Basal Ganglia

Question 1

What is the role of basal ganglia? (4 answers)

Answer 1

Regulate intensity of slow movements
Inhibit unnecessary movement
Regulate cognition
Motor program switch

Question 2

What five structures are included in the basal ganglia?

Answer 2

Caudate, putamen, globus pallidus, substantia nigra and subthalamic nucleus

Question 3

Define basal ganglia.

Answer 3

Collection of nuclei situated deep within the cerebral hemispheres.

Question 4

What is disinhibition? How does it relate to basal ganglia?

Answer 4

Excitation by double inhibition, i.e. when there are two inhibitory neurons in sequence. The direct pathway is excitatory to the motor thalamus by disinhibition.

Question 5

How many % of substantia nigra dopamine cells have to be dead before clinical signs of Parkinson’s disease show?

Answer 5

More than 80%

Question 6

What is the cause of Parkinson’s disease? What is the consequence on substantia nigra cells?

Answer 6

The loss of dopaminergic input to caudate and putamen. The cells in the substantia nigra degenerate and are lost.

Question 7

What are the four classic motor signs of Parkinson’s disease?

Answer 7

Tremor at rest
Rigidity
Bradykinesia
Loss of postural reflexes

Question 8

What three parts compose the corpus striatum?

Answer 8

Caudate nucleus, putamen, and globus pallidus

Question 9

How many parts of the globus pallidus are there? How many of substantia nigra? Name them.

Answer 9

External and internal GP
Pars compacta (input)  and pars reticulata (output)

Question 10

What comprises the dorsal striatum? What about the ventral striatum?

Answer 10

Dorsal = caudate and putamen
Ventral = accumbens

Question 11

Where is the substantia nigra? Where is the subthalamic nucleus?

Answer 11

Base of midbrain

Ventral thalamus

Question 12

Where does the head of the caudate nucleus fit into? Where does the caudate nucleus end?

Answer 12

The lateral aspect of the anterior horn of the lateral ventricle (concave recess).
The temporal lobe.

Question 13

Which nuclei forms the lateral wall of the lateral ventricle? (Coronal section)

Answer 13

Caudate

Question 14

Input to the basal ganglia

Answer 14

Forebrain - frontal cortex, parietal cortex,temporal cortex

Midbrain - substantia nigra (pars compacta)

Question 15

Output from basal ganglia

Answer 15

Thalamus and cortex

Question 16

What is the main type of neuron involved with basal ganglia?

Answer 16

Medium spiny neurons

Question 17

How many places does a dopaminergic axon synapse on a medium spiny neuron?

Answer 17

Three - cell bodies, spines and dendritic shafts

Question 18

Describe convergence in terms of basal ganglia loops.

Answer 18

There are large dendritic trees of striatal output neurons (medium spiny neurons) and decreasing cell number.
The cortex has 150,000,000 neurons which reach 30,000 in the striatum, which reach 100 in the external GP and 1 in the internal GP.

Question 19

What is ballismus? What is athetosis? What causes them?

Answer 19

Involuntary sudden jerky movements.
Involuntary smooth ‘sinuous’ movements.
Both caused by damage to cells in striatum, i.e. in Huntington’s.

Question 20

How is Huntington’s managed?

Answer 20

Neuroleptics (dopamine antagonists)
Atypical antipsychotics
SSRI for depression
Benzodiazepines

Question 21

What causes Huntington’s?

Answer 21

It is hereditary (autosomal dominant mutation).

The symptoms are caused by loss of GABA-ergic neurones in striatum.

Question 22

How can Huntington’s be seen in MRI?

Answer 22

Enlargement of ventricles and shrinkage of basal ganglia

Question 23

Symptoms of Huntington’s

Answer 23

Hyperkinesis
Extra involuntary movements
Dementia

Question 24

How is Parkinson’s treated?

Answer 24

Early PD - levodopa, dopamine agonists, MAO-B inhibitors
PD with motor and non-motor complications - same PLUS COMT inhibitors, apomorphine, amantadine
Advanced life-limiting PD - deep brain stimulation

Question 25

Describe the steps of the direct pathway (basal ganglia).

Answer 25

Excitatory (glutamate) axons from the sensory and association cortices –>caudate and putamen

• ->internal globus pallidus (VIA GABA so inhibitory)
• ->motor thalamus (EXCITATORY BY DISINHIBITION, as internal GP normally has tonic inhibition to thalamus)
• ->supplementary motor cortex (excitatory)

ALSO The substantia nigra excitatory dopaminergic axons –>caudate and putamen

Outcome is…change in cortical motor program.

Question 26

Describe the steps of the indirect pathway (basal ganglia).

Answer 26

The output from the caudate/putamen

• -> the external globus pallidus (inhibitory)
• -> subthalamic nucleus (inhibitory)
• -> internal globus pallidus (excitatory)
• -> motor thalmus (inhibitory)
• -> supplementary motor cortex

Question 27

Dopamine increases the action of which pathway? By which receptor? What does this receptor do?

Answer 27

Direct pathway via D1 receptors (and it decreases the action of the indirect pathway via D2 receptors).
D1 increases CAMP and increases sensitivity of striatal cells to glutamate.