© 2010
  University of Idaho
  All rights reserved.
  Psychology Dept.
  University of Idaho
  Design - P&D  CTI

First of all when, you talk about listening, feeling, hearing, or whatever, you do not talk about just one system.  Instead, you talk about three different systems.  That is, the concepts that’s related to sensation, perception and cognition.  The first thing that we need to understand is that all the sensory systems operate the same, but they use different mechanisms.  What we have first of all is some kind of physical stimulus that’s in our environment.  That physical stimulus can be anything.  It can be weight, it can be heat, it can be cold, or it can be light.  It can even be the auditory sensation that you call speech.

Whatever the system is, the stimulus emits some sort of energy.  That energy then activates some sort of receptor system within our body.  In essence, when we talk about the concept of sensation (like we see on slide three) what we’re basically talking about is the receptor system that’s designed to transduce or convert some particular physical energy  into some kind of action potential which we then use and recognize.

Now, once you have that particular stimulus coming into your system, you then organize the physical stimuli in some kind of neural energy.  You do that through an electrical-chemical reaction.  Now, as you continue to organize it, we move into the concept of what we call perception.  As we see in slide four, perception is how you are going to organize the particular energy sequence.  That is, of all those action potentials that are coming in and you’re going to filter.  So, you have multiple different sounds coming into your environment right now but you’re only primarily concentrating on my voice.  That filtering information through the reticular activating system and other structures is extremely, extremely important and basically progresses as we go through the different types of systems.

Ultimately, through this process, you begin to develop and recognize some particular pattern.  As a consequence, you process the material in our brains.  That brings us to the next major point, and that is the concept we call cognition.  Basically, cognition allows you to determine what the particular patterns of the particular stimuli mean. 

Each of these systems or different patterns of stimuli use different brain systems, depending upon the particular stimulus.  For example, the visual things that you might see are going to be working in the occipital lobe, while the auditory stimuli you’re hearing right now are basically being controlled and recognized in the temporal lobe. 

So, let’s kind of summarize these concepts that we’ve talked about for the last couple seconds or so.  First of all, when you talk about sensation, perception and cognition, you need to remember that sensation is involved with detecting the stimulus and converting it to action potentials.  Perception is involved with organizing those particular action potentials, and cognition is involved with providing some meaning to the particular organization so we can understand what that particular stimulus needs.

Now, within all of these systems, as we talk about the senses and the different sensory systems, there are a couple that we focus on in relation to the sensation of physical stimuli we have in our environment that is related to touch and other things.  Basically, that is related to what we call the somatosenses.  Basically, the somatosenses provide information relating to events on the skin and to events occurring within the body, and as we can see here, there are two major groups.  There’s the cutaneous senses which are basically related to signals from the skin, (touch, pressure, and on and on), and the group called kinesethia which basically provides information about our body position and movement.  These systems are ultimately getting information from our receptors within our joints, limbs, muscles, and tendons.  But the big thing that we talk about in relation to all of the somatosenses is the concept that we call touch.  

In touch we need to recognize that there are lots and lots of different receptors involved. 

However, as we can see in slide eight, there are three main groups of receptors that we talk about.  There are nociceptors, cutaneous and subcutaneous mechanical receptors, plus muscle and skeletal mechanical receptors. 

So let’s start talking about what the skin is made of.  This is on slide nine.  You’ll see this same picture a little bit later on.  This is a kind of an overview of the skin and some particular structures.  I’ve also highlighted some of them that I think that are important.

The first of these receptors that we want to talk about, as we see in slide 10, are what we call nociceptors.  Nociceptors are receptors responsible for detecting pain.  The first of these types are what we call free nerve endings.  Free nerve endings within the skin respond to different stimuli.  They also respond to heat, acids, and a substance you know in hot chili peppers (capsasin).  There are four major types of nociceptors and listed here.  Basically what they’re designed to do is designed to identify different types of pain.   

Now in addition to nociceptors, we also have other types of receptors as well.  These are cutaneous and subcutaneous mechanical receptors.  These systems are responsible for touch sensations and we have a wide variety of different types.  There are Meissner’s corpuscles which are responsible for flutter, Pacinian corpuscles which are responsible for vibration, and others as well.  These are again listed in slide 12.

Again, these, as we see in slide 13, you can see that these corpuscles tend to be much deeper than some of the other corpuscles and the nociceptors which tend to be more toward the surface.

Well, now we’ve talked about a variety of receptors that we have (nociceptors, cutaneous and subcutaneous mechanical receptors), let’s talk a little bit about a concept that’s extremely important with all of this.  That is the concept of pain which we see in slide 14. 

As we move on into slide 15, we see that there are a variety of different pain receptors.  There are nociceptors which are basically free nerve endings.  Again, they’re basically activated by mechanical and this chemical stimulation.  However, we need to know that there are different systems that we have for touch and pain.  Basically we have two, the dorsal column/medial lemniscal system and the anterolateral system. 

Let’s talk about the dorsal column/medial lemniscal system first.  As we see in slide 17, this system is primarily involved with discriminative touch.  It also is involved in detecting vibration and perceiving and understanding the form and nature of objects.  It also receives stimuli within tissues of the arm (called stereognosis), and it’s also extremely important in weight discrimination. 

Well, what are these structures used in the dorsal column/medial lemniscal system and anterolateral system.  Well, as we can see in slide 18, once the information is linked to the spinal cord, it uses the Fasciculus Gracilis and Fisciculus Cuneatus) in the dorsal column of the spinal cord which we’ll talk about in a couple sections.  Ultimately this signal is going to go up the spinal cord and cross at the medulla.  Once in the medulla, it goes and enters what we call the medial lemniscal pathway.  From the pathway, it goes on into the thalamus) ultimately goes into the lateral nucleus and posterior lateral groups of the thalamus).

Once we now have the information in the thalamus, the signal then synapses and then moves on to other structures (specifically the primary and secondary somatosensory cortex or what we call Broadman’s area 312), and it goes into the posterior parietal lobe as well.

Figure 19 shows you how this works.  In essence what you’re going to have is some kind of action potential coming into the system.  It’s going to go into the dorsal horn which we’ll talk about shortly, and then it’s going to move up the dorsal column until it gets to the medulla, then it crosses over, goes up into the mid brain and then goes on up into the somatosensory cortex.

Well what about the anterolateral system, what’s it used for?  Well as we see in slide 20, the anterolateral system is responsible for pain, cold and temperature and tickle and it’s also responsible for detecting touch.  It’s not as fine as the systems that we had with the dorsal column and medial lemniscal system.  This system works a little bit differently.  Here the signal crosses right at the spinal cord.  So the information is going to come into the anterolateral system, and it’s going to cross over to the opposite side of the spinal cord.  So my right arm is going to cross to the left side of my spinal cord.  Then information will use what is called the lateral spinothalamic track of the spinal cord.  That information is then going to go up to the reticular formation, the tectum, other structures, and ultimately end up in the thalamus.  Again, once the signal gets into the thalamus, it then is going to go on into areas 312 and the posterior parietal lobe.

Again as we saw in slide two, the spinothalamic track is on the opposite side.  So, I have a signal coming in from the right side, it’s crossing over to the left side of my system, going up the spinal cord into the thalamic structures, and then finally, on to the parietal lobe. 

So now we’ve talked about two different types of systems, but we still really haven’t talked about the third major type of system.  These are basically muscle and skeletal mechanical receptors.  As we see on slide 23, there are lots of different types.  Basically they relate to muscle spindles and joint capsule mechanical receptors.  What we see is these systems and receptors are going to tell us where our limbs are, how much stimulation our muscle groups have had (which we’ve talked about earlier), and how much contraction and relaxation that our different limbs and joints have done.  Basically, it gives us a feedback loop to where our joints, arms, and other extremities are in time and space.

So, when we talk about sensation we need to remember there are lots of different systems involved.  And if you damage something within your spinal column, your thalamus, or whatever, you may have very major difficulties in sensing particular types of stimuli.  Again, while some of these structures may be very easily diagnosed for damage, often times it becomes difficult and we need to have more refined different neuropsychological batteries that detect and identify where the damages has occurred.  So again, as we’ve talked about in the past, a combination approach becomes extremely important for understanding where the damage is, rather than using a medical only, or a neuropsychological approach only.

Well, as we continue, we will examine the next and final system in this group.  These are what we call memory structures, so until we then get to them, we hope you have a great day.