What is sensory adaptation versus sensory amplification?
So let's go into adaptation first.
So sensory adaptation is change over time
and the responsiveness of the sensory receptor
to a constant stimulus.
And what this basically is, is downregulation
of a sensory receptor somewhere on your body.
So for example, if we were to take our hand
and place it on a table.
So the hand is placed on the table.
As soon as the hand touches the table,
there are a whole bunch of pressure receptors
throughout your fingers, in your palm.
And they all experience a change in pressure.
And these pressure receptors all simultaneously
send a signal to the brain.
After a few seconds of your hand being placed on the table,
the pressure receptors are no longer firing.
And in fact, you can even forget that your hand
is touching the table.
So this occurs because of adaptation.
Another way we can think of this is
if we draw a pressure receptor here.
So this pressure receptor is in our hand.
This is the cell body, the axon over here,
and the axon terminal.
As soon as the hand rests on the table,
there is pressure from the weight of your hand touching
the table, there's pressure.
And this causes the cell to fire in action potential.
And this action potential reaches the brain.
Over a period of time, however, as soon
as your hand is just resting on the table,
there's no longer any change in pressure.
So this cell is no longer sending a signal to the brain.
And in fact, if you started to press your hand down
on the table, then all of a sudden
there would be again a change in pressure.
But then if you hold your hand pressed on the table,
then there's no longer any change in pressure.
And basically this is in a nutshell what adaptation is.
Adaptation is different cells in your body responding
to a change in a stimulus.
If the stimulus is no longer changing,
then there's no longer any information
that's being sent to the brain.
In contrast, amplification is an upregulation.
So upregulation of some sort of stimulus in the environment.
So for example, if we take a ray of light--
and in previous videos, we talked about vision
and how a ray of light is converted
into an electrical impulse that is sent to your brain.
So the ray of light hits a photoreceptor in your eye.
And it actually triggers a cascade of events.
So for example, we can say that if it will hit one molecule,
and that molecule can activate two molecules.
And then those two molecules can each activate two and so on.
So eventually, what happens is one ray of light
can actually cause a cell to fire.
And when this cell fires an action potential,
it can actually be-- it might be connected to maybe two cells.
And these two cells then also fire an action potential
to two more.
And so on and so forth.
And by the time the signal that this cell started
reaches the brain, it's been amplified.
And so this is basically amplification in a nutshell.
And adaptation is important, because if the cell is
overexcited-- If any cell is excited too much,
it can actually be harmful to the cell.
And it can actually die.
So it's really important to have this adaptation.
So for example, if this was a pain receptor instead
of a pressure receptor, and if there is too much of a pain
signal-- so for example, one molecule
that can actually cause pain receptors to be activated
is capsaicin.
And we spoke about this in another video.
So if there's too much capsaicin, for example,
it can actually cause the cell to die.
And so that's why it's important to downregulate a cell.
It's important to adapt to any type of stimulus
in the environment, in order for the cell both
not to die, and then also for your brain
to not be overwhelmed with information.