Basal Ganglia

Question 1

Coloquially, the basal ganglia is known for what function?

Answer 1

Motor learning

Question 2

Answer 2

Question 3

What are the 4 loops of the basal ganglia?

Answer 3

1. Motor
2. Oculomotor
3. Prefrontal
4. Limbic

Question 4

In general, what is the pathway of information in the motor loop of the basal ganglia?

Answer 4

Motor cortex –> striatum –> pallidum –> thalamus –> cortex

Question 5

What are the 2 major functions of the motor loop of the basal ganglia?

Answer 5

Question 6

Answer 6

Question 7

What arteries of the brain supply the basal ganglia?

Answer 7

Anterior cerebral artery

Middle cerebral artery

Posterior cerebral artery

Question 8

The striatum receives excitatory input from the […]

The putamen of the striatum receives inhibitory input from the […]

Answer 8

Cortex

Substantia nigra (pars compacta)

Question 9

There is a direct and indirect pathway for information to get from the cortex through the basal ganglia and to the thalamus (and then ultimately back to the cortex). Describe these 2 pathways

Answer 9

NOTE: only the putamen is shown here, however the circuitry is the same for the caudate nucleus which is also part of the striatum.

Question 10

What is the baseline effect of the basal ganglia acting on the thalamus?

Answer 10

Tonic inhibition (tonic means resting state). Most of the time, the thalamus is being acted upon by the basal ganglia in a manner that inhibits the thalamus from sending feedback to the brain. The inhibition must be lifted from the thalamus in order for a voluntary movement to be performed and for the basal ganglia to tell the cortex “that move was good” or “that move was not good”

Question 11

What is the central goal of the direct pathway and how does it accomplish this goal?

Answer 11

• To release the thalamus from inhibition so that it can increase the likelihood that you will perform the desired intended movement.
• Input from motor cortex causes release of glutamate onto striatum, which causes striatum to release GABA onto the globus pallidus internal and substantia nigra, which results in a decrease in the amount of GABA that these structures release onto the thalamus, thus lowering the level of inhibition of the thalamus. This results in an increase in the excitatory signaling by the motor cortex.

Question 12

What is the central goal of the indirect pathway?

How does it accomplish this goal?

Answer 12

• To increase the inhibition of the thalamus in order to decrease the likelihood that you will perform the undesired or unintended movement
• Motor cortex releases glutamate onto striatum, which causes striatum to release GABA onto globus pallidus external, which inhibits this structure and causes it to release less GABA onto the subthalamic nucleus, which decreases the inhibition of this structure so it can release more glutamate onto the globus pallidus internus, which results in increased GABA secretion by the GPI onto the thalamus which results in increased inhibition of the thalamus, which results in less glutamate from the thalamus going back to the motor cortex and thus decreased muscle movement.

Question 13

The substantia nigra is located in the […] and releases […] onto the […] which is used to […]

Answer 13

Midbrain

Dopamine

Striatum

Modulate the effects of the basal ganglia

Question 14

What effect does dopamine from SN have on the striatum for the direct pathway?

Answer 14

This results in an excitatory response that enhances voluntary movement

Question 15

What effect does dopamine from SN have on the striatum for the indirect pathway?

Answer 15

Inhibits the indirect pathway, which is itself inhibitory of the thalamus. Thus the net result is an increase in thalamic excitation of the cortex

Question 16

How is the substantia nigra altered in Parkinson’s disease?

Answer 16

There is a loss of dopaminergic neurons in the substantia nigra nigrostriatal pathway, which results in less enhancement of voluntary movement so you are less able to make the movements you want to make.

Question 17

What is the main symptom of Parkinson’s disease?

What are the other symptoms?

Answer 17

Hypokinesia (reduced movement b/c you are less able to make the movements you want to make)

• Difficulty initiating movement
• Bradykinesia (slow movement)
• Shuffling gait
• Tremor
• Impaired balance

Question 18

The treatment for parkinson’s disease is L-DOPA.

• Why don’t patient’s just get dopamine directly?
• What other molecule must be given with L-DOPA in order for it to be effective?

Answer 18

• Dopamine doesn’t cross the blood brain barrier, L-DOPA does
• Dopa-decarboxylase inhibitor so that all of LDOPA given does not get converted to Dopamine in periphery

Question 19

Why can anticholinergic medications be effective in treating parkinson’s?

Answer 19

In normal functioning, the actions of Dopamine and Ach on the striatum are kept in balance to coordinate effective motor movements. In Parkinson’s this balance is destroyed by the loss of Dopamine so Ach activation without the presence of Dopamine results in poorly controlled muscle movement. Reducing the effect of Ach signaling in the striatum can restore the balance of Ach and Dopa and decrease symptoms.

Question 20

In huntington’s disease (tri nucleotide repeat disorder), what brain structure is lost?

Answer 20

Striatum

Question 21

What is the main symptom of Huntington’s disease?

What are other important symptoms to recognize?

Answer 21

Hyperkinesia (increased muscle movement that is poorly controlled)

• Involuntary jerking or writhing
• Muscle rigidity
• Slow or abnormal eye movements
• Impaired gait, posture, balance

Question 23

What is hemiballism?

Answer 23

Ballistic movements of the limbs that occur due to damage of the subthalamic nucleus. Following a stroke, these movements are one sided.

Question 24

Answer 24

Question 25

What disease causes the brain pathology seen below?

Answer 25

Huntington’s disease

Question 26

What are the 3 subdivisions of the internal capsule?

Answer 26

Question 27

The internal capsule is a collection of afferent and efferent fibers connecting the cerebral cortex to the brainstem. What are the ascending pathways that run through the:

• Anterior limb
• Genu
• Posterior limb

Answer 27

• Motor tracts and limbic system information
• Somatic sensory
• Visual and auditory

Question 28

The internal capsule is a collection of afferent and efferent fibers connecting the cerebral cortex to the brainstem. What are the descending pathways that run through the:

• Anterior limb
• Genu
• Posterior limb

Answer 28

• Frontal eye fields and frontal pontine fibers
• Corticobulbar and corticoreticular
• Corticospinal and corticorubral

Question 29

Answer 29

Question 30

Answer 30

Question 31

What supplies blood to the head of the caudate nucleus?

Answer 31

Anterior cerebral artery

Question 32

What supplies blood to the putamen and globus pallidus externus?

Answer 32

Middle cerebral artery

Question 33

What supplies blood to the globus pallidus internus and subthalamic nucleus and substantia nigra?

Answer 33

Posterior cerebral artery

Question 34

Answer 34

Question 35

Answer 35

Question 36

Answer 36

Question 37

Answer 37

Question 38

Answer 38

Question 39

Answer 39

Question 40

Answer 40

Question 41

Deep brain stimulation to the […] and […] of the basal ganglia can be used as a treatment for parkinson’s disease.

Answer 41

Globus pallidus interni and subthalamic nuclei —> DBS INHIBITS the action of this area