Okay, now --
now that we have a sensory
stimulus coming in,
we need to detect that and that needs
to go through a sensory pathway.
So it’s a really, really
cool unique thing.
And now with all these different
types of sensory receptors,
that allows us to actually capture all the
different senses that we’re inundated with.
And again, I think you and I all take this
for granted when we’re thinking of all the
different stimulus that we, on an everyday
basis, deal with, interact with and assess.
But when you start getting down to
the physiology behind in the fact
that, “Oh my God. We actually
detect a lot of different things.”
It’s super cool
So sensory receptors are
sensory nerves that are --
one of two things, either
a cell or nerve endings.
And they can detect both
internal and external stimulus.
So things that are happening
within our own bodies or things
that are happening from the
outside affecting our bodies.
Activation initiates a signal transduction
by creating graded or action potential.
So you remember from
the biology sections,
an action potential has an
all or none activation.
It causes opening of voltage-gated ion
channels, you have influx of ions.
That whole process can be initiated through
activation of these, of these receptors.
So sensory pathways begin
with the receptor.
The receptor then gets activated and
it goes through some ganglion cells
and then through another process,
it goes through the spinal cord,
it gets sent up to the central
nervous system where it’s processed.
So the idea is, think of
your body as an antenna
and it’s trying to detect
all types of stimulus.
And all that information
into whatever medium it is, into
basically an electrical signal,
because everything in our
body is electrochemical.
And now it gets converted, gets
passed along the ganglion cells,
goes up through the spinal cord,
through the central nervous
system where your brains says,
“Okay, what just happened? Let me interpret
that and let me respond to that.”
So we’re going to walk
through that in a sort of a
flowchart here so this
makes a little more sense.
So a receptor activated
by a sensory stimulus
and that will all be done
through a sensory receptor.
So that sensory receptor
will then initiate a --
sorry, will activate a
sensory ganglion cell.
And that’s a term that you should
know, a sensory ganglion cell,
and that will cause an action
potential or graded potential.
And that cascade, the electrical
signal, will then continue
and it will go to the spinal
cord and that signal is then
sent up and processed in the
central nervous system.
So here’s kind of a scary
looking complicated diagram
and we’re going to break it down
to something pretty simple.
And what you’re seeing here
is an individual and various
types of sensory pathways
that can be activated.
So we can have things
like your taste bud.
You can have your derma
layer in your skin.
And really the point
that I want you to have
here is that you have
a receptor somewhere.
Whether it’s taste,
whether it's dermal,
whether it’s, you know, your urinary bladder
which would be an internal receptor
and it’s going to get activated.
And once it’s activated, it will initiate
that sequence of having electrical signal
and that will go down
the ganglion cell.
And what you’re seeing here in the
middle of this looking thing with an X
is the spinal cord has been transacted
and you’re seeing the dorsal horn.
And it’s going to actually
go cross lateral.
So it’s going to -- what you’re
feeling on the, say, your right hand
is actually going to cross
the spinal cord and go up
to the left side of your brain
and vice versa for either side.
So what we’re looking at here
is the movement of information.
So activation of the sensory
receptor going into an
electrical signal up the
spinal cord to the brain.
for the MCAT, for example, I don’t think
you’re going to need to redraw a diagram
like this, but you would need to understand
that process that we just outlined.
And we’ll do it again through
this diagram, which is again,
an arbitrary diagram showing
various types of receptors.
At the very top where you see A, B, and C,
we’re seeing different types of receptors,
whether it’s a
free nerve ending,
whether it’s a sensory cell,
whether it’s a peripheral cell.
They’re going to get activated.
And they’re all designed to detect
a certain type of stimulation.
And now we’ll activate
the ganglion cells.
Those get sent down and through
the spinal cord up to the
central nervous system, in the
CNS, where they’re processed.