Cerebellum: Structure, Circuitry & Function Flashcards
What is the cerebellum subdivided into?
- Flocculonodular lobe
- Vermis
- Anterior lobe
- Posterior lobe
Mid-sagittal section: arbor vitae (tree of life)
- Located posterior to the brain stem and the 4th ventricle
-
Vermis:
- lingual (next to the superior medullary velum)
- nodule (next to the inferior medullary velum)
- Primary fissure
- Horizontal fissure
- Tonsil
What is the blood supply to the cerebellum?
3 Pairs of Arteries:
-
Superior cerebellar (SCA):
- from basilar artery
-
Anterior inferior cerebellar artery (AICA):
- from basilar artery
-
Posterior inferior cerebellar artery (PICA):
- from vertebral artery
External features of the cerebellum:
-
folia: numerous convolutions
- Latin, “leaves”
Anatomical Lobes (3):
- Anterior Lobe
- Anterior to the primary fissure
- Posterior Lobe
- Posterior to the primary fissure
- Includes cerebellar tonsils (medial inferior part):
tonsillar herniation is of clinical significance
- Flocculonodular Lobe
How is the flocculonodular lobe subdivided?
-
1 nodule
- part of the vermis
- 2 flocculi
- Separated from the posterior lobe by the posterolateral fissure
- Forms the vestibulocerebellum:
- control of equilibrium, balance, and eye movements
- mediates vestibulo-ocular reflex (VOR)
Longitudinal subdivisions:
-
Vermis: along the midline
- Part of the spinocerebellum:
- control of axial and proximal limb movements
- Part of the spinocerebellum:
-
Intermediate zone of cerebellar hemisphere
- Part of the spinocerebellum:
- control of distal limb movements
- Part of the spinocerebellum:
-
Lateral zone of cerebellar hemisphere
- part of the cerebrocerebellum:
- planning and initiation of movements
- part of the cerebrocerebellum:
What are the excitatory afferents in the cerebellum?
Two excitatory afferents:
-
Climbing fibers:
- From contralateral inferior olivary nucleus
- Synapse directly with Purkinje cells
-
Mossy fibers:
- From all other sources
- Synapse with granule cells, which activate Purkinje cells
What are the 5 major neuronal types?
-
Purkinje cells: inhibitory
- output neurons of the cerebellar cortex
- Granule cells: excitatory
- Golgi cells: inhibitory interneurons
- Basket cells: inhibitory interneurons
- Stellate cells: inhibitory interneurons
Cerebellar Cortical Layers (3):
- Molecular layer
- Purkinje cell layer
- Granular layer
What makes up the molecular layer?
- Dendrites of Purkinje cells
- Parallel fibers from axons of granule cells (excitatory)
- Climbing fibers from the contralateral inferior olivary nucleus (excitatory)
- Stellate cells (inhibitory)
- Basket cells (inhibitory)
How are the dendrites of Purkinje cells oriented in the molecular layer?
perpendicular to the axis of the folium
Parallel fibers from axons of granule cells (excitatory):
- Each granule cell axon reaches the molecular layer
- bifurcate to form parallel fibers that run parallel to the axis of the folium
- Each parallel fiber can excite up to 500 Purkinje cells
Climbing fibers from the contralateral inferior olivary nucleus (excitatory):
- Synapse with dendrites of Purkinje cells
- Each Purkinje cell receives input from only 1 climbing fiber
- Each climbing fiber innervates 1 – 10 Purkinje cells
Purkinje cell layer:
- Purkinje cells (inhibitory; GABA):
- output goes only to the deep cerebellar nuclei
Granular layer:
- Granule cells (excitatory)
- Golgi cells (inhibitory)
- Mossy fibers (excitatory):
- Synapse with many granule cells
Deep Cerebellar Nuclei (DCN):
-
Major output neurons of the cerebellum as a whole
- not the Purkinje cells of the cerebellar cortex
-
Receive excitatory input:
- from collaterals of afferents to the cerebellar cortex
- climbing and mossy fibers
-
Receive inhibitory input:
- from Purkinje cells of the cerebellar cortex
- Output is excitatory
DCN sets of nuclei (4):
-
Dentate nuclei:
- Largest
- Most lateral
- Receive projections from the lateral zone of the cerebellar hemispheres
-
Interposed nuclei (made up of Emboliform nuclei + Globose nuclei):
- Intermediate in position
- Receive projections from the intermediate zone of the cerebellar hemispheres
-
Fastigial nuclei
- Most medial
- Receive projections from the vermis and some input from the flocculonodular lobe
Describe the synaptic circuit involving climing fibers:
Climbing fibers ⇒ excitatory to Purkinje cells ⇒ inhibitory to DCN ⇒ excitatory output to other brain regions
Describe the synaptic circuit involving mossy fibers:
Mossy fibers ⇒ excitatory to granule cells, which form parallel fibers ⇒ excitatory to Purkinje cells ⇒ inhibitory to DCN ⇒ excitatory output to other brain regions
Describe the synaptic circuit involving inhibitory interneurons:
-
Molecular layer:
- Basket cells and stellate cells ⇒ inhibitory to Purkinje cells
-
Granule cell layer:
- Golgi cells ⇒ inhibitory to granule cells
**What makes up the vestibulocerebellum? **
Flocculonodular Lobe and
inferior vermis
Vestibulocerebellum:
Functions
- Controls balance and equilibrium while standing or moving
- Controls eye movements
- Coordinates movements of the head and eyes
Vestibulocerebellum:
Afferent Inputs
Afferent inputs:
- Vestibular labyrinth (ipsilateral semicircular canals and maculae of the utricle and saccule) projects directly to the Vestibulocerebellum
- Vestibular labyrinth also projects to the vestibular nuclei in the medulla, which then projects to the vestibulocerebellum via the Juxtarestiform body (next to the Restiform body)
- Visual centers (LGN, superior colliculus, and the visual cortex) project to pontine nuclei, which then project to the vestibulocerebellum