionic sympathetic outflow nerve tract from the spinal cord. Each of the thoracic, and the first and second lumbar nerves contribute a white ramus communicans to the adjoining sympathetic ganglion , unlike the gray rami ...
The second-order neurons ascend to the brain stem and thalamus in the ventrolateral, or anterolateral, quadrant of the contralateral half of the spinal cord, forming the spinothalamic tract. [1] The spinothalamic tract is the main pathway associated with pain and temperature perception, which immediately crosses the spinal cord laterally. [1]