NEURO 375 CEREBELLUM QUESTIONS AND ANSWERS 2024.

why is the cerebellum considered part of the motor system? because though damage to the cerebellum still allows movement to occur, patient has: - gait imbalance, poor postural control - poor coordination of voluntary movements, slurred speech (brocha's area = pre motor area for speech) what are the functions of the cerebellum all unconscious - controls equilibrium and balance - controls posture and muscle tone - coordinated purposeful movements - also involved in sensory information processing how does the cerebellum coordinate movements, posture... 1. receives sensory information (ie. via ipsilateral spinocerebellar tract about muscle tone and joint position in space) and compares it with the willful command from pre-motor cortex 2. cerebellum advises the cortex on how much, how many, and how fast to the pre-motor cortex (ie via dentatothanamocortical tract) 3. the pre-motor cortex sends the revised commands to the UMN in the primary motor cortex then down the corticospinal tract what are the two afferent tracts to the cerebellum 1. corticopontocerebellar tract 2. dorsal and cuneocerebellar tracts corticopontocerebellar tract motor areas of the cortex associated with planning and executing movements (pre- and supplimentry) send plans to the pontine nuclei (synapse) fibres from pontine nuclei decussate and travel through the MIDDLE cerebellar peduncle to contralateral cerebellum spinocerebellar tract (dorsal) provides sensory info to cerebellum during ongoing movements 1. proprioceptive info from muscles and tendons enter through the dorsal spinal cord and synapse in Clarke's nucleus (in lamina VII of c8-l2) 2. second-order neurons ascend ipsilaterally in the dorsolateral spinal cord 3. second-order fibers enter the ipsilateral cerebellum through the inferior cerebellar peduncle spinocerebellar afferents are mossy fibers in the cerebellum and ∴ stimulate granule cells with glutamate Cuneocerebellar tract also provides info of muscles and tendons during ongoing movement 1. proprioceptive info from muscles and tendons of upper limbs (above c8) enter dorsal spinal cord 2. first order neurons ascend to medulla in the anterio-lateral spinal cord 3. first-order neurons synapse in accessory cuneate nucleus in the medulla 4. second-order neurons travel to ipsilateral cerebellum through the inferior cerebellar peduncle once in the cerebellum, these afferents are mossy fibres and ∴ stimulate granule cells with glutamate How does the cerebellum respond to input stimuli (spinocerebellar tract info, corticopontocerebellar info..)? send modifications (how much, how fast, how many) to thalamus which relays the info to the pre and supplimentry motor corticies How is the cerebellum continuously involved in ongoing movements - cerebellum compares intended movements with actual (in coordination with sensory inputs) movement and corrects for errors as the movement evolves - cerebellum ∴ plans movement and keeps you balanced while performing movements What are the three types of cerebellar disorders ? 1. Ataxia 2. Forced "intentional" tremor (while moving) 3. Vertigo cerebellar damage - Ataxia ataxia = lack of coordination of muscle and movements - awkwardness of posture and gait - tendency to fall to SAME side of lesion (spinocerebellar tract = ipsilateral) Ataxia - Dysmetria - improper measuring of distance in muscular acts - overshooting the goal in reaching for a target Ataxia - dysdiatochokinesia - inability to perform rapidly alternating muscular movements - able to reach target but takes longer time and is awkward (more movements required) Cerebellar damage - forced (intentional) tremor - cerebellar damage = does not allow for proper activation of ONLY certain muscles from firing (less inhibition of movement by cerebellum - less GABA from cerebellum due to damage) - tremor evident during voluntary movements how is the cerebellum similar in structure to the cortex ? - has folia (like gyri) and fissures (like sulci) - is folded - has grey matter on outside, white matter medial and deep nuclei what are the 3 blood vessels that supply the cerebellum Posterior inferior cerebellar artery (PICA) - branch of vertibral artery Anterior inferior cerebellar artery (AICA) - branch of basilar artery Superior cerebellar artery - branch of basilar artery what are the 3 cerebellar peduncles 1. Superior cerebellar peduncle - information from cerebellum going to midbrain and THALAMUS ( ie. dentatothalamocortical tract) 2. Middle cerebellar peduncle - information from cortext to pontine nuclei which project to contralateral cerebellum (corticopontocerebellar tract) 3. Inferior cerebellar peduncle - information from spinal cord and medulla to ipsilateral cerebellum (spinocerebellar tract) What are the 3 lobes of the cerebellum? 1. Anterior 2. posterior 3. Flocculonodular note anterior and posterior lobes separated by primary fissure Cerebellum homunculus - antreior lobe = body and limbs (trunk along vermis) - posterior lobe superior vermis = head - posterior lobe inferior vermis = back What is the flocculonodular lobe? flocculi on either side + nodule - inferior to floor of 2/3 4th ventricle cerebellar tonsil lobule of the posterior lobe medial to each flocculi overview of cerebellar circuitry 1. afferent tracts excite neurons in the cerebellar cortex or the deep nuclei with GLUTAMATE mossy fibre afferents : spinocerebellar, corticopontocerebellar, vestibulocerebellar... clibming fibre afferents :from inferior olivary nuclei 2. perkinje fibres in the cerebellar cortex are the only axons that travel to the deep nuclei and are GABAergic (more excitation from afferents = less inhibition to deep nuclei) 3. Deep nuclei are the only output axons of the cerebellum that send GABAergic info to the thalamus 4. thalamus relays info to cortex what are the three cell layers of the cerebellar cortex molecular layer perkinje cell layer (one cell thick) granule cell layer Perkinje fibers - only output neuron of the cerebellar cortex - send GABAergic axons to deep cerebellar nuclei - dendrites lie in one plane - receive glutamatergic info from mossy fibres, climbing fibres ans from granule cells circuitry of cerebellar cortex - Purkinje cell bodies in perkinje layer Purkinje axons project through granule layer to form the cerebellar white matter (travel to deep nuclei) Purkinje dendrites in molecular layer - granule cell bodies in granule layer - granule cell axons project up to molecular layer (parallel fibres) synapses in cerebellar cortex - climbing synapse with purkinje dendrites in molecular cell layer and with deep cerebellar nuclei *Glu - mossy fibres synapse with granule cells in granule cell layer and with deep cerebellar nuclei *Glu - granule cells synapse with purkinje dendrites in molecular layer *Glu