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Neuroanatomy > Basal Ganglia > Flashcards

Basal Ganglia Flashcards

1
Q

Why is the term basal ganglia a misnomer?

A

Ganglia are collections of cell bodies outside of the CNS

Should be called basal nuclei (nuclei are collections of cell bodies surrounded by white matter).

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2
Q

What constitutes the lentiform nucleus?

A

Putamen

GP

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3
Q

In which section of the SN is the pars compacta?

RC

A

The posterior part is the pars compacta

More ventral is the pars reticularis

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4
Q

The traditional classification of BG?

A

Lentiform nucleus (putamen, GB)

Claustrum

Caudate nucleus

Amygdaloid body

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5
Q

Clinical classification of BG?

A

Lentiform nucleus

Caudate nucleus

Subthalamus

SN

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6
Q

Corpus striatum=

A

Caudate nucleus

Putamen

Globus pallidus

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7
Q

Striatum (neostriatum)

A

Caudate

Putamen

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8
Q

Paleostriatum=

A

Globus pallidus

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9
Q

Why are the caudate nucleus and putamen grouped as neostriatum?

A

As they are functionally and embryologically similar

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10
Q

Components of generating motor movement mot

A

Prefrontal cortex -> Premotor area and SMA -> BG -> Thalamus -> Primary motor cortex-> Corticospinal fibres

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11
Q

Descending connection of cortex with BG

A

Descending cortical fibres stimulate (glutamate) neostriatum (caudate and putamen) as corticostriatal fibres.

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12
Q

After stimulation by corticostriatal fibres, where do efferents from the striatum go?

A

GPi (striatopallidal fibres) inhibitory (GABA + Substance P)

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13
Q

What happens after GPi stimulated by striatum?

A

Sends inhibitory fibres to the thalamus (pallidothalamic fibres) which then feeds back to the cortex (glutaminergic thalamocortical fibres)

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14
Q

When at rest, what is the predominant input on the motor cortex from the basal ganglia?

A

GPi is actively firing and inhibiting thalamocortical stimulation

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15
Q

How does the direct pathway result in movement?

A

Corticostriatal fibres cause inhibition of the inhibitory pallidothalamic fibres releasing thalamocortical fibres and allowing corticospinal outflow.

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16
Q

Draw the direct pathway

A
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17
Q

What is the purpose of the direct and indirect pathway

A

If you want to flex fingers, not only should the finger flexors activate (direct pathway) but the antagonistic muscles, in this case the finger extensors, should relax, this is mediated through an inhibitory (indirect) pathway

18
Q

To which part of the GP do striatopallidal fibres of the indirect pathway project?

A

The GPe

19
Q

To where do fibres from the GPe project?

A

Subthalamus

20
Q

Where do fibres in the indirect pathway project to from the subthalamus?

A

To the GPi

21
Q

What fibre loop constitutes the additional part in the indirect pathway?

A

GPe-> subthalamus -> GPi

22
Q

What is the consequence of firing of the indirect loop of the basal ganglia

A

Inhibition of the striatopallidal inhibition of the pallidosubthalamic inhibition of subthalamopallidal excition of the pallidothalamic inhibition of firing.

Net= increased inhibition of thalamocortical firing.

23
Q

Draw the indirect pathway

A
24
Q

Difference between indirect and direct pathway

A

Direct pathway shorter

Doesn’t involve the subthalamus

Firing results in disinhibition of thalamocortical fibres leading to them firing.

Indirect pathway longer

Involves subthalamus

Firing causes inhibition of thalamocortical fibres.

25
Q

Which structures in the basal ganglia are derived from the telencephalon?

A

Caudate

Lentiform nucleus

26
Q

What is the role of dopamine in the basal ganglia circuit?

A

Nigrostriatal fibres from the pars compacta project to the putamen and release dopamine on to both the direct and the indirect pathways.

Facilitate initiation of movement.

Therefore it stimulates direct pathway (D1 receptors) and inhibits (D2) indirect pathway.

27
Q

D1 receptors

A

Excitatory

28
Q

D2 receptors

A

Inhibitory

29
Q

Dopaminergic vs glutaminergic action on the indirect pathway?

A

Antagonistic

30
Q

As what should the pars reticularis of the SN be considered?

A

Should be functionally considered as downwards displaced GPi as it has the same connections.

31
Q

What is the counterbalance to dopaminergic action in the putamen?

A

Cholinergic neurones

Has an inhibitory effect on the direct pathway

Has an excitatory effect on indirect pathway

32
Q

What is the aetiology of lead-pipe rigidity in PD?

A

Normally corticoreticular fibres are inhibiting the reticular formation.

In PD there is reduced activity of corticoreticular fibres, this leads to disinhibition of reticulospinal fibres (which normally determine tone)

Subsequently, there will be increased tone in both flexors and extensors.

33
Q

What is the aetiology of tremor in PD?

A

Unopposed cholinergic activity in the lentiform nucleus through overstimulation of reverberating circuits.

Dopamine normally prevents these alternating movements at rest.

34
Q

How does Hungtington’s disease cause chorea?

A

Causes degeneration of GABAnergic (enkephalin) neurones in the indirect pathway (particularly in caudate nucleus).

Causing loss of inhibition of cortical firing-> chorea

35
Q

Different classes of dyskinesia

A

Chorea

Athetosis

Dystonia

Hemiballismus

Tardive dyskinesia

Wilson’s

36
Q

Pathology of HD

A

CAG trinucleotide repeat in Huntingtin gene on chromosome 4

37
Q

Embryological origin of globus pallidus

A

Diencephalon

38
Q

What are the three major sources of input onto striatum

A

Cortex

Intralaminar nuclei of thalamus

Pars compact of the SN

39
Q

What are the three major destinatinos for pallidal efferents

A

Ventral lateral and ventral anterior thalamic nucleiS

STN

Brainstem reticular formation

40
Q

Ventral lateral and ventral anterior thalamic tract

A

Major outflow pathway of the basal ganglia

Fibres projected from the globus pallidus to the thalamus are carried in two bundles- the ansa lenticularis and the lenticular fasciculus.

These fibre bundles fuse to reach the thalamus as the thalamic fasciculus

Thalamic nuclear fibres project to prefrontal and premotor cortex

41
Q
A

Neuroanatomy (18 decks)

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