Cerebellum and Brainstem: Deep Structures Flashcards
What is the function of the cerebellum?
The cerebellum functions to anticipate and smooth out movements of the trunk and limbs through both slow feedback pathways that allow for long term improvement of motor tasks and through a fast forward mechanism that regulates second to second movements and keeps them on track.
It compares intention with performance to compensate for error in movement.
The cerebellum sequences incoming sensory patterns and detects temporal changes in the sequence of sensory events. For example, a baseball player relies heavily on the cerebellum to hit a ball thrown at 90 miles per hour and to improve this ability every time he goes to bat. Similarly, the pitcher relies on the cerebellum to throw the ball with ever increasing precision so the batter will miss it.
T or F. The cerebellum also contributes to non-motor functions such as cognitive memory, emotion and affective processing.
T.
Cerebellum anatomy. What are the three main lobes?
anterior, posterior, and flocculonodular (blue)
Describe the homuncular distributions of the cerebellum
The vermis and paravermian portions control the axial musculature (that is the neck and trunk muscles) while the lateral hemispheres control the limbs (that is the arms and legs).
The flocculonodular lobe is heavily involved in what?
maintaining balance and in coordinating head and eye movements with the vestibular system.
This slide presents on the left a silver stained section through the deep cerebellar nuclei and the medulla of the brainstem. On the right is a drawing of this same section with the deep nuclei in color.
The deep cerebellar nuclei serve as what?
the primary relay points for efferent fibers traveling from cerebellar cortex (that is the Purkinje cells) to other brain regions.
The lateral hemispheres of the cerebellum project where?
to the dentate nuclei
Where do the paravermal zones of the cerebellum project to?
the globose and emboliform, collectively known as the interpositus nuclei
Where does the vermis of the cerebellum project to?
the fastigial nuclei.
A key clinical point is that damage to these deep cerebellar nuclei cause what?
severe ataxia, far worse than the ataxia arising from damage to the much larger cerebellar hemispheres.
What are the three major tracts that carry all afferent and efferent nerve fibers to and from the cerebellum?
Superior, Middle, and Inferior cerebellar peduncles
Below: (A) shows the ventral aspect of the cerebellum with the three fiber bundles color coded and the lower figure (B) presents a dorsal view of the brainstem with the cerebellum removed, once again with the connecting peduncles to the cerebellum color coded.
How is cortical motor info sent to the cerebellum?
1) Cortical motor “intent” is sent to nuclei in the pons which forward the information to the contralateral cerebellar hemisphere for processing.
Where does cortical motor info enter the cerebellum?
2) This information enters the cerebellum via the middle cerebellar peduncles.
What happens to cortical motor info once processed in the cerebellum?
3) Once processed, that information is sent back to the cortex via the dentate nuclei.
The superior cerebellar peduncle is the major outflow pathway to the forebrain via what tracts?
the dentatorubrothalamic tract and the dentatothalamic tract.
What do dentatothalamic fibers carry?
information from the lateral portions of the anterior and posterior cerebellar cortices to the contralateral ventrolateral nucleus (VL) of the thalamus and thence onto the motor cortex to smooth out the movement in the limbs ipsilateral to the cerebellar hemisphere of origin. The final common pathway for this coordinated movement is through the corticospinal tract.
In addition to proprioceptive input from the posterior spinocerebellar tract, the inferior cerebellar peduncle carries what fibers?
fibers from the cerebellovestibular and cerebello-olivary tracts (affarents).
What do the cerebellovestibular and cerebello-olivary tracts carry?
Information from the vermis and flocculonodular lobes through the emboliform, globose and fastigial (EGF) nuclei to the vestibular nuclei, the olivary nuclei, and the brainstem reticular formation. These pathways are important in maintaining balance
What are the main afferent tracts into the superior cerebellar peduncle?
anterior spinocerebellar tract
acoustic and optic information
What are the main efferent tracts from the superior cerebellar peduncle?
dentatorubrothalamic tract
dentatothalmic tract
What are the main afferent tracts into the middle cerebellar peduncle?
pontocerebellar tract
What are the main afferent tracts into the inferior cerebellar peduncle?
vestibulocerebellar tract
olivocerebellar tract
posterior spinocerebellar tract
What are the main efferent tracts from the superior cerebellar peduncle?
cerebellovestibular tract
cerebelloolivary tract
How is the cerebellar cortex organized?
3 layers of grey matter including:
the outer molecular layer,
the Purkinje Cell layer and
then the deepest is the granule cell layer.
The cerebellar gray matter contains five different neuron types. In the outer molecular layer are what cells?
the Basket and Stellate cells
The middle layer of the cerebellum grey matter is comprised solely of Purkinje cells, and the granule layer contains what?
the Golgi and Granule cells.
_________ are the only output neurons of the cerebellar cortex
Purkinje cells
Purkinje cells synapse on one of the deep nuclei that in turn send their efferent fibers outside the cerebellum.
The only direct input or afferent to the Purkinje cells from the outside are what?
the climbing fibers that have their origin in the olivary nuclei.
The other input from outside the cerebellum is through the mossy fibers that first synapse in the cerebellar glomeruli.
Within the cerebellar glomeruli the mossy fibers synapse with what?
Granule and Golgi cell dendrites and with Golgi axon terminals. The Granule cell then passes this modified information along to the Purkinje cell.
What cells have an inhibitory effect on the Purkinje cells?
The Stellate and Basket cells
The cerebellum may be divided anatomically into three functional units, namely:
the vestibulocerebellum, spinocerebellum and cerebrocerebellum.
In evolution, the vestibulocerebellum is the oldest part of the cerebellum and has been called the archicerebellum.
The spinocerebellum is the next oldest part and has been called the paleocerebellum.
The cerebrocerebellum is the newest addition to the cerebellum and is also known as the neocerebellum
Where do the vestibular nuclei then send this processed information once it comes back from the fastigial nucleus?
down the spinal cord in the vestibulospinal tract to exert truncal stability and balance.
There are two main types of afferent input to the spinocerebellum. Describe the second
Near the border of the lateral ventral horn of the lower thoracic and lumbar spinal cord are neurons that resemble motor neuron called spinal border neurons. These neurons receive input from higher centers just like the lower motor neurons and send back a “copy” of the motor instructions to the anterior cerebellum. They send axons via the anterior (ventral) spinocerebellar tract which accesses the anterior cerebellum via the superior cerebellar peduncle or SCP. These fibers participate in maintaining posture of the lower limbs.
Output from the cerebrocerebellum goes primarily where?
to the dentate nucleus which projects to the red nucleus, and from there, to the ventral lateral nucleus of the thalamus via the dentatorubrothalamic tract.
There is also a parallel direct path to the thalamus from the dentate via the dentatothalamic tract.
Ex. of cerebellum in motor learning. The ability to learn to alter dart-throwing technique while wearing prisms that bend the path of light 15° to the right requires the correct analysis of visual sensory information and motor output.
In the Middle graph, the effects of prism spectacles on the dart-throwing ability of a normal subject. When the spectacles are first put on, the subject’s throws become wide to the left. After a little practice the throws become reasonably accurate again. When the spectacles are removed, throws deviate to the right but then quickly become accurate again.
In the Right graph, the effects of prism spectacles on the dart-throwing ability of a patient with degenerative disease of the cerebellum. In this case there is no compensation for the prism spectacles, and throws are wide to the left for as long as the spectacles are worn.
The next series of Netter drawings present cross-sectional views of the brainstem. I have selected only four of the fourteen levels presented in your textbook.
The brainstem figure in the upper left hand corner identifies the level of the section with a red line. These sections were selected to provide you with knowledge of fiber tracts/pathways important for clinical decision making. The four sections include some but not all of the 12 cranial nerves.
I have labeled with yellow arrows structures that you should be able to identify on unlabeled brainstem cross-sections. You should also be familiar with the function of each of these structures.
Note the MRI brain image below the figure indicating the location by the red box for this structure in the human brain.
What does the medial lemniscus carry?
The medial lemniscus carries vibration and proprioception information to the thalamus from the contralateral nucleus gracilis and cuneatus where the axons in the posterior columns terminated.
What is the lateral geniculate body?
The lateral geniculate body is the thalamic relay nucleus for visual information. It receives 85% of the optic tract fibers while about 15% terminate in nuclei in the superior colliculus.
The optic tract emerges from the optic chiasm and 85% of its fibers end in the lateral geniculate.
The substantia nigra is closely involved with the basal ganglia that modulates motor movements. When the substantia nigra degenerates, it loses its black pigment, appears pale on autopsy specimens and is associated with Parkinson’s disease in life.
What is the medial longitudinal fasciculus or MLF?
is the midline fiber pathway connecting the vestibular nuclei and the CN nuclei III, IV, VI to coordinate head and eye movements.
This is a cross-section through the mid-pons. I will not redefine structures already presented on the previous slide but it is important to note the change in location of the fiber tracts, especially the spinothalamic tracts, the medial lemniscus, the medial longitudinal fasciculus, and the corticospinal tracts.
The mesencephalic, main sensory nucleus, and motor nucleus of CN V are three nuclear components of the trigeminal nerve nuclei.
Note that the mesencephalic nucleus originates in the mesencephalon or midbrain, hence its name, but extends into the pons.
The pontine nuclei as noted earlier are a collection of neurons in the pons that receive input from the neocortex and send crossing fibers through the middle cerebellar peduncle.
What is the locus coeruleus?
is a noradrenergic brainstem nucleus involved in emotions, arousal and the sleep/wake cycle.
The raphe nuclei in the pons are involved in what?
mood, vigilance and levels of alertness, and sleep/wake cycles. They release serotonin to the rest of the brain.
Selective serotonin reuptake inhibitors, or SSRI antidepressants, are thought to act in these nuclei and their targets.
This is a cross-section through the upper medulla. I will not redefine structures already presented on the previous slides but it is important to note the change in location of the fiber tracts, especially the spinothalamic tracts, the medial lemniscus, the medial longitudinal fasciculus, and the corticospinal tracts.
The inferior and medial vestibular nuclei regulate what?
balance.
What is the nucleus and tractus solitarius or NTS?
Sensory nuclei for taste (from CN VII, IX and X) and for various chemo/baroreceptors (from CNs IX, X).
The nucleus tractus solitarius is important in the gag reflex, the carotid sinus reflex, the aortic reflex, the cough reflex, the baroreceptor and chemoreceptor reflexes, several respiratory reflexes and reflexes within the gastrointestinal system regulating motility and secretion.
The descending spinal nucleus and tract of CN V receive information about what?
crude touch, pain and temperature from the ipsilateral face through input from cranial nerves V, VII, IX, and X.
It extends down into the upper cervical spinal cord where it merges with the substantia gelatinosa of the dorsal horn.
The inferior olivary nucleus sends climbing fibers that synapse on the cerebellar Purkinje cells.
The pyramid is the name given to the corticospinal tract fibers in the medulla.
The reticular formation is a network of neurons and axons that reside in the brain stem tegmentum and are involved in arousal (midbrain and upper pons), respiration and heart rate control in the medulla.
This is a cross-section through the lower medulla. I will not redefine structures already presented on the previous slides but it is important to note the change in location of the fiber tracts, especially the spinothalamic and the corticospinal tracts.
The fasciculus cuneatus and fasciuculus gracilus carry proprioception and vibration information from the arms and legs respectively.
The decussation of the pyramids is where the descending corticospinal tracts cross to the other side. The arm fibers decussate first and make up the medial portion of the upper cervical corticospinal tract. The leg fibers decussate more caudally and make up the lateral portion of the upper cervical corticospinal tract.
A lesion at the decussation can produce a “crossed paralysis” such as left arm, right leg, by involving uncrossed arm fibers and crossed leg fibers on one side, the right in this example. This is rare and more often quadriparesis followed by death result from a severe lesion at this level.
This is a Netter slide showing the sensory CN nuclei on the left in blue, the motor CN nuclei on the right in red, and the parasympathetic nuclei on the right in purple. You should have a reasonable idea of the rostral caudal location for the CN nuclei, i.e. in the midbrain, pons, medulla or transitions points between these general brainstem areas.
