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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.
Presynaptic neuronal voltage-gated N-calcium channels are largely responsible for the release of this glutamate as well as the neuropeptide, substance P. [5] The expression of presynaptic neuronal voltage-gated N-calcium channels increases after a nerve lesion or repeated stimulation. [ 5 ]
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.
As in the sympathetic nervous system, efferent parasympathetic nerve signals are carried from the central nervous system to their targets by a system of two neurons. The first neuron in this pathway is referred to as the preganglionic or presynaptic neuron.
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 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 from the intermediolateral nucleus in the lateral grey column of the spinal cord are carried in the white ramus communicans to the paravertebral ganglia of the sympathetic trunk. Once the preganglionic nerve has traversed a white ramus communicans, it can do one of three things.
Axon terminals (also called terminal boutons, synaptic boutons, end-feet, or presynaptic terminals) are distal terminations of the branches of an axon. An axon, also called a nerve fiber, is a long, slender projection of a nerve cell that conducts electrical impulses called action potentials away from the neuron's cell body to transmit those ...