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Sensory adaptation and amplification
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Created by Ronald Sahyouni.
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At0:48, you mention that the pressure receptors don't fire anymore, because of adaptation, which is why you "forget" that your hand is on the table. Isn't there a more neurological explanation for this? Suppose you live near a highway, and so don't perceive the cars driving all day. Yet, if you listen, you will hear them. Similarly, we can "listen" to our hand being on the table, even if most of the time, we do not feel it. From what I understand, is that you won't feel the pressure on your hand, even if you listen. How does this work? Do we tell the neurons in the hands to start firing again?(5 votes)
There's a difference between sensory adaptation and habituation. (Which hasn't been discussed in this video but should be.)
Sensory adaptation is innate, meaning you don't "choose" to get used to the signal/stimulus. The cells aren't responding to the stimulus in the same way anymore. So you CAN'T choose to pay attention to this initial stimulus.
Example: Someone who is wearing perfume/cologne cannot choose to smell it at the same high intensity as if it was first sprayed on. After a while, you no longer notice the smell. You adapted to this olfactory signal. So, you put on more perfume/cologne to recapture the smell, since you no longer can capture that initial stimulus. (You are increasing this intensity by applying more perfume/cologne.)
Another example: You jump in the pool and the water feels cold. But after a while, you feel warmer. Your sensory receptors adapted to the water temperature. If you want your sensory receptors to start firing again, you would need to take a break from the stimulus... such as leaving the pool and returning to the water MUCH later.
Sensory habituation is learned and voluntary. You can CHOOSE to pay attention to the stimulus whenever you want to. You can choose to feel the shoes on your feet, the clothes on your body, which you have been tuning out because you weren't paying attention to the stimulus. This stimulus is unchanging, so you "tune it out."
Another personal example: If I go to a sushi restaurant, I hear the constant chopping of the chef's knife as he preps the food. But my brain eventually tunes out that sound (sensory habituation) as I focus on a more important source of sound, such as the person sitting in front of me.
Habituation is voluntary and learned. You learn to tune out sounds (or other signals), so you're not wasting energy on listening to sounds that aren't important. I'm "choosing" to focus on the person in front of me. I'm also learning how to tune out the sound of chopping knives.
Bottom line... the difference between adaptation and habituation is this:
*If you can't recapture the initial stimulus, it is adaptation. If you CAN recapture the initial stimulus, it is adaptation.*(22 votes)
I am confused because this video explains amplification/upregulation with an example of light entering the eye and making photoreceptors trigger action potentials…. in a previous video you said that light entering eye would be an example of down regulation because your eye will adapt and become desensitized to light…. So would light entering eye be down regulation or amplification/upregulation or both? Also, you said phototransduction cascade causes rods to turn off which would cause them to not be able to produce action potentials because NA channels will be closed…… so… which one is right? Does a rod fire an action potential when it is on or off? Because in this video you say light activates the photoreceptor and triggers an action potential which leads to amplification… but that wouldn't make sense if rods can't make action potentials when light hits them because they turn off.. Also, when looking at other websites they say that rods and cones never make action potentials only the retinal ganglion do.. Also, is this whole process the same for cones?? Thanks for your help, I really appreciate it!!!!(4 votes)
Each light activated rhodopsin molecule can activate as many as 800 transducin molecules. Each transducin activate 1 PDE ( phosphodiesterase), but each PDE converts 6 cGMP to 6 GMP, closing about 200 CNGs ion channels. All from one photon of light. This is a great example of amplification. Confusing video though. Had to look it up. Good luck :)(4 votes)
- Suppose the neurons responsible for pain perception is subjected to sensory adaptation, then why do so many patients with chronic pain visit hospital? Also, as the lecturer pointed out, why wouldn't those neurons die due to constant stimulation?(3 votes)
- Many types of sensory information do adapt and decrease the number of action potentials sent to the brain in the face of constant stimuli, such as smell, touch, noise and more, however, pain receptors do not adapt. They continue to send action potentials and this is why pain medications are used in such large amounts. These receptors are made to respond many times a second, they do not quit and they do not die.(5 votes)
I'm confused. At the end, he talks about the adaptation of nociceptors, but I thought nociceptors did not adapt because pain is an indication that something is wrong so the nervous system wants us to know that.(2 votes)
Hi Estefania, you are right, pain receptors do not adapt or are very slow in adapting (based on current research). Thus, they can result in nerve damage overtime unlike other receptors like pressure that adapt (so if most receptors were like pain receptors, we would have lots of nerve damage).
However Ron was specifically referring to pain induced by capsaicin (active ingredient in chilli pepper). Capsaicin works a little different , which in a way result in adaptation / downregulation of pain.
Capsaicin acts by binding to a receptor in the cell wall of nerve endings and triggering an influx of calcium ions into the neuron. Eventually, the nervous system interprets this cascade of events as pain or heat , depending on which nerves are stimulated. At the same time this flood of calcium, leads to temporary adaptation/ down regulation of pain.
So basically, you can consider this as exception to the rule of pain receptors.
So you can say that capsaicin causes pain however results in the adaption of pain (kind of a miracle drug for pain) . Thats why lot creams sold over the counter to help reduce pain contains the active ingredient capsaicin. However, this adaptation is considered as temporary.
I hope this helps. :)
source: Science daily/ the naked scientist
http://www.sciencedaily.com/releases/2009/02/090223221232.htm
http://www.thenakedscientists.com/HTML/science-news/news/1637/(4 votes)
- He mentions sensory amplification as a form of upregulation. In an earlier video, in a different section, he goes through each of the senses and explains their role in sensory adaptation. Sight especially underwent downregulation in light adaptation, but upregulation in dark adaptation. So is sight's upregulation a form of sensory amplifcation or sensory adaptation?(2 votes)
- http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3501690/
Sensory adaptation can increase or decrease our receptors sensitivity to the stimulus. If it is an increase then it is sensory amplification. The fact that receptors change their sensitivity if stimulus changes or the environment changes is fascinating.(1 vote)
I think the example of amplification was little misleading. If I understood it correctly, amplification is just opposite of adaptation where the perception of a constant stimuli becomes exaggerated over time. Does my understanding really fit into that example?(2 votes)
Is there really such a clear cut difference between sensory adaption and amplification? I thought that sensory adaption was adapting to changes in environment which included both sensory desensitization (downregulating of receptors) and sensory amplification (upregulating of receptors).(2 votes)
What's the reason for amplification if too much amplification is a negative thing?(1 vote)
0:48
Video transcript
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.