Anatomy-Basal Ganglia

Question 1

Main components of the basal ganglia

Answer 1

Caudate, Putamen, Globus Pallidus, Subthalamic nucleus, Substantia Nigra

Question 2

Lentiform nucleus

Answer 2

Putamen + Globus Pallidus

Question 3

Corpus striatum

Answer 3

Caudate + Putamen + Globus Pallidus

Question 4

Striatum

Answer 4

Caudate + Putamen

Question 5

What CNS structure does the basal ganglia receive in put from and where does its output go to? What about the cerebellum?

Answer 5

Basal Ganglia: input from prefrontal cortex, output to thalamus and on to supplemental motor area. Cerebellum: input from prefrontal cortex, output to thalamus and on to lateral premotor area.

Question 6

What is the role of the basal ganglia in movement?

Answer 6

Initiating and terminating movements. Regulating the amount of movement executed.

Question 7

What is the role of the cerebellum in movement?

Answer 7

To compare the intended movement with the executed movement.

Question 8

Which nuclei are the input and output nuclei of the basal ganglia? What nuclei are intrinsic to the basal ganglia?

Answer 8

Input: Striatum (caudate/putamen). Output: Medial pallidial segment & Substantia Nigra Pars Reticulata. Intrinsic: lateral pallidial segment and subthalamic nuclei only communicate with other basal ganglia.

Question 9

What other symptoms do you see in patients with problems with their basal ganglia?

Answer 9

Motor dysfunction, oculomotor dysfunction, dementia, personality changes. This is because the oculomotor, prefrontal and limbic loops all run through the same basal ganglia pathway as the motor loop does.

Question 10

Name 4 main inputs to the basal ganglia.

Answer 10

Cerebral cortex (glutamate), Substantia Nigra Pars Compacta (Dopamine), Centromedian nucleus (glutamate), Raphe nuclei (Serotonin)

Question 11

Efferent fibers of the striatum

Answer 11

Spiny neurons. Axons leave the striatum and communicate with other nuclei of the basal ganglia. There are 2 types: neurons that produce GABA/Substance P and others that produce GABA/Enkephalin

Question 12

Interneurons of the striatum

Answer 12

Aspiny neurons. They are completely confined to the striatum and modulate spiny neurons with different neurotransmitters, ACh being the most clinically important.

Question 13

What are the excitatory and inhibitory connections in the basal ganglia?

Answer 13

Direct pathway is inhibitory. Indirect pathway: Excitatory

Question 14

How does the direct pathway modify thalamus activity?

Answer 14

Cerebral cortex releases glutamate on striatum -> GABA/Substance P neurons activated -> GABA released on output nuclei (MPS & SNr) -> output nuclei activity reduced -> thalamus excitation -> glutamate activation of supplemental motor area -> facilitation of movement

Question 15

How does the indirect pathway modify thalamus activity?

Answer 15

Cerebral cortex releases glutamate on striatum -> GABA/Enkephalin neurons activated -> inhibition of lateral pallidal segment -> less GABA released on STN -> increased STN activity -> more glutamate released onto output nuclei -> thalamus inhibited -> activity of SMA inhibited -> movement suppressed.

Question 16

How do the direct pathway and indirect pathway work together?

Answer 16

Direct pathway activates the precise motor movement and the indirect pathway inhibits pathways that may interfere

Question 17

What is the overall effect of acetylcholine released by aspiny neurons on the basal ganglia?

Answer 17

Favors the indirect pathway. ACh binding to GABA/Substance P spiny neurons in the direct pathway inhibits them. ACh binding to GABA/Enkephalin spiny neurons in the indirect pathway activates them.

Question 18

What is the overall effect of dopamine released by the pars compact on the basal ganglia?

Answer 18

Favors the direct pathway. Dopamine binding to GABA/Substance P spiny neuron D1 receptors in the direct pathway activates them. Dopamine binding to D2 receptors on the GABA/Enkephalin spiny neurons and cholinergic aspiny neurons in the indirect pathway inhibits them.

Question 19

Different types of basal ganglia disorders (movement disorders)?

Answer 19

Hyperkinetic: more dopamine or less ACh, direct pathway imbalance. Hypokinetic: less dopamine or more ACh, indirect pathway imbalance.

Question 20

What are symptoms characteristic of Parkinson’s disease?

Answer 20

Bradykinesia, rigidity, resting tremor, postural/gate instability. Loss of dopaminergic neurons in the substantia nigra pushes the basal ganglia balance towards hypokinesia. Consequently patients also have a difficult time starting to walk because initiating movements is difficult with depressed basal ganglia function.

Question 21

Mutation in Huntington’s disease

Answer 21

CAG repeats that cause degeneration of the GABA/Enkephalin neurons in the striatum.

Question 22

Why do patients with Huntington’s disease develop chorea? What other symptoms do they present with?

Answer 22

Degeneration of the GABA/Enkephalin neurons pushes the basal ganglia towards hyperkinesia. They also present with hypotonia, psychiatric symptoms (depression, anxiety, irritability) and dementia.

Question 23

How do you treat Parkinson symptoms?

Answer 23

Supplement dopamine or stimulate the output nuclei

Question 24

How do you treat Huntington symptoms?

Answer 24

Dopamine depletion

Question 25

How does a vascular lesion in the subthalamic nucleus affect the basal ganglia?

Answer 25

Hemiballism. This pushes the basal ganglia towards hyperkinesia, this condition is especially associated with ballismus (flailing movements).