Motor Control 1 Flashcards
What are the 3 levels of motor control?
- High
- Middle
- Low
What is the function of high motor control?
Strategy
What is the function of middle motor control?
Tactics
What is the function of low motor control?
Execution
What structures are responsible for high motor function?
- Association neocortex
- Basal ganglia
What structures are responsible for middle motor control?
- Motor cortex
- Cerebellum
What structures are responsible for low motor control?
- Brain stem
- Spinal cord
Strategy
The goal and the movement strategy to best achieve this goal
Tactics
The sequence of spatiotemporal muscle contractions to achieve a goal smoothly and accurately
Execution
Activation of motor neuron and interneuron pools to generate goal-directed movement
By what pathways is the brain connected to the spinal cord?
- Lateral pathways
- Ventromedial pathways
What do lateral pathways control?
Voluntary movements of distal muscles- under direct cortical control
What do ventromedial pathways control?
Posture and locomotion under brain stem control
What is the longest lateral pathway?
Corticospinal tract (~1 million axons)
Where does the corticospinal tracts originate?
- 2/3 originates in areas 4 and 6 of the frontal motor cortex
- The rest is somatosensory
Where does the corticospinal tract decussate?
At medulla/spinal cord junction
Where do the corticospinal tract axons synapse?
Ventral horn motor neurones and interneuonres in order to control muscles
What type of pathway is the rubrospinal tract?
Lateral pathway
Where does the rubrospinal pathway originate?
- Rednucleus of the midbrain
- Inputs from the same cortical areas as the CST
What would lesions in the CST and RST result in?
- Fine movement of arms and hands would be lost
- Can’t move shoulders, elbows, wrist and fingers independently
What would lesions in the CST alone cause?
- Fine movement of arms and hands would be lost
- Can’t move shoulders, elbows, wrist and fingers independently
- The functions would reappear after a few months as the RST takes over
What lateral pathways control voluntary movements?
- Corticospinal tract
- Rubrospinal tract
What 2 ventromedial pathways control posture and locomotion?
- Vestibulospinal tract
- Tectospinal tract
What does the vestibulospinal tract do?
Stabilises the neck
What does the tectospinal tract do?
Ensures eyes remains stable as body moves
What ventromedial pathways control trunk and antigravity muscles?
Pontine and medullary reticulospinal tracts
Where do the pontine and medullary reticulospinal tracts originate?
Brain stem
What do the pontine and medullary reticulospinal tracts reflexly do?
Maintain balance and body position
What do the pontine and medullary reticulospinal tracts do?
Innervate trunk and antigravity muscles in the limbs
What do the pontine and medullary reticulospinal tracts use?
Sensory information about balance, body position and vision
What do voluntary movements such as throwing require input from?
Motor cortex via lateral pathways
What does the motor cortex directly activate?
Spinal motorneurones and frees them from reflex control by communicating via nuclei of ventromedial pathways
What do the primary motor cortex and pre-motor cortex areas plan and control?
Precise voluntary movements
What do upper motor neurones in the cortex and brainstem target?
Lower motor neurones in the spinal cord
What do some UMN and LMN do?
Form circuits that control reflexes such as the stretch and withdrawal reflexes
What is the distribution of the LMN?
Somatotropic
Describe the somatotropic distribution of LMN.
Medial ones control axial and proximal limb muscles, lateral ones innervate distal limb muscles
What do white matter tracts differ in?
Origin and function
What do medial descending tracts from the brainstem control?
Posture and balance and orienting mechanisms
What do lateral descending tracts from the cortex control?
Precise skilled voluntary movements
Where is the primary motor cortex?
Precentral gyrus
What lies rostrally to the primary motor cortex?
A mosaic of premotor areas
What do we need to know to plan movement in the cerebral cortex?
- Where the body is in space
- Where it wants to go
- Select a plan to get there
What is the somatotropic organisation in the primary motor cortex?
Motor homunculus area 4
How can epileptic seizures march across the body?
Can begin with abnormal finger movements, then hand, then arm, shoulder, finally face.
What can Penfield electrical stimulation be used for in epileptics?
To decide areas of the brain to be spared surgically
What do area 6 neurones do?
Drive complex movements on either side of the body
What is area 4?
Primary motor cortex
What are the 2 somatotopically organised motor maps in area 6?
- Premotor area PMA
- Supplementary motor are SMA
What does the SMA innervate?
Distal motor units directly
What does the PMA connect?
Reticulospinal neurones innervating proximal motor units
Why is the somatotopic motor map not precise?
-It does not represent upper motor neurones causing individual muscle movements
What does microstimulation in a specific area of primary motor cortex elicit during purposeful movements on contralateral arm?
-Coordinated movements of hand and mouth
OR
-Movements that bring hands into central space to inspect/manipulate objects
What is a mental image of body in space generated by?
Somatosensory, proprioceptive and visual inputs to posterior parietal cortex (areas 5 and 7).
Where are decisions taken about what actions/movements to take and their likely outcome?
Prefrontal and parietal cortex
What junction is located in area 6?
Junction where signals what actions are desired are converted into how the actions will be carried out.
What does PET show during practised voluntary finger movements?
Blood flow increases in somatosensory, posterior parietal areas + prefrontal cortex, areas 6 and 4
What area is active if you think about movements?
6
When does area 4 become active?
By doing an action by activating the neurones of the CST and RST
What fires before a movement?
Decision making neurones in cortical PMA
What are decision making neurones in command centres?
Neurones in the premotor area (PMA) that fire action potentials one second before a movement occurs
When do PMA mirror neurones fire?
When self or others perform specific actions
What may mirror neurones underpin?
Emotions and empathy
When may mirror neurones be dysfunctional?
In autism
