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Neurology > Basal Ganglia (17) > Flashcards

Basal Ganglia (17) Flashcards

0
Q

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

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

What is the function of the basal ganglia?

A

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

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2
Q

What two structures compose the striatum?

A

Caudate and putamen

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3
Q

What two structures make up the lentiform nucleus?

A

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

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4
Q

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

A
  1. Subthalamic nucleus

2. Substantia nigra

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5
Q

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

A

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)

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6
Q

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

A

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

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7
Q

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

A

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

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9
Q

What structure does the caudate lie just lateral to?

A

The lateral ventricle

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10
Q

The thalamus is located _______ to the putamen

A

Medial

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11
Q

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

A

Insular lobe of cortex

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12
Q

What structure does the tail of the caudate end as?

A

Amygdaloid nucleus (is inferior to the putamen )

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13
Q

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

A

Somatic or Dorsal basal ganglia.

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

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14
Q

What are neostriatum and paleostriatum?

A

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

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15
Q

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

A

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

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16
Q

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

A

Superior colliculus

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17
Q

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

A

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

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18
Q

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

A

Pars compacta—> superior part

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19
Q

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?

A

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

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20
Q

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?

A

Tegmentum (so just superior to 4th ventricle)

*has excitatory input to globus pallidus and substantia nigra

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21
Q

What is a main function of the Subthalamic nucleus?

A

Defines the output rhythm of the basal ganglia

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22
Q

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?

A 
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)
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23
Q

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?

A 
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
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24
Q

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

A

GABA

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25
Q

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

A

To globus pallidus externa (GPe)

26
Q

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

A
  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
27
Q

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

A

Dynorphin

28
Q

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

A

D2 receptors ; their function is to inhibit conflicting movement

29
Q

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

A

D1 receptors

30
Q

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

A

Initiating limb movement

31
Q

What is the function of striato-SNc neurons?

A

Regulate DA neurons in the pars compacta of substantia nigra

32
Q

What is the function of striato-SNr neurons?

A

Initiating eye/head movement

33
Q

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

A

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

34
Q

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

A

Parvalbuminc-containing interneurons

35
Q

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

A

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

36
Q

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

A

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

37
Q

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

A

Modulate projection neurons –> oppose DA action

38
Q

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

A

Inhibit projection neurons—> sharpens activity

* these neurons are lost in Huntington’s disease

39
Q

What structure do fibers from the GPe project to?

A

Subthalamic nucleus

40
Q

What structure do fibers from the GPi project to?

A

Motor thalamus

41
Q

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

A
  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
42
Q

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

A

Pars reticulata of substantia nigra

43
Q

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

A

Pre-motor cortex –> area #6

* is anterior to the motor cortex, the area just anterior to the central sulcus

44
Q

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

A

Motor cortex–> area #4

* motor cortex is just anterior to central sulcus and posterior to the pre-motor cortex

45
Q

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

A

GPi—> motor thalamus—> motor cortices

46
Q

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

A
  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

47
Q

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

A

Pyramidal neurons from layer 5

Aka corticostriatal neurons

48
Q

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?

A

Glutamate - usually on the tips of the spines

49
Q

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?

A

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

50
Q

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

A

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)

51
Q

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

A

Facilitates target-oriented movement

52
Q

What is the function of the indirect pathway?

A

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

53
Q

Basically, how does the direct pathway allow for movement?

A

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

54
Q

Basically, how does the indirect pathway work?

A

Inhibits output from the motor thalamus–> “brakes” for the direct pathway

55
Q

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

A
  1. Nucleus accumbens
  2. Olfactory tubercle
  3. Ventral palladium
    * but the main focus in this lecture is the somatic or dorsal basal ganglia
56
Q

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

A

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

57
Q

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

A

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

58
Q

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

A

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

59
Q

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

A

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

63
Q

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

A

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

64
Q

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

A

The GPi

Neurology (23 decks)

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