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Functional Neuroanatomy > Task 2 - Basal Ganglia > Flashcards

Task 2 - Basal Ganglia Flashcards

1
Q

Basal Ganglia

A

Set of nuclei deep within cerebral hemispheres:

  • caudate
  • putamen
  • globus pallidus
  • substantia nigra (base of midbrain)
  • subthalamic nucleus (ventral thalamus)
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2
Q

Basal Ganglia functions

A

Subcortical loop linking cerebral cortex areas with upper motor neurons in primary and premotor cortex and in brainstem

  • modulate activity in anticipation of and during movements
  • important for voluntary motor movements
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3
Q

Striatum

A

Caudate + Putamen

  • input zone of basal ganglia: mostly from association areas in frontal and parietal lobes
  • > corticostriata pathways
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4
Q

Putamen input

A

Primary and secondary somatic sensory cortices in par. lobe

  • secondary visual cortices in occipital and temporal lobe
  • premotor & motor cortices in frontal lobe
  • auditory association areas in temporal lobe
  • > neural firing prior to limb and trunk movement
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5
Q

Caudate input

A

Multimodel association areas

Motor areas of frontal lobe controlling eye movements
-> neural firing prior to eye movement

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6
Q

Medium spiny neurons

A

Destination of neurons from cerebral cortex

  • > allow integration from cortical, thalamic, and brainstem
  • firing associated with occurrence of movement
  • > axons arising converge in pallidum
  • > connect striatum with other regions (brain stem, thalamus, globus pallidus)
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7
Q

Pallidum

A
  • Globus pallidus
  • Substantia nigra pars compacta
  • > main sources of output from basal ganglia
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8
Q

Basal Ganglia Projections

A

Main output inhibitory:

  • caudata & putamen: inhibitory to globus pallidus and substantia nigra pars reticulata
  • > influences activity of upper motor neuronos located in motor cortex and brainstem
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9
Q

Basal Ganglia role

A

Gatekeeper in initiation of movements
-> facilitates initiation of motor programs that express movement and suppresses competing or non-synergistic motor programs that would interfere

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10
Q

Substantia nigra pars reticulata pathway

A

Caudate and Putamen inhibitory pathway towards substantia nigra pars reticulata

  • > itself has inhibitory pathway to superior colliculus (eye movements)
  • > if subst. nigra is inhibited enough superior colliculus is less inhibited leading to movement
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11
Q

Direct Pathway

A 
From striatum (-) and globus pallidus internal segment (-) to VA/VL complex of thalamus (+) to frontal cortex
-> functions to open physiological gates that initiate movement (release of thalamic neurons driving uppoer motor neurons from tonic inhibition)
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12
Q

Indirect Pathway

A

Reinforces suppression of inappropriate movements;
serves to increase tonic inhibition;
-striatum to external segment from which it projects to subthalamic nucleus (excites internal segment) and internal segment directly (-)
-> antagonizes activity of direct pathway
-> functions to close physiological gates that terminate movements

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13
Q

Gate Model of Basal Ganglia

A

Proposes that the output of the Thalamus as result of basal ganglia circuit only gives binary yes-or-no output back to cortex

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14
Q

Center-Surround Model of Basal Ganglia

A

Focused selection:

  • Indirect pathway activation: surround region of globus pallidus (reinforces suppression)
  • direct pathway activation: inhibition of center of neurons in internal segment
  • > both active at same time: output also provides alternative action instead of just yes v no
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15
Q

Dopamine Modulation of Basal Ganglia Circuits

A
  • Dopaminergic cells in substantia nigra pars compacta
  • medium spiny neurons of striatum project to it and it projects back
  • > dopamien modulation excites direct pathway via effect on D1 receptor
  • > inhibites indirect pathway (effect on D2 receptor)
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16
Q

Result of dopamine modulation

A

Less inhibition of basal ganglia towards thalamus when goal of movement is associated with larger reward

17
Q

Tonic Inhibition

A

Sustained, stron inhibition by default

-> no need of further input to sustain inhibition

18
Q

Transient Inhibition

A

Inhibition that needs to be specifically activated

-> needs input to sustain inhibition

19
Q

Movement Diseases

A

Parkinson’s
Huntington’s
Hemiballismus

20
Q

Parkinson’s

A

Caused by loss of nigrostriatal dopaminergic neurons, which serve to increase responsiveness to direct pathway and decrease responsiveness to indirect athway

  • > inhibitory outflow of basal ganglia abnormally high
  • > hypokinetic movement disorder (failure of disinhibition)
  • > difficulty initiating movements
21
Q

Huntington’s

A

Degeneration of medium spiny neurons projecting to external segment of globus pallidus

  • > absence of inhibition via indirect pathway
  • > restraining influence of basal ganglia lost, upper motor neurons are activated by inappropriate signals
  • > hyperkinetic movement disorder: undesired ballistic and choreiform movements due to failure of inhibition
22
Q

Hemiballismus

A

Violent involuntary movements as result of damage to subthalamic nucleus (normally serves to increase inhibition of movements)
-> hyperkinetic movement disorder

23
Q

Deep Brain Stimulation

A

Treatment for hyper-/hypokinetic movement disorders

  • implantation of battery-powered generator units;
  • > produce electrical discharges passed through wires to electrodes implanted bilaterally into brain
  • common stimulation sites: internal segment of globus pallidus, subthalamic nucleus
  • > provides stable and structured patterns of neural activity (can facilitate initiation and termination of movement)
  • > can excite and inhibit nuclei
24
Q

Motor Programs

A

result from innate programming of CNS circuits combined with epigenetic arrangements leading to development of appropriate and fine-tuned motor programs

25
Q

Orientation Movements

A

Motor programs controlling eye and body orientation towards different objects in surrounding world
-> controlled by tectum (superior colliculus)

26
Q

Pathways terminating motor activity

A

Glutaminergic subthalamic nucleus: can terminate movment by exciting inhibitory pallidal output neurons
-> receives excitation from cortex; disinhibition via indirect pathway

27
Q

Motor Loops

A

Body movement loop

Oculomotor loop

28
Q

Non-motor loops

A

Prefrontal loop

Limbic loop

29
Q

Body movement loop

A
  1. motor, premotor, somatosensory cortex
  2. putamen
  3. lateral globus pallidus, internal segment
  4. vetral lateral and ventral anterior nuclei (thalamus)
30
Q

Motor Loop Components

A
  1. cortical input
  2. striatum
  3. pallidum
  4. thalamus
31
Q

Oculomotor loop

A
  1. Posterior parietal prefrontal cortex (frontal & supplementary eye fiel)
  2. caudate
  3. globus pallidus internal, subst. nigra pars reticulata
  4. mediorsal and ventral anterior nuclei thalamus
32
Q

Prefrontal loop

A
  1. dorsolateral prefrontal cortex
  2. anterior caudate
  3. globus pallidus internal, subst. nigra pars reticulata
  4. mediodorsal and ventral anterior thalamus
33
Q

Limbic Loop

A

Emotional Loop:

  1. amygdala, hippocampus, orbitofrontal, anterior cingulate, temporal cortex
  2. ventral striatum
  3. ventral pallidum
  4. mediodorsal nucleus

Functional Neuroanatomy (4 decks)

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