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Functional Neuro > Task 2 > Flashcards

Task 2 Flashcards

1
Q

what is the basal ganglia?

A

= comprises a set of grey matter structures
components involved in movement
- corpus striatum = input zone
-> caudate
-> putamen
- pallidum = main sources of output
-> globus pallidus
-> substantia nigra pars reticulata

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2
Q

what is the corpus striatum?

A
  • input zone of the basal ganglia
  • consists of
    -> caudate
    -> putamen
  • strongest projections from association areas
  • activity of the cell may encode the “DECISION TO MOVE” towards a goal
    = rather than the actual movement
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3
Q

what is the caudate?

A
  • part of the corpus striatum (with putamen)
  • receives cortical projections
  • does not process sensory information
  • its neurons fire prior to eye movement
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4
Q

What is the putamen?

A
  • part of the corpus striatum (with caudate)
  • receives input from
    -> parietal lobe (= somatic sensory cortices)
    -> occipital lobe (= visual information)
    -> frontal lobe (= motor cortices)
    -> temporal lobe (= auditor association aresas)
  • its neurons discharge in anticipation of limb/ trunk movements
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5
Q

What is the input zone ?

A
  • the destination of most pathways from other brain regions
  • collateral axons of excitatory glutamatergic synapse project on medium spiny neurons
  • low spontaneous activity
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6
Q

what are medium spiny neurons?

A
  • class of cells in the corpus striatum
  • destinations of incoming axons from the cerebral cortex
  • receives input from a lot of brain structures
    = big number of spiny neurons contacted by a single axon
  • dopaminergic = main input
  • when active, the firing is associated with the occurrence of movements
  • neurons increase the rate of discharge before an impending movement
    ->part of movement selection process
  • GABAergic = inhibitory
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7
Q

What is the output?

A
  • medium spiney neuorns (of caudate & putamen)
    -> give rise to inhibitory GABAergic projection
    -> those end in the globus pallus & substantia nigra pars reticulata
    -> this resembles the cortico-striatal pathway
  • regions the basal ganglia projects to
    -> tectum
    -> brainstem areas
  • main output is inhibitory
  • high spontaneous activity = quiescent medium spiny neurons
    -> prevention of unwanted movement (double inhibition)
    -> tonic inhibition of thalamus & superior colliculus
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8
Q

what is the globus pallidus?

A
  • for control of limb movement
  • part of the pallidum
  • send to ventral anterior & ventral lateral nuclei of the thalamus
  • interacts directly with circuits of upper motor neuorns in frontal cortex
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9
Q

what is the substantia nigra pars reticulata ?

A
  • projects to the superior colliculus
  • controls orienting movements of eyes and head
  • part of the pallidum
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10
Q

what are circuits within the basal ganglia?

A
  • direct pathway
    -> fast
    -> direct
    -> inhibitory connections from the striatum to GP / SN
  • indirect pathway
    -> slower
    -> roundabout route to GP / SN
  • hyper-direct pathway
    -> direct pathway from cerebral cortex to subthalamic nuclei = excitatory
    -> faster stop
    -> supports the indirect pathway
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11
Q

What is the direct pathway?

A
  • transiently inhibitory projections from
    -> the caudate and putamen project to tonically active inhibitory neurons (globus pallidus)
  • they then project to the VA/VL complex of the thalamus
  • transiently excitatory inputs to the caudate and putamen
    -> from the cortex and substantia nigra
  • transiently excitatory input from the thalamus back to the cortex
  • initiation of movement
  • pallidum has tonic inhibition = constant inhibition of the thalamus
  • Movement can only happen if pallidum is inhibited

= + cortex
= facilitation of movement

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12
Q

what does tonic mean? what does transient mean ?

A

tonic
= coinstant activity (+/-)
= highly spontaneous

transient
= not active by themselves

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13
Q

what do the neurotransmitters mean exactly?

A

glutamate +
GABA -

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14
Q

what happens in the direct pathway when the cortex is active?

A
  • inhibited internal segment of globus pallidus
    -> less tonic inhibition for the thalamus
  • excited thalamus
  • GO = movement
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15
Q

what is the indirect pathway?

A
  • transiently active inhibitory neurons from the caudate and putamen
    -> project to tonically active inhibitory neurons of the external segment of the globus pallidus
  • the globus pallidus (external segment) neurons project to the subthalamic nucleus
    -> receives strong excitatory input from the cortex
  • the subthalamic nucleus projects to the internal segment of the globus pallidus
    -> its transiently excitatory drive acts to increase the disinhibitory action
    -> opposing to the direct pathway = MODULATION

= basal ganglia increases in inhibition
= antagonist to direct pathway

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16
Q

what happens in the indirect pathway when the cortex is active?

A
  • internal segment of globus pallidus = excited
  • incrase inhibitory outflow of basal ganglia
    -> increase inhibition of thalamus
  • NO GO
17
Q

what are non-motor loops ?

A
  • basal ganglia has parallel loops that originate in different regions of the coretx
    -> engage in specific subdivisions of basal ganglia + thalamus
  • prefrontal loop
    -> initiation & termination of cognitive processes (planning)
    -> WM
    -> attention
    -> involving DLPFC and the head of caudate
  • limbic loop
    -> regulates emotional & motivational behaviour
    -> transition from one mood to another
18
Q

what might be the cause of the tourette´s syndrome?

A

might be due to excessive activity in basal ganglia loops
-> regulate the cognitive circuitry of the prefrontal speech areas

19
Q

what are theories of the basal ganglia?

A
  • centre sourround model
  • gate-keeper function model
20
Q

what is the centre sourround model?

A
  • centre-surround functional organisation of the two pathways
    -integration of cortical input by the striatum
    -> activates direct and indirect pathways

direct pathway
- centre
- focus on particular functional units
- axons from striatum synapse densly on single pallidal neurons
- activation
-> results in the disinhibition of the VA/VL complex
-> results in the expression of the intended motor program
-> reinforces the strongest motor program

indirect pathway
- surround
- covers broader range of functional units
- neurons from subthalamic nucleus are distributed evenly through internal segment
- activation (simultaneously)
-> neurons are driven by excitatory inputs from the subthalamic nuclei
-> reinforces the suppression of a broad set of competing motor programs
-> illuminates the weaker programs

21
Q

what is the gatekeeper function model?

A
  • two opposing pathways
  • basal ganglia can act as gatekeeper of cortcial activity
  • strong inhibitory baseline
    -> keeps motor system in check
    -> allows possible movements to become activated without triggering movement

direct pathway
- faster = decreased inhibition
- target neurons in the output nuclei = inhibited
-> hindering the connection to the thalamus
- leads to excitation of the thalamus + cortical motor areas
= BREAKS THEM DAM with strongest input

indirect pathway
- striatal activation
-> increased inhibition of the cortex
- slower (catches up with the direct pathway)
-> increases the inhibition
= BUILDS THE DAMN AGAIN - catches up with the direct pathway

22
Q

what happens when dopamine is taken into consideration in the gatekeeper function model?

A

Direct pathway
- D1 receptors
- (+)
- EPSP

indirect pathway
- D2 receptors
- (-)
- IPSP

=> opposing effects on both pathways
dopamine release has the effect of
-> promoting selected actions = direct pathway
-> discouraging non-selected actions = indirect pathway

23
Q

what happens in the direct pathway in a dopaminergic modulation?

A
  • excitatory input to spiny neurons
  • D1 receptor cells = EPSP
  • increased responsiveness to cortical input
  • GO = MORE GO
  • ACTIVATION OF INITIATION
24
Q

what happens in the indirect pathway in a dopaminergic modulation?

A
  • inhibitor input to spiny neurons
  • D2 receptor cells = IPSP
  • decreased responsiveness to cortical input (!!in the indirect pathway)
  • LIFTING THE BREAK
  • ACTIVATION OF MOVEMENT
25
Q

what happens in Parkinson´s disease?

A

-hypokinetic disorder
= difficult to initiate/terminate movements
- slower movements
- loss of dopaminergic neurons
-> abnormally high inhibitory outflow of BG
-> more difficult to generate the transient inhibition from the caudate and putamen

treatment
- L-Dopa = producing dopamine
- deep brain stimulation

26
Q

what is Huntington´s disease?

A
  • hyperkinetic disorder
    = too much + inappropriate movement
  • external segments ahve incrased activity
    -> less inhibition

Functional Neuro (5 decks)

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