Cerebellum Flashcards
Function(s) of the Cerebellum
- Coordinate movements
- Maintain posture
- Motor learning (procedural memory)
receives a lot of sensory input, but does not interpret it
lesions do not cause lasting motor paralysis - it causes motor DYSFUNCTION
Organization of Gray Matter in the Cerebellum
- Molecular Layer - next to pial surface; few neurons; cell bodies of basket and stellate cells
- Purkinje Layer - Purkinje cell bodies
- Granular Layer - deepest layer; granule cells and a few Golgi cells
- White Matter - neuronal axons
be familiar with histological images
Purkinje Cells
EFFERENTS
output cells from the cerebellar cortex
- inhibits cerebellar nuclei and the vestibular nuclei (GABA)
highly differentiated, many dendrites
Granule Cells
Smallest neurons, only excitatory neurons, NT is glutamate
Stellate Cells
axons synapse with Purkinje cells and inhibit them; star-shaped dendrites
Golgi Cells
Inhibitory; NT is GABA, large/scattered neurons with short axons
Basket Cells
axons synapse with Purkinje cells and inhibit them; NT is GABA
Name the two types of afferent fibers
1: Climbing Fibers
2: Mossy Fibers
Both are excitatory fibers; send collaterals to the deep cerebellar nuclei in addition to their respective synapses
Name the deep cerebellar nuclei
- emboliform nucleus
- dentate nucleus
- globose nucleus
- fastigial nucleus
Climbing Fibers
- Afferent fibers
- From the inferior olive in the medulla
- Myelinated, excitatory influence on Purkinje cells
- Convey info about movement errors to the cerebellum
Mossy Fibers
- Afferent fibers
- From SC, reticular formation, vestibular system, and pontine nucleir (everywhere but inferior olive)
- Synapse w/ granulocytes in granular layer
- Somatosensory, arousal, equilibrium, and cerebral cortex motor info to cerebellum
Vestibulocerebellum
- Functional name for flocculonodular lobe
- Receives info from vestibular receptors (CN VIII and vestibular nuclei), also from visual areas
- Send output to vestibular nuclei
- FXN: influence eye movements and postural muscles of the head and body
Spinocerebellum
- Functional name for vermis and paravermal region
- Somatosensory info, internal feedback from spinal interneurons and sensorimotor cortex
- FXN: control ongoing movement via brainstem descending tracts
- Vermis control postural muscles
- Paravermis controls UMNs (move limbs, gait and station)
Ponto/Cerebrocerebellum
- Input from cerebral cortex via the pontine nuclei
- FXN: coordination of voluntary movements, planning of movements, and timing
- coordinates fine movements for fractionation*
From where does the cerebrocerebellum receive afferent fibers?
From the cerebral cortex:
- Mossy fibers from the cortico-pontocerebellar and cortico-reticulocerebeller
- Climbing fibers from the cortico-olivocerebellar
From where does the spinocerebellum receive afferent fibers?
From the spinal cord:
-Mossy fibers form the anterior/posterior spinocerebellar tracts and the cuneocerebellar tract
From where does the vestibulocerebellum receive afferent fibers?
From the vestibular system:
-Mossy fibers from the vestibular nuclei and CN VIII
What information is carried by the afferent fiber pathways?
unconcsious proprioception about limb movement
Describe the posterior spinocerebellar tract
SC afferent fiber pathway
- axons carrying unconscious proprioception from lower limb
- 1st order neuron enters via the dorsal root ganglion
- ascends in gracile fasiculus
- synapse in nucleus dorsalis of Clark (gray matter from C8-L2)
- 2nd order neuron ascends in dorsolateral funiculus
- enters the cerebellum bia the inferior cerebellar peduncle
Describe the cuneocerebellar tract
SC afferent fiber pathway
- axons carrying unconscious proprioception from upper limb
- 1st order neuron enters via the dorsal root ganglion
- ascends in the cuneate fasiculus
- synapses in accessory/lateral/external cuneate nucleus in the lower medulla
- 2nd order neuron from the accessory cuneate nuscleus ascends to the cerebellum
- enters via the inferior cerebellar nucleus
Big picture information about the anterior spinocerebellar tract
- carries unconscious proprioception from the lower extremity; also Pacinian/Meissner/Meckel corpuscle
- CROSSES 2X (in the anterior white commissure and after entering the superior cerebellar peduncle)
Superior Cerebellar Peduncle
- major efferent for globose, emboliform, and dentate nuclei
- afferent fibers from the ventral spinocerebellar tract
Middle Cerebellar Peduncle
- largest peduncle
- in the area of the pons
- relays afferent fibers from pontine nuclei to cortex
Inferior Cerebellar Peduncle
Main afferent pathway from SC
Function of Vestibulocerebellum
Eye movements and neck/trunk movements
Function of Spinocerebellum
axial/lower extremity movements, gait, station
Function of Cerebrocerebellum
precise/coordinated movements of extremities (mainly the upper extremity)
Cerebrocerebellum transmits to:
- Dentate nucleus
- Some globose/emboliform (interposed) nuclei
Spinocerebellum transmits to:
- Globose/Emboliform (interposed) nuclei (paravermal region sends info here)
- Fastigial nucleus (info from the vermis)
- Dentate nucleus
Vestibulocerebellum transmits to:
- Vestibular nucleus (bypasses the deep cerebellar peduncle; takes the inferior cerebellar peduncle and leaves via the juxtarestiform body)
- Some fastigial nucleus
Dentate Nucleus targets:
red nucleus, thalamus, VL of thalamus
Interposed nuclei targets:
red nucleus, thalamus, VL of thalamus
Fastigial nucleus targets:
reticular formation and vestibular nucleus
Describe the effect of unilateral cerebellar lesions, and explain the mechanism of the effect
Unilateral lesions affect the ipsilateral side
-crosses to the opposite red nucleus, but crosses again when going back down
Common sign of cerebellar lesions
Ataxia
- voluntary, normal strength, jerky, and inaccurate movements
- not associated with hyperstiffness
- wide base gait, stumble
- when damage is unilateral, fall to side of lesion
Describe lesions of vestibulocerebellum
- between vestibular system and flocculonodular lobe
- nystagmus*
- truncal ataxia
- truncle instability (titubation)
What is truncal ataxia?
difficulty maintaining sitting and standing balance
What is truncal instability/titubation?
Anterior-posterior tremor, can’t tandem walk (sobriety test)
Describe lesions of spinocerebellum
- between cutaneous/proprioceptive info from SC to the vermis/paravermal regions
- gait and truncal ataxia (wide, staggering base)
Describe midline ataxia
Caused by vestibulocerebellar and spinocerebellar disease
- truncal instability (titubation and gait ataxia)
- equilibratory (gait) ataxias
What is gait ataxia?
wide based, irregular steps with lateral veering (toward side of lesion)
What is dysarthria?
slurred, poorly articulated speech
-scanning speech: spoken words are broken up into separate syllables, often separated by a notable pause, spoken w/ varying force
What is movement decomposition?
movements are broken up into their individual compents
Describe dysdiadochokinesia?
inability to rapidly alternate your movements
Describe dysmetria?
inability to accurately move an intended distance
Describe action tremors/intention tremors
- shaking of limb during voluntary movement
- tremor worsens as a patient tries to touch their target (worse at the end of the movement)
Describe cerebroserebellum lesions
- lateral hemispheres of the cerebellum
- dysarthria, ataxic gait, decomposition of movements, limb ataxia (dysdiadochokinesia, dysmetria, action tremors)
Describe appendicular ataxia
- dysfunction of the cerebellar hemispheres that results in ataxia of the extremities
- also ataxia of speech (scanning dysarthria)
- hypotonia, decomposition of movement, dysmetria, dysdiadochokinesia
How can you differentiate between cerebellar ataxia and sensory ataxia?
Cerebellar ataxia: normal vibratory sense, proprioception, and ankle reflexes
Sensory ataxia: abnormal vibratory sense, proprioception, and ankle reflexes; can stand with feet together when eyes are open
Describe cerebellar ataxia
Positive Romberg test (unable to stand with their feet together), normal vibratory sense/proprioception/ankle reflexes
Describe sensory ataxia
Positive Romberg test when eyes are closed (can stand with feet together when eyes are open), abnormal vibratory sense/proprioception/ankle reflexeS
Tests to run to examine the cerebellum
Vestibulocerebellum and Spinocerebellm:
- station
- walking
- tandem gait
Cerebrocerebellum:
- rapid alternating movements
- finger-to-nose/toe-to-finger
- heel-to-shin
- rebound and check reflex
- speech
