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  University of Idaho
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  Psychology Dept.
  University of Idaho
  Design - P&D  CTI

The cerebellum appears very similar to the cortex and like the cortex, it has two major hemispheres.  Ultimately, it’s connected to the Pons by three bundles of axons that we call cerebellar peduncles.  These three cerebellar peduncles are listed here; the superior, middle and inferior.  In general, the cerebellum’s function (as we see in slide three) is to evaluate movement and adjust motor movement while it’s in progress.  It does a lot of integration and evaluation of incoming information and is extremely important for body balance and motor running.  Now, as we can see in the next slide, the cerebellum has three distinct regions. It has the cerebeller cortex which is the outer covering and is mostly composed of neurons.  It has an internal white matter which are basically myelinated axons and fiber tracks, and finally, it has three major pairs of deep nuclei; the Fastigal, the Interposed, and the Dentate.  Each of these nuclei is going to receive information from the cerebeller cortex and send information back to the cerebeller cortex and on to other brain structures. 

Now as we said before, there are three major tracks of neurons that connect the cerebellum to the brain stem and these were the peduncles.  As we can see here, the superior cerebellar peduncle has the most connections and most of this input begins in very deep nuclei.  Anatomically, the cerebellum surface has a lot of basically convolutions called folia, or what we call leaves that run from side to side. The cerebellum also has three distinct lobes separated by two fissures.  So, as you can see, there are a lot of similarities that we have to our cortex. 

The first of these is the paralateral fissure and as we can see here, it separates the body of the cerebellum from the Focculonodular lobe and as the primary fissure in the body of the cerebellum.  It also separates the anterior lobe from the posterior lobe.  These lobes are going to be important functionally a little later on.

In essence, the fissures are going to define a ridge that we have in the midline of the cerebellum called the vermis.  On each side of the vermis are the two cerebeller hemispheres.  The hemispheres are divided like the cortex into lateral and intermediate regions and each is important for its own specific motor functions that go along with it.

The flocculonodular lobe or the vestibulocerebellum is the most primitive of the cerebellum.  It’s going to be getting information from the vestibular areas of the brain, specifically structures that are in the semicircular canals, the otoliths and other structures.  It’s extremely important for balance and eye movements.  When you damage the structure, as we see in slide 10, you basically have problems with eye movements during head rotations.  You also have problems with limbs and body structures during standing or walking.  Finally, you have problems maintaining balance.  As we can see in slide 10, patients can separate their legs.  But, when they move their legs, it’s relatively irregular, and they often fall.  However, they can move their arms and legs accurately when lying down or when their head is actually supported with some kind of other device.

The vermus, as we see in slide 11, gets information from visual, auditory and vestibular areas.  It also gets information from the somatosensory areas as well.  It ultimately helps our proximal muscles of the body and limbs.  In essence, the vermus is going to be extremely important in controlling your posture, your locomotion, and gaze. 

Another major zone, as we see in slide 12, is the intermediate zone.  The intermediate zone gets basically somatosensory information from limbs and ultimately helps control the distal muscles of the limbs and fingers. 

The next major structure related with the vermus and the intermediate zones is called the spinocerebellum.  This structure is going to receive information from the spinal cord and information from the lateral and dorsal spinal cerebellar tracks.  Ultimately this information is going to be obtained from leg, muscles and joints, and other major structures.   It sends information to structures that’s going to develop into what we call rubrospinal and the corticospinal tracks (which we’ll learn about as we talk about the spinal cord).  These are pathways that are going to go down to motor areas of the muscles and help us move.  Ultimately the function of these tracts (as we see in slide 14) is to influence muscles and muscles of the limbs.  If you don’t have this kind of control, what you get is a lack of limb deceleration.  That is, when you try to grab something, you overshoot the system.  So, ultimately this is going to be extremely important for rhythmic activity during locomotion.  Just walking somewhere or walking toward something means that you would either hit it or fall down or other things. 

The Spinocerebellum also contains inverted somatotopic maps of the head and other structures.  Basically the head is at the bottom of the vermus.  So, the whole system is upside down in relation to the way we feel about the system.

The cerebrocerebellum are the lateral parts of the hemispheres.  They only receive information from the cortex and are very, very, very, very, very important for planning and mental rehearsal of competence motor actions and conscious assessment of movement errors.  As we can see here, it’s extremely important in perceptual and cognitive functioning.  That is, if you want to reach and grab that telephone over there, you might not be able to if you damage this particular structure.  Other examples include throwing a baseball, or other kinds of things that involve combinations of rhythmic functions.

So as we can see here in slide 16, if you damage a structure, you basically are going to disrupt motor planning, have prolonged reaction times, and to compensate, you must plan out every movement that you want to do before you actually do it. 

The classic way to examine this is using the Halstead Reitan finger tapping test.  Basically what you see in the finger tapping test is that the rhythm is very irregular and that the motions vary in duration and force.  So, what you see, (as we see in slide 17) is that medial cerebellar lesions interfere with only accurate execution of response, while lateral cerebellar lesions interfere with the timing of events.  Of course timing also disrupts other cognitive tasks as well.  So, as we saw from earlier systems when we were talking about neuropsychological tests, just some basic types of tasks (ala finger tap) can show some very, very important differences and where damage is located within some particular structure.

So some questions that neuropsychologists and other psychologists ask include, “is one tone longer than the other?”  “Is speed of an object faster than the other?”   Ultimately, the dentate is important for tasks requiring complex spatial or temporal arrangements, and conducting complex motor movements.

So now we’ve talked a little bit about some structures within the cerebellum, what are some disorders?  Well, there are a lot of disorders that one could have with damage to the cerebellum.  Remember this damage can occur from a variety of mechanisms.  It can occur from tumors and strokes of course.  But it also can occur with head trauma; and one classic way to get head trauma is in an automobile accident. 

I’ve thrown in a couple of examples on slide 19.  One of these is hypertonia where you look at a knee jerk reflex.  So, you go to the doctor’s office and they hit your knee with the percussion hammer.  You flex the leg, but it doesn’t come back nice and smoothly.  Instead it kind of oscillates coming back.  Another example is ataxia where you have is a lack of coordination.  You also get a delay when initiating a particular response with the limb you’re trying to move.  And of course you also get errors in range and irregularity of movement as well. 

One classic test to look at these disorders is called the hand alteration task.  Basically what you do is put both hands out, then have the fingers of one hand hit the alternate palm of the other hand.  When you start doing that, you get some kind of tremor when you’re trying to stop that particular movement.  In essence, what is going on is that the antagonistic muscles are trying to stop the movement.

So, as we see in slide 21, when you damage the cerebellum, usually you have jerky, exaggerated and erratic motor movements, and movements are also very poorly coordinated.  So, if one wants to see the importance of the cerebellum, think about a gymnast who is a balance beam, and they’re doing flips, twirls, and assorted other things.  If one cannot do those things, or one has damage to the cerebellum, the person is not going to be able to do those functions without getting injured. 

Another example is thinking about a baseball pitcher throwing a baseball.  Initially what you see is a pitcher that is very, very good throwing it nice and smooth and even.  However, a person with damage to their cerebellum would not be able to do that; their movements would be jerky and assorted other kinds of things.

So, the cerebellum is extremely, extremely important in motor movement and helping to control our movements.

In general, what we have now are three major systems.  We’ve talked about the primary cortex and it’s involvement in motor movement, and now we’ve talked about two groups of structures that are also involved with motor movement; that is the basal ganglia and now the cerebellum.  So, as one can see, when one damages any one of these structures, you have major, major problems.

We’ll continue when talking about another type of movement that’s going to be involved in other areas in the next section.  So, until then, we hope you’re enjoying this class and that you have a good day.