The Cerebellum Flashcards
Describe the functional organization of the cerebellum.
- Spinocerebellum/paleocerebellum: Vermal zone and paravermal cerebellar cortex. The Paravermal Zone makes connections through the interposed nuclei and fine tunes limb movements. The Vermal Zone has efferent connections through the fastigial nucleus and is involved in the control of axial musculature, posture and balance. Integration of head/eye movements
- Corticocerebellum/neocerebellum: Lateral portions of lobes. Connections through dentate nucleus. Involved in higher level movement coordination and planning/initiating movement
- Vestibulocerebellum: Made of the floculondular lob and is connected to vestibular nucleus of the medulla
What is the general functional role of the flocculo-nodular lobe?
It is involved in vestibular control and vestibular reflexes. Thus, it has a role in axial control and balance, eye movement, the vestibuloocular reflex, vestibule-colic reflex and the vestibule-spinal reflex.
What is the general functional role of the vermal and paravermal regions?
The vermal region is involved in axial control, posture, locomotion and gaze reflexes. The paravermal zone modulates stretch and withdrawl reflexes.
Describe the connections of the cerebellar deep nuclei.
There are 4 cerebellar deep nuclei on each side:
- Dentate nucleus
- Globose and emboliform which together make the interposed nucleus
- Fastigial Nuclei
The Dentate nucleus has connections from the lateral hemispheric zone. It is involved in planning, initiation and coordination of voluntary movements.
The Interposed nucleus is connected to the paravermal zone and fine tunes movements of the limbs.
The fastigial nucleus has connections form the vermal zone and is involved in control of axial musculature, posture, balance and integration of head and eye movements.
What is the general functional role of the neocerebellum (the large lateral hemispheres)?
The lateral hemisphere regions modulates the brain cortices involved in movement.
What types of deficits arise from cerebellar damage?
Cerebellar deficits are always ipsilateral. The cause loss of coordination and equilibrium, but not loss of sensation or muscle strength. To have obvious motor effects, lesions must be of the deep cerebellar nuclei or must be of large portions of cortex. There are several general classes of defects that arise from cerebellar lesions (see below) as well as intention tremors, nystagmus and dysarthria
What are the cellular constituents of the cerebellar cortex?
The cerebellar cortex has 3 layers (from superficial to deep)
- Molecular layer
a. Lots of parallel fibers (processes of granule cells)
b. Dendrites of Purkinje cells
c. Stellate and basket cells – inhibitory interneurons - Purkinje cell layer
a. Contains cell bodies of Purkinje cells - Granular layer
a. Many many granule cells (these cells extend processes superficially to become parallel fibers)
Which cells of the cerebellar cortex have inhibitory actions?
Purkinje cell outputs on deep cerebellar nuclei are inhibitory, i.e. activity in Purkinje cells turns off the nuclei.
There are also inhibitory interneurons in the cerebellar cortex. Basket cells and stellate cells are inhibitory. Excitation of these cells by parallel fibers results in inhibition of neighboring Purkinje cells, or lateral inhibition. Thus, activation of basket cells and stellate cells causes activation of the deep nuclei by inhibiting an inhibitor.
Golgi cells are also excited by parallel fibers. These cells provide feedback inhibition of granule cells
What inputs to the cerebellum are carried by climbing fibers?
The contralateral inferior olivary nucleus sends information via climbing fibers, which travel in the inferior cerebellar peduncle to all of the functional zones of the cortex. Each climbing fiber makes many contacts with a Purkinje cell, so that each time there is an action potential in the climbing fiber, there will be a lot of depolarization of the Purkinje cell. This functions as an error signal.
Describe the role of the climbing fiber input in motor learning. Explain the sequence of events that occurs in the cerebellar cortex during visual-motor learning (like that demonstrated in class).
The normal operation of the cerebellum is to direct planned motor outputs in accordance with expectation (planned in the inferior olive) and actual motor performance (spinal afferents arriving in cerebellum as mossy fibers). When the inferior olive detects a discrepancy between the planned movement and actual motor performance, it generates action potentials in the climbing fibers creating an error signal at the Purkinje cell. The signals from the climbing fiber in COMBINATION with signals from the mossy fiber depolarizations will result in a weakening of the synapses responsible for those movements. This is very similar to the mechanism for long term potentiation.
What are the Efferent Connections in the Cerebellum?
•Vermal cerebellum
- Through fastigial nucleus, sends efferent info to the vestibular nucleus and pontine reticular formation
- Info descends in medial descending system via the lateral vestibulospinal tract and pontine reticulospinal tract
- Equilibrium and posture control
•Paravermal
- Through interposed nuclei, sends efferent into through interposed nuclei
- Info goes to contralateral red nucleus
- Motor output directed through rubrospinal tract (part of lateral descending system)
•Lateral
- Info sent via the dentate nucleus
- Goes to contralateral ventrolatral thalamus
- Projects to primary motor cortex, associated motor cortex and other elements of cortex
What are the Afferent Connections in the Cerebellum?
•Floculonodular Lobe: Vestibular input
•Vermal and paravermal Zones: Spinal cord input
2 somatotopic distributions, arranged head to head with axial body more medially and limbs more laterally
•Lateral: No direct afferents!
- Cortex projects to pontine nuclei which project and end in lateral zone
- Contains collateral corticospinal and corticobulbar fibers
- Cortical input is from contralateral cortex
