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Neuro B4 - WLB > Basal Ganglia Motor Control - Ruff > Flashcards

Basal Ganglia Motor Control - Ruff Flashcards

1
Q

What is the function of the basal ganglia in selecting actions?

A
  • Promotes one action while suppressing others
  • “Actions” can include complete motor programs or cognitive processes

E.x. Friend waves to you while your phone rings, what do you choose to do?

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2
Q

What are the components of the basal ganglia?

A
  • Corpus striatum (input zone)
    • Caudate nucleus
    • Putamen
  • Pallidum (output zone)
    • Globus pallidus (external & internal)
    • Substantia nigra pars reticulata
  • Subthalamic nucleus
  • Substantia pars compacta
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3
Q

Where does afferent input into the Corpus Striatum come from?

A
  • Ipsilateral cortex
  • Substantia niagra pars compacta
  • Subcortical structures via thalamus
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4
Q

Does input to the basal ganglia outnumber outputs OR does output outnumber input?

A

***Inputs far outnumber outputs

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5
Q

What kind are 90% of neurons in the striatum?

A

Medium spiny neurons

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6
Q

What are the two kinds of medium spinal neurons in the striatum and what signal do they convey?

A
  • GABA/Substance P
    • project to internal Globus pallidus and Substantia nigra pars reticulata
    • GABAergic - inhibitory
  • GABA/Enkephalin
    • project to Globus pallidus externa
    • GABAergic - inhibitory
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7
Q

What is the somatotopic arrangement in the basal ganglia?

A

Caudate nucleus: eye movement

Putamen: limb movement

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8
Q

What are the three main pathways in the basal ganglia and their function?

A
  • Direct
    • Disinhibits selected actions, allowing them to occur
    • Net: excitatory
  • Indirect
    • Inhibits actions other than the one selected
    • Net: inhibitory
  • Hyperdirect
    • Suppresses all movement
    • Net: inhibitory
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9
Q

Describe the three steps of the direct pathway at rest.

A
  • Striatum inhibits → Globus pallidus internal
    • not tonically active
  • Globus pallidus internal inhibits → VA/VL thalamus
    • tonically active
  • VA/VL thalamus excites → Motor Cortex
    • not tonically active
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10
Q

What are the four steps of the direct pathway when activated?

A
  • Cortex transiently excites → Striatum
  • Striatum inhibits → Globus pallidus internal
  • Inhibited GPi → allows VA/VL thalamus active
  • Active VA/VL thalamus excites → Motor cortex
    • MOTOR OUTPUT!!!
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11
Q

How does activation of the direct pathway allow eye movements and locomotion to occur?

A
  • Cortex transiently exites → Striatum
  • Striatum inhibits → Substantia nigra reticulata
  • Inhibition of substantia nigra reticulata → allows brainstem to excite:
    • superior colliculus (eye movements)
    • Pedunculopontine Tegmental Nucleus (locomotion)
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12
Q

What are the six steps in suppressing conflicting actions via the Indirect Pathway?

A
  • Cortex excites → Striatum
  • Striatum inhibits → Globus pallidus externa
  • Inactive Globus pallidus externa → allows Subthalamic nucleus to be active
  • Subthalamic nucleus excites → Globus pallidus interna
  • Globus pallidus interna inhibits → VA/VL thalamus
  • Inhibited VA/VL thalamus → NO excitation of Motor Cortex
    • DECREASED MOTOR OUTPUT!
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13
Q

What are the four steps in the Hyperdirect Pathway to suppress motion?

A
  • Cortex directly excites → Subthalamic nucleus
  • Subthalamic nucleus excites → Globus pallidus interna
  • Globus pallidus interna inhibits → VA/VL thalamus
  • Inhibited VA/VL thalamus → NO excitation of Motor Cortex
    • DECREASED MOTOR OUTPUT!
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14
Q

What pathway uses GABA/Substance P and has D1 dopamine receptors?

A

Direct Pathway - Excitatory

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15
Q

What pathway uses GABA/Enkephalin and has D2 receptors?

A

Indirect - Inhibitory

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16
Q

What are the steps in the complete circuit if the Substantia nigra compacta releases dopamine on D1 & GABA/Substance P in the Striatum?

A
  • Activated Striatum inhibits → Substantia nigra reticulata
  • Inhibited Substantia nigra reticulata → allows brainstem to be active
  • Active brainstem → INREASED MOTOR OUTPUT

OR

  • Activated Striatum inhibits → Globus pallidus interna
  • Inhibited Globus pallidus interna → allows VA/VL thalamus to be active
  • Active VA/VL thalamus excites → Motor Cortex
    • INCREASED MOTOR OUTPUT
17
Q

What are the steps in the complete circuit if the Substantia Nigra compacta releases dopamine on GABA/Enkephalin and D2 in the Striatum?

A
  • Inhibited Striatum allows → Globus pallidus externa to be active
  • Globus pallidus externa inhibits → Subthalamic nucleus
  • Inhibited Subthalamic nucleus doesn’t excite → Globus pallidus interna ???
  • Unactived Globus pallidus interna cannot inhibit → VA/VL thalamus???
  • Uninhibited VA/VL thalamus → excites Motor cortex???
    • INCREASED MOTOR OUTPUT?
18
Q

What part of the basal ganglia is affected by Parkinson’s disease?

A

Substantia Nigra compacta

(normally releases Dopamine)

19
Q

What are the common symptoms of Parkinson’s disease?

A
  • Hypokinesia/akinesia
    • Paucity of movements
    • Lack of facial expression
  • Bradykinesia (slow movements)
  • Shuffling gait
  • Rigidity (lead-pipe or cogwheel)
  • Postural instability
  • Tremor at rest (opposite of cerebellum lesions)
20
Q

How does impaired substantia nigra compacta cause the symptoms of Parkinson’s disease?

A

No Dopamine release → Decreased/No Motor output from motor cortex

21
Q

What is the treatment for Parkinson’s disease?

A
  • L-DOPA/Carbidopa
  • Deep brain stimulation
22
Q

What part of the basal ganglia is affected in Huntington’s disease?

A

Caudate nucleus and Putamen

(also frontal/temporal cortex)

23
Q

What are the common symptoms of Huntington’s disease?

A
  • Rapid, jerky movements
  • Hyperkinesia → akinesia as degeneration of the striatum progresses
  • Cognitive as well as motor dysfunction
  • Onset usually in midlife
24
Q

How does impaired Striatum cause the symptoms observed in Huntington’s?

A

Striatum unable to inhibit Pallidum

  • Globus pallidus interna fires less
  • Globus pallidus externa fires more → inhibiting Subthalamic nucleus
  • Result: INCREASED MOTOR OUTPUT

Neuro B4 - WLB (17 decks)

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