The Cerebellum Flashcards
cerebrocerebellum
Most developed in primates, particularly humans
Regulation of highly skilled movements via the planning and execution of complex spatial and/or temporal sequences
spinocerebellum
Median zone of cerebellar hemispheres
Receives input from the spinal cord
Arranged similarly to spinal cord (distal = lateral, proximal/vermis = medial)
vestibulocerebellum
Oldest
Within the caudal inferior lobes (flocculus and nodulus)
Receives input from vestibular nuclei and is involved in VOR and postural movements
Name the 3 deep cerebellar nuclei
Dentate nucleus
Interposed nuclei
Fastigial nucleus
What do cerebellar peduncles do?
make connections between the cerebellum and other parts of the nervous system
What does the superior peduncle do?
(Almost) entirely efferent, projects to the thalamus –> upper motor neurons in primary and premotor regions
Also projects to the superior colliculus
Middle cerebellar peduncles (general)
afferent pathway from the pons in the brainstem
biggest peduncle
Inferior cerebellar peduncles
Smallest and most complex, consisting of both afferent and efferent connections
What provides the largest input to the cerebellum? Describe the projections (what peduncle?)
cerebral cortex
most inpu tgoes to cerebrocerebellum
cortical axons are not a direct projection
- Arrive via pontine nuclei on the ipsilateral side
- Pontine nuclei receive input from almost all areas of cerebral cortex and superior colliculus
- Axons from pontine nuclei (transverse pontine fibers) cross the midline and enter the cerebellum via the middle cerebral peduncle
Describe the sensory pathways that project to the vestibulocerebellum
Vestibular axons from cranial nerve VIII
Axons from vestibular nuclei in the medulla
Relay neurons in the dorsal nucleus of Clarke and external cuneate nucleus of the caudal medulla
Send axons to spinocerebellum conveying proprioceptive information from the upper and lower parts of the body
Proprioceptive signals from the face
Relayed via the mesencephalic nucleus to the spinocerebellum
Brainstem nuclei provide visual and auditory information complimenting proprioceptive information
Describe how somatic sensory input is topographically mapped in the spinocerebellum
In a “fractured” somatotopic map
Each small area of the body is represented multiple times
Vestibular and spinal inputs remain ipsilateral as the pass through the inferior cerebellar peduncle
Where does the superior olive project? What does it do there?
to cerebellar cortex and deep nuclei
- Involved in the learning and memory functions of the cerebellum
- Receives input from cerebral cortex, reticular formation, and spinal cord
- Olivo-cerebellar exit the inferior olive, cross the midline and enter via the inferior cerebellar peduncle
What four areas does the cerebellum project to?
premotor cortex (motor planning)
motor cortex (motor execution)
brainstem (motor execution)
lower motor neurons (balance and VOR)
Where does the cerebrocerebellum project to?
Axons of deep cerebellar nuclei and the vestibulocerebellar cortex project to upper motor neurons that control axial and proximal limb musculature (medial ventral horn)
closed loop connections of the cerebellum to non-motor areas
Cortex –> Cerebellum –> Cortex
Allow for modulation of cerebellar input
Used in the coordination of non-motor planning, such as problem solving
Open loop connections of the cerebellum to motor areas
cortex –> cerebellum –> motor/premotor cortex
used in motor planning
Where do closed loop vs. open loop cerebellar projects go to?
closed: non-motor areas
open: motor areas
What are the projections from the cerebrocerebellum involved in?
Lesions disrupt motor planning and prolong reaching time (CCAS thing)
Individual components of a movement can be elongated and sequential
Known as decomposition of movement
Described by patients as having to “think about moving”
Also has a purely cognitive role
Timing of purely mental or cognitive tasks
Language
- Word associations in addition to motor movements involved in speech
Pegboard completion tasks
What are the projections from the spinocerebellum involved in?
- Output directed towards upper motor neurons that govern the execution of movement
- Fastigial nuclei (within the midline) projects to the reticular nuclei and vestibular complex that give rise to tracts controlling axial and proximal limb musculature
- Interposed nuclei (more lateral) project to thalamic circuits that interact with motor regions in the frontal lobe
What mechanism does the spinocerebellum use to regulate movements?
Feed forward!
Lesions can cause cerebellar hypotonia and dysmetria (errors in direction and extent of movement), ataxia (curved hand path during reaching), and terminal tremor.
Improper muscle recruitment
Describe spinocerebellum projections to the superior colliculus
deep
Via dentate and interposed nuclei from the lateral portions of cerebellar cortex
Terminates on motor neurons in the deep layers of the SC on contralateral side
Involved in the modulation of saccades
How does the VOR normally operate? How could minifying glasses change this?
Vestibulocerebellum modulate eye, head, and neck movements that compensate for linear and rotational movements of the head
Normally, VOR operates to keep eyes stationary while head moves
Vestibulocerebellum allows for adaptation to altered visual world
What is the ultimate destination of the two types of afferent inputs to the cerebellum? (name types)
purkinje cells
from two types of afferent inputs: mossy fibers and climbing fibers
Both groups form excitatory synapses but terminate differently in cerebellar cortex resulting in different firing patterns in the purkinje neurons.
What are mossy fibers?
Originate from nuclei in the spinal cord and brain stem
Carry sensory information from the periphery and cerebral cortex
Terminate on excitatory synapses on the dendrites of granule cells
Axons of the granule cells travel great distances along the long axis of the cerebellar folia in the molecular layer
Innervate large number of Purkinje neurons
Each Purkinje cell receives input from up to 1 million granule cells!
What are climbing fibers?
Originate from the inferior olivary nucleus and convey somatosensory, visual or cerebral cortical information
Wrap around the cell bodies and proximal dendrites of Purkinje neurons like vines on a tree, making numerous synaptic connections
Purkinje cells receive synaptic input from a single climbing fiber, although each climbing fiber contacts ~1-10 Purkinje neurons
What cells are involved in the local circuit inhibition of purkinje cells? Where does it occur?
Local circuit inhibition of Purkinje Cells
Basket cells and stellate cells
Receive input from parallel fibers and provide inhibitory input to the Purkinje cell dendrites
Occur in the upper layers of cerebellum
Combined
Deep excitatory loop
Cortical inhibitory loop
Basic circuit repeated over and over again within every subdivision of cerebellum in all mammals!
Describe the 2 stages of the cerebellar circuits starting with mossy and climbing fiber collaterals.
Mossy and climbing fiber collaterals drive activation of neurons in deep cerebellar nuclei
- Excitatory loop that converges on the output stage of cerebellar processing
Purkinje cells respond to excitatory drive of ascending fibers with an inhibitory output
- Convey the product of computation performed by the inhibitory cortical loop
Climbing fibers convey an error signal or “teaching signal”, mossy fibers contain contextual information about the circumstances in which the error occurred and the intended movement.
- Error signal derived from inputs that the inferior olive receive from multiple structures (including cerebral cortex and spinal cord)
What is a teaching signal?
conveyed by climbing fibers: “SOMETHING’s WRONG”
mossy fibers contain contextual info about the circumstances in which the error occured and the intended movement: “WHAT WERE THE CIRCUMSTANCES
together, there’s a computation, and then an adjusted movement.
error signals derived from inputs that the inferior olive received from multiple strucutres (including cerebral cortex and spinal cord)
