TASK 3 - CEREBELLUM Flashcards
cerebellum
- located in hindbrain
- metencephalon (cerebellum + pons)
- played critical role in development of cortical/ cognitive functions
- allows info input into and out of cerebellum
- -> input via brainstem into cerebellum
- -> output via pons out of cerebellum –> into cortex
structural divisions
- laminated cerebellar cortex on surface
- cerebellar deep nuclei deep in white matter
structural divisions
- lobes
- anterior lobe: somatosensory info
- posterior lobe: output to cortex
- flocculonodular lobe: oldest cerebellar structure
structural divisions
- vermis + hemispheres
- vermis: runs along midline of cerebellum, separates 2 hemispheres
functional divisions
1. cerebrocerebellum
= lateral hemispheres
- receives input from the CEREBRUM
- planning, initiation of movement + sensory feedback of motor movements
- coordination of voluntary movements
- cognitive, emotional control
functional divisions
2. spinocerebellum
= vermis
- input from SPINAL cord
- visual + auditory signals (relayed in brainstem nuclei)
- regulates body + limb movements and muscle tone
- compares info from where body stand and where it should be –> if discrepancy: corrects error signal
functional divisions
3. vestibulocerebellum
= floculonodular/flocular lobe
- input from VESTIBULAR complex
- regulates balance, posture, eye movements
pathways
- via cerebellar peduncles
2. via deep cerebellar nuclei
pathways
1. cerebellar peduncles
= white matter connections
- connections between the cerebellum and other parts of the nervous system
- contain fine branching nerve fibres
- cerebellar peduncles
a) superior
= largest output structure/ almost entirely efferent pathway
- origin: deep cerebellar nuclei neurones –> to upper motor neurones in deep layers of superior colliculus –> delay in dorsal thalamus –> primary motor, premotor areas of cortex
- limbic movements
- cerebellar peduncles
b) middle
= biggest peduncle; afferent pathway to cerebellum; descending
- origin: pontine nuclei (neurones in the base of the contralateral pons) –> receives input from many sources (almost all cortical areas and superior colliculus) –> axons (transverse pontine fibres) cross midline and enter cerebellum via middle cerebellar peduncle
- regulates info from proprioception (orient body in space) + regulates other sensory functioning
- cerebellar peduncles
c) inferior
= smallest but most complex peduncle
- contains afferent + efferent pathways
1) afferent ascending = axons from vestibular nuclei, spinal cord and brainstem tegmentum (inferior olive)
2) efferent = axons project to vestibular nuclei and reticular formation - proprioceptive info (how different body parts relate to one another
pathways
2. deep cerebellar nuclei
= in each cerebellar hemisphere there are 4 major deep nuclei
- each receiving input from different parts of cerebellum
a) fastigal nuclei
b) interposed nuclei (x2)
c) dentate nuclei
input
- major destination of input: cerebrocerebellum
1. top-down/descending: cerebral cortex via pons
2. bottom-up/ascending: from vestibular inputs, inferior olive, spinal cord
input
1. descending
= cerebral cortex via pons
- axons synapse on ipsilateral neurones in pontine nuclei
- pontine nuclei give rise to transverse projections that cross midline (form middle cerebellar peduncle) –> relays cortical signals to contralateral cerebellar hemisphere
- signals derived from one cerebral hemisphere are processed by the neural circuits in the opposite cerebellar hemisphere
- majority arises from primary and pre-motor cortices (frontal), primary and secondary somatic sensory cortices (anterior parietal) and higher order visual regions (posterior parietal)
input
2. ascending
= from vestibular inputs, inferior olive, spinal cord
- vestibular and spinal inputs: remain ipsilateral from point of entry in brainstem (travelling inferior cerebellar peduncle)
- -> right half of cerebellum is concerned with right part of the body
output
1. ascending
a) cerebrocerebellar pathway = to pre-motor + associational cortices of frontal lobe –> motor planning
- feedback loop: collaterals to parvocellular red nucleus in midbrain –> inferior olives
- closed loops: to non-motor areas of the cortex from which signals originated (–> coordination of non-motor programs)
- open loops: input from multiple areas, output to motor cortices
- -> run in parallel
b) spinocerebellar pathways = to upper motor neurones –> execution of movement
- laterally positioned interposed nuclei –> via superior peduncle –> thalamus and frontal lobes
output
2. descending
a) spinocerebellar pathways = directed to upper motor neurones responsible for execution of movement
- fastigial nuclei (vermis) –> inferior peduncle –> reticular formation + vestibular complex –> give rise to tracts governing axial + proximal limb muscles
b) vestibulocerebellar pathway - inferior peduncle –> vestibular complex that governs movement of eyes, head, neck, compensating for linear + rotational accelerations of the head
cellular organisation
- layers
- molecular layer
- apical dendrites of Golgi cells - Purkinje cell layer
- contains Purkinje cell bodies - granule cell layer
- contains granule cell bodies
cellular organisation
- Purkinje cells
= ultimate destination of afferent pathways
- input from cerebral cortex to Purkinje cells is indirect
- huge dendrites that branch out –> receive input from heaps of parallel fibres
- inhibitory (GABAergic)
- projections to deep cerebellar nuclei that serve to shape discharge patterns
cellular organisation
- mossy fibres
= indirect input
- come from all sorts of sources (cortex, brainstem, spinal cord)
- synapse on deep cerebellar nuclei + granule cells
- -> granule cells give rise to parallel fibres –> synapse on Purkinje cells
cellular organisation
- climbing fibres
= direct input
- inferior olive –> climbing fibres –> Purkinje cell + deep nuclei
cellular organisation
- local circuit neurones
= modulate inhibitory output of Purkinje cells by inhibiting them after excitatory input from parallel fibres
- basket cells: lateral inhibition that may focus spatial distribution of Purkinje cell activity
- stellate cells
cellular organisation
- Golgi cells
= receive input from parallel fibres and then inhibit those exact cells
