The whole system of the nervous
system is quite complex.
It’s quite convoluted, there
are lots of components.
So these are lots of topics
that you’re going to delve
into when you get into the
physiology or biology section.
So, thankfully there’s
some overlap here.
So it shouldn’t be the first
time you’re seeing this.
But nevertheless, we’re going
to work through all the really
important points that you really
need to know for the MCAT.
So, the basic unit in our brains,
really in our body, would be the neuron
or it’s the term that's used
sort of analogous is a cell.
So when you hear the term brain cell or
neuron, they’re essentially the same thing.
And these brain cells or
neurons in general can
be specialized based on
where they’re located.
So we said they’re the basic functional and
structural unit of the nervous system.
Each one is highly specialized to
transmit and process information
and that’s done through the process of
action potentials and synaptic transmission.
So action potentials are the electrochemical
signals of the nervous system.
And neurons are really neat and that they
actually employ two modes of information.
So they use electrical
through the action potential
and we’ll see the movement of
ions is what’s behind that.
And then we have the chemical side,
so looking at neurotransmitters.
So, our three basic buckets are,
we have an electrical signal which
is the action potential, which
travels down the length of an axon.
And then we’re going to have a
synapse between two neurons.
And at that point, we
initiate the chemical signal.
And this is where the
action potential initiates
release of the neurotransmitter
across the synapse.
And then, ultimately, that signal is
converted back to electrical signal,
and so the postsynaptic side continues the
electrical signal via an action potential.
So we should understand that we’re going
from electrical to chemical to electrical.
And another point to remember is that
at no point or any of these neurons
actually in contact, so there’s always a
synapse between two different neurons.
So, you should be familiar with
the structure of a neuron.
So again, this is a pretty
question that you’re
probably going to get.
It’s looking at all the
You should be familiar
with the main parts
including the soma which is the
sort of the head of the neuron.
And then you’ll notice inside that
cell soma, you’ll have the cell body.
And then we have an axon and axon
runs down the length of the neuron
and then it’s wrapped in myelin,
which is a fatty insulator,
and you’ll notice
breaks in that myelin.
So if you look down the length of the axon,
you’ll notice you’ll have little breaks.
Those little breaks are known
as “Node of Ranviers”.
So again, another term you should
definitely be familiar with.
And at the end, you’ll
have your dendrites.
And the dendrites are
what synapse to make a
with the next neuron.
So, these are the basic sort of structures
that we need to be familiar with
especially the cell body, the soma, axon,
the dendrites, and the node of Ranvier.
as I mentioned, you’re
going to have a synapse
which is a term that we use to indicate
that one neuron is talking to another.
Now, in this equation,
we’re going to have
a synapse and we’re going to have
everything else coming before that synapse,
which would be presynaptic or
presynapse and then we’re going to have
the neurons that’s on the other
side or the receiving end
of that synapse and that would
be a postsynaptic neuron.
Now, the way things work are, at
the end of a dendrite or a bouton,
which refers to that sort of bulbous
end of the presynaptic side,
you’ll have vesicles or
these little bubbles.
And these vesicles are storage
compartments that actually contain
embedded in that neuron.
So each neuron typically is
associated with one neurotransmitter.
So, if that neurotransmitter
contains say GABA,
which is the inhibitor
in your transmitter,
we would call that presynaptic
Meaning that in its vesicles,
that contains molecules of GABA.
If it contains glutamate,
which is the excitatory
would have glutamatergic.
Now, when the appropriate conditions are
met and it’s time for that electrical
signal to be passed along through the
synapse through the postsynaptic side,
that’s done through release of this
neurotransmitter that is stored in the vesicles.
And the vesicles fuse
to the presynaptic side
through a process that we called
And that refers to these vesicles
traveling down to the base of the
presynaptic side fusing with the
membrane and dumping their contents.
So that process is
and that’s how it releases its
neurotransmitter into the synapse.
It floats around in the synapse and then
it binds to a little receptor on the
postsynaptic side and these are collectively
known as “postsynaptic receptors”.
So I think you’re getting,
you’re catching the drift
here of pre versus post in
a synapse, and everything
is, therefore, labeled
neuron, postsynaptic neuron,
And this is the process of how we
go from electrical to chemical.
And once we get to the other side in terms
of activating a postsynaptic receptor,
that opens ion channels and reconverts
the signal back t an electrical
signal that travels down the length
of the receiving postsynaptic neuron.
So that was a lot I kind of just threw
at you there so you might want to rewind
this and watch it a few times and we’re
going to take a look at this image.
And then, on the next slide, we’ll get into
some sort of different processes as well.
So this will come up again.
I’m going to walk you through
that process a few times.