Cerebellum Flashcards
Cerebellum regulates
Movements
How does cerebellum regulate movements?
Indirectly through modulation of upper motor neurons
What forms the network loop of the cerebellum? What is networked?
Basal ganglia
Are formed with the cerebral cortex and mediated by the thalamus
Three regions of the cerebellum?
Cerebrocerebellum
Spinocerebellum
Vestibulocerebellum
Where is the cerebrocerebellum located?
Lateral portion of the hemispheres of cerebellum
What does the cerebrocerebellum receive signals from?
Indirect connections to/from the cerebral cortex
What is function of cerebrocerebellum?
Regulation of skilled movements
Planning and execution of complex spatial and temporal sequences
Where is the spinocerebellum located?
Median (vermis) and intermediate (paravermal) regions of the cerebellum
What is input of spinocerebellum?
Direct inputs from the spinal cord
Function of spinocerebellum?
Intermediate regulates movements of distal muscles
Median (vermis) regulates movements of proximal muscles and some eye movements (smooth pursuit and saccades)
Where is the vestibulocerebellum?
Caudal-inferior portion of cerebellar lobes
Input of the vestibulocerebellum?
From vestibular nuclei
Function of the vestibulocerebellum?
Regulates vestibular reflexes
Vestibuloocular reflex
Balance through the VSR and VCR
Grey matter in the cerebellum?
A layered cerebellar cortex on surface
Deep cerebellar nuclei
Deep cerebellar nuclei connect to?
Output connections from the cerebellum to variety of brain regions
Describe the saggital sectioning of the cerebellum and their projections
Cerebrocerebellum - dentate nucleus
Intermediate cerebellum - interposed nuclei
Vermis cerebellum - fastigial nucleus
Vestibulocerebellum - vestibular nuclei
Three main pathways between cerebellum and other parts of the nervous system?
Superior CRB peduncle
Middle CRB peduncle
Inferior CRB peduncle
Function of the superior CRB peduncle?
Almost entirely efferent
Origination of the superior CRB peduncle?
Deep nuclei (interposed and dentate)
Projections of the superior CRB peduncle?
1) thalamus that in turn projects to upper motor neurons in the primary motor and premotor cortices + others
2) Projects to upper motor neurons in superior colliculus
Function of middle CRB peduncle?
Afferent pathway
Origination of the middle CRB peduncle?
Contralateral pontine nuclei
Function of the inferior CRB peduncle?
Smallest afferent and efferent path
Origination of the inferior CRB peduncle?
Afferent - vestibular nuclei, spinal cord, inferior olivary complex
Efferent - vestibular nuclei, reticular formation, superior colliculi
Where does SCA arise from and what does it feed?
Basilar artery
Superior and lateral cerebellum
Superior CRB peduncle
Superior portion of middle CRB peduncle
Dentate nucleus
Where does AICA arise and what does it feed?
Basilar artery
Lower 2/3 pons
Ventrolateral cerebellum
Middle CRB peduncle
Where does PICA arise and what does it feed?
Vertebral artery
Lateral medulla
Inferior vermis
Posterior intermediate cerebellum
Lateral cerebellum
Three inputs to the cerebellum?
Cerebral cortex
Sensory nuclei
Inferior olive
Cerebral cortex input to the cerebellum via?
Largest source of input
To lateral CRB and some intermediate CRB
Via pontine nuclei
Describe path of neurons from cortex to cerebellum
Project ipsilaterally to pontine nuclei
Cross within pons to enter contralateral cerebellum
Enter via middle CRB peduncle to reach the cerebro-CRB and intermediate CRB
Sensory nuclei of the cerebellum? What are the pathways?
Vestibular nerve and nuclei project ipsilaterally to vestibulocerebellum
Proprioceptive input from spinal cord (Dorsal nucleus of clarke), from caudal medulla (external cuneate nucleus), and mesencephalic trigeminal n to reach ipsilateral spinocerebellum. Enteres via the inferior cerebellar peduncle
Inputs and function of inferior olive?
Receives inputs from cerebral cortex (motor), somatosensory (spinal cord and brainstem), and reticular formation to integrate motor commands with the somatosensory signals resulting from execution of movement.
The inferior olivary nucleus is also known as?
The error detector!
Integration of sensory and motor commands
Inferior olive enters the cerebellum via?
Project to entire contralateral cerebellum
Via inferior cerebellar peduncle
Somatotopic map of cerebellum?
Axial control - medial
Distal control - lateral
Projection of efferent output of the cerebellum?
First to deep cerebellar nuclei
Then to upper MN in brainstem or thalamic nuclei
Then to upper MN in the cerebral cortex
Describe input of deep cerebellar nuclei
From different regions of cerebellar cortex
Vestibulocerebellum directly to vestibular complex in the brainstem. these upper MN influence reflexes of VSR, VCR and VOR
Cerebrocerebellum output via?
Dentate nucleus
Pathway of cerebrocerebellum output?
Dentate nucleus to terminate in the contralateral premotor and motor cortex (after relay in thalamus)
Cerebrocerebellum output function?
Planning of movements
Output of spinocerebellum via?
Fastigial nucleus
Interposed nuclei
These are organized somatotropically
Pathways of the spinocerebellum?
Fastigial (medial) to inferior CRB peduncle to reticular formation and vestibular complex
Lateral interposed nuclei project via superior CRB peduncle to thalamus to primary motor region and superior colliculus
Functions of spinocerebellum tracts
Fastigial - modulates axial and proximal limb musculature
Interposed - volitional limb movements
Dentate nucleus projects via and to where? Then where?
Via superior cerebellar peduncle
To contralateral VL thalamus
From there to premotor and motor association cortices of the frontal lobe (planning an execution of volitional movements)
Additionally terminates contralaterally at superior colliculus
Direct cerebellar hemisphere projection?
Directly to vestsibular complex
Modulate VOR and VSR/VCR
Describe the circuits of the fastigial nuclei
Medial fastigial via inferior CRB peduncle to reticular formation for control of proximal limb and axial musculature) also to ipsilateral superior colliculus
Superior colliculs then can go to reticular formation as well
CRB via reticular formation and vestibular nuclei exert bilateral modulation of balance
Describe the layers of the cerebellum
Superifical - molecular layer of dendrites from purkinje neurons, incoming axons, and interneurons
Middle - purkinje cell layer which has cell bodies in a single row
Deep layer - granule layer with granule cells
Granule cells comprise?
50% of the total neurons in the CNS
Where are interneurons in the cerebellum?
Middle and deep layer
Two afferents of the cerebellum?
Mossy fiber
Climber fiber
Describe the mossy fiber system
Formed by most of the input sources to cerebelllum from the cerebral cortex, spinal cord, brainstem (except inferior olives)
Pathway of mossy fiber system?
Enter cerebellum and synapse with deep cerebellar nuclei on granule cells
Granule cells give rise to axons called parallel fibers that ascend to the molecular layer where they bifurcate to form T-shaped branches extending parallel to the surface of the molecular layer
Describe the climbing fiber system?
Originate in the inferior olivary complex in the medulla
Pathway of climbing fiber system?
Enters cerebellum and makes contact with deep cerebellar nuclei directly on the purkinje cells
Function of the climbing fiber system?
Error detector
Contrast between the mossy and climbing fiber systems?
Mossy is segregated into zones (vestibular, spinal, cerebrocerebellar)
Climbing is the whole cerebellum
Describe parallel fibers
Connectivity is divergent
Purkinje cells receive 200,000 synapses from parallel fibers
Each granule cell contacts thousands of purkinje cells
Massive contacts done at the level of distal dendrites of the purkinje cells
Describe climbing fiber
Numberous synaptic contacts to purkinje cell but from a single climbing fiber (~1500 connections to the proximal dendrites or the cell body)
These synaptic contacts are the most powerful in the nervous system
From purkinje cells signal?
Synapses with output neurons in the deep cerebellar nuclei
Each input fiber will contact?
Mossy/climbing fibers will contact both the deep cerebellar nuclei and the purkinje cells to be excitatory
Describe the deep excitatory loop
Deep cerebellar nuclei and their excitatory afferents
What shapes output of deep excitatory loop?
The purkinje inhibitory loop
How does purkinje inhibitory loop work?
Inverts the sign of the input signals (responding to excitation with inhibitory output)
Describe error and the purkinje inhibitory loop
Parallel fiber input is weak and can be modulated by the climbing input (error input)
If no error, then input from inferior olives is rhythmic and habituates reducing the input to the purkinje cells and deep nuclei
Overall output is reduced
If error, then no habituation and correcting signal is generated to the upper MN
