00:01
In this lecture, I am going to describe the
sensory and motor pathways in the spinal cord.
00:09
At the end of this lecture, I want you to
be able to describe both the motor pathways
and the sensory pathways, so you have a very
good understanding of these pathways.
00:21
I also would like you to know the difference between
the various ganglia in the body and be able
to tell the difference histologically,
when you see images of the structures.
00:36
Well, let's just make sure that we are aware of the
autonomic nervous system again before we then try
to put all these together and try to describe
the structure of the spinal cord in more detail
and show the pathways of all the sensory
and motor neurons, somatic motor and also
visceral motor neurons. Well, just to recall
that there are a number of functional divisions
of the autonomic nervous system. There is
the efferent innervation to smooth muscle,
we're unaware of. Efferent innervation
means it is exiting the spinal cord or
the brain. They are visceral motor neurons,
they are causing contraction of smooth muscle,
components of cardiac muscle and also the
contraction of muscle around glands to increase
or decrease secretion. They are going to be
divided into two components, the sympathetic
components and the parasympathetic components.
And as I mentioned earlier, they have opposite
effects, but it is worth remembering also
that when we see these neurons travelling
to their destinations, they are also accompanied
by sensory neurons that are taking information
back from the viscera. Now, it is important
also to understand that when I describe the
ventral horn neuron, that was stimulated by
that pyramidal cell very early on the lecture,
that ventral horn cell was only the one cell
needed to innervate skeletal muscle.
02:31
The axon of that ventral horn cell travelled all the
way out of the ventral horn, all the way down
to innervate the skeletal muscle that is designed
and joined on to innervate. It could be all
the way down to the muscles in your toe. In
the case of the autonomic nervous system,
in the case of the need to innervate the smooth
muscle and glands etc. that I have mentioned,
there are two neurons involved. Neurons we
called preganglionic and neurons we called
postganglionic. And I will describe that in
more detail as we go through. But it is an
important point. Somatic motor neurons are
only one neuron, whereas the autonomic neurons
require two neurons.