Neurology 17- Basal Ganglia

Question 1

What are the functions of the basal ganglia?

Answer 1

• Provides a feedback mechanism to the cerebral cortex for the initiation and control of motor responses.
• Will increase or decrease the cortical stimulation relayed by the thalamus
• helps program sequences of movement
• facilitates wanted movements and inhibits unwanted movements

Question 2

What are the 2 parts of the substantial nigra?

What type of neurone do each contain?

Answer 2

• substantia nigra parta reticularta (SNr)
• Substantia nigra pars compacta (SNc)
• SNC largely contains dopaminergic neurone- stained dark blue do to the presence of neuromelanin
• SNr contains large, multipolar GABAergic neurons

Question 3

Know how to label the basal ganglia on slide 11

Answer 3

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Question 4

If you stimulate an inhibitory neurone what happens and why?
If you remove a stimulation what will happen to its target neurone?

Removal of inhibition will?

Answer 4

1. That neuron will become more inhibitory because it releases more of its expected neurotransmitter-does more of whatever its programmed to do.
2. It will inhibit the neuron- coz membrane potential has moved further away from firing threshold (polarised)
3. removal of inhibition will stimulate a neuron-why? coz teh membrane potantil moves closer to
   firing thresholjd. you inhibit the neuron that inhibiting the
   target neuron

Question 5

How does the basal ganglia work>

Answer 5

1. The basal ganglia act on the motor thalamus, which acts on the motor cortices-basal controls thalamus which controls cortex

! 2. There are no descending spinal tracts from the basal ganglia-if they want to influence motor control they have to exert influence through thalamus to cortex.

! 3. Most of the circuitry is ipsilateral and projects to the same side of the brain- If we have a R sided pathology we will see signs on left
-Its ipsilateral to the motor centre and motor projects to the contralateral side

! 4. Basal ganglia affect movements on the contralateral side

Question 6

Describe how the direct pathway acts to stimulate movement?

slide 17

Answer 6

• Cortex decides it wants to move→ stimulates Striatum (caudate nuclueas and putamen)→ The striatum inhibit the globus pallidus internal andsubstantia niagra pars reticularta via gaba. These guys job normally is to inhibit the thalamus. So coz their inhibited they cant inhibit the thalamus so it can stimulate the cortex to create movement.

Question 7

How does the indirect pathway work to inhibit movement?

slide 19

Answer 7

Cortex decides it doesn’t want to move → sends stimulatory message via glutamate to Striatum→ Which sends an inhibitory signal (like in the direct pathway) but it inhibits a different part of globus pallidus→ EXTERNAL→ whose role is to normally inhibit the subthalamic nuclei which means theses nuclei become more active whos job is to stimulate the internal segment of the globus pallidus whos normal role is to inhibit the thalamus.

Question 8

What is the role of the substantial nigra and how does it work?
20

Answer 8

• SNc contains dopaminergic neurons-excites direct pathways and inhbitis indirect pathways
• synapse onto the neostriatum via the nigrostriatal fibres
• dopamine release from axon terminals

-get too much dopamine you get too much inhibition of the indirect pathway

(hyoerkineasia)