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Functional Neuroanatomy > Problem 2 > Flashcards

Problem 2 Flashcards

1
Q

Basal ganglia

A

Refers to the large + functionally diverse set of nuclei that lie deep within the cerebral hemisphere

a) caudate nucleus
b) putamen
c) Globus pallidus

d) substantia nigra
e) subthalamic nucleus

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2
Q

What is the Input zone of the Basal ganglia ?

A

The (corpus) striatum that includes the

  1. Putamen
  2. Caudate nucleus

–> both are joined by bridges of gray matter that extent through the internal capsule

“striped body”

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3
Q

Medial spiny neurons

A

Large, spread out dendrites that integrate info from a variety of sources

AND: their firing is associated with the anticipation of movement

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4
Q

What is the output zone of the Basal ganglia ?

A

The Palladium which includes the

  1. Globus pallidus
  2. Substantiv nigra pars reticulata
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5
Q

Which areas are major sources of input to the basal ganglia ?

What are they called ?

A
  1. Nearly all regions of the cerebral cortex especially

a) Association areas of FL + PL
b) Temporal, insular + cingulate cortices

  1. Corticostriatal pathway

–> consists of parallel pathways serving different functions + input is glutaminergic

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6
Q

The cortical inputs to the caudate vs putamen are not the same. These differences in input reflect functional differences between the two nuclei.

Name these functional differences + their sources of input.

A
  1. Caudates neurons fire in anticipation of eye movements

–> receives input from

a) multimodal association cortices
b) motor areas from FL that control eye movements

  1. Putamens neurons fire in anticipation of limb + trunk movements

–> receives input from

a) primary + secondary somatic sensory cortices (PL)
b) visual cortices (OL)
c) premotor + motor cortices (FL)
d) Auditory association cortices (TL)

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7
Q

What does the fact that different cortical areas project to different regions of the striatum imply ?

A

That the corticostriatal pathway consists of multiple parallel pathways serving different function

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8
Q

What is evidence for the fact that the striatum is functionally subdivided according to its inputs ?

A
  1. Visual + somatic sensory cortical projections are topographically mapped within different regions of the putamen
  2. Cortical areas that are functionally interconnected give rise to overlapping projections in the striatum

–> this means that functionally distinct pathways project in parallel from the Cortex to the striatum

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9
Q

Local circuit neurons

Internerons

A

Modulate the effectiveness of cortical synaptic activation arriving from distal dendrites

–> synapse close to the soma

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10
Q

Double inhibiton

A

Constant activation in pallidum tonically inhibits neurons in the thalamus

–> useful for selecting a response in a competitive system

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11
Q

Direct pathway

A
  1. Medial spiny neurons
  2. Striatum
  3. Internal segment of Globus pallidus (Pallidum)
    - -> inhibited, thus no tonic inhibition
  4. Thalamus
    - -> excited
  5. Cortex

–> main function is to remove tonic inhibition which enables the excitability of the thalamus which will drive upper motor neurons

INITIATION OF VM

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12
Q

Indirect pathway

A
  1. Medial spiny neurons
  2. Striatum
  3. External segment of the Globus pallidus
    - -> will tonically inhibit the internal segment
  4. Internal segment is excited
    - -> increased inhibitory outflow of the BG
  5. Thalamus
  6. Cortex

–> main function is to increase the inhibitory influences of the basal ganglia, thus antagonizing the actions of the direct pathway

REINFORCING THE SUPPRESSION OF INAPPROPRIATE MOVEMENTS

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13
Q

Afferent neurons of the palladium give rise to … ?

A

GABA-neurons that terminate in the pallidal nuclei

–> converge on specific neurons + broader subsets, which elicits weak influence over many neurons but strong influence over a specific subset

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14
Q

Efferent neurons of the pallidum give rise to … ?

A
  1. Thalamus
    - -> inhibited by GP internal
  2. Subthalamic nucleus
    - -> inhibited by GP external
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15
Q

In which way are the 2 pathways (indirect vs direct) organized ?

A

In a centre surround fashion

  1. Direct pathway = centre
    - -> focuses on particular functional units + activates intended motor programs
  2. Indirect pathway = surround
    - -> focuses on broader range of functional units + inhibits competing motor programs

=> both become active at the same time to simultaneously make recommendations about what to do/not to do

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16
Q

Dopaminergic modulation

A

When the goal of movement is associated with a larger reward, dopamine is released in the striatum

–> strengthens connections in direct pathway (motor program more likely to get the “go”) + vice versa

17
Q

In which way does the Basal ganglia have a gatekeeper function

A
  1. Processing among indirect pathway is slower
  2. Less inhibition from direct pathway followed by more inhibition from indirect pathway
  3. Strong inhibitory baseline keeps motor system in check, allowing for possible movements to become activated without triggering movement
  4. As a specific motor plan gains strength, the inhibitory signal is decreased for selected subgroup of spiny neurons
  5. This movement representation breaches the gate, thus winning the competition ( winner takes it all sytem)
  6. Striatal neurons have a high threshold for activation due to their intrinsic membrane properties and tend to remain in a down state
  7. Under an appropriate level of dopamine activation, they can respond to a sufficiently large excitatory input from the cortex + thalamus
18
Q

Treatment options for parkinson’s disease ?

A
  1. Deep brain stimulation
  2. L-dopa
    - -> used to produce dopamine
  3. Ion chelators
    - -> to segregate iron
19
Q

Hemiballismus

A

Characterized by

  1. Hyperkinetic movement disorder
  2. Damaged sub thalamic nucleus
  3. Low inhibitory outflow
20
Q

Non-motor loops of the Basal ganglia

A

Refer to the parallel loops that engage specific subdivisions of the BG + thalamus, thus affecting areas outside of the motor cortices

a) Prefrontal loop
b) Limbic loop

21
Q

Prefrontal loop

A

Initiation + termination of cognitive processes

e.g.: planning, WM, attention

–> non motor loop

22
Q

Limbic loop

A

Regulates emotional + motivated behavior and the transition from one mood to another

–> non motor loop

23
Q

Why is an integration of all loops (including the non-motor ones) necessary ?

A

So no deterioration of cognitive + emotional functioning occurs

24
Q

What is wrong in people with Parkinsons ?

A

Hypo-kinetic - too little movement

–> degeneration of dopamine neurons, thus GP internal is not as inhibited

THALAMUS IS INHIBITED

25
Q

What is wrong in people with Huntingtons ?

A

Hyperkinetic - too much involuntary movement

–> due to deterioration of spiny neurons, thus sub thalamic nuclei will not excite GP internal

THALAMUS NOT INHIBITED

=> affects indirect pathway

Functional Neuroanatomy (6 decks)

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