Basal Ganglia (Week 4--Chesselet) Flashcards Preview

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Basal ganglia

Ensemble of interconnected brain regions

Striatum: caudate nucleus and putamen

Globus pallidus (external and internal segments)

Substantia nigra (pars compacta and pars reticulata)

Subthalamic nucleus (only recently included in definition of basal ganglia)


Lentiform nucleus

Putamen and globus pallidus

(just because they are close together)


Are the caudate and putamen separate structures?

Not really, the caudate and putamen are two parts of the same structure (the striatum)

However, the internal capsule (white myelinated fibers) go through this structure to create the caudate medially (near ventricles) and the putamen laterally

Caudate and putamen have same connections, except for somatotopic arrangements


External globus pallidus (GPe) vs. Internal globus pallidus (GPi)

Have VERY different connections and functions

GPe: projects within the basal ganglia; uses GABA; gets input from medium spiny neurons from striatum that use enkephalin; indirect pathway, uses D2 receptors, inhibitory

GPi: projects outside the basal ganglia; uses GABA; gets input from medium spiny neurons from striatum that use substance P; major output pathway of striatum (projects to/inhibits VA,VL of thalamus); direct pathway, uses D1 receptors, excitatory


Substantia nigra pars compacta (SNc) vs. Substantia nigra pars reticulata (SNr)

Very different

SNc: contains dopaminergic neurons projecting to caudate-putamen (striatum)

SNr: contains GABAergic neurons projecting outside the basal ganglia


Ansa lenticularis

Output from the internal pallidum (GPi) to the thalamus

Lenticular fasciculus, or "H2 field of Forel" is same?


Inputs to the basal ganglia

The main "entry" into the basal ganglia is input to striatum

These inputs come mainly from the cerebral cortex


What regions of the cortex project to what regions of the striatum?

Medial cerebral cortex projects to caudate nucleus (more medial!)

Lateral cerebral cortex projects to putamen (more lateral!)


Two things about the cortex to striatum connections that are important to remember

1) Convergence: a huge region of cortex (almost the whole thing) projects to a small striatum

2) Topographical organization: medial cortex projects to caudate and lateral cortex projects to putamen


Inputs to the striatum

Cerebral cortex (not directly though!): uses glutamate

Nigrostriatal pathway (SNc to both putamen and caudate): uses dopamine; modulates input, not direct input (?)

Thalamus (centrum medianum/parafascicular nucleus): uses glutamate

Dorsal raphe: uses serotonin; modulates input, not direct input

Basolateral nucleus of amygdala: uses glutamate


Basal ganglia "loops"

Inputs, outputs and internal connections are topographically organized which results in "parallel circuits"

Motor loop

Oculomotor loop

Prefrontal loop

Limbic loop

So patient with basal ganglia disorder will have symptoms in multiple regions (not just motor!)


Motor loop

1) Motor, premotor, somatosensory cortex

2) Putamen

3) Lateral globus pallidus internal (GPi)

4) Ventral lateral (VL) and ventral anterior (VA) nuclei of the thalamus

5) Primary motor, premotor, supplementary motor cortex


Oculomotor loop

1) Posterior parietal, prefrontal cortex

2) Caudate

3) Globus pallidus internal (GPi), substantia nigra pars reticulata (SNr)

4) Mediodosal and ventral anterior (VA) nuclei of the thalamus

5) Frontal eye field, supplementary eye field


Prefrontal loop

1) Dorsolateral prefrontal cortex

2) Anterior caudate

3) Globus pallidus internal (GPi), substantia nigra pars reticulata (SNr)

4) Mediodorsal (MD) and ventral anterior (VA) nuclei of the thalamus

5) Dorsolateral prefrontal cortex


Limbic loop

1) Amygdala, hippocampus, orbitofrontal, anterior cingulate, temporal cortex

2) Ventral striatum

3) Ventral pallidum

4) Mediodorsal nucleus of the thalamus

5) Anterior cingulate, orbital frontal cortex


Neurons in the cortex vs. neurons in the striatum

Cortex: pyramidal neuron

Striatum: medium spiny neuron


What are the neurons of the striatum?

95% efferent neurons (medium spiny neurons): use GABA; 50% to GPi/SNr use GABA/substance P; 50% to GPe use GABA and enkephalin

5% interneurons: use GABA or ACh; few but important

Note: see that most of the efferent neurons out of the striatum are inhibitory


Main outputs of basal ganglia

Main "exits" are outputs from internal pallidum (GPi) and substantia nigra pars reticulata (SNr)


Types of inputs to caudate vs. putamen

Caudate = cognitive = inputs from limbic prefrontal areas

Putamen = motor = inputs from motor and sensory regions


Medium spiny neuron and output of striatum

Neurons of the striatum

Very spiny dendrites

Spines receive inputs from the cortex (use glutamate)

Shafts receive dopaminergic inputs from SNc (use dopamine)

GABAergic and project outside the striatum

Two main classes based on their output projections (enkephalin output to GPe and substance P output to GPi/SNr)


Interneurons of the striatum

Few interneurons (5%) but they are important functionally

Drugs that block muscarinic ACh receptors help in Parkinson's disease ("dopamine/ACh balance" important therapeutically)

Important in processing cortical info within the striatum


Input to the subthalamic nucleus (of the basal ganglia)

Cortex directly projects to subthalamic nucleus and is excitatory

Called "hyperdirect pathway" and is functionally important


Outputs from the basal ganglia originate from which two regions?

Internal palladium (GPi)

Substantia nigra pars reticulata (SNr)


Outputs from basal ganglia (originating from GPi and SNr) use which NT?



Where do outputs from GPi project to?

Thalamic motor nuclei (VA, VL)

Reticular formation


Where do outputs from SNr project to?

Thalamic nuclei of the thalamus (VA, VL and dorsomedial nucleus)

Reticular formation

Superior colliculus


How does the basal ganglia send information back to the cortex

Via the thalamic motor nuclei (VA, VL)


Dorsal vs. ventral part of internal palladium

Neurons in dorsal part of internal pallidum more involved in movements based on internal cues (remembered sequences)

Neurons in ventral part of internal pallidum more involved in movements guided by external cues


Conections within the basal ganglia

Striatum sends GABAergic projections to GPe, GPi, SNc (just a little), SNr

Two distinct pathways:

1) Striatum --> GPi and SNr (contains GABA and substance P)

2) Striatum --> GPe (contains GABA and enkephalin)


Subthalamic nucleus

Only excitatory pathway WITHIN the basal ganglia (uses glutamate)

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