L16 Cerebellum Flashcards
LO 16.1 Anatomical divisions of the cerebellum
Positioned in the posterior cranial fossa
Superiorly covered by the tentorium cerebelli (dural reflection)
10-12% of total brain volume
Blood supply (highly variable)
- Posterior inferior and anterior inferior cerebellar arteries
- Superior cerebellar artery
- ^all vertebral artery system
Features:
- arbor vitae
- Culmen
- primary fissure (superior)
- fastigium (trunk)
- Medullary vellum (MV, sup and inf) - forms roof of 4V. wm, fibres and fibrous astrocytes).
- Inferior MV - choroid plexus
LO 16.2 Location of deep cerebellar nuclei and their connections with the cerebellar cortex
Medullary centre, each side of cerebellum
- Fastigial nucleus (most anteromedial)
- Interposed nucleus: globose & emboliform nuclei
- Dentate nucleus (most lateral) - crumpled sheet of cells, resembles inferior olivary nucleus. Most fibres of SCP originate here
LO 16.3 Anatomy of cerebellar peduncles: which fibre tracts (broadly) do they carry?
Inferior - afferents from SC and BS.
Middle - afferents from contralateral pontine nuclei
Superior - major efferents to red nucleus and thalamus
LO 16.4 Functional divisions of cerebellum
By “structure” = “function”:
- Archicerebellum (flocculonodular lobe) = vestibulocerebellum
- Paleocerebellum (culmen and pyramis of vermis) = spinocerebellum
- Neocerebellum (the rest; hemispheres, tonsils) = pontocerebellum
LO 16.5 Internal circuitry of the cerebellar cortex
Within folium - “leaves” of the CBC - fibres come from I/MCP, through medullary centre before numerous branching: Mossy fibres (excitatory) bifurcate many times to form “rosettes” (MfR) - a special synapse with many granule cells
- Each MfR synapses about 20 granule cells
- Granule cells produce parallel fibres (excitatory)
- Parallel fibres (PF) contain Purkinje cells (PC), Golgi cells and basket cells (GC, BC, inhibitory)
- BCs grab cell body of PCs in “baskets” and have inhibitory effect on neighbouring rows
- PFs excites PCs in its own path, inhibits PCs in the path of the PF next to it - “most excited PF wins”
- PFs contact GCs, send inhibitory feedback to MfR and cuts off signal == sharpening of the signal in space and time
Climbing Fibres (CF; +++) coming from the contralateral inferior olivary complex contact PCs
- Each CF excites about 2-10 PC; each PC only receives 1 CF
- Repeated CF firing will slow down PC activity (“long-term depression”, cerebellar learning?)
Only output from cerebellar cortex is via PCs: GABAergic, inhibitory. Target the deep (central) cerebellar nuclei:
- Dentate (cerebroCB) - projects to contralateral VL nucleus of thalamus, then cortex
- Globose, emboliform, fastigial (spinoCB) - project to contralateral red nucleus and reticular formation (RF)
- Lateral vestibular (Deiters) nucleus (vestibuloCB) - vestibulospinal tract and RF
16.6 Circuitry of the cerebellum: how it connects with other parts of the CNS
Output to SC (indirect):
- Rubrospinal tract (negligible in humans)
- Lateral vestibular tract (descending, motor; vestibulocerebellum)
Input from SC:
- Spinocerebellar tract(s) ascending
- Somatosensory (“unconscious” proprioception)
See attached circuitry diagrams
LO 16.7 Relationship between lesions to particular parts of the cerebellum and deficits which they might cause (also whether ipsi- or contralateral)
ArchiCB - unsteadiness, swaying, falling. Tendency to fall backwards when walking. Muscle tone not changed all the time. Signs usually bilateral
NeoCB - loss of muscle tone and fatigue, asynergia, dysmetria, intention tremor, dysdiadochokinesia (inability to perform rapid successive movements), nystagmus, speech disturbances (slurred speech, separating of syllables)
Based on circuitries and observed deficits from specific lesions, the cerebellum is involved in the following functions:
- Maintaining posture and balance while standing and moving (vestibuloCB)
- Monitoring the movement as it’s executed (spinoCB)
- Coordinating synergy of muscle activity in groups of muscles to generate complex mvmts (cerebroCB)
- Integration of sensory input to help plan and execute complex and precise mvmt essential in activities such as sports or playing musical instruments (spino, visuo, audio, most likely cerebroCB too). Automation of such movements through cerebellar “learning” (cerebellum as a computer?)
True or False? Each side of the Cerebellum affects the ipsilateral side of the body
True.
Cerebellar lesions will show ipsilaterally
True.
Cerebellar lesions will show ipsilaterally
Describe some of the multiple inputs the cerebellar cortex receives.
- Vestibular inputs reach the flocculus and vermis
- SC projects to the vermis and medial hemisphere
- Cerebral cortex projects to the cerebellum by way of pontine nuclei
- Climbing fibres arise in the contralateral inf olivary nucleus
- Visual and auditory info reaches the cerebellum
True or False? The tonsil is part of the anterior lobe.
False - posterior lobe
What divides the cerebellum into anterior and posterior lobes?
The primary fissure
Describe the tracts in origin and destination of the cerebellar peduncles
Inferior - afferents from SC and BS.
Middle - afferents from contralateral pontine nuclei
Superior - major efferents to red nucleus and thalamus
Describe the incoming fibres through the middle cerebellar peduncle.
MCP is the input route for info from cerebral cortex
Corticopontine fibres traverse the internal capsule and cerebral peduncle and terminate in pontine nuclei
- Pontocerebellar fibres then project through the contralateral MCP to nearly all areas of the cerebellar cortex
Describe the incoming fibres through the inferior cerebellar peduncle.
ICP is the major input route for fibres from the:
- Inferior olivary nucleus
- Vestibular nuclei
- Reticular formation
- Spinal cord
(ICP also contains some cerebellar efferents, particularly those bound for vestibular nuclei)
