Basal Ganglia

Question 1

Basic Function of the Basal Ganglia

Answer 1

-movement & modulation

Question 2

Parts of the Basal Gangila

Answer 2

• Caudate Nucleus (very small ventrally placed part called tail of the caudate)
• Putamen
• Globus Pallidus (just internal or medial to putamen)
• Interconnected: subthalamic nucleus

Question 3

Substantia Nigra

Answer 3

• black stuff which is an important cell group interconnected with the basal ganglia (black b/c there are neurons in the substantia nigra that have the black pigment melanin)
• located at base of midbrane
• has axons that travel into the head of the caudate, the putamen, the tail of the caudate, & form dopaminergic terminals there

Question 4

Basal Ganglia: 2 Categories of Structure

Answer 4

• somatic (dorsal) basal ganglia: movement control

- limbic (ventral) basal ganglia: motivation, reward, effect (nucleus accumbens, olfactory tubercle, vetral pallidum)

Question 5

Tail of Caudate Nucleus

Answer 5

-sweeps around posteriorly, bends & comes forward and curls under the main body of the caudate, ending rostrally at the amygdaloid nucleus

Question 6

The thalamus is located ? to theputamen?

Answer 6

medial

Question 7

Striatum

Answer 7

-the caudate & putamen (striped in appearance due to fibers bundles passing through it to & from the cortex)

Question 8

Organization of the Substantia Nigra

Answer 8

• upper part: pars compacta: dopaminergic neurons are arranged in a compact layer (part with melanin)
• below: pars reticulata: net-like mesh of fibers, few dopaminergic neurons (resemble globus pallidus in chemistry, shape & function)

Question 9

Subthalamic Nucleus

Answer 9

• important associated with basal ganglia

- above the cerebral peduncle, below the bulk of the thalamus

Question 10

Stratum

Answer 10

-contains 2 main types of neurons
neurons associated with spiny dendrites & neurons with aspiny dendrites
-Aspiny: 5%, has dendrites that do not possess stubby protrusions on them, 30 microns in width at cell body
-Spiny: 95%, 15 microns in width at cell body

Question 11

Spines

Answer 11

• stubby portrusions coming off dendrites
• specialized for receiving terminals from other brain regions
• neurons that need to integrate info from diverse sources posses spines
• transmit decision to other brain areas

Question 12

Spiny Neuron Appearance

Answer 12

-railroad tract or ladder-like appearance
-long axon that leaves the striatum - projection neurons
(aspiny are short & do not leave the striatum-local circuit neurons or interneurons)

Question 13

Striatal Projection Neurons

Answer 13

• different types of spiny neurons are present in striatum
• differ by projection target & neuropeptide content
• Neurotransmitter: GABA

ENK Neuron: makes GABA & opioid neuropeptide (enkephalin), project to GPe (D2 Type Dopamine)
Substance P-containing striatal projection: makes substance P, project to the GPi, SNc, SNr (D1 Type Dopamine)

Question 14

Neuropeptides

Answer 14

-adjunct neurotransmitters that neurons often use, but they can also be neurochemical signatures for defining neuron subtypes

Question 15

Distribution of Spiny Neurons in Striatum?

Answer 15

• intermingled Substance P & Enkephalin neurons
• Substance P contains another neuropeptide thats also an opioid neuropeptide (dynorphin)
• sub P project to GPi and substantial nigra pars reticulata
• enkephalin project to GPe

Question 16

Striato-GPe Function

Answer 16

-Inhibit conflicting movement

Question 17

Striato-GPi Function

Answer 17

-promote limb movement

Question 18

Striato-SNr Function

Answer 18

-promote eye movement

Question 19

Striato-SNc Function

Answer 19

-regulate DA neurons

Question 20

4 Types of Interneurons in Striatum

Answer 20

1. Cholinergic: target of therapies directed at basal ganglia disease, big cell body, ACh as neurotransmitter - survive in HD
2. Paralbuminergic: has Ca binding protein, GABA neurotransmitter, larger than projection neurons & smaller than large cholinergic interneurons
3. Somatostatinergic: contains somatostatin (also neuropeptide), identify by neurostain, neurotransmitter is GABA/NO, same size as spiny neurons - survive in HD
4. Calretinergic: calcium binding protein, same size as spiny neurons, GABA as neurotransmitter
   - make up 5% of neurons - survive in HD

Question 21

Huntington’s Disease

Answer 21

• does not affect somatostatin interneurons or NPY+
• stratum sustains severe neuron loss & atrophy
• striatal projection neurons, which make up 90% of striatum dies

Question 22

Neurons of Globus Pallidus

Answer 22

• have long aspiny dendrites that form a disk-shaped tree that ramifies in the vertical plane of globus pallidus (GPe, GPi)
• many striatal neurons send their terminals onto the dendrites of any given globus pallidus neuron & any given globus pallidus neuron integrated info from the many striatal neurons that project to it
• both GPe/GPi are GABAergic (send axons out of the globus pallidus to their target area)

Question 23

GPe

Answer 23

-projects to subthalamic nucleus

Question 24

GPi

Answer 24

-projects to motor thalamus (VP & VL)

Question 25

Motor Thalamus

Answer 25

-2 nuclei make up the motor thalamus 1. Ventral Anterior Nucleus 2. Ventral Lateral Nucleus (C - caudalis) (O - oralis) -anterior nuclear group is toward the front, and the pulvinar is toward the back -midline is located above the dorsomedial nucleus VA - located at front of the motor thalamus, VL region behind the VA VL - oral part in front, caudal part in back

Question 26

VA

Answer 26

-projects to pre-motor cortex

Question 27

VL

Answer 27

-projects to motor cortex

Question 28

What are the major sources of input to the striatum?

Answer 28

-cortex, thalamus, substantia nigra (cerebral cortex - almost all projects) (intralaminar thalamus) (dopaminergic input from the substantia nigra pars compacts)

Question 29

Corticostriatal Neurons

Answer 29

- project to striatum - layer 5 pyramidal neurons - also send motor commands to the spinal cord & pre-motor neurons of the hindbrain

Question 30

Location of Dopaminergic Terminals?

Answer 30

-caudate & putamen (not GPe & GPi)

Question 31

Inputs to Striatal Spiny Neurons?

Answer 31

- Cerebral Cortex input ends on the tips of the spines of the spiny neurons (glutamate as neurotransmitter) - Substantia nigra dopaminergic input ends on the sides of the spines (modulate cortical input to spines) - Large aspiny neurons (ACh) - Meidum spiny neurons (GABA)

Question 32

Interplay of Striatal Input to Globus Pallidus & Subthalamic Nucleus Input

Answer 32

- while the GPe projects to the subthalamic nucleus, the subthalamic nucleus mainly projects back to GPi - subthalamic inputs wrap around the smooth dendrites of the GPi neurons, which also receive terminals from striatal substance P-containing neurons