Cerebellum

Question 1

What is the output & role of the vermal cerebellum?

Answer 1

Receives input from spinal cord representing axial musculature

Outputs through the fastigial nucleus travel to the vestibular nucleus and pontine reticular formation; from there, information descends in the medial descending system via the lateral vestibulospinal tract and pontine reticulospinal tracts

Involved in control of axial musculature, posture, and balance

Question 2

What is the output and role of the paravermal cerebellum?

Answer 2

Receives inputs from spinal cord representing distal musculature

Outputs through the interposed nuclei to the contralateral red nucleus; directs motor output through the rubrospinal tract which fine-tunes movements of the limbs

Question 3

What is the role of the lateral cerebellar hemispheres?

Answer 3

Receives input from the contralateral motor cortices by way of the pontine nuclei

Output through the dentate nucleus sends information to the contralateral VL thalamus, and from there to motor cortices

Involved in planning and initiation of movement

Question 4

What are the 4 deep cerebellar nuclei?

Answer 4

Fastigial
Globose + Emboliform (Interposed)
Dentate

Question 5

What are the 3 Ds of Ataxia?

Answer 5

Dysmetria - consistent over/under shooting of a motor target

Decompensation of movement

Dysdiadochokinesia - impaired ability to perform rapid alternating movements

Question 6

What are signs of a cerebellar lesion?

Answer 6

HANDS + Tremor

Hypotonia
Ataxia
Nystagmus
Dysarthria 
Stance and Gait abnormalities 
Tremor

Question 7

What are the 3 layers of the cerebellar cortex?

Answer 7

Molecular layer
Purkinje Cell layer
Granule cell layer

Question 8

Components of the molecular layer of the cerebellar cortex

Answer 8

Purkinje Cell dendrites
Parallel fibers (from granule cells) 
Stellate cells
Basket cells
Golgi cells

Question 9

Role of Golgi cells

Answer 9

Golgi cells reside in the molecular layer; when excited by parallel fibers they provide feedback inhibition onto granule cells

Question 10

Role of basket and stellate cells

Answer 10

Inhibitory interneurons residing in the molecular layer; when excited by parallel fibers, provide feedback inhibition of Purkinje cells

Activation of these cells releases deep cerebellar neurons from inhibition

Question 11

Role of Purkinje cells

Answer 11

Purkinje cells fire spontaneously at a rate of 50-100Hz to continually suppress deep cerebellar neurons

Question 12

Input to Purkinje cells - 2 types

Answer 12

1. Climbing fibers from the contralateral inferior olivary nucleus; direct excitation of Purkinje cells by climbing fibers causes complex spikes
2. Mossy fibers from primary vestibular afferents and pontine nuclei; mossy fibers synapse on granule cells, which excite Purkinje cells by way of parallel fibers causing simple spikes

Question 13

Role of the vestibulocerebellum

Answer 13

i.e. Flocculonodular lobe

Receives input from vestibular sensory cells and sends outputs to axial motoneurons via the vestibular nucleus; primary function is balance

Question 14

Climbing fibers

Answer 14

Originate in the contralateral inferior olivary nucleus; axons cross the midline and enter the inferior peduncle, from which they enter the cerebellar cortex to innervate Purkinje cells

Question 15

Mossy fibers

Answer 15

Originate from several sources:

Lateral cuneate nucleus in the medulla (relaying proprioceptive info from the upper extremities)

Vestiular nuclei

Ponteine nuclei (relaying information from cerebral cortex to cerebellum)

End in the cerebellar cortex to synapse on granule cells

Question 16

Pontine nuclei

Answer 16

Relay information from the cerebral cortex to the cerebellum; axons from the pontine nuclei on one side cross the midline to enter the contralateral middle cerebellar peduncle; they then enter the cerebellum to end as mossy fibers, which synapse onto granule cells

Question 17

How does output leave the cerebellum?

Answer 17

The cerebellar cortex sends information to the deep cerebellar nuclei; from deep cerebellar nuclei information flows through the superior cerebellar peduncle to the brainstem; axons cross midline and synapse in the VA/VL thalamus (via dentate nucleus) or in the Red Nucleus (via interposed nuclei)

Question 18

Pontine nuclei

Answer 18

Receive information from ipsilateral motor and pre-motor cortex; project to contralateral cerebellum, ending as mossy fibers