The Cerebellum

Question 1

cerebrocerebellum

Answer 1

Most developed in primates, particularly humans

Regulation of highly skilled movements via the planning and execution of complex spatial and/or temporal sequences

Question 2

spinocerebellum

Answer 2

Median zone of cerebellar hemispheres

Receives input from the spinal cord

Arranged similarly to spinal cord (distal = lateral, proximal/vermis = medial)

Question 3

vestibulocerebellum

Answer 3

Oldest

Within the caudal inferior lobes (flocculus and nodulus)

Receives input from vestibular nuclei and is involved in VOR and postural movements

Question 4

Name the 3 deep cerebellar nuclei

Answer 4

Dentate nucleus

Interposed nuclei

Fastigial nucleus

Question 5

What do cerebellar peduncles do?

Answer 5

make connections between the cerebellum and other parts of the nervous system

Question 6

What does the superior peduncle do?

Answer 6

(Almost) entirely efferent, projects to the thalamus –> upper motor neurons in primary and premotor regions

Also projects to the superior colliculus

Question 7

Middle cerebellar peduncles (general)

Answer 7

afferent pathway from the pons in the brainstem

biggest peduncle

Question 8

Inferior cerebellar peduncles

Answer 8

Smallest and most complex, consisting of both afferent and efferent connections

Question 9

What provides the largest input to the cerebellum? Describe the projections (what peduncle?)

Answer 9

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

Question 10

Describe the sensory pathways that project to the vestibulocerebellum

Answer 10

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

Question 11

Describe how somatic sensory input is topographically mapped in the spinocerebellum

Answer 11

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

Question 12

Where does the superior olive project? What does it do there?

Answer 12

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

Question 13

What four areas does the cerebellum project to?

Answer 13

premotor cortex (motor planning)

motor cortex (motor execution)

brainstem (motor execution)

lower motor neurons (balance and VOR)

Question 14

Where does the cerebrocerebellum project to?

Answer 14

Axons of deep cerebellar nuclei and the vestibulocerebellar cortex project to upper motor neurons that control axial and proximal limb musculature (medial ventral horn)

Question 15

closed loop connections of the cerebellum to non-motor areas

Answer 15

Cortex –> Cerebellum –> Cortex

Allow for modulation of cerebellar input
Used in the coordination of non-motor planning, such as problem solving

Question 16

Open loop connections of the cerebellum to motor areas

Answer 16

cortex –> cerebellum –> motor/premotor cortex

used in motor planning

Question 17

Where do closed loop vs. open loop cerebellar projects go to?

Answer 17

closed: non-motor areas
open: motor areas

Question 18

What are the projections from the cerebrocerebellum involved in?

Answer 18

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

Question 19

What are the projections from the spinocerebellum involved in?

Answer 19

• 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

Question 20

What mechanism does the spinocerebellum use to regulate movements?

Answer 20

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

Question 21

Describe spinocerebellum projections to the superior colliculus

Answer 21

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

Question 22

How does the VOR normally operate? How could minifying glasses change this?

Answer 22

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

Question 23

What is the ultimate destination of the two types of afferent inputs to the cerebellum? (name types)

Answer 23

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.

Question 24

What are mossy fibers?

Answer 24

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!

Question 25

What are climbing fibers?

Answer 25

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

Question 26

What cells are involved in the local circuit inhibition of purkinje cells? Where does it occur?

Answer 26

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!**

Question 27

Describe the 2 stages of the cerebellar circuits starting with mossy and climbing fiber collaterals.

Answer 27

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)

Question 28

What is a teaching signal?

Answer 28

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)