Survival depends upon sensation and perception. Sensation is an awareness of changes in the internal and external environment and takes place in the peripheral nervous system, specifically in the sensory division of the peripheral nervous system. Perception is the conscious interpretation of that stimuli.
The meaning of the information is involved. And that takes place in the central nervous system, in the brain. So it turns out that survival depends upon sensation and perception.
When we think about sensory perception, there are three levels at which perception occurs. And remember, all of perception... is happening inside of the brain, but at higher and higher levels of ability.
Feature abstraction would allow you to have an understanding of a specific texture or shape, for example. Quality discrimination would give you the sub-modalities of a sensation. And pattern recognition is the most sophisticated level of understanding that we have.
This is where we start to see the patterns in the stimuli themselves. All right, so when we classify sensory receptors, let's take a look at the level of the sensors, and these are all in the periphery, remember. We're going to be classifying sensory receptors based on three concepts. Stimulus type, location, and structural complexity.
Stimulus type is the way that we usually classify receptors. Examples of this would be... mechanoreceptors, if you're thinking about feeling touch or feeling vibrations or feeling stretch.
These are examples of mechanoreceptors that are found in your inner ear, and these are some mechanoreceptors that are found in your skin. Also, we have thermoreceptors, photoreceptors, chemoreceptors, and nociceptors, and we'll talk about examples of all this stuff in class. The second way to classify sensory receptors is based on location. We have exteroceptors, which pick up on information from outside.
We have visceroceptors, also called interoceptors. They are picking up on what's inside of your body. We're usually thinking about something that's inside of the blood, for example. And lastly, we have what we call the sixth sense, which is proprioception, which is an awareness of where you are in space.
The last way that we classify sensory receptors is based on structural complexity. So complex structures, complex sensors would be a sense organ such as the eye or the retina or the nasal epithelium, which we'll be talking about this week. And simple would be something like a dendritic nerve ending of sensory neurons, and these would be more numerous.
Inside of this, if we were just to look at these hair cells here, the hair cells would be classified as mechanoreceptors because they're picking up on vibrations that moved into the ear canal and then vibrated a bunch of fluids and tapped on a bunch of balls and so on. We'll talk about that process. But at the end of the day, they are pressed. They are responding to pressure. So they are mechanoreceptors.
They are also extroceptors because they're responding to something from outside, the outside world. And they are also considered simple. If you look at the entire cochlear organ, what's called the organ of Corti as a whole, it spirals around and allows for all of these hair cells to be present kind of like on a base that spirals around this structure.
That would actually be a complex sensory receptor. Okay, so here's examples of extra receptors and proprioceptors. So just very quickly, I wanted to talk about somatic sensation, which includes touch, pressure, and temperature. And we're going to be looking at encapsulated receptors. Most of these are mechanoreceptors.
They have varied distribution all around your body. Okay, Meissner's corpuscles are also called tactile corpuscles. Petunian corpuscles are also called lamelated corpuscles.
Then there are muscle spindles, Golgi tendon organs, and Ruffini's corpuscles. These will sense muscle stretch. And then there are joint kinesthetic receptors, which are in the articular capsules of the synovial joints. These are all encapsulated, which means that the sensory nerve ending is buried inside of connective tissue. And that means that they are not as sensitive as something that is not encapsulated.
So here's examples. Tactile corpuscles, lamellar corpuscles, the ruffini endings, the muscle spindles, the Golgi tendon organs, and the joint kinesthetic receptors. And you can read a little more information about those. And then we have unencapsulated receptors. These would mostly be found in the epithelium and in the connective tissues.
These include free dendritic nerve endings. These are found in most of your body's tissues, temperature and pain mostly. There are also tactile discs.
You may remember that this is in the deepest layer of the epidermis, the stratum basale of the epidermis. You have a representation of nervous sensation there, and those are the tactile discs. And then lastly we have hair follicle receptors, very sensitive, they wrap around the base of a hair and they allow for a very very like just slight whisper touches one of your hairs and these guys are going to fire. So very very sensitive.
I think the last thing I want to talk about in this video, one more thing, is adaptation also called habituation also known as desensitization. The concept here is that some sensory receptors stop sending a signal after a certain point. They become less responsive.
The action potentials decline. Even though the sensation still exists, they simply stop sensing it. Some receptors will habituate quickly. Some will respond slowly.
These are called phasic receptors. And then some are... Some will never habituate at all. And we'll talk about examples in class.