Basal Ganglia Flashcards
Why is the term basal ganglia a misnomer?
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).
What constitutes the lentiform nucleus?
Putamen
GP
In which section of the SN is the pars compacta?
RC
The posterior part is the pars compacta
More ventral is the pars reticularis
The traditional classification of BG?
Lentiform nucleus (putamen, GB)
Claustrum
Caudate nucleus
Amygdaloid body
Clinical classification of BG?
Lentiform nucleus
Caudate nucleus
Subthalamus
SN
Corpus striatum=
Caudate nucleus
Putamen
Globus pallidus
Striatum (neostriatum)
Caudate
Putamen
Paleostriatum=
Globus pallidus
Why are the caudate nucleus and putamen grouped as neostriatum?
As they are functionally and embryologically similar
Components of generating motor movement mot
Prefrontal cortex -> Premotor area and SMA -> BG -> Thalamus -> Primary motor cortex-> Corticospinal fibres
Descending connection of cortex with BG
Descending cortical fibres stimulate (glutamate) neostriatum (caudate and putamen) as corticostriatal fibres.
After stimulation by corticostriatal fibres, where do efferents from the striatum go?
GPi (striatopallidal fibres) inhibitory (GABA + Substance P)
What happens after GPi stimulated by striatum?
Sends inhibitory fibres to the thalamus (pallidothalamic fibres) which then feeds back to the cortex (glutaminergic thalamocortical fibres)
When at rest, what is the predominant input on the motor cortex from the basal ganglia?
GPi is actively firing and inhibiting thalamocortical stimulation
How does the direct pathway result in movement?
Corticostriatal fibres cause inhibition of the inhibitory pallidothalamic fibres releasing thalamocortical fibres and allowing corticospinal outflow.
Draw the direct pathway
What is the purpose of the direct and indirect pathway
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
To which part of the GP do striatopallidal fibres of the indirect pathway project?
The GPe
To where do fibres from the GPe project?
Subthalamus
Where do fibres in the indirect pathway project to from the subthalamus?
To the GPi
What fibre loop constitutes the additional part in the indirect pathway?
GPe-> subthalamus -> GPi
What is the consequence of firing of the indirect loop of the basal ganglia
Inhibition of the striatopallidal inhibition of the pallidosubthalamic inhibition of subthalamopallidal excition of the pallidothalamic inhibition of firing.
Net= increased inhibition of thalamocortical firing.
Draw the indirect pathway
Difference between indirect and direct pathway
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.
