Cerebellum Anatomy and clinical correlation

Question 1

Overview of the cerebellar functions

Answer 1

Modulates motor output by influencing projections through the corticospinal tract and brainstem (vestibulospinal tract, rubrospinal tract, etc.)

“Sensorimotor integration” work is what the cerebellum is described as

Overall functions:

• helps maintaining balance and posture
• regulates eye movements
• coordinates ongoing movement in time and space
• motor planning and learning
• contributes to coordination and sequencing of cognitive processing

damage does not lead to paralysis, but instead uncoordinated choppy movements (ataxia)

Question 2

Why is 3 a key number for the cerebellum?

Answer 2

3 pairs of cerebellar peduncle

3 lobes

3 functional and anatomical divisions

3 cell layers in the cerebellar cortex

Question 3

Inferior cerebellar peduncle

Answer 3

Bundle that contains mainly fibers that arise in the spinal cord or medulla.

Forms reciprocal connections between the cerebellum and vestibular structures

mostly afferent fibers

Question 4

Middle cerebellar peduncle

Answer 4

Continuous with the basilar pons

Conveys pontocerebellar fibers that arise from the pontine nuclei

Mostly afferent fibers

Question 5

Superior cerebellar peduncle

Answer 5

Contains predominantly cerebellar efferent fibers that orginate in the cerebellar nuclei

These efferent fibers travel to the brainstem and diencephalon to send signals to these areas.
- these fibers decussate in the midbrain

Question 6

The three lobes of the cerebellum and how they are separated

Answer 6

Anterior lobe (spinocerebellum) 
- separated via primary fissure 

Posterior lobe (pontocerebellum) 
- separated via the tonsils 

Flocculonodular lobe (vestibulocerebellum) 
- separated via flocculus and nodule

Question 7

4 pairs of cerebellar nuclei

Answer 7

1) Fastigial nuclei:
- located immediately adjacent to the midline And in vermis zone
- projects bilaterally through the inferior cerebellar peduncles to brain stem
- functions to inhibit targets via GABA release

2/3) Globose nuclei and emboliform:(interposed nuclei)
- functionally related to the intermediate zone
and excite neurons in the brainstem/ thalamic nuclei (use glutamate and aspartate)

4) Dentate nucleus:- appears as an undulating sheet of cells
- functionally related to the lateral zone and excite neurons in the brainstem/ thalamic nuclei (use glutamate and aspartate)

Question 8

Nucleocortical fibers

Answer 8

Neurons from cerebellar nuclei that move to the cerebellar cortex to excite targets
- positive feedback mechanism.

Question 9

Purkinjie cells in the cerebellar cortex

Answer 9

only fibers that exit the cerebellar cortex (only fibers that institute projection)

Large, goblet shaped cells with fan-shaped dendritic tree appearance

Question 10

Golgi cells

Answer 10

Inhibitory interneurons in a layer deep to the purkinje cells

Question 11

Granule cells

Answer 11

Excitatory interneurons in the cerebellar cortex that stimulate specifically the purkinje cells

Question 12

Mossy vs climbing fibers (fibers that provide synaptic inputs into the cerebellum)

Answer 12

Mossy:

• arise from numerous regions
• ascend through cerebellar white matter and function to form excitatory synapses onto dendrites of granule/golgi cells

Climbing:

• arise exclusively from contralteral olivocerebellar projections (from inferior olivary nucleus)
• wrap around cell body and dendrites of purkinje cells
• each fiber functions to form roughly 10:1 ratio of excitatory synapses on purkinje cells

Question 13

Afferent sources to the cerebellum

Answer 13

Spinal cord
- via spinocerebellar tracts

Brainstem

• via olivocerebellar fibers from inferior olivary nuclei
• via pontocerebellar fibers from the contralateral basilar pons
• via corticopontine fibers from the ipsilateral basilar
• via secondary vestibulocerbellar fibers from vestibular nuclei
• via reticulocerbellar fibers from the reticular nuclei

Other
- via primary vestibulocerbellar fibers from the vestibule itself

Question 14

Review of the afferent spinocerebellar tracts

Answer 14

Posterior spinocerebellar tract
- proprioception from lower limb and trunk

Cuneocerebellar tract
- proprioception from upper limb

Anterior(ventral) spinocerebellar tract
- conveys information about whole lower limb movements and postural adjustments

Rostral spinocerebellar tract
- converts information about whole upper limb movements and postural adjustments

Question 15

Efferent projects of the cerebellum

Answer 15

Only from purkinje cells and project to the deep cerebellar nuclei

Spinocerebellum and vestibulocerbellum purkinje -> fastigial nucleus

Pontocerebellum -> interposed and dentate nuclei

Question 16

Cerebellum output via fastigial neurons

Answer 16

Provides excitatory inputs from the inferior peduncle to:

• bilateral vestibular nuclei
• contralateral reticular nuclei

Question 17

What does the vestibulocerebellum output regulate?

Answer 17

Regulates activity of neurons in the medial and lateral vestibular nuclei

Functions to regulate balance and eye movements

Question 18

What does the spinocerebellum output regulate?

Answer 18

Regulates activity from the anterior lobe to regulate body and limb movements

Question 19

Pontocerebellar output

Answer 19

Projects to the interposed and dentate nucleus

• then to the red nucleus and ultimately to the rubrospinal tract
• or to the VL nucleus of the thalamus and ultimately to the corticospinal tract

Functions in learning, planned movements and evaluating proprioception

Question 20

Lesions in the vestibulocerebellum

Answer 20

Leads to balance, gait and nystagmus issues

Truncal ataxia is more prevalent than extremty ataxia

Question 21

Lesions in the spinocerebellum

Answer 21

Cause movement disorders and general gait instability

Question 22

lesions in the Pontocerebellum

Answer 22

Cause dysmetria, hypotonia, decreased tendon reflexes, tendency to lean or fall towards the lesion side.

Ataxia in the extremities is more prevalent than truncal ataxcia

Question 23

Lesion of the midline (medial) cerebellum

middle cerebellar syndrome

Answer 23

very common in alcoholic degeneration of the cerebellum

Structures involved:
- fastigial nuclei

Clinical presentation

• truncal and gait ataxia (falls to the ipsilateral side if unilateral)
• nystagmus
• intense dizziness/vertigo/nause/vomiting
• can show bilateral truncal/ gait ataxia, but never contralateral by itself*

Question 24

Why does the cerebellum control the ipsilateral sides?

Answer 24

Because it “double-crosses” or decussates twice

Question 25

Lesions of the lateral cerebellar hemispheres

Answer 25

Structures involved:
- interposed and potentially the dentate nucleus

Clinical presentation:

• ipsilateral limb ataxia
• dysmetria
• dysdiadochokinesia
• intention tremors

Question 26

Dysdiadokinesia

Answer 26

Impairment of conducting alternating movements

Question 27

Friedrichs ataxia

Answer 27

Autosomal recessive genetic disorder which contains a mutant frataxin gene (GAA triplet repeat)

Causes degeneration of the spinocerebellar posterior columns, corticospinal tracts, and cerebellar purkinje fibers

Clinical presentation:

• ataxia of the trunk and limbs bilaterally
• muscle weakness and nystagmus
• concomitant cardiomyopathies

Treatment is supportive care for the symptoms