00:01
So now that you know a little bit about the basic
structural components of neurons, let us have
a look and see now how we can further subdivide
these neurons into three different types.
00:16
In the previous slide, we looked of course
at the motor neuron. It was a somatic neuron
that supplied skeletal muscles that brought
about the contraction of skeletal muscle.
00:28
It is voluntary, we are aware of it. Now
the other type of motor neuron is the visceral
neuron that innervates smooth muscle as well
as components of the heart that increase the
rate of impulse travelling or impulse conduction
by specialized cardiac muscles called
Purkinje fibres that brings about an increase
or maybe a decrease in the heartbeat.
00:59
And these visceral neurons can also innervate
glands and increase secretion rate or decrease
it, whatever the case maybe. Now I have also
got the term efferent neuron. They are to
describe both the somatic neurons and also
the visceral neurons. Efferent means exiting,
the brain and spinal cord. Think of e for
efferent, e for exiting, and it is why I
remember that all efferent neurons are motor
neurons. The next type of neuron is the sensory
neuron and again we have somatic components
and visceral components. The somatic sensory
neurons are from the periphery and they give
us information about touch and temperature,
pain and pressure and various other sensations
that we are aware of. We also are sometimes
aware of certain aches and sensations in internal
organs or in mucous membranes and that sort
of sensory information comes in through visceral
efferent neurons. Visceral means from the
internal parts of the body. Now I use the
word afferent. Then an afferent neuron to
describe a sensory neuron. Think of the word
afferent, the letter "a". A for arriving, the
impulses are arriving into the brain or
spinal cord with sensory information.
02:44
Now besides having motor neurons and sensory neurons,
there are interneurons. They are much smaller.
02:51
Sometimes they are called intercalated neurons
or even integrative neurons. But their job
is really just to communicate between those
sensory and motor neurons and also between
various other neurons that we find in the
spinal cord in the brain. Say they create integrating
networks, so that the information brought into
the brain or spinal cord is then transferred
to other neurons for processing by these particular
interneurons. Now here is a diagram to actually
describe what the structure of some of these
neurons look like. And I just want you
really to concentrate on the two diagrams
on the right-hand side of this particular
picture. The first one is the motor neuron. Notice
it has got a dendritic tree or dendroid branch
around the cell body or soma. Those dendrites
remember, receive information from other interneurons,
where the information is then processed by the
cells. And then the impulse is fired and travelled
down the long axon you see labelled there
as well. Only one axon travelling down from
the motor neuron. It's called a motor neuron
or a multipolar neuron. Now on the next section,
you see a sensory neuron, on the next diagram.
Notice its cell body sits out on its own and
it actually has two processes, two long axons
extend one to the periphery and one into the
central nervous system or the brain. That
is because this is a sensory neuron and one
part of the axon is bringing information in
from the periphery and then the other part
of the axon travels pass the cell body and brings
information into the brain or spinal cord.
05:08
And we are going to see later on that cell body
you can see of the sensory neuron is
actually located outside the brain and spinal
cord in a sensory ganglion. Remember, I mentioned
at the very start of this lecture, that a ganglion
is a collection of cell bodies outside the
central nervous system. Well this is an example
of where one of these sensory neuron cell
bodies is located. It is often called a pseudounipolar
or unipolar sensory neuron, because it has only got
one little process, one little pole coming
from the cell body whereas the motor one has
a number of different processes coming such
as all the dendrites and also the one long
process, the axon. We will talk about the
bipolar or retinal neurons when we look at
the eye in a later lecture.
06:11
Well here is another diagram showing you some enormous
communicating neurons that have enormous dendritic
trees. Have a look at the pingy cell that
we are going to see in the next lecture in
the cerebellum. It has an enormous array of dendritic
branches so to disappear a middle cell in
the hippocampus and that is because these
two neurons are getting an enormous amount
of information to process before they then fire
off their axons to control or at least influence
some body functions, some activity via other
nerves. Integrative neuron is another term
used for these neurons that I've mentioned before.
High massive branches of dendritic trees that
perceive and receive information. So in summary
just have a look at this little diagram and
make sure more importantly for this lecture
that you know structurally the difference
between the motor neuron and the sensory neuron.
Because what we are going to do now,
we can't actually see where these cell bodies are
located within the central nervous system and spinal
cord and within the ganglia just outside the
spinal cord.