Lecture 18 - Basal Ganglia

Basal Ganglia

A group of subcortical nuclei that modulate movements by regulating upper motor neuronal circuits.

Corpus Striatum

Another name for the striatum, consisting of the caudate and putamen, meaning 'striped body'.

Medium Spiny Neurons (MSNs)

Striatal neurons that receive axonal input, characterized by large dendritic trees to integrate input.

Corticostriatal Pathway

The pathway through which cortical inputs from various lobes project to the striatum.

Direct Pathway

MSN projections to the internal segment of the GP, facilitating voluntary movement by releasing thalamic neurons from inhibition.

Indirect Pathway

MSN projections to the external segment of the GP which antagonizes the direct pathway, aiding in focused selection of motor programs.

Dopaminergic Modulation

The process by which dopamine affects basal ganglia circuits, involving D1 and D2 receptor activation.

D1 Receptors

Dopamine receptors linked to increased cAMP, enhancing excitatory cortical input.

D2 Receptors

Dopamine receptors linked to decreased cAMP, suppressing excitatory inputs from the cortex.

Output of Basal Ganglia

MSNs are GABAergic and terminate in the globus pallidus and substantia nigra, inhibiting thalamus and superior colliculus.

Parkinson's Disease

A movement disorder characterized by tremors, rigidity, and slowness, resulting from the degeneration of dopaminergic projections.

Huntington's Disease

A neurodegenerative disorder characterized by jerking muscle movements and cognitive defects due to MSN projection degeneration.

Thalamus

A brain structure that receives GABAergic inhibition from GP and SNr outputs, influencing motor commands.

Caudate Nucleus

Part of the striatum involved in receiving input from association cortices and motor areas controlling eye movements.

Putamen

Part of the striatum receiving inputs from somatosensory, visual, premotor, motor, and auditory areas.

Globus Pallidus

A key output structure of the basal ganglia, divided into internal and external segments.

Substantia Nigra

A structure associated with the basal ganglia, divided into pars compacta (dopaminergic input) and pars reticulata (output).

Tonically Active GABAergic Cells

Cells in the GP and SNr that provide ongoing inhibition to upper motor neurons.

Disinhibition

The process by which MSNs inhibit GABAergic cells in GP and SNr, allowing upper motor neurons to initiate movement.

Ventral Anterior and Ventral Lateral Nuclei

Thalamic relay nuclei affected by GP neurons that influence motor cortex output.

Superficial Colliculus

A structure influenced by SNr neurons that affects head and eye movements.