Basal Ganglia

Direct pathway .....

facilitates movements

Indirect pathway ...

inhibits unwanted movements

What are the main OUTPUTS from the basal ganglia?

1. *Globus Pallidus* (INTERNAL segment) 2. *Substantia nigra* (RETICULAR) Project --> *Thalmus*

The "basic circuits" of the basal ganglia are a series of parallel circuits that go from the cerebral cortex, through the basal ganglia to the thalamus and then back to the cerebral cortex again - what are the main ones?

1. *Motor Loop* --> learned movements 2. *Cognitive Loop* --> motor intentions 3. *Oculomotor Loop* --> voluntary saccades 4. *Limbic Loop* --> emotional aspects of movements

The basal ganglia influence is to modulate the level of excitation of the thalamic nuclei; it achieves this by which *two pathways*?

Direct Pathway Indirect Pathway

What are the parts of the Globus Pallidus?

External segment (GPe) Internal Segment (GPi)

What is the main NT used for basal ganglia output?

GABA - inhibitory

Direct Pathway to affect cortical output

*Cortex* --> (excites) *Striatum* --> (inhbits) *GPi* --> (inhibits) *Thalamus* --> *facilitates Cortex*

The Indirect Pathway to affect cortical output

*Cortex* --> *excites Striatum* --> inhibits *GPe* --> inhibits *Subthalamic nucleus* --> excites *GPi* --> *inhibits Thalamus* --> *facilitates Cortex* (which when activated works to INHIBIT the Cortex)

What is the major NT for the INPUT of info to the basal ganglia?

*Glutamate* (excitatory)

The Substantia nigra (compact part) modulates..

*The Striatum*; using dopamine it can *excite the direct pathway*, or *inhibit the indirect pathway*.

Parkinson's Tx

- *Deep Brain Stimulationg (DBS)* = "Pacemakers for the brain" - It affects movement by using electrical impulses generated by wire electrodes surgically placed in the brain to stimulate a target area in the brain such as: thalamus, subthalamus, globus pallidus

Parkinson's Disease

- *Loss of substantia Nigra (compact)*; dopaminergic neurons - Depigmentation due to loss of neuromelanin - Sx: *Tremor; muscle rigidity; impaired postural reflexes*; bradykinesia; hypokinesia; decreased blinking; expressionless face; absence of arm movements when walking - *Decreased direct pathway + increased indirect pathway* --> Enhanced output from Globus Pallidus leading to inhibition of Thalamus and diminished cortical output.

Main functions of the basal ganglia

- Exerts influence altering *motor activity* through the cerebral cortex; it achieves this *by facilitating and suppressing neuronal activity*. - AKA it modulates cortical output w/ relation to movement

Hemiballism

- Lesion in the *contralateral subthalmic nuclei*; usually caused by stroke involving the PCA - Sx: *wild flailing movements of arm & leg*

Huntingdon's Disease of "Chorea"

- Marked by *decrease in the caudate nucleus & putamen* - Autosomal dominant mutation of Huntingtin gene - Ages 30-50 - Sx: *rapid movements of the face, tongue, lips*; may be accompanied by dementia & personality changes

Main components of the basal ganglia

- Nucleus Accumbens - Globus Pallidus - Subthalamic nucleus - Caudate Nucleus - Putamen - Substantia nigra

Basal Ganglia Syndromes

- TOO MUCH inhibition leads to *insufficient activation* of the cortex --> LOSS of movement = Parkinson's Disease - TOO LITTLE inhibition leads to *too much stimulation* of the cortex --> EXCESS movement = Huntington's Chorea; Hemiballism

The Basal Ganglia produces distinctive movement abnormalities if hindered...

- slowed or diminished movements - involuntary movements - generalized alterations in muscle tone

What parts of the Basal Ganglia are part of the *Striatum*?

Caudate nucleus Nucleus accumbens Putamen

What are the parts of the Substantia nigra?

Compact part (SNc) Reticular Part (SNr)

What composes the *Lenticulate Nucleus* of the basal ganglia?

Putamen Globus Pallidus (pallidum)

What is the principle INPUT to the basal ganglia?

The *cerebral cortex* inputs into the *Striatum + Subthalamic Nucleus* of the basal ganglia.