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Nervous System: Unit III > Basal Ganglia > Flashcards

Flashcards in Basal Ganglia Deck (11)
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Role of basal ganglia in motor control

  • modulation of motor performance via interconnections with the motor cortices.
  • major feedback loop to motor and association cortex
  • in general, serve a role in motor program selection.



Major source of input to basal ganglia

  • Cerebral cortex
  • primarily: frontal lobe areas and sensorimotor areas that have a greater role in the planning and initiation of movement.


Characteristics of Parkinson's disease

  • Resting tremor, difficulty initiating movements, slowness
  • etiology: loss of dopamine neurons in the substantia nigra.                 


Probable mechanism of Parkinson's

  • Substantia nigra sends dopaminergic axons back to the striatum.
  • The action of dopamine in striatum is probably largely excitatory, since Parkinson's disease, which includes degeneration of substantia nigra neurons and loss of dopaminergic input, is marked by a paucity of movement.


Output of basal ganglia: inhibitory vs. excitatory

  • Inhibitory.
  • GPI → (GABA -) @ Thalamus → (Glu +) Cortex.
  • output of the basal ganglia is directed to the thalamus via the pallidothalamic fibers from the GPI which are GABA-nergic and from there back to the cortex.
  • Basal Ganglia provide resting inhibition of the thalamus until a signal comes from the cortex causing the disinhibition of the the thalamus via the direct pathway.



Genetic cause of Huntington's Disease

  • autosomal dominant
  • site of mutation @ short arm of the 4th chromosome.
  • Normal humans have 17-34 CAG repeats, HD have > 40.


Characteristics/presentation of Huntington's Disease

  • Striatal damage produces athetosis or chorea.
    • Chorea = continuous rapid movements of the face, tongue or limbs (usually distal portions).
    • Athetosis indicates slow, writhing, ceaseless movements of hand, sometimes lips, tongue, neck and foot.  


HD impact on basal ganglia

  • caudate = most affected region of basal ganglia


"Direct path" from cortex to basal ganglia and back to cortex

  • Cortex → excites through striatum Caudate/Putamen with glutamate
  • glutamate → which inhibits GPI with GABA →
  • stops inhibiting Thalamus with GABA → which can then excite the cortex with glutamate


Stroke @ subthalamic nucleus impact

  • subthalamic nucleus = integral piece of the indirect pathway.
  • If stroke that destroyed the STN then a great degree of thalamic inhibition would be lost ==> hemiballismus
    • e.g. stroke @ small ganglionic branch of posterior cerebral artery
  • Disinhibition would rule, hence the flailing of arms and legs on one side. 


Type of stimulus used in deep brain stimulation for Parkinson's patients

  • Hyperpolarizing.
  • Main problem in Parkinson's = STN and GPI cause inhibition of the thalamus.
  • DBS would work to remove such inhibition, otherwise known as encourage disinhibition.
  • Hyperpolarizing the STN or GPI would do just that without the need for medications.