Sensory adaptation and amplification

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.