Task 3 - Cerebellum Flashcards
Cerebellum Purpose
Balance, smooth movements, timing of movements; corrects:
- gets info via afferent nerves from cortical areas
- gets spatial information from muscle spindles and other receptors (state estimation)
- sends feedback to motor areas
Cerebellar cortex
Cerebrocerebellum
Spinocerebellum
Vestibulocerebellum
Cerebrocerebellum
- lateral cerebellar hemisphere
- input directly from cortex
- regulates and guides highly skilled movements (e.g. planning and execution of complex movements)
Spinocerebellum
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
Vestibulocerebellum
- caudal inferior lobes (flocculus + nodulus)
- input from vestibular nuclei in brainstem
- regulates movement underlying posture & equilibrium + vestibulo-ocular reflex
Cerebellar Pedunles (pathways)
Superior cerebellar peduncles
Middle cerebellar peduncles
Inferior cerebellar peduncle
Superior cerebellar peduncles
Brachium conjunctivum
- almost entirely efferent
- deep cerebellar nuclei -> dorsal thalamus -> premotor & primary motor areas
- deep cerebellar nuclei -> superior colliculus
Middle Cerebellar peduncles
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
Inferior cerebellar peduncle
Restiform body
- smallest pathway
- afferent: from vestibular nuclei, spinal cord, tegmentum (stay ipsilateral)
- efferent: to vestibular nuclei & reticular formation
Cerebellar Input
- 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)
Cerebellar Output
To deep cerebellar nuclei:
- dentate nucleus (cerebrocerebellum)
- two interposed nuclei (paramedial)
- fastigial nucleus (vermis)
Ascending Cerebellar Output
Cross at decussation of superior peduncle in midbrain then to thalamus & upper motor neurons in brainstem & cortex
- > cerebrocerebellar pathways
- > spinocerebellar pathways
Cerebrocerebellar pathways
- for premotor & associational cortices of frontal lobe
- > motor planning
- feedback loops: to parvocellular red nucleus in midbrain -> inferior olives
Closed loops
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
Open loops
input from multiple areas, output to motor cortices
Spinocerebellar Pathways
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
Vestibulocerebellar pathway
Inferior peduncle -> vestibular complex: governs movement of eyes, head, neck, compensating for linear & rotational accelerations of the head
Purkinje Cells
Destination of afferent pathways
- huge outbranching dendrites; receive input from parallel fibers
- inhibitory (GABA)
- project to deep cerebellar nuclei to shape discharge patterns
Indirect cerebellar input
Mossy fibers from various sources (cortex, brainstem, spinal cord) and synapse on deep cerebellar nuclei & granule cells
-granule cells give rise to parallel fibers
Direct cerebellar input
Inferior olive -> climbing fibers that synapse on Purkinje cells and deep cerebellar nuclei
Local circuit neurons
Modulate inhibitory output of Purkinje cells by inhibiting them after excitatory input from parallel fibers
-Basket cells & stellate cells inhibit purkinje cells (lateral inhibition)
Golgi cells
receive input from parallel fibers and inhibit granule cells
Long-term depression of climbing fibers
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
Timing Hypothesis
Cerebellum critical for sensorimotor learning: generates predictions that are temporally precise
- > cerebellum supplies precise timing needed for activating effectors
e. g. airpuff experiment
Forward Model
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
Inverse Model
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
Attenuation of self-produced tactile stimulation
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
Cerebellar Ataxia
jerky and imprecise movements
Nystagmus
Difficulty of maintaining fixation in eyes -> drift from target, then jump back
Dysdiadochokinesia
Difficulty performing rapid alternating movements
Action/intention tremors
Over & undershooting of movements
TMS cerebellar ataxia diagnosis
TMS can induce cerebellar inhibition of M1
- > cerebellar ataxia: impaired cerebellar inhibition
- > normal cerebellar inhibition with TMS: ataxia not originating from lesion to cerebellum
