Cerebellum

Cerebellar Anatomy

We’ve been looking at the cerebellumThe brain region responsible for balance, coordination, and fine motor control. mostly in sagittal or lateralAway from the midline of the body. views.  When you examine it in a coronal section A cut or slice of the body or an organ for study., it appears very different. Similarly, viewing it from the anteriorThe front of the body or toward the front when standing in the anatomical position. or posterior shows a distinct appearance.  It is not just one big softball at the back of your skull.  Just like the cerebrumThe largest part of the brain, responsible for thought, memory, and voluntary movements., the cerebellum has a left and a right hemisphere.  You can see that in these coronal views. 

Instead of having a fissureA deep groove in the brain’s surface. separating these two lobes, there is a median structure called the vermisThe central part of the cerebellum that helps control posture and balance..  The vermis can be divided into a posterior and an anterior lobe. It can then be further divided into 9 distinct lobes. This level of detail is beyond what we require. The vermis separates the hemispheres, is good enough!  As you can see from this superficialNear the surface of the body. and lateral view, the cerebellum has all these folds called folia.  These increase the surface area of the cerebellum, making it as powerful as the big brain hat.

Arbor vitae

We cut the cerebellum in a transverse or sagittal section. As shown in this brain top right, we get this really striking feature.  This is able to be seen with the naked eye in dissections.  We call this arrangement of gray and white matterThe outer portion of the spinal cord made of myelinated nerve fibers that transmit signals. the arbor vitaeThe tree-like white matter structure in the cerebellum that aids in coordination..  Since this is a part of the brain, the outer most cortex or bark would be gray matterThe inner portion of the spinal cord composed mostly of neuron cell bodies and synapses..

 I don’t care what color shows up in a microscope slide.  Outer cortex is gray matter in the brain.  There are some stains for which white matter takes up the stain more readily than the gray matter.  This makes the white matter have a darker color, even though it is, well, white matter.  Just remember that what you see in the microscope is not what is in the body.  That tissue in the microscope has been sliced and dried. It is then fixed, dried again, and stained to the liking of the person making the slide. 

Cerebellar Cells

There are basically two kinds of cellsThe basic structural and functional units of life. in the cerebellum: granule cells and Purkinje cells.  Granule cells make up that gray matter cortex or that outer bark of the cerebellum.  Granule cells is a pretty general term that could refer to astrocytesStar-shaped glial cells in the CNS that support neurons and maintain the blood-brain barrier. and other neuroglia as well as neuron nucleiClusters of neurons in the CNS responsible for processing information..  We put the label granule on them because they are in the cortex.  In the minilecture on the cerebral cortexThe outermost layer of the brain, responsible for higher-order thinking and processing., we learn about the big brain hat’s cortex. It is made up of six distinct layers. These layers consist of granule cells. 

Purkinje cells are a little more specialized. They have a lot, A LOT of dendritesBranch-like extensions from a neuron that receive signals from other neurons..  This increases the surface area over which these cells can receive and transmit action potentials.  We will see these cells again in the heart and in the digestive system.  But, looking at both of these cell types, they have lots of surface area for quick transmission.  The axons of these cells extend into the premotor cortex in the cerebrum. They also reach the red nucleusA midbrain structure involved in motor coordination. in the midbrainThe upper portion of the brainstem involved in visual and auditory processing.. Additionally, they extend to the superiorAbove or toward the upper part of the body. colliculi on the ponsA part of the brainstem that connects the cerebrum to the cerebellum and helps regulate breathing..

Cerebellar Peduncles

If you have not yet viewed the minilectures, viewing this slide could be difficult. These minilectures cover the medulla oblongataThe lowest part of the brainstem controlling vital functions like breathing and heart rate., pons, and midbrain.  These are the structures of the brain stem from inferiorBelow or toward the lower part of the body. to superior.  You can locate the ventricles on the pons and midbrain making this the dorsalRelating to the back side of the body. and this the ventralRelating to the front or belly side of the body..  We had these structures called the cerebral peduncles. The cerebrum rested on them. There are also cerebellar peduncles. The cerebellum rests on them. 

These structures aren’t just for support, they contain gray matter or unmyelinated axons that connect the cerebellum to the cerebrum.  Important to Parkinson’s disease is the superior cerebellar peduncle in the midbrain.  Recall that in Parkinson’s the substantial nigra fails to produce dopamineA catecholamine neurotransmitter involved in motor control, motivation, and reward..  Also recall that this here is the red nucleusThe control center of the cell that contains DNA and directs cellular activities..  All these structures are affected with Parkinson’s because they all work to form cerebellar output to the cerebrum.  When you premotor cortex is compiling the info to determine a movementA fundamental property of life involving motion of the body or its parts., it’s like the cerebellum isn’t weighing in. 

Cerebellar Functions

Overall, your cerebellum is involved in posture and balance.  Now, this sounds like two simple tasks, but it is not.  To control your postural muscles and balance, the cerebellum must receive a lot of information from the spinocerebellar ascending tract.  Proprioceptors in your lower limbs have important information that the cerebellum needs to know.  But, that’s not all.  Your cerebellum needs some visual input too.  It can get that from the midbrain that’s involved in neckNarrow region just below the head; common fracture site. movements and reflexesAutomatic responses to stimuli. for visual and auditory stimuliChanges in the environment that are detected by sensory receptors.. 

Once the cerebellum compiles all the incoming info, it determines an output that it will send to the premotor cortex.  This output will involve instructions for moving large muscles for large movements to control your position in space.  The cerebellum is also involved in patterned movements, whether they be big patterns like dance moves, or small patterns like playing piano.  Both of these action involve spatial perception.  Where are you standing?  Where are your fingers?