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BASAL GANGLIACOMPONENTS
CONNECTIONSFUNCTIONAL NEURONAL CIRCUITS
FUNCTIONSDISORDERS & TREATMENT
COMPONENTSSubcortical nuclear massesCaudate nucleusPutamenGlobus pallidusSubthalamic nucleusSubstantia nigra
Caudate nucleusCaudate nucleus+Putamen (Corpus Striatum/Neostriatum)Phylogenetically more recentAnt limb of Internal capsule lies between
Caudate N Putamen
Putamen & Globus pallidusLenticular Nucleus (bean shaped)PaleostriatumTwo parts - External segment(Gpe) - Internal segment(Gpi)
Substantia Nigra2partsDorsomedial—Pars compactaVentrolateral---Pars reticulataRich in copper content
Oxygen consumption of BG is high. Red nucleus ,claustrum &Amygdala are functionally related to BG
Subthalamic nucleus/body of LuysBiconvex mass of grey matter, lateral to red nucleus & dorsal to Substansia nigra
Connection of Basal GangliaAfferent connectionsTerminate in neostriatum &
excitatory(cholinergic neurons)1. Corticostriate projection2. Thalamostriate fibres
Internuclear connections1. Dopaminergic Nigrostriatal tracts-2. GABA-ergic inhibitory projections3. Subthalamic nucleus via glutamic acid
secreting excitatory neurons
Efferent connectionsGlobus pallidus &Substantia nigra Gpi via thalamic fasciculus ThalamusGpi via Ansa lenticularis tract subthalamic
nucleusSNpr ThalamusInhibitory –GABAergic
Connections of Basal gangliaFeedback circuit
Similarities & Dissimilaritiesbetween B G & CerebellumBoth receive
informationfrom all parts of
cerebral cortex & project back to motor cortex via the VL & VA
thalamus
Cerebellum receives large synaptic input from spinal cord (not BG)
Cerebellum has direct influence on major EP pathways(V Spinal &Rspinal)
BG-indirect influence.
Functions of Basal GangliaNeurons discharge before movements begin.BG Thalamus areas related to MC
descending tracts (Planning & Programming)
Inhibits stretch reflex by stimulation of Caudate N(damage—rigidity)
Neostriatum regulates subconscious gross movements in groups of muscles.(decortication—loss of fine movements in distal parts)
Functions of Basal GangliaCaudate nucleus –cognitive process(interconnections with orbitofrontal lobe &
prefrontal lobe)Dysarthric aphasiaGlobus pallidus-muscle tone for skilled
movementsSubstantia nigra—centre for coordination of
impulses for skilled movementsControl of normal automatic &
associated movements
Parkinson’s disease(Paralysis agitans)
Agitans ,Shaking palsyRigidity Tremor(hyperkinesia)Weakness of movements(hypokinesia)
Parkinson’s disease 7-10 million people worldwide affectedmales>femalesDopaminergic neurons &dopaminergic
receptorsDegeneration of dopaminergic neurons in
nigrostriatal pathway 60%-80%.Phenothiazine drugsMPTP- 1 methyl-4phenyl-1,2,5,6
tetrahydropyridine
Characteristic features
Rigidity –large proximal muscles of limbsProtagonists &antagonistsBiceps,knee flexors,sternomastoidsPosture of flexionStatue –advanced casesIncreased ¥ motor discharge –muscle
spindleHyperkinetic feature
Symptoms and Signs
TremorResting (static)tremorFinger,hands,lipsRegular,rhythmic,alternate contraction
of antagonist &agonist muscles 6-8/secPill rolling movement in emotional states,anxiety etc
Tremor
Akinesia & Hypokinesia
Difficulty in initiating voluntary movement-fine mov in fingers
Defects in fine variation in speech-slow monotonus
Mask like faceGait –festinant-slow shuffling gaitTendon jerks—difficult to elicit
Chorea & AthetosisSpontaneous involuntary movements-
blockade in thalamocortical circuitChorea-Caudate NucleusRapid irregular involuntary movements
athetosis
Lenticular nucleusContinuous slow twisting movements