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 straightforward MCAT
question that you’re probably going to get.
It’s looking at all the different components.
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
noncontact connection 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.
Now,
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
the neurotransmitter 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 neuron “GABAergic”.
Meaning that in its vesicles, that contains molecules of GABA.
If it contains glutamate, which is the excitatory
neurotransmitter, you 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 “exocytosis”, exocytosis.
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 called “exocytosis”
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 accordingly, presynaptic
neuron, postsynaptic neuron, postsynaptic receptor.
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.