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1.2.8 The visceral nervous system
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From the course by Peking University
Advanced Neurobiology I
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From the lesson
Anatomy of the Nervous System
Let's start with a basic introduction of neuroanatomy.
Meet the Instructors
Yan ZhangProfessor
School of Life Sciences, Peking University
Yulong LiResearch Fellow
School of Life Sciences, Peking University
The visceral nervous system.
The visceral nervous system controls the movement of our visceral and
will get the input information from our visceral system.
There are two parts of the visceral system,
one is the motor nerve, the other one is the sensory nerve.
The motor nerve, there are two major components for the motor nerve.
One is the sympathetic system, the other one is the parasympathetic system.
These two systems are most likely counterpart to each other.
Lots of the function, or lots of the effect from
these two systems can for each other.
In our spinal cord system, lots of the nerves
start from the spinal cord myelinated here
by Schwann cells or dendricite cells.
For periphery system, most of the time, it's a Schwann cell.
The myelination itself will increase the transport
efficiency of the electric signals through the nerve.
The somatic motor neuron normally is myelinated
pretty well and then through the spinal chord.
The motor neuron send out the motor information to the muscle and
then the ACh is acetylcholine is one of the major neurotransmitters
released by the nerve terminal of the motor neuron.
Acetylcholine will get into or
through the synaptic cleft, get onto the muscle surface or
bind to the acetylcholine receptors on the muscle surface and
then the muscle surface can contract upon
receiving acetylcholine stimulation.
For automatic motor neurons,
sometimes these neurons are not myelinated and then for
the presynaptic, sometimes, there's a relay in this system.
Before the relay, the nerves
are mostly myelinated and after the relay,
sometimes the post-ganglion part of this neuron can be unmyelinated.
Then for this system, the effector sometimes can be muscle but
most of the time it's not muscle, itself, it is sometimes your
bracing system, sometimes it's a gland cell.
From the spinal cord, the nerves can
be just one nerve from the spinal cord to the effector or
there can be a relay between the spinal cord and the effector.
Th main differences between the somatic motor system,
motor neurons and the visceral motor system can be compared in this table.
Normally, the effector of the somatic motor system is just our skeletal muscles.
For our visceral system, this can be cardiac system,
smooth muscle or our glands and the kinds of fiber
of the somatic system, as we see right here, is often very simple.
It's only one kind.
And then for,
our visceral system, there's two kinds, the sympathetic system and
parasympathetic system and then, the relay for two system.
For our somatic movement motor system there's often single neurons.
There's no relay between the spinal cord and effector.
For the visceral system,
normally, there are two neurons and in preganglionic neurons and
in postganglionic neurons, there is a relay in between.
In the fibers for the two system for the somatic motor system,
normally, there are six myelinated fibers.
There are six fibers as we see here and then it's well myelinated.
For the visceral system, the preganglion part is myelinated but
still if you compare to the somatic system,
it's very thin and lightly myelinated and
then the postganginium part is unmyelinated.
For the visceral motor system, as we mentioned the above,
there are sympathetic part or sympathetic system and
the parasympathetic part system.
The parasympathetic part has a sympathetic ganglia.
The paravertebral ganglia is located right beside the spinal cord.
Let's get back to our lecture.
The sympatethic trunk consists by paravertebal ganglia and
interganglionic branches and
lies on two sides, either side of are vertebral columns,
from the base of skull to the very bottom part.
The prevertebral ganglions is just in the front of our spinal cord.
The distribution of our sympathetic nerve system.
This table lists the position of each sympathetic nerve.
For the parasympathetic system,
we have parasymphetic ganglias.
The cranial portion in the brain stem is
the ciliary ganglion pterygopalatine ganglions and
the submandibular ganglions,
otic ganglions, and terminal ganglions.
Sacral portions of the ganglions, the preganglionic
fibers from the sacral parasympathetic system nucleus leaves the spinal cord
with anterior root of the spinal nerves at S2 to S4 of regions.
These are the spinal nerves that control different part of our visceral systems.
The main differences between the sympathetic system and
parasympathetic system is for sympathetic ganglions,
we have one relay between the CNS system and our effector.
For the pairing and for the preganglion part, it's
normally myelinated, for the postganglion part, it's normally unmyelinated.
For the parasympathetic ganglion part normally from
the CNS system, we have very long axons to the ganglion.
In the preganglion part is myelinated and
in the postganglion part is unmyelinated to the effector.
This table compares the two systems,
the sympathetic system and the parasympathetic system and
then the lower center for both systems are different.
One is from the lateral gray horn of spinal cord segment T1 to L3.
The other one is from the parasympathetic nucleus and
sacral parasympathetic nucleus located in our brain stem.
In the ganglia cells, for the ganglia cells, the sympathetic system,
the ganglias are located in paravertebral and
the prevertebral locations, and then for
the parasympathetic system, it's often located in terminal.
The preganglia part for the sympathetic system is often shorter and
the parasympathetic system it's often longer.
Then accordingly, the postganglion part for
sympathetic system is often longer and for
parasympathetic system it's often shorter.
For the pre- to postganglion cells and
for sympathetic system, is one to many and then for
parasympathetic system, it is often one to a few.
From this part, the pre- to the post- effect, is one to many or one to a few.
The sympathetic system is distributed throughout the whole body.
But for the parasympathetic system, the location of the system
is often limited to our head, our visceral of the throat
and then our abdomen or our pelvis.
For the different action of these two systems, for sympathetic system,
it's often prepared for the emergency situation.
For the other system, the parasympathetic system is often conserve energy.
So these two systems to the emergency system is the pro and
the con situation to the emergency.
Normally, the sympathetic system will increase our heartbeat,
increase our blood pressure, and for the parasympathetic system,
it decreases the heartbeat and it decreases our blood pressure.
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