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Med Neuro Block 3 > Basal Ganglia: Structure, Circuitry & Function > Flashcards

Basal Ganglia: Structure, Circuitry & Function Flashcards

1
Q

The basal ganglia is located beneath the ________ ______ and lateral to the ______ ________.

A
  • cerebral cortex
  • dorsal thalamus
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2
Q

Components (5):

A
  1. Striatum
  2. Globus pallidus
  3. Subthalamic nucleus (of Luys)
  4. Substantia nigra
  5. Nucleus accumbens: Ventral striatum
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3
Q

Striatum components:

A
  • Caudate nucleus
  • Putamen
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4
Q

Globus pallidus components (2):

A
  • external or lateral segment (GPe)
  • internal or medial segment (GPi)
  • Putamen + Globus Pallidus = lentiform or lenticular nucleus
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5
Q

Substantia nigra components (2):

A
  • pars compacta (SNc; dorsal): dopaminergic
  • pars reticulata (SNr; ventral): GABAergic
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6
Q

Blood supply of the basal ganglia:

A
  • Anterior cerebral artery
    • Medial striate artery
  • Middle cerebral artery
    • Lateral striate artery
    • Anterior choroidal artery
  • Posterior communicating artery
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7
Q

What neurotransmitters are used in the cortex and the striatum?

A

​Cortex ⇒ Striatum

  • Cortex:
    • glutamate
  • Striatum:
    • acetylcholine, GABA, substance P, enkephalin
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8
Q

What is the direct pathway?

A

Striatum ⇒ GPi and SNr ⇒ Thalamus ⇒ Premotor & Supplementary motor area

  • Striatum inhibits the inhibitory output from GPi and SNr to the Thalamus
    • GABA & substance P
  • Thalamus is disinhibited ⇒ excites the cortex
    • released from the inhibitory influence of GPi & SNr (GABA), i.e., excited
  • MOVEMENT IS FACILITATED
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9
Q

What is the indirect pathway?

A

Striatum ⇒ GPe ⇒ Subthalamic ⇒ GPi & SNr ⇒ Thalamus ⇒ Premotor & SMA

  • Involves GPe and the Subthalamic nucleus
  • Striatum inhibits the inhibitory output from GPe to the Subthalamic nucleus
    • Striatum: GABA & Enkephalin
    • GPe: GABA
  • Subthalamic nucleus (released from the inhibitory influence of GPe) excites the GPi and SNr
    • inhibits the Thalamus
    • Subthalamus: Glutamate
    • GPi & SNr: GABA
  • Inhibited Thalamus is less able to excite the Cortex
  • MOVEMENT IS INHIBITED
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10
Q

Nigrostriatal pathway:

A
  • dopaminergic
  • facilitates movement by acting on both direct and indirect pathways
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11
Q

How does dopamine affect the output in the striatum?

A
  • Neurons with D1 dopamine receptors:
    • Excites the Direct Pathway
    • Facilitate movement
  • Neurons with D2 dopamine receptors:
    • Inhibits the Indirect Pathway
      • inhibiting the inhibitory pathway
    • Leads to disinhibition of the thalamus
    • Facilitate movement
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12
Q

What is the end result of dopamine involvement in the basal ganglia?

A

facilitation of movement

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13
Q

Cholinergic neurons in the striatum:

A
  • Acetylcholine is the neurotransmitter of intrinsic neurons in the striatum
  • These cholingergic neurons do not project outside of the striatum
  • Inhibit striatal neurons of the Direct Pathway
  • Excite striatal neurons of the Indirect Pathway
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14
Q

What is the end result of acetylcholine involvement in the striatum?

A

inhibition of movement

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15
Q

Connections outside of the basal ganglia:

A
  1. Extrinsic inputs to the basal ganglia terminate mainly in the striatum. They are from:
    • Cerebral cortex (motor, sensory, association, and limbic): topographical projections (corticostriatal pathway)
    • Intralaminar nuclei of the thalamus: also topographically organized (Thalamostriatal pathway)
  2. Extrinsic outputs from the basal ganglia arise mainly from the globus pallidus and substantia nigra, pars reticulate (SNr)
    • ​Both of them are GABAergic. They project to:
      • Motor nuclei of the thalamus
      • Superior colliculus of the midbrain
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16
Q

Connections within the basal ganglia:

Striatum

A
  • Projects to the globus pallidus
    • ​both internal and external segments
    • striatopallidal pathway
  • Projects to the substantia nigra
    • both reticulata and compacta
  • Reciprocally connected with substantia nigra, pars compacta
    • nigrostriatal and striatonigral pathways
    • SNc ⇒ striatum ⇒ SNc
17
Q

Connections within the basal ganglia:

Subthalamic nucleus (glutamatergic)

A
  • Receives input from the motor and premotor cortices
  • Reciprocally connected with the globus pallidus, external segment
  • Projects to GPi & SNr
18
Q

Connections within the basal ganglia:

Substantia nigra

A

Receives from and projects to the striatum

19
Q

GENERAL FUNCTIONAL SIGNIFICANCE OF THE BASAL GANGLIA:

A
  1. Involved in the regulation of movement:
    • through direct and indirect connections with the cerebral cortex
    • influence descending motor systems
    • corticospinal and corticobulbar tracts
  2. Forms the major component of the extrapyramidal motor system
    • ​​however, there is extensive interconnections and cooperation between the extrapyramidal and the pyramidal systems in the control of movement
  3. Involved in the control of eye movements and in the memory of orientation in space
  4. Contributes to cognition
  5. Related to limbic functions
20
Q
  1. Disorders of the basal ganglia is usually a disruption of ___________ metabolism.
  2. Abnormal movements are commonly caused by a release of the system from __________.
A
  1. transmitter
  2. inhibition
21
Q

Symptoms of basal ganglia dysfunction:

A
  • Involuntary movements: tremor at rest, athetosis, chorea, ballism, and dystonia
  • Akinesia and bradykinesia
  • Changes in posture and muscle tone
  • Muscle rigidity
22
Q

Parkinson’s Disease (Paralysis agitans):

A
  • Degeneration of dopaminergic cells in SNc
  • Tremor at rest, rigidity, and bradykinesia
23
Q

Huntington’s Disease:

A
  • Degeneration of cholinergic and GABAergic neurons in the striatum
  • Inherited; mutation in chromosome 4 causes numerous CAG repeats (encodes for glutamine)
  • Chorea, athetosis, and dystonia
24
Q

Tardive dyskinesia:

A
  • Results from long term use of antipsychotic agents, which block dopamine transmission
  • Involuntary movements, especially of the face and tongue
25
Q

Hemiballismus:

A
  • Lesion of the subthalamic nucleus
  • Violent “ball-throwing” movements of the contralateral arm
26
Q

Cerebellum:

  • Direct input from the spinal cord
  • No direct output to the spinal cord
  • Connections with the brain stem
  • Indirect input from the cortex
  • Projects via thalamus to the cortex
  • Output is excitatory
  • Coordinates the execution of movements:
    • Compares intended with executed
  • Lesion: ipsilateral symptoms
  • Ataxia, impaired balance, intentional tremor
A

Basal ganglia:

  • No input from the spinal cord
  • No direct output to the spinal cord
  • Connects with and part of it is in the brain stem
  • Direct input from the cortex
  • Projects via thalamus to the cortex
  • Output is inhibitory
  • Planning and execution of complex motor strategies:
    • amplitude & velocity of movements
  • Lesion: often contralateral symptoms
    • can be bilateral
  • Too much or too little movements, tremor at rest

Med Neuro Block 3 (14 decks)

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