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

Basal Ganglia: Structure, Circuitry and Function Flashcards

1
Q

Basal ganglia is embryonically developed from

A

telencephalon mainly

and also the diencephalon and the mesencephalon

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2
Q

What makes up the striatum

A

caudate nucleus and putamen

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3
Q

What makes up the lenticular n. or the lentiform n.

A

putamen and globus pallidus (external/lateral segment and internal/medial segment)

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4
Q

what makes up the basal ganglia

A
  • caudate nucleus
  • globus pallidus (internal and external segment)
  • Subthalamic nucleus
  • Substantia nigra: pars compacta and pars reticula
  • Nucleus accumbens=ventral striatum
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5
Q

The basal banglia is supplied by

A
  1. anterior cerebral artery branch: medial striate artery
  2. Middle cerebral artery branches: Lateral striate artery and anterior choroidal artery
  3. Posterior communicating artery
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6
Q

What is the effect of the indirect pathway

A
  • thalamus is inhibited

- movement is inhibited

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7
Q

What is the effect of the direct pathway

A
  • thalamus is disinhibited

- movement is facilitated

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8
Q

Describe the direct pathway

A
  • Cortex excites Striatum (Caudate and Putamen)
  • Striatum inhibits Globus Pallidus and Substantia nigra
  • Substantia Nigra (pars reticula) and Globus pallidus (internal segment) inhibit Thalamus. BUT bc they were inhibited they don’t really inhibit the thalamus so the thalamus is disinhibited
  • The disinhibited thalamus excites the supplementary motor area and premotor cortex
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9
Q

Describe the Indirect Pathway

A
  • Cortex excites Striatum (Caudate and putamen)
  • Striatum inhibits Globus pallidus (external segment)
  • Globus pallidus (external segment) inhibits Subthalamic nucleus
  • Subthalamic nucleus excites Globus pallidus (internal segment) and Substanstia nigra (pars reticulata)
  • Bc globus pallidus (internal segments) and substantia nigra (pars reticulata) were activated they are now able to fully inhibit the thalamus so the thalamus is inhibited and movement is inhibited
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10
Q

What are the two components of the circuits that are the main output for the basal ganglia

A
  • Globus pallidus (internal segment) and Substantia Nigra (pars reticulata)
  • They are inhibitory
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11
Q

In general is the basal ganglia excitatory or inhibitory

A

inhibitory

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12
Q

is the cerebellum excitatory or inhibitory

A

excitatory

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13
Q

Describe the Nigrostriatal pathway

A
  • substantia nigra pars compacta releases dopamine which works on the striatum.
  • works on both the direct and indirect pathways to facilitate movement
  • involed in parkinsons
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14
Q

what are the two types of output neurons in the striatum that dopamine affects

A

Neurons with D1 dopamine receptors

Neurons with D2 dopamine receptors

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15
Q

Neurons with D1 dopamine receptors

A

-excite the direct pathway (which facilitates movement)

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16
Q

Neurons with D2 dopamine receptors

A

Inhibits indirect pathway (which inhibits movement) which leads to disinhibition and facilitates movement!

you are inhibiting the pathway that inhibits movement, so movement is not inhibited, it is facilitated

17
Q

Thus what is the effect of dopamine

A

to facilitate movement

18
Q

Effect of Ach on the striatal neurons

A
  • Inhibit striatal neurons of the Direct pathway
  • Excite striatal neurons of the indirect pathway
  • Both result in inhibition of movement
  • these effects are opposite of dopamine which facilitates movement by exciting the direct and inhibiting the indirect
19
Q

Extrinsic inputs to the basal ganglia terminate mainly

A

in the striatum

20
Q

Extrinsic inputs to basal ganglia terminate mostly in the striatum (caudate and putamen) they are from:

A

-Cerebral cortex (motor, sensory,
association, and limbic): topographical
projections (corticostriatal pathway)

-Intralaminar nuclei of the thalamus: also
topographically organized
(Thalamostriatal pathway

21
Q

Extrinsic output from the basal ganglia arises

mainly from

A

the globus pallidus and substantia

nigra, pars reticulata. which are both GABAergic

22
Q

where do the output signals from the globus pallidus and substantia nigra (pars reticulata) project to

A
  • motor nucleus of the thalamus

- superior colliculus of the midbrain

23
Q

How does the Striatum connect within the basal ganglia

A

-Projects to globus pallidus, both internal (direct) and external (indirect) segments (striatopallidal
pathway)

-Projects to substantia nigra, both reticulata (direct) and compacta (Striatonigral)

-Reciprocally connected with substantia nigra, pars compacta (nigrostriatal and
striatonigral pathways)

24
Q

How does the Subthalamic nucleus (glutamatergic) make connections within the basal ganlgia

A
  • Receives input from the motor and premotor cortices
  • Reciprocally connected with the globus pallidus, external segment
  • • Projects to globus pallidus, internal segment and substantia nigra, pars reticulata
25
Q

How does the substantia nigra make connections within the basal ganglia

A

Receives from and projects to the striatum

Striatonigral and Nigrostriatal

26
Q

General Functional significance of the basal ganglia

A
  • involved in the regulation of movement: through direct and indirect connections with the cerebral cortex, the basal ganglia influence descending motor systems (e.g. corticospinal and corticobulbar tracts)
  • involved in habit learning and skill acquistion
  • forms the major component of the extrapyramidal system: however there are extensive interconnections and cooperation between the extrapyramidal and the pyramidal system n the control of movement
  • involved in the control of eye movements and the memory of orientation in space
  • contributes to cognition
  • related to limbic functions
27
Q

Dysfunctions of the basal ganglia

A
  • disorders of the basal ganglia are usually a disruption of transmitter metabolism
  • abnormal movements are commonly caused by a release of the system from inhibition
28
Q

symptoms of basal ganglia disfunction

A

-involuntary movements:
*tremor at rest
*athetosis
*chorea
*ballism
*dystonia
-akinesia and bradykinesia
changes in posture and muscle tone
-muscle rigidity

29
Q

Parkinson’s Disease (Paralysis agitans)

A
  • degeneration of dopaminergic cells in SNc

- tremor at rest, rigidity, bradykinesia

30
Q

Huntington’s Disease

A
  • degeneration of cholinergic and GABAergic neurons in the striatum
  • inherited; mutations in chromosome 4 causes numerous CAG repeats (encodes for glutamine)

-choreas, athetosis, dystonia

31
Q

Tardive dyskinesia

A
  • results from long-term use of antipsychotic agents, which block DA transmission
  • involuntary movements especially of the tongue and face
32
Q

Hemiballismus

A
  • lesion of the subthalamic nucleus

- violent “ball-throwing” movements of contralateral arm

33
Q

Similarities between cerebellum and Basal Ganglia

A
  • no direct output to the spinal cord
  • connections with the brainstem
  • projections via thalamus to cortex
34
Q

Differences between the cerebellum and the basal ganglia

A
  • cerebellum has direct input from the spinal cord, and the basal ganglia has no input from the spinal cord
  • cerebellum has INDIRECT input from the cortex, and basal ganglia has DIRECT input from the cortex
  • cerebellar output is excitatory and basal ganglia output is inhibitory
  • cerebellum coordinates the execution of movements and compares them with intended movements, the basal ganglia PLANS and executes complex motor strategies: amplitude and velocity of movement

-Cerebellar lesion=ipsilateral symptoms
and
basal ganglia lesion=often contralateral but sometime can be bilateral

-cerebellar lesions cause ataxia, impaired balance, and intentional tremor,
and
basal ganglia lesions cause too much or too little movements, and tremor at rest

Med Neuro Block 3 (10 decks)

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