Cerebellum Anatomy and clinical correlation Flashcards
Overview of the cerebellar functions
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)
Why is 3 a key number for the cerebellum?
3 pairs of cerebellar peduncle
3 lobes
3 functional and anatomical divisions
3 cell layers in the cerebellar cortex
Inferior cerebellar peduncle
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
Middle cerebellar peduncle
Continuous with the basilar pons
Conveys pontocerebellar fibers that arise from the pontine nuclei
Mostly afferent fibers
Superior cerebellar peduncle
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
The three lobes of the cerebellum and how they are separated
Anterior lobe (spinocerebellum) - separated via primary fissure
Posterior lobe (pontocerebellum) - separated via the tonsils
Flocculonodular lobe (vestibulocerebellum) - separated via flocculus and nodule
4 pairs of cerebellar nuclei
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)
Nucleocortical fibers
Neurons from cerebellar nuclei that move to the cerebellar cortex to excite targets
- positive feedback mechanism.
Purkinjie cells in the cerebellar cortex
only fibers that exit the cerebellar cortex (only fibers that institute projection)
Large, goblet shaped cells with fan-shaped dendritic tree appearance
Golgi cells
Inhibitory interneurons in a layer deep to the purkinje cells
Granule cells
Excitatory interneurons in the cerebellar cortex that stimulate specifically the purkinje cells
Mossy vs climbing fibers (fibers that provide synaptic inputs into the cerebellum)
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
Afferent sources to the cerebellum
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
Review of the afferent spinocerebellar tracts
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
Efferent projects of the cerebellum
Only from purkinje cells and project to the deep cerebellar nuclei
Spinocerebellum and vestibulocerbellum purkinje -> fastigial nucleus
Pontocerebellum -> interposed and dentate nuclei
Cerebellum output via fastigial neurons
Provides excitatory inputs from the inferior peduncle to:
- bilateral vestibular nuclei
- contralateral reticular nuclei
What does the vestibulocerebellum output regulate?
Regulates activity of neurons in the medial and lateral vestibular nuclei
Functions to regulate balance and eye movements
What does the spinocerebellum output regulate?
Regulates activity from the anterior lobe to regulate body and limb movements
Pontocerebellar output
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
Lesions in the vestibulocerebellum
Leads to balance, gait and nystagmus issues
Truncal ataxia is more prevalent than extremty ataxia
Lesions in the spinocerebellum
Cause movement disorders and general gait instability
lesions in the Pontocerebellum
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
Lesion of the midline (medial) cerebellum
middle cerebellar syndrome
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*
Why does the cerebellum control the ipsilateral sides?
Because it “double-crosses” or decussates twice
Lesions of the lateral cerebellar hemispheres
Structures involved:
- interposed and potentially the dentate nucleus
Clinical presentation:
- ipsilateral limb ataxia
- dysmetria
- dysdiadochokinesia
- intention tremors
Dysdiadokinesia
Impairment of conducting alternating movements
Friedrichs ataxia
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
