Basal Ganglia

Question 1

What are basal ganglia?

Answer 1

Neural structures deep within cerebral hemispheres

Question 2

What is the function of basal ganglia?

Answer 2

Regulate movement

Process info. relating to emotion, motivation and cognition

Question 3

How do basal ganglia regulate movement?

Answer 3

• regulate intensity of slow/stereotypes movements
• inhibit antagonistic unnecessary movements
• switch motor programs to stop or start movements

Question 4

What are the neural structures within the basal ganglia?

Answer 4

• caudate nucleus
• putamen
• globus pallidus
• substantia nigra (motor)
• subthalamic nucleus (motor)

Question 5

What are the features of the caudate nucelus?

Answer 5

C shaped
in frontal lobe
head, body, tail
tail tapers ending in temporal lobe

Question 6

What are the features of the putamen?

Answer 6

Large rounded
Forebrain
Connected to caudate at caudate head region

Question 7

What are the features of the globus pallidus?

Answer 7

Internal segment (GPi) sends output to thalamus
External segment (GPe) relays info between basal ganglia nuclei and globus pallidus

Question 8

What are the features of internal capsule?

Answer 8

White matter structure

Separates lentiform nucleus and caudate nucleus

Question 9

What is the blood supply to the caudate nucleus?

Answer 9

Middle cerebral artery

Anterior cerebral artery

Question 10

What is the blood supply to the putamen?

Answer 10

Middle cerebral artery

Anterior cerebral artery

Question 11

What is the blood supply to the globus pallidus?

Answer 11

Middle cerebral artery

Anterior choroidal

Question 12

What is the blood supply to the internal capsule?

Answer 12

Middle cerebral artery
Anterior cerebral artery
Anterior choroidal

Question 13

What is the input into the basal ganglia?

Answer 13

Cerebral cortex (frontal and parietal)
Substantia nigra

Question 14

How does the cerebral cortex project to the basal ganglia?

Answer 14

Project directly to caudate nucleus and putamen
From association areas in frontal and parietal cortex
Projections are corticostriatal pathway

Question 15

How does the substantia nigra project to the basal ganglia?

Answer 15

In midbrain
Dopaminergic input to caudate nucleus and putamen
Nigrostriatal pathway

Question 16

Where do the substantia nigra and cerebral cortex input into?

Answer 16

Input zone of basal ganglia

caudate nucleus and putamen = corpus striatum

Question 17

What are the main neurons in the corpus striatum?

Answer 17

Medium spiny neurons

75%

Question 18

What does corpus striatum convergence produce?

Answer 18

dendritic trees of medium spiny neurons 
inputs converge = 
- cortical neurons (glutamatergic)
- substantia nigra neurons (dopaminergic)
- local circuit neurons (GABAergic)

these all converge on globus pallidus and substantia nigra reticulata

Question 19

What is the order of the corpus striatum convergence?

Answer 19

Cortex -> corpus striatum -> globus pallidus external -> globus pallidus internal or substantia nigra reticulata

Question 20

What is the output of the basal ganglia?

Answer 20

• subthalamic nucleus
• VA/VL thalamic nuclear complex
• superior colliculus (controls eye movement)

Question 21

What are the features of the subthalamic nucleus?

Answer 21

small paired nuclei
below thalamus
input from cerebral cortex and external globus pallidus
projects to internal globus pallidus and substantia nigra reticulata

Question 22

What are the features of the VA/VL thalamus complex?

Answer 22

Input from internal globus pallidus
Projects directly to motor cerebral cortex areas
Loop within cerebral cortex

Question 23

What is the input into the corpus striatum?

Answer 23

Cortical

Via excitatory glutamate neurons

Question 24

Where are there inhibitory neurons?

Answer 24

Corpus striatum and globus pallidus

GABAergic inhibitory neurons

Question 25

What is disinhibition?

Answer 25

Inhibition of inhibition Produces excitation Double inhibition 2 inhibitory neurons in sequence

Question 26

What is an example of a direct pathway?

Answer 26

Excitatory Glutamatergic axons -> caudate and putamen -> internal globus pallidus -> motor thalamus and back to motor cortex

Question 27

What is an example of an indirect pathway?

Answer 27

Caudate and putamen inhibit globus pallidus external which inhibits subthalamic nucleus which excites globus pallidus internal which inhibits motor thalamus so that motor thalamus remains fixed and so supplementary motor cortex output remains fixed

Question 28

When is the direct and indirect pathway active/inactive?

Answer 28

At rest/undergoing repetitive movement => direct inactive and indirect is active Tonic inhibitory input to motor thalamus prevents change in movement When you want a change in movement direct pathway becomes active

Question 29

What receptors are expressed by the corpus striatum neurons?

Answer 29

D1 or D2

Question 30

What is the role of the D1 receptor?

Answer 30

- increases cAMP - increases sensitivity of corpus striatum neurons to glutamate - projects to internal globus pallidus directly

Question 31

What is the role of dopamine on pathways?

Answer 31

Increases action of direct pathway via D1 receptors to activate motor program change Decreases action of indirect pathway via D2 receptors to block motor program change

Question 32

What is the role of dopamine?

Answer 32

Allows motor programs to change and stop and start

Question 33

What are hypokinetic movement disorders?

Answer 33

e. g. Parkinson's - if balance of inhibitory signals in direct and indirect pathways are altered - can also get hyperkinetic movement disorders which is not PD

Question 34

What are the characteristics of Parkinson's?

Answer 34

Resting tremor Slowness of movement (bradykinesia) Muscular rigidity Minimal facial expressions

Question 35

What is the cause of motor function defects in Parkinson's?

Answer 35

- loss of dopaminergic neurons in substantia nigra compacta which project to caudate and putamen

Question 36

What are the 3 stages of Parkinson's?

Answer 36

- early: cardinal symptoms, no medication related complications - PD with motor and non-motor complications, medication side effects, unrelieved symptoms - advanced life limiting with significant disability

Question 37

How to manage early PD?

Answer 37

Levodopa Dopamine agonists MAO-B inhibitor

Question 38

How to manage 2nd stage PD?

Answer 38

COMT inhibitor Apomorphine Amantadine

Question 39

How to manage 3rd stage PD?

Answer 39

Deep brain stimulation

Question 40

What is an example of a hyperkinetic movement disorder?

Answer 40

Huntington's

Question 41

How is Huntington's inherited?

Answer 41

- autosomal dominant

Question 42

What are the characteristics of Huntingtons?

Answer 42

Mood alterations Personality alterations Defects in memory and attention Involuntary movements

Question 43

What causes Huntington's?

Answer 43

Defects in motor function due to loss of GABAergic neurons in corpus striatum which project to globus pallidus

Question 44

What is chorea?

Answer 44

Rapid involuntary jerk type movements, non-purposeful, dance like, distal Greek to dance

Question 45

What is athetosis?

Answer 45

Slow involuntary smooth writing type movements, non-purposeful, writhing, distal Greek to throw

Question 46

What is ballismus?

Answer 46

Rapid involuntary wild flinging type movements, non-purposeful, wild flinging, proximal greek for not fixed