Basal Ganglia

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Function of Basal Ganglia

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Regulate Movement
Help Cortex to smoothly orchestrate motor behaviors

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What happens if you have lesions in the basal Ganglia??

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the cortex is unable to properly direct motor control which results in movement disorders...
ex: Parkinson's

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Basal Ganglia Includes these five parts

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caudate nucleus
putamen
globus pallidus
subthalamic nucleus
substantia nigra

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Striatum is made up of the:

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caudate and putamen

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Caudate Nucleus

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“C” shape of caudate follows the ventricular system, through lateral ventricle to temporal lobe
Mass of tissues anteriorly, tapers rapidly
Forms the medial border of the anterior limb of the internal capsule.

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Caudate Nucleus Forms:

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Forms the medial border of the anterior limb of the internal capsule.

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Putamen

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Embryologically arise from the same cell mass as caudate
-Caudate and putamen indistinguishable in terms of embryonical origin, histology, physiology
-Lateral to the caudate; coextensive with the insula

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Lenticular (lentiform) nucleus

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Putamen + Globus Pallidus
Putamen forms the outermost portion of the lenticular nucleus.
The globus pallidus is more MEDIAL.

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Globus Pallidus

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Anatomically and physiologically very different from the striatum
Medial to putamen
Different in function than the putamen
Has a lateral or external segment (GPe) and an internal segment (GPi)

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General Functions of Basal Ganglia

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*General motor control*
-Regulates movement; Helps cortex to smoothly orchestrate motor behaviors
Eye movements
Cognitive function
Emotional function

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General Motor Function

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-Involved in the initiation and maintenance and direction of movement
-Modulate movements
-These structures are regarded as feedback loop to the motor cortex
-The function of the basal ganglia -"brake hypothesis".

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Input of Basal Ganglia

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All inputs to basal ganglia arrive via striatum (caudate + putamen)

Main inputs to the caudate and putamen:
Cerebral cortex (all)
Substantia Nigra (pars compacta-DA)
Thalamus (centromedial nucleus- “CM”)

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Outputs of Basal Ganglia

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There are NO descending pathways that go from the BG directly to the spinal cord
BG affect function mediated by the ipsilateral cortex and thus affects movements of the contralateral side of the body
Arise from 1. Globus Pallidus (internal),
2. Substantia Nigra (pars reticularis)
Project mainly to VA*-VL complex, (VA-premotor cortex and VL-motor cortex)
Closed feed backloop: cortexstriatum,
G. pallidus, thalamus, cortex

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Intrinsic Connections
2 predominate pathways

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opposite effects on motor activity
Direct: striatum-->GPi or substantia Nigra (pars reticularis)
Indirect: striatum-->Gpe-->subthalamic nucleus-->Gpi or substantia Nigra (pars reticularis)

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Direct and Indirect Pathway Differences

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Direct pathway TURNS UP motor activity (increases excitatory drive from the thalamus to the cortex, increased Corticospinal tract activity and muscle activity)
Indirect pathway TURNS DOWN motor activity

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2 parts of substantia nigra

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Pars compacta- dopaminergic neurons, project to the striatum (nigrostriatal axon terminals release dopamine into the striatum---ultimately increases motor activity)

Pars reticularis- no dopamine, project to VA and VL

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Subthalamic Nuclei

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Interconnection between globus pallidus and subthalamic nucleus
Inhibitory control of subthalamic nucleus (STN)---ultimately decreases motor activity

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**Hypokinetic
Lesions in Basal Ganglia

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Parkinson’s Disease- lesion of the Substantia Nigra (pars compacta) loss of dopaminergic neurons- degenerated Nigrostrial pathway
Hypokinesia, rigidity, tremor and loss of postural reflexes

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**Hyperkinetic
Lesions in Basal Ganglia

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Hungtington’s Chorea- Lesion of the striatum (dance movement)

Hemiballismus-Lesion on Subthalamic nucleus- (wild flinging motion of contralateral extremity)