Task 3 - Cerebellum

Question 1

Cerebellum Purpose

Answer 1

Balance, smooth movements, timing of movements; corrects:

1. gets info via afferent nerves from cortical areas
2. gets spatial information from muscle spindles and other receptors (state estimation)
3. sends feedback to motor areas

Question 2

Cerebellar cortex

Answer 2

Cerebrocerebellum
Spinocerebellum
Vestibulocerebellum

Question 3

Cerebrocerebellum

Answer 3

• lateral cerebellar hemisphere
• input directly from cortex
• regulates and guides highly skilled movements (e.g. planning and execution of complex movements)

Question 4

Spinocerebellum

Answer 4

Median (Vermis) and paramedian (more lateral) zone of hemisphere

• input directly form spinal cord
• paramedian zone: distal muscle movements
• Vermis: movement of proximal muscles and eyes

Question 5

Vestibulocerebellum

Answer 5

• caudal inferior lobes (flocculus + nodulus)
• input from vestibular nuclei in brainstem
• regulates movement underlying posture & equilibrium + vestibulo-ocular reflex

Question 6

Cerebellar Pedunles (pathways)

Answer 6

Superior cerebellar peduncles
Middle cerebellar peduncles
Inferior cerebellar peduncle

Question 7

Superior cerebellar peduncles

Answer 7

Brachium conjunctivum

• almost entirely efferent
• deep cerebellar nuclei -> dorsal thalamus -> premotor & primary motor areas
• deep cerebellar nuclei -> superior colliculus

Question 8

Middle Cerebellar peduncles

Answer 8

Brachium pontis

• afferent (contralateral)
• most areas of cortex & superior colliculus -> cell bodies in pontine nuclei of ponts -> transverse pontine fibers cross over via middle cerebellar peduncles -> cerebellar cortex & deep nuclei

Question 9

Inferior cerebellar peduncle

Answer 9

Restiform body

• smallest pathway
• afferent: from vestibular nuclei, spinal cord, tegmentum (stay ipsilateral)
• efferent: to vestibular nuclei & reticular formation

Question 10

Cerebellar Input

Answer 10

• cortex via pontine to cerebrocerebellum (only contralateral)
• spinal cord & medulla -> spinocerebellum (innervates by proprioceptive axons from lower & uper body parts)
• trigeminal complex -> spinocerebellum (proprioceptive signals from face)
• vestibular nuclei & axons of 8th cranial nerve -> vestibulocerebellum: (info from ear)
• auditory & visual signals via brainstem to vermis
• from inferior olives & locus creruleus (learning and memory function)

Question 11

Cerebellar Output

Answer 11

To deep cerebellar nuclei:

• dentate nucleus (cerebrocerebellum)
• two interposed nuclei (paramedial)
• fastigial nucleus (vermis)

Question 12

Ascending Cerebellar Output

Answer 12

Cross at decussation of superior peduncle in midbrain then to thalamus & upper motor neurons in brainstem & cortex

• > cerebrocerebellar pathways
• > spinocerebellar pathways

Question 13

Cerebrocerebellar pathways

Answer 13

• for premotor & associational cortices of frontal lobe
• > motor planning
• feedback loops: to parvocellular red nucleus in midbrain -> inferior olives

Question 14

Closed loops

Answer 14

Cerebrocerebellum sending projections back to same cortical (non-motor areas) from which its input signal originated in

• > may influence coordination of non-motor programs
• run in parallel to open loops

Question 15

Open loops

Answer 15

input from multiple areas, output to motor cortices

Question 16

Spinocerebellar Pathways

Answer 16

Directed to upper motor neurons for execution of movement:
Vermis -> inferior peduncle -> reticular formation & vestibular complex which give rise to tracts governing axial & proximal limb muscles

Question 17

Vestibulocerebellar pathway

Answer 17

Inferior peduncle -> vestibular complex: governs movement of eyes, head, neck, compensating for linear & rotational accelerations of the head

Question 18

Purkinje Cells

Answer 18

Destination of afferent pathways

• huge outbranching dendrites; receive input from parallel fibers
• inhibitory (GABA)
• project to deep cerebellar nuclei to shape discharge patterns

Question 19

Indirect cerebellar input

Answer 19

Mossy fibers from various sources (cortex, brainstem, spinal cord) and synapse on deep cerebellar nuclei & granule cells
-granule cells give rise to parallel fibers

Question 20

Direct cerebellar input

Answer 20

Inferior olive -> climbing fibers that synapse on Purkinje cells and deep cerebellar nuclei

Question 21

Local circuit neurons

Answer 21

Modulate inhibitory output of Purkinje cells by inhibiting them after excitatory input from parallel fibers
-Basket cells & stellate cells inhibit purkinje cells (lateral inhibition)

Question 22

Golgi cells

Answer 22

receive input from parallel fibers and inhibit granule cells

Question 23

Long-term depression of climbing fibers

Answer 23

LTD in purkinje cells in response to parallel fiber inputs:

• affects only parallel fibers active at same time as climbing fibers
• internalization of AMPA receptors for glutamate (-> smaller EPSP)
• weakens inhibitory loop increasing deep nuclei response

Question 24

Timing Hypothesis

Answer 24

Cerebellum critical for sensorimotor learning: generates predictions that are temporally precise

• > cerebellum supplies precise timing needed for activating effectors
  e. g. airpuff experiment

Question 25

Forward Model

Answer 25

set of motor commands is transformed into prediction of their outcome in terms of sensory consequences of the move by the cerebellum - > predicts wheteehr motor program will achieve its goal before its carried out - > used to plan & control movement

Question 26

Inverse Model

Answer 26

Inverts information flow of forward model by inputting the desired goal of the movement - > back-calculating motor commands that are required - > disproven: TMS of cerebellum would affect whole movement, not the case

Question 27

Attenuation of self-produced tactile stimulation

Answer 27

Due to sensory predictions made by forward model - > right anterior cerebellar cortex selectively deactivated for self-produced tactile stimuli - > somatosensory & anterior cingulate cortex less activated by self-produced tactile stimulus

Question 28

Cerebellar Ataxia

Answer 28

jerky and imprecise movements

Question 29

Nystagmus

Answer 29

Difficulty of maintaining fixation in eyes -> drift from target, then jump back

Question 30

Dysdiadochokinesia

Answer 30

Difficulty performing rapid alternating movements

Question 31

Action/intention tremors

Answer 31

Over & undershooting of movements

Question 32

TMS cerebellar ataxia diagnosis

Answer 32

TMS can induce cerebellar inhibition of M1 - > cerebellar ataxia: impaired cerebellar inhibition - > normal cerebellar inhibition with TMS: ataxia not originating from lesion to cerebellum