Control of movement Flashcards
What are ballistic movements?
based on a set of pre-programmed instructions and er therefore rapid, but at the expense of accuracy (little opportunity for compensation for unexpected changes)
e.g. Returning tennis serve, swatting a fly
What are pursuit / visual feedback movements?
Motor commanded continually update according to sensory feedback (e.g. visual) so are therefore highly accurate, although slow
How is movement affected during a stroke and why?
Reduced blood flow to said area reduces innervation
Causes reduced muscle movement or control in contralateral side due to decussation of muscle fibres
What is the role of the basal ganglia in movement?
Receives input from prefrontal cortex and outputs to premotor area via the thalamus
Initiates movement and plans complex voluntary movement
How does Parkinson’s affect movement and why?
Loss of dopaminergic neurons in basal ganglia - explains tremor as find it difficult to intiate movements
How does Huntington’s affect movement and why?
destroys cells in basal ganglia, resulting in:
- Choreas (involuntary jerk)
- speech and swallowing difficulty
- Cognitive decline
What is the role of cerebellum in movement?
Has input mainly from sensory cortex and outputs to primary motor cortex via the thalamus
Coordination - enables smooth execution of movement
What type of motoneuron innervates skeletal muscle?
alpha-motoneurons - provide final common output
What are motonuclei and how does their location affect function?
collection of the columns in ventral horn of motoneuron pods of each muscle
In Cerical - control arm and upper body movements
In Thoracic - Control trunk
In Sacral - Control legs
How can the strength of a muscle contraction be increased?
Recruitment of motor units
How does the basal ganglia function to increase movement?
Works through the direct pathway:
- primary motor cortex excites putamen, increasing its activity
- This follows direct pathway to DECREASE (putamen has inhibitory effect) GPi
- GPi is also inhibitoy so decreased activity will INCREASE activity of thalamus
- This results in increased excitation of muscles
Primary motor cortex also initiates substantia nigra - excites direct pathway and inhibits indirect pathway
How does the basal ganglia work to decrease movement?
Works through indirect pathway:
- Putamen activity is increased by orimary motor coretx
- This increases inhibition of GPe, decreasing activity
- This therefore reduces inhbitory effect on GPi, increasing activity
- Increased inhibition in thalamus, decreasing activity
- lower excitation of primary motor cortex so reduced motor stimuli
Subthalamic nucleus is stimulated by descending motor pathways, causing increased activity of GPo, further increasing inhibitory effect on thalamus.
Subthalamic nucleus is inhibited by GPe so in indirect pathway when GPe activity reduced, this response is further increased, resulting in reinforcement of decreased motor signals
