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MHD Neuro > Basal Ganglia (+Disorders) & Thalamus+Internal Capsule > Flashcards

Basal Ganglia (+Disorders) & Thalamus+Internal Capsule Flashcards

1
Q

Major Divisions of the Basal Ganglia

A
  1. Striatum (gets input from cerebral cortex)–function
    1. Caudate (Nucleus)
    2. [Nucleus accumbens]
    3. Putamen
  2. Lenticular nucleus–geographic
    1. Putamen
    2. Globus Pallidus (pallidum)
      1. internal segment=GPi
      2. external segment=GPe (efferent and projects into thalamus)
  3. Subthalamic nucleus (STN)-indirect motor pathway
  4. Substantia nigra (SN)-secrete Dopamine
    1. compact part (SNc)
    2. reticular part (SNr)
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2
Q

What is the Basal Ganglia “circuitry”?

A

there are both excitatory and inhibitory components

  1. Cortex EXCITES the Striatum (putamen)
  2. Striatum (putamen) INHIBITS GPi + SNr
    1. GPi=beginning of efferent pathway (takes 2 different routes)
      1. ansa lenticularis
      2. lenticular fasciculus (H2 field of Forel)
      3. 1+2 come together: thalamic fasciculus (H1 field of Forel)
  3. GPi + SNr INHIBIT Thalamus
  4. Thalamus EXCITES Cortex
  • BG have no major outputs to LMNs
    • Influence LMNs via the cerebral cortex
  • Input to striatum from cortex is excitatory
    • Glutamate=NT
  • Principal output from BG is via GPi + SNr
    • (inhibitory) Output to thalamus, GABA=NT
  • Thalamocortical (thalamus to cortex) projections are excitatory
    • Concerned with motor “intention”
  • Balance of excitatory & inhibitory inputs to striatum, determine whether thalamus is suppressed
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3
Q

BG circuits are parallel loops, what are the four types?

A
  • different pts project to diff pts of the striatum (caudate or putamen) which then influences diff pts of the thalamus.
  • ***Motor loop
    • Concerned with performing learned movements
    • important link for agonist and ANTagonist to work synergistically
  • Cognitive loop
    • Concerned with motor “intention”; tie in pts of cerebral cortex
  • Limbic loop
    • Emotional aspects of movements
  • Oculomotor loop
    • Concerned with voluntary saccades (fast eye-movements)
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4
Q

What are the two different types of the Motor Circuit?

A

Direct and IN-Direct

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5
Q

Direct Pathway

A

Direct

  • association cortex (and SN-potentiate eachother) EXCITES striatum (caudate/putamen)
  • Striatum (caudate/putamen) INHIBITS GPi
  • Thalamus (VA/VL) disinhibited
  • Thalamus (VA/VL) facilitates cortical (premotor cortex) activity
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6
Q

IN-Direct Pathway + Associated Diseases

A

IN-direct:

  • association cortex (and + SN-potentiate eachother/- SN) EXCITES striatum (caudate/putamen)SN has two parts:
    • D1 (excitatory) and D2 (inhibitory)
    • +/- depending on what pt of striatum (or muscles) are being inhibited at the time
  • striatum (caudate/putamen) inhibits GPe (and GPi)
  • GPe disinhibits STN (inhibition of the inhibitor)
  • (VA/VL) Thalamus inhibited (several players)
  • cortical (motor cortex) activity suppressed

Parkinson Disease:

  • DEgenerated SN (D1 and D2)=
    • INCREASED striatum (caudate/putamen) inhibition of GPe
    • DIMINISHED striatum (caudate/putamen) inhibition of GPi
    • End result: GP is LESS inhibited, so it is MORE inhibitory on thalamus=thalamus is less excitatory

Huntington Disease

  • DEgenerated output from GPi=
    • more INHIBITION of GPi (directly), less excitation of GPi (IN-directly from STN)
    • leads to less tonic inhibition of (VA/VL) Thalamus and INCREASED excitation of the motor cortex
    • Final Outcome: EXCESS movement
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7
Q

What is the “basic” pathway of sensory information to the thalamus?

A
  1. information gets collected
    1. spinal nerve: touch/proprioception and pain/temp
  2. Transmitted (up the SC to the VPN)
    1. dorsal columns
    2. anterolateral tract
  3. Looked at and analyzed in the VPN
  4. Interpreted in the somatosensory cortex
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8
Q

What are the divisions of the Diencephalon

A
  • Epithalamus (pineal gland, habenula, stria medullaris)
  • ***Dorsal thalamus​
    • Internal medullary lamina=main divider (the Y)
      • Anterior division nuclei
      • Medial division nuclei
      • Lateral division nuclei
    • Intralaminar nuclei
    • Thalamic reticular nuclei-along lateral of lateral
    • Midline nuclei
  • Subthalamus (subthalamic nucleus, zona incerta)
  • Hypothalamus
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9
Q

What are the common functional principles of the Thalamus?

A
  • Thalamic nuclei “decide” what information passes (to other pts of the cortex or other nuclei)
  • Classification of nuclei – location and input/outputs
  • Consist of projection (majority) and inhibitory neurons
    • mnay are within the reticular nucleus
  • Inputs into the thalamus (two broad groups)
    • Specific – e.g., posterior column/medial lemniscus pathway
      • Glutamate=NT
    • Regulatory – Majority (Cortex, thalamic reticular nucleus, reticular formation, aminergic projections)
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10
Q

What are the three groupings of functional thalamic groups?

A
  1. Specific or relay nuclei
    1. Well defined inputs and projections/outputs
    2. Anterior, ventral anterior (VA), ventral lateral (VL), ventral posterior (*VP), lateral dorsal, medial and lateral geniculate
  2. Association nuclei
    1. Reciprocally connected to association cortex (BUT, dont receive any primary sensory info)
    2. Lateral posterior, pulvinar, medial dorsal nuclei
  3. Non-specific nuclei
    1. Not the same point-to-point connections like relay nuclei
    2. projections to broad areas of cerebral cortex, responsible for level of alertness
    3. Intralaminar and thalamic reticular nuclei
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11
Q

Specific or Relay Nuclei

A
  • **Regulatory Inputs from:
    • cerebral cortex
    • reticular formation
    • reticular nucleus
  • Specific inputs from:
    • subcortical sites
    • basal ganglia
    • cerebellum
    • retina
    • spinal cord
    • sensory info from the ST pathway or medial lemniscus
  • Specific and regulatory inputs both impact the relay nuclei
  • Relay nuclei then projects to functional areas:
    • motor cortex
    • visual cortex
    • somatosensory cortex
    • auditory cortex
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12
Q

How does the specific or relay nucleus ensure specificity?

A

somatotopic organization (**VPN)

  • there is a smaller, ventral posteromedial nucleus for the head (+ mouth)
  • there is also a larger, ventral posterolateral nucleus for the rest of the body (with specific locations for the hands and the feet)

Connections of relay nuclei

  1. from globus pallidus to-VA-to prefrontal cortex
  2. VL
    1. from globus pallidus to-VL-to supplementary motor area
    2. from cerebellum to-VL-to motor cortex
  3. from medial, spinal, and trigeminal tract to-VP(N)-to somatic sensory cortex
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13
Q

Association nuclei

A
  • Regulatory inputs:
    • cerebral cortex
    • reticular formation
    • reticular nucleus
  • Head to, and come back from:
    • (specific inpputs) Association Areas (prefrontal, parietal-occipital-temporal); higher cortical level of interpretation
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14
Q

Non-specific nuclei

A
  • there is a thin sheet of neurons that overlap the thalamus which ocntain the cells of the reticular nucleus but are NOT pt os the reticular formation
  • Factors involved:
    • lemniscal fibers
    • thalamocortical neuron
    • dendrodendritic synapse
    • fiber from reticular formation
    • cells of reticular nucleus
  • act as a sort of filtering mechanism, another layer of regulation
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15
Q

A. What are the four major components of the Internal Capsule?

B. List the important fibers, etc. of the IC

A

A.

  1. anterior limb IC
  2. genu IC
  3. posterior limb IC
  4. retro lentiform part

B.

  • thalamocortical fibers
  • dentatothalamocortical fibers
  • thalamic projection to somatic sensory cortex
  • optic radiation
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16
Q

What are thalamic peduncles?

A
  • thalamus has inputs and outputs (efferents)-tracts/bundles of fibers=thalamic peduncle
  • There are four total: anterior, posterior superior, inferior
17
Q

Six most important (and specific) thalamic nuclei to remember

A
  1. BG, cerebellum-> VA/VL-> motor areas (precentral gyrus, adjacent frontal areas)
  2. **ML, STT (spinal components)->VPL->somatosensory cortex (postcentral gyrus)
  3. **ML, STT (trigem components-position sense+pain->VPM->somatosensory cortex (postcentral gyrus)
  4. brachium of the inferior colliculs (auditory)->medial geniculate->auditory cortex (transverse temporal gyri)
  5. optic tract (visual)->lateral geniculate->visual cortex (occipital lobe)
  6. mammillothalamic tract (from hippocampus)->anterior->cingulate gyrus
18
Q

Vascular (stroke) anatomic lesions and syndromes

A
  • when different parts of the thalamus suffer stroke they are associated with specific neurologic features or problems (related to their primary functions)
  • Anterior: language (dominant) and memory deficits [polar artery]
  • Lateral (VPL, VPN): motor and sensory deficits [thalamogeniculate artery]
  • Medial: vigilance, arousal, and memory deficits [paramedian artery]
  • Posterior: higher visual deficits [posterior choroidal artery]

MHD Neuro (17 decks)

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