Control of movement Flashcards
What is the basal ganglia?
Describe the movement circuits
This is a collection of interconnected nuclei in the brain which is key for successful motor control
What is the key role of the basal ganglia?
Key role appears to be in action selection i.e selecting the right action for the given situation
What can damage to the basal ganglia do?
Cause disorders of movement
What are the 6 parts of the basal ganglia?
- Striatum (caudate nucleus, putamen)
- globus pallidus externa (GPE)
- Globus palludus interna (GPI)
- Thalamus
- Subthalamic nucleus (STN)
- SUBSTANTIA NIGRA (SN)
Define hyperkinetic and hypokinetic
Hypokinetic (not enough movement) – usually not enough dopamine
Hyperkinetic (to much movement) – to much dopamine “not quite true”
The rate (Alexander and Delong) model for how the basal ganglia affect movement
Describe this model
Changes in firing rate (of output nuclei) determines the degree of thalamic inhibition and therefore amount of movement possible
What is Parkinson’s disease?
• Clinically dominated by a lack of movement: bradykinesia
In parkinson’s the substantia nigra degenerates so there isn’t enough dopamine
The inhibitory output nucleus of the basal ganglia turns up
It inhibits the thalamus and inhibits the motor cortex
The rate of firing of the output nucleus goes up
Define Hyperkinesia - Hemiballismus
Hemiballismus is a flinging movement of one side of the body
typically caused by a subthalamic nucleus stroke
he subthalamic nucleus is a key node in the ‘stop’ pathway
If that is removed then there is an excessive inhibition or an inhibitory output nucleus
The Gpi/SNr nucleus is not stopping the thalamus
Anatomically these models don’t make sense because there are more connections in the basal ganglia
What occurs in Deep brain stimulation surgery?
- Electrodes are implanted into the subthalamic nucleus connected to a neuro-stimulation/ pacemaker
- To block subthalamic nucleus
- Stops too much movement
Means model does not work as blocking STN should lead to more movement
It’s not rate by the rhythm that matters
• Pick up these oscillations at 20Hz beater frequency
• See pathologically enhanced beaten frequencies in parkinsons
What does beta suppression with levodopa correlate to?
- Beta suppression with levodopa correlates with reduction in Parkinson’s symptoms
- Beta suppression with deep brain stimulation correlates with reduction in Parkinson’s symptoms
Delayed return of bradykinesia offers DBS correlated with delayed return of beta
Therefore beta control strongly correlates with movement control in people with diseases like Parkinson
What is movement?
What do we need to do to move or not move?
Movement if the change from one (stable) sensory state to another (stable) sensory state
In order for this to work you need:
• To turn down current sensory state (e.g turn down network that is supporting sitting still)
• To have an accurate prediction of new sensory state (create plan of new state such as standing up)
• To have a mechanism to rate how important it is to do this movement rather than to stay in the current state or do anther movement
• To have ways of stabilising the new sensory state
What is abnormal in Parkinson’s disease?
What is treatment for it?
- Actual movement in Parkinsons disease appear normal, it is there initiation, scaling (size and vigour) and position is abnormal
- High beta means that the current sensory state is excessively stable, therefore can’t initiate or stabilise new movement…all movement (action) has a high “cost”: Treatment – providing levodopa which supresses beta.
- Treatment providing levodopa supresses beta.
What does low beta mean and what is the treatment?
Pathologically low beta means current sensory state is unstable, so that new unwanted patterns of movement can arise and come onto without will.
Treatment: dopamine receptor antagonists which increase beta activity
e.g tourette’s syndrome
What occurs in chorea and dystonia?
In chorea and dystonia, core control of movement seems normal with “noise” added on top – a different level of movement control problem.
