50 - Cerebellum and Motor Activity

what are the 4 main roles of the cerebellum? what are the 3 sources of input to the cerebellum? what activity does the cerebellum influence?

(3) Influences activity of upper motor neurons via projections to thalamus (VA/VL) (4) Influences activity of lower motor neurons via Descending tracts from brainstem nuclei (e.g. vestibulospinal, rubrospinal) Corticospinal tracts (via thalamic influences on upper motor neurons)

describe the pathway of the cerebrocerebellar efferents

*axons from Purkinje* cells in lateral cerebellar *hemispheres* synapse w/ neurons in *dentate nuclei*, the largest of the deep cerebellar nuclei. Dentate neurons, in turn, send axons to targets in the *red nucleus* and *motor thalamus* via the *superior* cerebellar peduncle. .

what are the flocculi? what is the nodulus? what can happen to the tonsils?

*flocculi* = two tufts of cerebellar parenchyma visible on the anterior (ventral) surface of the cerebellum just below the middle cerebellar peduncle *nodulus* = a small subdivision of the cerebellar vermis *Chiari malformations* 1 - cerebellar tonsil ectopia 2 - displacement of cerebellum and medulla *cerebellar tonsils* = have tendency to become deformed when the brain is displaced inferiorly by an expanding intracranial mass ("tonsillar herniation" - a potentially catastrophic clinical event associated with brainstem compression).

*state the:* - deep cerebellar nuclei - afferent axons - efferent axons *for the following:* vestibulocerebellum spinocerebellum - vermal spinocerebellum - paravermal cerebrocerebellum

.

*what happens if a lesion in the:* - vermis - paravermal/lateral regions - lateral lesions

.

describe pathway of spinocerebellar *a*fferents

.

describe the pathway of the vestibulocerebellar *e*fferents

.

how does motor learning work in the cerebellum?

.

how many cerebellar peduncles are there? what do they contain?

.

what are the *2 types of fibers* that give *input* to the cerebellar cortex? are these fibers *excitatory or inhibitory*? what will this *input influence*? where in the cerebellar cortex is the *output* from? where do *most purkinje cells* send axons to?

.

what are the 3 functional divisions of the cerebellum?

.

what are the 3 layers of the cerebellar cortex?

.

what covers the cerebellum? what 3 groups of arteries supply the cerebellum?

.

what is in the molecular layer of the cerebellar cortex?

.

what is the *input* to the *inferior olive*? what is the *output* to the *inferior olive*?

.

describe pathway of spinocerebellar *e*fferents

Axons from the spinocerebellum comprise two groups. The first group is composed of axons from the fastigial nuclei, deep cerebellar nuclei near the midline that receive signals from Purkinje cells in most parts of the cerebellar vermis. Axons from the fastigial nuclei descend through the inferior cerebellar peduncle to influence the lateral vestibular nuclei and parts of the brainstem reticular formation. The second group of axons originates in the interposed nuclei, deep cerebellar nuclei that process information from the paravermal part of the cerebellar cortex. These axons leave the cerebellum via the superior cerebellar peduncle to synapse with neurons in the red nucleus and motor thalamus.

Summarize the cerebellar cortical circuitry.

Climbing fibers originate exclusively in the (contralateral) inferior olivary nuclei. the mossy fibers excite granule cells, which in turn send excitatory signals to Purkinje cells by way of parallel fibers. Golgi cells, in contrast, inhibit granule cells, thereby decreasing stimulation of the Purkinje cells by the granule cell axons (parallel fibers).

what can happen to the cerebellar vermis?

Dandy-walker syndrome

what is the input to the *vermal* subdivision of the *spinocerebellum*? what is the *output*? what is the *role* of the *vermal subdivision* of the spinocerebellum?

In general, the vermal portion of the spinocerebellum receives sensory information related to proximal muscle groups Ventral (anterior) spinocerebellar projections originate in the contralateral lumbosacral gray matter of the cord, cross the midline and ascend in the ventral spinocerebellar tracts, enter the superior cerebellar peduncle and re-cross to enter the cerebellum ipsilateral to their side of origin. Vestibular projections to the vermis are bilateral, and enter the cerebellum via the inferior cerebellar peduncle.

describe the pathway of the cerebrocerebellar afferents

Input to the cerebrocerebellum (neocerebellum) comes from axons originating in the *contralateral basal pons* and the *contralateral inferior olive*. The basal pontine neurons that project to the cerebellum receive extensive signals from the cerebral cortex, and send their axons into the cerebellum via the middle cerebellar peduncle. Olivary projections travel to the cerebellum via the inferior cerebellar peduncle.

describe the pathway of the vestibulocerebellar *a*fferents

Projections to the vestibulocerebellum include *axons originating in the vestibular complex in the brainstem* as well as *axons originating in the vestibular apparatus of the inner ear* and the inferior olive (not shown). These axons reach the vestibulocerebellum via the *inferior cerebellar peduncle*.

what are the *purkinje cells*? what are they the ultimate target of? what are they the source of? where do they receive their *excitatory signals* from? where do they receive their *inhibitory signals* from?

Purkinje cell dendrites receive direct excitatory input from climbing fibers that come from the contralateral inferior olive Purkinje cells also receive excitatory input from mossy fibers, but the excitatory input from mossy fibers on Purkinje cells is indirect. Mossy fibers excite granule cells, which then send excitatory axons (parallel fibers) into the molecular layer. Parallel fibers, in turn, travel along the long axis of a given cerebellar folium, where they are able excite the dendrites of multiple Purkinje cells.

where do purkinje cells send their axons?

Purkinje cells are the only source of output from the cerebellar cortex. There are two basic types of projections that leave the cerebellum, namely: 1) a few inhibitory Purkinje cell axons from the flocculonodular lobe, and 2) the far more numerous excitatory axons from the deep cerebellar nuclei.

*granule cells* are the neurons *excitatory or inhibitory*? what fibers send *input* to the granule cells? where does the *output* go to? what are these axons called?

The dendrites of granule cells branch in the granule cell layer, where they receive excitatory input from axons called mossy fibers (more on these in a moment) and inhibitory input from the axons of Golgi cells. Their axons, in turn, ascend into the molecular cell layer as so-called parallel fibers, where they branch and travel along the long axis of the cerebellar folium to excite Purkinje cell dendrites, Golgi cell dendrites, and the dendrites of other interneurons (specifically "basket cells" and "stellate cells", discussed below) in the molecular layer.

what is the input to the *paravermal* subdivision of the *spinocerebellum*? what is the *output*? what is the *role* of the *paravermal subdivision* of the spinocerebellum?

The interposed nuclei send their fibers into the superior cerebellar peduncle, where they cross to ascend to the magnocellular portion of the contralateral red nucleus and to the VA/VL nuclei of the contralateral thalamus. Magnocellular neurons in the red nucleus that receive projections from the spinocerebellum send axons that cross and descend as the rubrospinal tract. The VA/VL nuclei of the thalamus, you will recall, project to the motor and premotor areas of the cerebral cortex. paravermal region receives information related to more distal muscles.

what does the *middle cerebellar peduncle* connect? what are the *afferent connections*? what are the *efferent connections*?

The middle cerebellar peduncles are massive white matter tracts that connect the cerebellum to the pons. They contain only afferent axons (that is, axons entering the cerebellum) that originate in neurons in the basal pons and cross the midline en route to the contralateral cerebellum.

where are the *golgi cells*? what kind of neurons are they? what kind of *input* do they receive? what kind of *output* do they send out?

Their cell bodies and axons lie in the granule cell layer, while their dendrites lie in the molecular layer.

what *activity does the cerebellum monitor and adjust*? what *kind of input does the cerebellum need to function*? what fibers deliver the inputs? cerebellum influences activity of *what two groups of neurons*? the *messages sent by the cerebellum* are defined by:

Two types of excitatory axons carry information to the cerebellum: the *mossy fibers and the climbing fibers*. Most of the afferent information reaching the cerebellum is conveyed by mossy fibers - *mossy fibers from the (dorsal spinocerebellar) tracts, vestibular nuclei,* go through the *INFERIOR cerebellar peduncle* the mossy fibers from the cerebral cortex go through middle cerebellar peduncles. cerebral cortex axons --> basal pontine neurons The second type of excitatory fiber carrying information to the cerebellar cortex is the climbing fiber. *climbing fibers from the contralateral inferior olive go through the INFERIOR cerebellar peduncle*

what does the *superior cerebellar peduncle* connect? what are the *afferent connections*? what are the *efferent connections*?

are composed predominantly of fibers projecting from deep cerebellar nuclei (more specifically, the dentate and interposed nuclei, which will be discussed shortly) to extra-cerebellar sites. In addition to their large numbers of efferent cerebellar projections, they also contain a few axon entering the cerebellum (afferent projections), mainly from the ventral (anterior) spinocerebellar tracts.

In lateral cerebellar lesions, deficits will be seen *ipsilateral to the lesion*. why?

decussation of dentate neurons on way up decussation of UMNs on way down leads to back to same side of cerebellar lesion

what makes up the cerebrocerebellum? what does it *influence*?

fine motor control motor learning & memory planning & timing of voluntary movements

what are the *inputs and outputs* for: dentate nuclei interposed nuclei fastigial nuclei

input from purkinje fibers of the cerebellar *hemispheric* cortex --> *dentate* nucleus --> *superior* cerebellar peduncle --> red nucleus and thalamus input from purkinje fibers of *paravermal* cortex --> *interposed* nuclei --> *superior* cerebellar peduncle --> red nucleus and thalamus input from purkinje fibers of *vermal* cortex --> *fastigial* nuclei --> *inferior* cerebellar peduncle --> vestibular complex

what is the cerebellar glomerulus? what occurs here?

intervening hypocellular, fibrillar zones termed cerebellar glomeruli.

what is the role of the dentate nucleus?

largest paired nuclei = *dentate nuclei*, which lie deep within the white matter of each hemisphere. *dentate nuclei* receive most of their input from the cortex of the *cerebellar* hemispheres, and send axons out through the superior cerebellar peduncles to the *red nucleus and thalamus*.

vermis nodulus tonsil

nodulus, a small subdivision of the cerebellar vermis flocculi and nodulus make up a functional unit known as the flocculonodular lobe

what does the *inferior cerebellar peduncle* connect? what are the *afferent connections*? what are the *efferent connections*?

originates in the medulla oblongata and connects that structure to the cerebellum.

where do the 4 *deep cerebellar nuclei* receive axons from? where do they send axons to?

purkinje cell layer is in the *cerebellar* cortex from lateral to medial, the dentate, the emboliform, the globose, and the fastigial nuclei ("don't eat gross food"). The largest of these paired nuclei are the dentate nuclei, which lie deep within the white matter of each hemisphere. dentate nuclei receive most of their input from the cortex of the cerebellar hemispheres, and *send axons out through the superior cerebellar peduncles* to the red nucleus and thalamus.

*spinocerebellum:* where do projections from *vermal* cortex go? where do projections from *paravermal* cortex go? what activity does the *spinocerebellum* influence?

spinocerebellum also receives input from the visual system and the inferior olivary nucleus.

*cerebrocerebellum* where does the input come from? where does the output go to? what does it influence?

the contralateral inferior olive also sends a significant number of projections to the lateral cerebellum via the inferior cerebellar peduncle. Purkinje cells of the cerebrocerebellum send their projections to the ipsilateral dentate nuclei dentate nuclei, in turn, send excitatory projections to the contralateral red nucleus and the contralateral thalamus (VA/VL). Parvocellular neurons in the red nucleus send projections downward to the ipsilateral inferior olive via a structure known as the central tegmental tract to form a feedback loop to the cerebellum.

what is the *input* to the *vestibulocerebellum*? what is the *output*? what is the main *activity* of the *vestibulocerebellum*?

vestibulocerebellum receives its sensory input from the vestibular labyrinth (semicircular canals and otolith organs) and vestibular nuclei (especially the inferior nuclei). Projections to the lateral vestibular nuclei (the spinocerebellum, discussed below, actually sends more input to the lateral vestibular nucleus than does the vestibulocerebellum) influence the activity of axial muscles and limb extensors via the lateral vestibuolospinal tracts, and thus enable the body to maintain proper posture and balance.