Basal Ganglia

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