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What is the Autonomic Nervous System? What is the Parasympathetic nervous system or the parasympathetic division of the Autonomic nervous system?
The parasympathetic division comprises a cranial portion,
emanating from the brainstem, and a sacral portion, originating
in the intermediate gray zone of the sacral spinal cord.
In contrast to the widespread activation
pattern of the sympathetic division, the neurons of the parasympathetic
division are activated in a more localized fashion.
There is also much less tendency for divergence of the
presynaptic influence to multiple postsynaptic neurons-on
average, one presynaptic parasympathetic neuron synapses
with 15 to 20 postsynaptic neurons. An example of localized
activation is seen in the vagus nerve, where one portion of
its outflow can be activated to slow the heart rate without
altering the function of the stomach.
Ganglia in the parasympathetic division are either
located close to the organ innervated or embedded within its
walls. Th e organs of the GI system demonstrate the latter pattern.
Because of this arrangement, preganglionic axons are
much longer than postganglionic axons.
16 сен 2024
