15 Basal Ganglia

Function

• direct for helpful movement
• indirect for unhelpful movement

• pars compacta/reticulata different parts of substantia nigra
• at rest: GP Internus and Pars Reticulata inhibits thalamus via GABA (tonic inhibition), no cortex stimulation
• action: direct/indirect pathway modulate thalamus

Direct Pathway

• cortex activate striatum via glutamate, which then inhibits pars reticulata and globus pallidus internus via GABA
• cortex also activates pars compacta that stimulates striatum via D1 dopamine to amplify the process

Indirect Pathway

• striatum stimulated and inhibit GP externus, thus disinhibit subthalamic nucleus that stimulates GP internus that inhibits thalamus
• cortex also stimulates pars compacta that inhibits striatum via D2
• D2 result: thalamus activated

Summary

Pars Compacta

• important because destroyed in parkinson's

Movement disorders

• hyperkinetic disorder: inhibition removed
• hypokinetic disorder: disinhibition not present