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What is the function of the basal ganglia?

Voluntary movement --> decision to move, direction of movement, motor expression of emotions
*receives cortical input and provides negative feedback to cortex to modulate movement : facilitate intended movements, while suppressing unwanted movements


What are the 3 main parts of the basal ganglia? Are they white or gray matter?

1. Caudate
2. Putamen
3. Globus pallidus (interna and externa)
* these are all gray matter nuclei located deep in the cerebrum, or telencephalon


What two structures compose the striatum?

Caudate and putamen


What two structures make up the lentiform nucleus?

Putamen and globus pallidus
*this is old nomenclature, but may still be used, although is incorrect b/c these two are entirely different structures; caudate and putamen are considered the one striatum b/c they actually share fibers


What two structures are interconnected with the main parts of the basal ganglia, but are structurally part of the diencephalon?

1. Subthalamic nucleus
2. Substantia nigra


Although the caudate and putamen are parts of the same structure, what separates them (as can be visualized on coronal section)?

Internal capsule
* these two are actually part of the same thing and are connected via the nucleus accumbens (a bridge at the anterior part that joins them)


What serves as the input nucleus to the basal ganglia? What kind of input does it receive from cortical and subcortical areas?

Striatum = receives mainly excitatory input from cortical and sub cortical structures


What serves as the output nucleus of the basal ganglia? What kind of output does it send and to what main structure?

Globus pallidus = sends inhibitory projections to the thalamus under normal conditions


What structure does the caudate lie just lateral to?

The lateral ventricle


The thalamus is located _______ to the putamen



What structure does the putamen lie just medial to, which is almost on the surface of the lateral aspect of the cerebrum?

Insular lobe of cortex


What structure does the tail of the caudate end as?

Amygdaloid nucleus (is inferior to the putamen )


The basal ganglia that concerns movement (the one this lecture focuses on) is also called what other two things? What is the other type?

Somatic or Dorsal basal ganglia.
The other is the limbic or ventral basal ganglia and is involved in motivation, reward, and affect


What are neostriatum and paleostriatum?

Completely inaccurate terms based on evolutionary ideas about the brain which are now known to be false


The substantia nigra is located at the base of the midbrain within what other structure?

Cerebral peduncle --> is the midbrain continuation of the internal capsule


The substantia nigra and cerebral peduncle are located at the same level as what posterior surface feature of the brainstem?

Superior colliculus


What kind of neurons are found in the substantia nigra? What two structures to they project to?

Dopaminergic neurons to the striatum and subthalamus
*no fibers to globus pallidus, which is why they are pale; neurons in and originating from the substantia nigra are dark due to the presence of melanin


In what specific region of the substantia nigra are dopaminergic fibers found? Is this the superior or inferior part?

Pars compacta---> superior part


What is the specific part of the substantia nigra that doesn't contain dopaminergic neurons? What basal ganglia structures is it similar to in terms of chemistry, shape, and function?

Pars reticulata--> is inferior part, very similar to the globus pallidus


The Subthalamic nucleus is just inferior to the thalamus and superior to ______ of midbrain. What kind of output does it send and to what 2 structures in the basal ganglia?

Tegmentum (so just superior to 4th ventricle)

*has excitatory input to globus pallidus and substantia nigra


What is a main function of the Subthalamic nucleus?

Defines the output rhythm of the basal ganglia


Which of the two main types of neurons in the striatum a make up 95% of the neuronal bulk? What do they have that the other type doesn't and what does it allow them to do?

Spiny neurons (SN)--> have dendritic spines, so can integrate info from other parts of brain; these neurons send long axons out of the striatum (the other neurons do not(
-also called projection neurons (indicating the fact they leave the striatum)


What are the other type of neurons in the striatum that make up 5% of the neurons within? What kind of neurons do they function as?

Aspiny neurons (A-neurons) ---> are interneurons, so don't send axons out of the striatum; also lack dendritic spines, so cannot integrate information coming in for other parts of brain
* these neurons do have larger cell bodies than do the spiny neurons


Which NT do ALL spiny/projection neurons from the striatum use?



Where do spiny/projection neuron subtype from the striatum that contain ENK (enkephalin) project to in the basal ganglia?

To globus pallidus externa (GPe)


Where do the spiny/projection neuron subtype from the striatum containing Substance P project to in the basal ganglia? (2 main structures)

1. Globus pallidus interna (GPi)
2. Substantia nigra (both pars compacta and pars reticulata!)
* the neurons that go to each of these 3 places are all distinct subtypes of substance P-containing spiny neurons


What other neuropeptide do Substance P-containing spiny neurons contain?



What dopamine receptor do striato-GPe neurons have? (ENK-spiny projection neurons) What is their function?

D2 receptors ; their function is to inhibit conflicting movement


What kind of dopamine receptor do all 3 subtypes of Subtance-P containing striatal neurons possess?

D1 receptors


What is the function of striato-GPi neurons? (Subtype of substance p containing striatal neurons)

Initiating limb movement


What is the function of striato-SNc neurons?

Regulate DA neurons in the pars compacta of substantia nigra


What is the function of striato-SNr neurons?

Initiating eye/head movement


Which of the four aspiny striatal interneuron subtypes doesn't use GABA as a NT? What does it use instead?

Cholinergic striatal interneuron---> uses acetylcholine as a NT
*important therapeutic target for basal ganglia disorders; also have the largest cell bodies of all the interneuron subtypes


Which apsiny striatal neuron subtype has intermediate size cell bodies (larger than spinous, but smaller than cholinergic aspinous)?

Parvalbuminc-containing interneurons


What type of aspinous interneuron also contains NPY and is important because they don't die in Huntington's?

Somatostatin-containing interneuron--> have small cell bodies and use GABA
*all but the cholinergic use GABA


What is the 4th type of interneuron other than cholinergic, parvalbuminergic, somatostatinergic?

Calretinergic interneuron---> also survive in Huntington's, as do cholinergic and SS-ergic


What is the function of the cholinergic interneurons in the striatum?

Modulate projection neurons --> oppose DA action


What is the function of the parvalbuminergic interneurons in the striatum?

Inhibit projection neurons---> sharpens activity
* these neurons are lost in Huntington's disease


What structure do fibers from the GPe project to?

Subthalamic nucleus


What structure do fibers from the GPi project to?

Motor thalamus


What two nuclei comprise the motor thalamus? Which has two subdivisions?

1. Ventral anterior nucleus
2. Ventral lateral nucleus (has caudalis (C) and oralis (O) subdivisions

* VA is at the front of the motor thalamus, and the VL behind the VA; the oralis is towards the front of VL with the caudalis behind


Other than the GPi, what other structure projects to the motor thalamus?

Pars reticulata of substantia nigra


What portion of the cortex does the ventral anterior nucleus of the motor thalamus project to? (Functional region and Brodmann area)

Pre-motor cortex --> area #6
* is anterior to the motor cortex, the area just anterior to the central sulcus


What area of the cortex does the ventral lateral nucleus of the motor thalamus project to? (Functional area and Brodmann area)

Motor cortex--> area #4
* motor cortex is just anterior to central sulcus and posterior to the pre-motor cortex


Output through which two structures therefore are primarily responsible for the basal ganglia's ability to control motor function?

GPi---> motor thalamus---> motor cortices


What are the two major inputs to the striatum? (From where rather)

1. Cerebral cortex (almost all cerebral cortex projects to striatum)
2. Pars compacta of Sunstantia nigra (dopaminergic input)

*also from thalamus (intralaminar thalamus) but function is unknown so don't focus on this


What type of neurons mainly project from the cortex to striatum? What layer of cortex are they found in?

Pyramidal neurons from layer 5
Aka corticostriatal neurons


What type of NT do the corticostriatal (pyramidal) neurons use when synapsing on the dendritic spines of striatal neurons? Where on the spines do these usually synapse?

Glutamate - usually on the tips of the spines


Where do the dopaminergic neurons from the pars compacta of substantia nigra usually synapse on the dendritic spines of striatal neurons? What is the functional importance of this location?

On the sides of the spines, closer to the soma than the glutaminergic corticostriatal input ---> allows the dopaminergic input to modulate the input being received from the cortex


The Subthalamic nucleus receives input from GPe neurons, where does it send projections back to?

To the GPi---> Subthalamic inputs weave around the dendrites of the GPi neurons, which also receive input from the substance P containing striatal neurons
*so GPi neurons recover input from both Subthalamic nucleus and striatum (via substance P containing neurons)


The basal ganglia can be thought of as two parallel striatal output circuits. What is the function of the direct pathway?

Facilitates target-oriented movement


What is the function of the indirect pathway?

Suppresses movement, especially superfluous movement not related to the targeted behavior that the basal ganglia produces.


Basically, how does the direct pathway allow for movement?

Releases the motor thalamus from its tonic inhibition--> more excitatory input to cortex and this more cortical output


Basically, how does the indirect pathway work?

Inhibits output from the motor thalamus--> "brakes" for the direct pathway


What three structures are involved with the limbic or ventral basal ganglia?

1. Nucleus accumbens
2. Olfactory tubercle
3. Ventral palladium
* but the main focus in this lecture is the somatic or dorsal basal ganglia


Describe how the corticostriatal neurons activate movement via the striatum in the direct pathway

Pyramidal corticostriatal neurons release glutamate, an excitatory NT, onto the Substance-P containing neurons --> this increases GABA release in the GPi, inhibiting the normally tonically high basal firing rate of GABA-ergic neurons from GPi to motor thalamus (inhibits the inhibition)---> increased activity from motor thalamus to motor cortex = more cortical stimulation and output --> movement


How does the dopaminergic input from the substantia nigra involved facilitation of the direct pathway?

Stimulation of D1 receptors on Substance P-containing neurons causes them to fire and release GABA onto neurons in the GPi (where these neurons synapse after leaving the striatum) ---> slows the usually high tonic rate of firing from GPi GABA-ergic neurons to motor thalamus----> increased excitation of cortex (motor cortex sends glutaminergic neurons to the cortex)
Basically : enhances the action of corticostriatal neurons, but does so via D1 receptors rather than glutamate


What structure is responsible for the tonic stimulation coming from the substantia nigra?

Subthalamic nucleus--> its fibers excite the SN, which in turn sends fibers back to the Subthalamic nucleus which inhibit it: feedback loop


How does the Substantia nigra play a large role in mediating the indirect pathway? Explain how it works

SN inhibits the action of cholinergic excitatory interneurons in the striatum via D2 receptors--> decreases the release of GABA from ENK neurons the synapse on, which travels to the GPe---> prevents stimulation of GABAergic neurons (and hence downstream inhibition) that leave the GPe and travel to the Subthalamic nucleus---> no inhibition of the excitatory glutaminergic fibers that go from Subthalamic nucleus to the GPi--> excitation of GABAergic neurons from GPi to motor thalamus enhances its inhibition of signaling to cortex
*SN counteracts any stimulatory input coming into stratum from the cortex


How are ENK neurons in the striatum involved in the function of the indirect pathway?

They have D2 receptors--> activated by dopaminergic neurons from SN--> inhibition of neurons to GPe--> inhibit release of GABA from nerves going from GPe to subthalamic nucleus, thus causing increased excitation of the glutaminergic neurons going from subthalamic nucleus to GPi--> stimulation of the GABAergic neurons going from GPi to motor thalamus --> enhanced GABA release/ inhibition of the excitatory glutaminergic neurons going to cortex from motor thalamus= decreased cortical stimulation


Which basal ganglia structure allows the indirect and direct pathways to interact with each other?

The GPi