Cerebellum

What are the two main afferents that reach the cerebellum?

1. Mossy fibers (these arise from pons, vestibular nuclei, or spin/cuneotracts) 2. Climbing fibers from CONTRALATERAL inferior olive. (Ipsilateral cortex --> olive --> decussates --> cerebellum and termination at PCs)

What are the 3 deep cerebellar nuclei and what cortical nuclei are they matched to?

1. Fastigial - Vermis 2. Interposed (aka emboliform and globiform in humans) - Paravermis 3. Dendate - Innervated by neurons in lateral hemispheres (appears squiggly, kind of like the olive, and C shaped) In the image, these will appear lighter colored because they are nuclei (cell bodies) and hence don't stain with myelin. Interposed nuclei are kind of within the squiggles, while fastigial are the smallest and located very close to midliine.

What are the hallmarks of lesions to the cerebellum?

ATAXIA (incoordination). Dysmetria, abnormal path of movement, action tremor, gait ataxia (wide base), oculomotor. Note that motor signs might be dissociated (vary between patients -- some might have more limb problems, others might have more gait problems.)

What are the specific names of the afferents that will eventually become the inferior cerebellar peduncle in the cerebellum?

MAINLY PURE INPUT TRACT 1. Olivocerebellar tract (from inferior olive) - carries CONTRALATERAL climbing fibers. 2. Cuneocerebellar tract (from lateral cuneate - proprioception UPPER body) 3. Dorsal spinocerebellar tract (from Clarke's nucleus at thoracic levels, carries proprioception from LOWER body Note that both cuneocerebellar and spinocerebellar are ipsilateral tracts - no crossing! Thus, the inferior peduncle carries both contra and ipsilateral fibers. It also carries efferent fibers from the vestibular system that control vestibular nuclei.

What is the name for the lateral hemispheres, and why?

Pontocerebellum. Neurons from cortex send axons to pons (at pontine nuclei) and this synapses at the CONTRALATERAL cerebellar hemispheres.

What other inhibitory neurons exist in the cerebellum besides granular cells

Basket cells and stellate cells. Both of these receive excitatory (granuole cell) input and inhibit Purkinje cells. They're found in the molecular layer. Golgi cells are found in the same level as granuole cells (granular layer), and these receive inputs from mossy/parallel fibers (aka granule cells) and these inhibit granuole cells.

What are smaller divisions of cerebellum called? What are folia, and what does it mean when they splay?

Cerebellum is separated into small divisions via fissures which are called lobules. Each lobule is composed of convoluted areas called folia; when these splay it's a sign of atrophy.

What are parallel fibers?

Granuole cells send off axons that divide into parallel fibers, and these parallel fibers innervates PCs (1000s of parallel fibers innervate each PC, which makes sense because the PC dendritic arbor is so huge).

What is the basis of the cerebellar circuit?

Input --> interneuron (granuole cells) --> output (Purkinje cells to deep cerebellar nuclei)

What are the main interneurons found in the cerebellar circuit? Where do they get their input from and what does it mean by "mossy fiber"?

Massive collections of excitatory interneurons. These have dendrites with "claws" that each grasps an axon terminal arising from 1. vestibular nucleus (flocculus, nodulus carried by ICP) 2. pontine nuclei (pontine nuclei carried by middle cerebral peduncle from lateral hemisphere) 3. spinal cord and medulla/spino and cuneocerebellar tracts (carried by ICP)

Does information within the cerebellum ever leave the cerebellum?

No! Aside from the flocculonodular lobule (which communicates with vestibular ganglion - see picture) no information leaves the cerebellum -- it just leaves the cerebellar cortex (gray matter) to go to DEEP cerebellar nuclei (located deep in its white matter)

What fibers does the superior cerebellar peduncle carry?

OUTPUT tract. It gets input from the deep nuclei of the cerebellum and sends it to the midbrain and higher structures. Note that the superior cerebellar peduncle DECUSSATES at the level of the midbrain (see slice between pons/midbrain) and many terminate in the red nuclei. However, others do not and continue to the VL thalamus and M1 (Note that in addition to containing outputs from the deep nuclei, it also has one unusual afferent that comes from intermediate zone of spinal cord and ascends as anterior spinocerebellar tract. [CLARIFY]

What fibers are carried in the middle cerebral peduncle, and where does it travel?

PURE INPUT TRACT. This contains axons from contralateral pontine nuclei (makes sense, as these tracts are hugging the pons) and terminates in lateral cerebellar hemispheres. These fibers carry major input from the cerebral cortex via the pons to the cerebellum (plan movements)

What are the three lobes of the cerebellum and what separates these lobes?

Primary fissure divides anterior from posterior lobe. Posterior lobe is the biggest, the one we mainly see when looking at the bottom of the brain; anterior lobe is kind of hidden under the cortex. The posterolateral fissure (horizontal) separates the superior/inferior portions as well as creates a new lobe: floculonodular.

Together, what do we all the vermis and paravermis? Why are they named this (has to do with their input)?

Spinocerebellum (as opposed to the vestibular cerebellum). This is because they are innervated by ascending tracts from the spinal cord and are concerned with movement underlying gait.

What is the action of purkinje cells in the cerebellum?

These are the output cells of the cerebellum, that send INHIBITORY signals to the deep nuclei from the cerebellar cortex. Typically this communication is contained within the cerebellum except in the case of the vestibular nuclei, in which the floccularnodular lobe sends to vestibular nucleus.

What are the main sagittal divisions of the cerebellum?

Vermis (middle) - area between the anterior and posterior lobes; note that vermis means worm, which may help to remember the parallel convolutions/folia Paravermis (intermediate) - mostly anterior lobe, a bit of posterior (These two make up spinocerebellum) Hemisphere (most laterally) - basically all posterior lobe (ponto cerebellum).

Where does the flocculonodulus receive input from?

Vestibular system. This is the most ancient part of the cerebellum, also known as the vestibulo-cerebellum. It gets input directly from vestibular ganglion and sends output directly to vestibular nuclei.

What is the inferior cerebellar peduncle, its locations, and the afferents it receives?

You can find the peduncles on the back of the brain, very close to the dorsal side of the medulla. The inferior, as its name implies, is closest to the bottom by the brainstem and SC -- thus it makes sense that the main input to this tract (afferent) comes from the spinal cord and medulla.