Control of Movement Flashcards
Why is movement difficult to replicate electronically?
→ The brain predicts movement
What are the basal ganglia?
→ A group of nuclei inside the brain
What kind of a disease is Parkinsons?
→ basal ganglia degenerative disease
What do the basal ganglia act as?
→ Relay stations
What are the 3 different circuits in the brain?
→ Motor
→ Associative
→ Limbic
How are the basal ganglia segregated?
→ Anatomically
What is the main output of the basal ganglia?
→ inhibitory
What are the 2 basal ganglia pathways?
→ One decreases output activity (increases movement)
→ One increases output activity (decreases movement)
What sends inputs to the basal ganglia?
→ The striatum
What is the indirect stop pathway?
→ Activates the inhibitory nucleus and makes movement less likely to happen
What is the direct go pathway?
→ Inhibits the inhibitory pathway
Where is dopamine produced?
→ In the substantia nigra
What is the Alexander and Delong model?
→ Changes in firing rate (of the output nuclei) determine the degree of thalamic inhibition and the amount of movement possible
What is bradykinesia?
→ A lack of movement
What happens in Parkinsons?
→ Substantia nigra degenerates
→ Not enough dopamine
→ Inhibitory output of the basal ganglia turns up
→ Inhibits the thalamus and inhibits the motor cortex
→ rate of firing of the output nucleus goes up
What is hemiballismus and what is it caused by?
→ A flinging movement of one side of the body
→ caused by a subthalamic nucleus stroke
What role does the subthalamic nucleus have?
→ it is a key node in the stop pathway
What happens if the subthalamic nucleus is removed?
→ excessive inhibition of the stop pathway or an inhibitory output nucleus
→ the Gpi/SNr is not stopping the thalamus
→ excessive movement
What is a clinical issue with the Alexander and Delong model?
→ lesioning the thalamus does not cause prominent akinesia
→ lesioning the GPi does not cause dyskinesia
What is the beta frequency?
→ 20-30 Hz
What is the firing like in people with motor disorders?
→ the neurons have a bursty pattern
→ the rate of firing is not abnormal but the pattern of firing is
in a normal situation what do brain electrodes pick up and what happens in Parkinsons?
→ lots of different frequencies firing
→ Everything becomes synchronised
When does dopamine release occur?
→ At the beginning of movement
People with Parkinsons still produce dopamine, why is this not enough for movement to occur?
→ There is a baseline level of dopamine release
→ additional dopamine release happens at the beginning of movement
→ people with Parkinsons have low baseline dopamine
→ When a stimulus occurs the additional dopamine released it not enough to pass the threshold for movement.
How do you define moving?
→ Change from one stable sensory state to another stable sensory state
What are the 3 things required for changing sensory states?
→ Turning down current sensory state
→ Accurate prediction of the new sensory state
→ Stabilising the new sensory state
What is involved in stabilising sensory states?
→ Beta power
What is beta power like when sitting still and why?
→ It is high
→ stops you having other unneeded movements such as jumping
If you want to move what happens to beta power?
→ It is turned down which allows you to change state
What allows prediction of movement in the brain?
→ The brain builds internal models of the world
What is the forward model?
→ Brain sends a copy of the movement to the cerebellum to check if the movement is correct
What does the forward model do?
→ Comparing what happened with what was expected to happen
What happens when there is damage to the cerebellum?
→ movement becomes steady and uncoordinated because the comparison can’t happen
→ the brain is unprepared for obstacles
What is abnormal in Parkinsons?
→ initiation
→ Scaling
→ and persistence of movement
