Adaptation of Sensory Receptors: Study with Video Lessons, Practice Problems & Examples

Adaptation refers to the reduction in receptor sensitivity to a constant stimulus, crucial for neural health. There are two main types of receptors: phasic receptors, which adapt quickly and report changes (e.g., thermoreceptors), and tonic receptors, which provide sustained responses (e.g., nociceptors and proprioceptors). Understanding these receptor types helps explain how our nervous system conserves energy while maintaining awareness of important stimuli, ensuring effective interaction with our environment.

Adaptation

Okay. So in this video, we're going to be talking about adaptation. Now, adaptation is a reduction in receptor sensitivity when it is in the presence of a constant stimulus. This is basically what's going to happen if we have some kind of stimulus in our environment that is constant, maintained, or unchanging. Our receptors will basically begin to stop responding to it after a while. That is adaptation. And this is very important for neural health. So we don't want our neurons to have to be firing constantly if they don't need to be. By adapting, we can kind of save energy and save metabolic resources and give our neurons a little bit of a break. Now in the peripheral nervous system, we see two types of adaptation and we basically have these two types of receptors. First, we have phasic receptors, and these are also called fast-adapting receptors. As you probably guessed, these phasic receptors will adapt very quickly when we have a constant stimulus. So basically, when that stimulus is first applied, they will respond to it, they'll send up action potentials, but then as long as that stimulus is maintained and unchanging, they'll kind of just stop and they'll slow down their firing rate. What phasic receptors really do is report changes in the environment. Next, we have tonic receptors, and these are also called slow-adapting receptors. These receptors actually exhibit very little adaptation; what they do is they provide a sustained response. So basically, even though that stimulus is constant and unchanging, they are going to keep on firing. They are not going to adapt to it. Even though we're talking about these two types of receptors, I don't want you to think about these as like these black and white boxes and we're going to be organizing sense receptors neatly into either box. It is much more nuanced than that. I would encourage you to think of adaptation more like a continuum where some receptors tend to act more phasic, some tend to act more tonic, and some of them will have both phasic and tonic properties and kind of fall somewhere in the middle there. To give you an example of a phasic receptor, a nice example here is a thermoreceptor because, remember, what do thermoreceptors do? They report changes in temperature, right? That's their entire job. So these tend to act phasic, so when you enter a room with a different temperature, they will respond to that very quickly. And then, as long as that temperature is constant and maintained, they will kind of slow down their firing rate. Now, I do want to be very clear that thermoreceptors are not purely phasic in their behavior; they do have tonic qualities. They just exhibit this one very classic phasic property, and that's why we're using them as an example. Over here on the tonic end, a classic example of a tonic receptor is a nociceptor or a pain receptor. These give you a very sustained response. They take a long, long time to adapt, and that's very important. Evolutionarily speaking, if we have pain somewhere in our body, we need to be aware of that pain, and we have to adjust our behavior accordingly. Right? So it's unfortunate, but very good for us that nociceptors are tonic in their behavior. Another great example of a tonic receptor is a proprioceptor, so those receptors that give us information about the location of our muscles and joints and information about how our body is moving through space. Right? And that information is constantly getting sent up to our brain, and that is super important information to help us be able to successfully navigate the world, to be able to walk across the room, even just sit upright in my chair. My brain has to be getting constant signals from the muscles in my back, in my abs, in my legs, and all of that positioning to be able to keep me upright. So those are nociceptors and proprioceptors tend to be very very tonic in their behavior. And an example of one that can kind of exhibit, sometimes they'll have phasic properties, sometimes they'll have tonic properties, are mechanoreceptors. So some types of mechanoreceptors, these are of course the ones that respond to things like pressure and vibration, some types will be very tonic, they'll be very, slow adapting, and they'll give you this very sustained information about whatever pressure you're encountering, for example. And then other types of mechanoreceptors really focus more on reporting changes in the environment and they adapt very quickly to those changes, again as long as that stimulus is constant. Alright. So that is adaptation in a nutshell and I will see you guys in our next video. Bye bye.

Adaptation of Sensory Receptors Example 1

Okay. So this one asks us, which of the following is an example of a tonic receptor? Now as a reminder, those tonic receptors are going to be the slow adapting receptors that give us that sustained response. So let's run through these and see what we have. Alright. So a is a receptor that adapts quickly to the sound of a ticking clock. That's sounding a little phasic to me, not tonic, so we'll cross that out. B is a receptor in the tongue that responds to the initial taste of a flavorful food but adapts quickly to the taste, sounding too phasic for my taste. And then c is a receptor in the skin that maintains its firing rate after you receive a paper cut. That's looking promising, right, that maintaining of the firing rate. So let's underline c for now, and then d is a receptor in the eye that detects rapid changes in light intensity. That's sounding a little phasic to me. So our answer is indeed c, a receptor in the skin that maintains its firing rate after you receive a paper cut. And remember, nociceptors are like the quintessential example of those tonic receptors. They're going to really maintain their firing rate and give you that sustained pain response so that we know that we are in pain and need to do something about that. Right? So I'll see you guys in the next one. Bye bye.

Which of the following is TRUE regarding phasic receptors?

• A. Phasic receptors respond to sustained stimuli and maintain their firing rate.
• B. Phasic receptors respond with a burst of action potentials when a stimulus is first applied and quickly adapt to the stimulus.
• C. Phasic receptors adapt slowly to changes in stimulus intensity.
• D. Phasic receptors exhibit continuous, constant firing in response to a stimulus.

Thermoreceptors tend to be phasic receptors because they:

• A. Take a long time to respond to a temperature change.
• B. Produce a generator potential.
• C. Produce a receptor potential.
• D. Alert us to changes in temperature but are less active when temperature is constant.

Here’s what students ask on this topic:

What is sensory adaptation and why is it important for neural health?

Sensory adaptation is the reduction in receptor sensitivity to a constant stimulus. This process is crucial for neural health because it prevents neurons from being overstimulated by unchanging stimuli, thereby conserving energy and metabolic resources. By adapting, neurons can focus on detecting new and potentially important changes in the environment, rather than being overwhelmed by constant, unimportant stimuli. This allows the nervous system to function more efficiently and helps maintain overall neural health.

What are the differences between phasic and tonic receptors?

Phasic receptors, also known as fast-adapting receptors, quickly reduce their firing rate in response to a constant stimulus. They are primarily responsible for detecting changes in the environment. An example is thermoreceptors, which respond to changes in temperature. Tonic receptors, or slow-adapting receptors, provide a sustained response to a constant stimulus. They continue to send signals as long as the stimulus is present. Examples include nociceptors (pain receptors) and proprioceptors, which provide continuous information about body position and movement.

How do thermoreceptors exhibit both phasic and tonic properties?

Thermoreceptors primarily exhibit phasic properties by quickly responding to changes in temperature. When you enter a room with a different temperature, they rapidly send signals to the brain. However, thermoreceptors also have tonic qualities, as they continue to provide some level of information about the constant temperature, although at a reduced firing rate. This dual behavior allows them to efficiently report both changes and sustained conditions in temperature.

Why are nociceptors considered tonic receptors, and why is this important?

Nociceptors, or pain receptors, are considered tonic receptors because they provide a sustained response to a constant stimulus. This means they continue to send pain signals as long as the painful stimulus is present. This sustained response is crucial for survival, as it ensures that we remain aware of potential harm and can take appropriate actions to avoid or mitigate injury. The continuous signaling helps us adjust our behavior to protect the affected area and promote healing.

What role do proprioceptors play in the body, and why are they tonic receptors?

Proprioceptors provide continuous information about the position and movement of our muscles and joints, helping us maintain balance and coordinate movements. They are tonic receptors because they send constant signals to the brain about the body's position, even when the position is not changing. This sustained response is essential for activities such as walking, sitting upright, and performing complex movements, as it allows the brain to make real-time adjustments to maintain posture and balance.