Basal Ganglia, Cerebellum & Diseases of Motor System Flashcards
Describe the basal ganglia
no direct input/projections with SC
Input via cerebral cortex
Outputs via thalamic nuclei
encodes start/stop/direction/amplitude/expression of movement
Describe the 4 subcortical nuclei of the basal ganglia
Striatum: caudate nucleus/putamen/nucleus accumbens (main input for BG)
Globes pallidus: internal (output nuclei sends GABA to thalamus) and external segment
Substantia nigra: pars reticulata (inhibitory output) and pars compacta (dopaminergic cells to striatum)
Subthalamic nucleus: BG connectivity, pacemaker defines sync/timing of BG outputs
BG: large grey matter masses control thalamus activity
Describe basal ganglia circuitry
complex wiring ensures well integrated input from different brain regions, ensures output is regulated
thalamus activity managed via balance of excitatory/inhibitory (tonic) pathways
direct pathway facilitates movement
indirect pathway inhibits movement
Describe the direct pathway
releases thalamus from tonic inhibition - voluntary movement
(inhibition of inhibitory GPi neurons)
+ve feedback loop
striatal neurons (D1 dopamine) receive input from dopaminergic neurons from SubNigra enhancing excitation
Describe the indirect pathway
increases tonic inhibition of thalamus - suppress movement
(inhibition of inhibitory GPe neurons)
-ve feedback loop
striatal neurons (D2 dopamine) input from SubNigra counters excitatory input, weaker pathway
What are the basal ganglia loops?
Motor: skeletomotor/oculomotor loops
Cognitive (prefrontal): higher cortical functions
Limbic: emotion
Describe the cerebellum
posterior fossa (10% of brain, 75% of brain neurons); evaluates difference between intended movement/actual motor response subconsciously
maintains balance/coordinates voluntary movements/motor learning/cognition
What are some cerebllar damage effects?
Reduced muscle tone
Impaired balance/motor learning
Disrupted spatial accuracy
Disrupted temporal coordination
Impaired cognition
Describe the cerebellum anatomy
2 symmetrical cerebellar hemispheres with parallel convolutions (folia) each with 3 lobes separated by fissures
thin outer grey matter, internal white matter
3 grey matter masses (dentate/interposed/fastigal nuclei)
Describe the cerebellar peduncles
Superior: somatosensory info to ant. lobe, afferent visual/auditory fibres to post. lobe, efferent from dentate to cerebral motor cortex
Middle: afferent carry voluntary movement info from motor cortex pons to post. lobe
no efferent
Inferior: afferent carry sensory info from vestibular nuclei in brainstem/muscle proprioreceptors via medulla to flocculonodular lobe
efferent carry info back and from vermis to inferior olivary nucleus
Describe the 3 functional regions of the cerebellum
Flocculondular lobe: vestibulocerebellum afferent input to lateral vestibular nuclei (balance/eye movement control)
Vermis (mid regions - spine cerebellum): vermis receives sensory input to fastigal nucleus (gaze/posture), mid region receives somatosensory input from limbs to interposed nucleus (limb coordination)
Cerebrocerebellum: input from cerebral cortex via dentate nucleus to PF, M, PM cortices (mental performance of complex motor actions/distal limb coordination)
Describe the microscopic layers of the cerebellum
Molecular layer: granule axons form parallel fibres, purkinje cells orient dendritic fields perpendicular to parallel fibres
Purkinje layer: receive input from climbing/parallel fibres, send GABA to deep nuclei (dentate) - inhibitory output
Granule layer: mossy fibres (main input) terminate here, contact granule cells/golgi neurons regulate cerebellar glomeruli (200 granule cells for each mossy fibres)
Describe 2 input sources for the cerebellum
Mossy fibres (SC/brainstem nuclei): excitatory connections to granule cell dendrites - parallel fibres - purkinje cell action potential
Climbing fibres (inferior olivary nucleus): around purkinje neurons; depolarises them/complex spike
Explain long-term depression
Climbing fibres reduce parallel fibre input to purkinje creating depression in synapses between them via calcium influx
Explain myasthenia gravis
signal transmission failure at neuromuscular junction
autoimmune cause, congenital cause, inherited
reduced ACh receptors/muscle activation
abnormal muscle fatigue, remission, relapse