Basal ganglia

Question 1

caudate (caudate nucleus)

Answer 1

One of the three major components of the basal ganglia (the other two are the globus pallidus and putamen).

Question 2

corpus striatum

Answer 2

General term applied to the caudate and putamen; name derives from the striated appearance of these basal ganglia nuclei in sections of fresh material.

Question 3

external segment

Answer 3

A subdivision of the globus pallidus.

Question 4

globus pallidus

Answer 4

One of the three major nuclei that make up the basal ganglia in the cerebral hemispheres; relays information from the caudate and putamen to the thalamus.

Question 5

hemiballismus

Answer 5

A basal ganglia syndrome resulting from damage to the subthalamic nucleus and characterized by violent involuntary movements of the limbs.

Question 6

Huntington’s disease

Answer 6

An autosomal dominant genetic disorder in which a single gene mutation results in personality changes, progressive loss of control of voluntary movement, and eventually death. Primary target is the basal ganglia.

Question 7

internal segment

Answer 7

A subdivision of the globus pallidus.

Question 8

medium spiny neuron

Answer 8

The principal projection neuron of the caudate and putamen.

Question 9

Parkinson’s disease

Answer 9

Neurodegenerative disease of the substantia nigra that results in a characteristic tremor at rest and a general paucity of movement.

Question 10

putamen

Answer 10

One of the three major nuclei that make up the basal ganglia (the other two are the caudate and the globus pallidus).

Question 11

substantia nigra

Answer 11

Basal ganglionic nucleus at the base of the midbrain that receives input from several cortical and subcortical structures. The cells of the substantia nigra pars compacta send their output to the caudate/putamen, while the cells of the substantia nigra pars reticulata send their output to the thalamus.

Question 12

subthalamic nucleus

Answer 12

A nucleus in the ventral thalamus that receives input from the caudate/putamen and participates in the modulation of motor behavior.

Question 13

What is the difference between the basal ganglia and the extrapyramidal system?

Answer 13

The term “extrapyramidal” includes all of the regions that affect movement other than the corticospinal tracts. These are all of the areas that influence motor performances other than those that directly generate the movement. The basal ganglia are part of this, but also the cerebellum. They don’t produce weakness or significant reflex changes, but can severely affect other aspects of motor performance.

Question 14

What are the components of the basal ganglia?

Answer 14

This is not a definitive list, but always includes the striatum (caudate and putamen), the globus pallidus (interna and externa), the subthalamic nucleus and the substantia nigra (pars compacta and reticulata). Some people include the VA/VL of the thalamus and another thalamic nucleus (the centromedian, which we did not discuss).

Question 15

What are the most important connections of the direct pathway?

Answer 15

Cerebral cortex to striatum (medium spiny neurons); striatum to GPi; GPi to VA/VL of the thalamus; VA/VL of the thalamus back to the cortex.

Question 16

Which of these pathways, striatum to GPi and the projection of GPi to VA/VL of the thalamus, are inhibitory (which ones are comprised of neurons releasing GABA)?

Answer 16

The projection of the striatum to GPi and the projection of GPi to VA/VL of the thalamus are both inhibitory.

Question 17

Where are the neurons located that provide dopamine to the basal ganglia?

Answer 17

They are in the substantia nigra, pars compacta.

Question 18

What does dopamine do to the direct pathway and how does it do that?

Answer 18

Dopamine excites the direct pathway by acting on D1 dopamine receptors on medium spiny neurons in the striatum. The medium spiny neurons in the direct pathway only express D1 receptors.

Question 19

When the direct pathway is activated what happens to the activity of neurons in each of the components of the direct pathway?

Answer 19

Activity in the direct pathway excites striatal neurons => inhibits tonic activity of GPi neurons => decreases inhibition of (i.e., excites) VA/VL neurons => excites cerebral cortical neurons.

Question 20

What are the symptoms of overactivity and underactivity of the direct pathway?

Answer 20

Overactivity produces abnormal, erratic, involuntary movements when attempting to move; underactivity produces difficulty initiating movement and slowness of movement.

Question 21

What are the most important connections of the indirect pathway?

Answer 21

erebral cortex to striatum (medium spiny neurons); striatum to GPe; GPe to subthalamic nucleus; Subthalamic nucleus to GPi; GPi to VA/VL of the thalamus; VA/VL of the thalamus back to the cortex.

Question 22

What does the indirect pathway do with regard to the area of cerebral cortex that it terminates in?

Answer 22

The indirect pathway decreases excitatory feedback from the thalamus to the cerebral cortex, resulting in broad inhibition of the region of the cortex.

Question 23

What does dopamine do to the indirect pathway and how does it do that?

Answer 23

Dopamine inhibits the indirect pathway by acting on D2 dopamine receptors on medium spiny neurons in the striatum. The medium spiny neurons in the indirect pathway only express D2 receptors.

Question 24

When the indirect pathway is activated what happens to the activity of neurons in each of the components of the indirect pathway?

Answer 24

Activity in the indirect pathway excites striatal neurons => inhibits tonic activity of GPe neurons => decreases inhibition of (i.e., excites) subthalamic nucleus neurons => increases tonic activity of GPi neurons => increases inhibition of VA/VL neurons => decreases excitation (i.e., inhibits) cerebral cortical neurons.

Question 25

What are the symptoms of overactivity and underactivity of the indirect pathway?

Answer 25

Overactivity produces generalized stiffness (rigidity) and slowness of movement; underactivity produces widespread, erratic involuntary movements at rest (chorea, athetosis and dystonia).

Question 26

What two nuclei are overactive in patients with Parkinson disease?

Answer 26

The GPi and the subthalamic nucleus are overactive (as is the Substantia nigra, pars reticulata).

Question 27

What is the difference between rigidity and spasticity?

Answer 27

igidity (which is due to extrapyramidal disease) has normal reflexes but markedly increased tonic activity of muscles that produces stiffness during attempted passive movement. It a slight tremor is present during this attempted passive movement, this is perceived as a ratchety feel (cogwheeling). Spasticity is due to increased muscle stretch reflexes (typically due to loss of descending inhibition). Quick movements are more resisted than slower movements and there may be a second reflex after the initial contraction, that being an overactive inverse myotatic reflex. This give the feel of a quick jerk followed by a relaxation (often called "class knife" spasticity. Basically, some level of spasticity accompanies hyper-reflexia associated with most severe upper motor neuron damage.

Question 28

What is the consequence of degeneration of medium spiny neurons (which are in the striatum) that are in the indirect pathway, such as occurs in Huntington disease?

Answer 28

This results in loss of the tonic inhibition afforded by the indirect pathway. This produces widespread, erratic involuntary movements at rest (chorea, athetosis and dystonia).

Question 29

What movement disorder is seen with major lesions of the subthalamic nucleus?

Answer 29

There is a flinging motion called hemiballism. This is most obvious when the patient attempts to hold the outstretched limb still.

Question 30

which side of the body would be symptomatic with unilateral damage to basal gangliar components?

Answer 30

The contralateral side.

Question 31

What are the basal ganglia components of the mesolimbic dopamine reward circuitry?

Answer 31

Ventral striatum.