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Sophie - The Nervous System - Year 2 > 21.4 Basal Ganglia > Flashcards

21.4 Basal Ganglia Flashcards

1
Q

Describe simply the subcortical loops that basal ganglia form.

A
  • Receive information from various cortical areas
  • They then process this information and pass it back to the cortex via the thalamus (ventral anterior and vental lateral nuclei)
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2
Q

The basal ganglia are ………, ………. structures.

A
  • Extrapyramidal (meaning that they do not pass through the pyramids of the medulla)
  • Subcortical
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3
Q

What separates the striatum?

A

Internal capsule lies between putamen and caudate nucleus

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4
Q

What is the neostriatum and paleostriatum?

A

Neostriatum (striatum): Caudate and putamen
Paleostriatum: Globus pallidus internal and external

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5
Q

Where does the basal ganglia receive its input?

A

Cortex (and intralaminar nuclei of the thalamus)
Corticostriatal pathway
Substantia nigra pars compacta (dopamine)

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6
Q

Which structure receives the input neurons?

A

Striatum medial spiny neurons

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7
Q

Summarise simply the function of the basal ganglia.

A
  • They are involved in selection of internally-generated goal-driven movements.
  • This is done because they receive information from the cortical areas and then output back to the pre-motor cortical areas via the thalamus

(In other words, the basal ganglia select motor activity that is not reflex, although it may be almost automatic due to learning)

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8
Q

What are the different basal ganglia you need to know about?

A
  • Striatum
    • Caudate
    • Putamen
  • Globus pallidus
    • Internal segment
    • External segment
  • Subthalamic nucleus
  • Substantia nigra
    • Pars compacta
    • Pars reticulata (similar to GPi)
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9
Q

Label this.

A
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10
Q

What is number 1?

A

Thalamus (Ventral anterior and ventral lateral nuclei)

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11
Q

What is number 2?

A

Caudate nucleus (part of striatum)

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12
Q

What is number 3?

A

Putamen (part of striatum)

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13
Q

What is number 4?

A

Globus pallidus (internal and external segments)

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14
Q

What is number 5?

A

Subthalamic nuclei

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15
Q

What is number 6?

A

Substantia nigra pars compacta

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16
Q

What is number 7?

A

Substantia nigra pars reticulata

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17
Q

Label this.

A
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18
Q

Label this.

A
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19
Q

Draw and describe the subcortical loops that the basal ganglia are involved in.

A
  • The blue box shows all of the basal ganglia
  • The striatum receives input from the cortex
  • It then outputs to the substantia nigra pars reticulata and internal globus pallidus (which are considered together), as well as the external globus pallidus
  • The external globus pallidus and subthalamic nucleus are interconnected, and the subthalamic nucleus also outputs to the substantia nigra pars reticulata and internal globus pallidus
  • Output from the basal ganglia is from the substantia nigra pars reticuluta and internal globus pallidus, to the thalamus and brainstem nuclei
  • The substantia nigra compacta also outputs back to the striatum
  • The thalamus outputs to the cortex and striatum, completing the loop
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20
Q

What are the two main pathways of transmission through the basal ganglia?

A
  • Direct pathway (1) -> Passes from the striatum to the substantia nigra pars reticulata/internal globus pallidus
  • Indirect pathway (2) -> Passes from the striatum to the external globus pallidus to the subthalamic nucleus to substantia nigra pars reticulata/internal globus pallidus to the
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21
Q

Can the neurons in the striatum that pass to the direct and indirect pathway be mapped?

A

No, they are all interspersed throughout the striatum.

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22
Q

Which neurons in the basal ganglia are dopaminergic?

A

Substantia nigra pars compacta

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23
Q

What sort of pathway is the nigrostriatal pathway?

A

Ascending dopaminergic

24
Q

Which basal ganglia pathway do D1 and D2 striatum neurons link to?

A
  • D1 -> Direct
  • D2 -> Indirect
25
Q

What is the function of the direct pathway?

A

Direct pathway is responsible for the INITIATION of movement
Increases firing of thalamus to cortex

26
Q

What is the function of the indirect pathway?

A

Aims to inhibit movements through increasing inhibition on the thalamus

27
Q

What is the overall effect of the a) direct and b) inidrect pathway on the thalamus?

A

a) direct pathway = STIMULATES thalamus by inhibiting SNr/GPi which holds the thalamus under inhibition (disinhibition of the thalamus)
b) indirect pathway = INHIBITS thalamus by activating SNr/GPi which project GABAergic fibres to the thalmus

28
Q

What effect does dopamine release on the striatum have?

A
  • Dopamine is excitatory at D1 receptors, so it stimulates the direct pathway
  • Dopamine is inhibitory at D2 receptors, so it inhibits the indirect pathway

Since the indirect pathway is inhibitory, the dopamine leads to an increase in movement via both pathways.

29
Q

How does the function of the basal ganglia differ to the cerebellum?

A

How does the function of the basal ganglia differ to the cerebellum?

30
Q

What is the nigrostriatal pathway?

A

Pathway which connects the substantia nigra pars compacta (SNc) in the midbrain and the striatum in the forebrain

31
Q

Which structure in the basal ganglia degenerates in Parkinson’s disease

A

Parkinson’s disease involves the degeneration of dopaminergic neurons in the substantia nigra pars compacta

32
Q

Which two places does the SNr/GPi project to?

A

VA/VL thalamus (GABA)
Brainstem: reticular formation, pedunculopontine nucleus, superior colliculus

33
Q

What is the action of the direct pathway on teh VL and VA thalamic nuclei?

A

The direct pathway facilitates movement by exciting the VA and VL thalamic nuclei
*through inhibition of GPi by striatum reducing its inhibitory output to the nuclei. (disinhibition)

34
Q

What is the action of the indirect pathway on the ventral anterior and lateral thalamic nuclei?

A

The indirect pathway inhibits movement by inhibiting the VA and VL thalamic nuclei.
*by inhibition of GPe by the striatum, decreasing its inhibitory effect on STN which then excites GPi, increasing its inhibitory output to VA/L nuclei.

35
Q

What are the principle neurotransmitters involved in the basal ganglia that you need to know? Where is each used?

A
  • Glutamate (excitatory)
    • From cortex to striatum
    • From subthalamic nucleus to internal globus pallidus (and internal globus pallidus + substantia nigra pars reticulata, although not mentioned)
    • From thalamus to cortex and striatum (not in spec)
  • GABA (inhibitory)
    • From striatum, external globus pallidus and internal globus pallidus (+ substantia nigra pars reticulata)
  • Dopamine (excitatory or inhibitory)
    • From substantia nigra pars compacta to striatum
36
Q

What neurotransmitters act on the striatum?

A
  • Glutamate from the cortex
  • Dopamine from the substantia nigra pars compacta
37
Q

What neurotransmitters does the striatum (medium spiny neurons) use?

A

GABA

38
Q

Summarise where glutamate is used in the basal ganglia system.

A
  • From cortex to striatum
  • From subthalamic nucleus to internal globus pallidus
  • From thalamus to cortex and striatum
39
Q

From where is GABA secreted?

A

Striatum, GPe and GPi.

40
Q

Summarise where dopamine is used in the basal ganglia system. What is its action?

A

From substantia nigra pars compacta to striatum
*Activates direct pathway and inhibits indirect pathway.

41
Q

What are Lewy bodies?

A
  • Cytoplasmic depositions in neurons
  • Made of aggregations of insoluble components, including α-synuclein and ubiquitin
  • They are part of Parkinson’s disease pathogenesis, but dopaminergic neurons are not the only ones affected
42
Q

Give an example of a toxin that can give rise to Parkinson’s disease.

A

MPTP

43
Q

What is MPTP toxicity?

A
  • MPTP is a prodrug to the neurotoxin MPP+
  • It causes permanent symptoms of Parkinson’s disease by destroying dopaminergic neurons in the substantia nigra of the brain
  • It does this by entering via dopamine transporters and being sequestered into mitochondria, where it inhibits complex I and leads to cell death
  • It is very rarely found in street drugs that are poorly synthesised (e.g. when trying to synthesise MPPP, an opioid)
44
Q

How can Parkinson’s disease treated?

A

Using L-DOPA (a precursor to dopamine) and carbidopa (an inhibitor of peripheral DOPA decarboxylase).

45
Q

What are some problems with use of L-DOPA to treat Parkinson’s disease?

A
  • The effects wear off after a few years -> On/off effects, such as gait freezing
  • There are also L-DOPA-induced dyskinesias (involuntary movements)
46
Q

How can Huntington’s disease be treated?

A

Using an anti-dopaminergic, such as:

  • Tetrabenazine
  • Neuroleptics
  • Benzodiazepines

This combats the imbalance between the direct and indirect pathways, so that the feedback to the cortex is reduced.

47
Q

What is degenerated in PD?

A

nigrostriatal dopamine neurons

48
Q

What is degenerated in Huntington’s disease.

A

GABA neurons (striatopallidal)

49
Q

Name a syndrome which has hypokinesia as a symptom

A

Parkinson’s (Hypokinesia = slow and decreased body movements)

50
Q

Name a syndrom which has hyperkinesia as a symptom?

A

Hutington’s
Ballism
Tourettes
Hyperkinesia = increase in muscular activity resulting in excess of movements

51
Q

What is Ballism? How does it differ from chorea?

A

Repetitive, but constantly varying, large amplitude involuntary movements of the (proximal parts of the) limbs
Violent flinging
Usually on one side of the body = hemiballismus
Chorea generally in the DISTAL limbs

52
Q

What can cause ballism?

A

Subthalamic lesions

53
Q

What are the words which describe the inability to make voluntary movements?

A

AKINESIA = inability to initiate voluntary movement
Bradykinesia = Slowness of initiation of voluntary movement with a progressive reduction in speed and range of repetitive actions

54
Q

What is meant by involuntary movements?

A

Tics (fast repeptitive movements
Tremors (at rest = parkinsons, intention tremor = cerebellum lesion)
Dystonia (muscles contract involuntarily and are rigid = Huntington’s)

55
Q

What are the symptoms associated with Parkinson’s disease?

A

Akinesia (hypokinesia and bradykinesia-slow initation of volutnary movement)
Tremor AT REST - involuntary
Rigidity
Postural instability
Shuffling gait

56
Q

What are the symptoms associated with Huntington’s? (4)

A

Chorea (irregular, involuntary and unpredictable movements - look restless and figidity like dancing)
Dystonia - muscles contract involuntarily
Rigidity
Cognitive decline = aggressive then depressed
(striatal atrophy)

Sophie - The Nervous System - Year 2 (46 decks)

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