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.
