Motor control 1 Flashcards
Identify the different functional areas of the brain in the diagram below
Motor control is a functional hierarchy and can be described as having 3 levels (high, medium, low)
Describe the 3 levels of motor control
High - Strategy:
- Concerned with Strategy - ie the goal and movement strategy to best achieve this
Medium - Tactics:
- Concerned with Tactics - the sequence of spatiotemporal muscle contractions to achieve a goal smoothly and accurately
Low - Execution:
- Concerned with execution - ie activation of motor neuron and interneuron pools to generate goal-directed movement
What areas of the Nervous system are involved with the 3 levels of motor control?
High (Strategy):
- Association neocortex - eg Broca’s etc
- Basal ganglia
Medium (Tactics):
- Motor cortex
- Cerebellum
Low (execution):
- Brainstem
- Spinal cord
Shown in the diagram below are two sets of motor tracts in the spinal cord
What names are given to these pathways and what are their purposes?
Lateral Pathways:
- Control voluntary movements of distal muscles (remember the spatial mapping?)
- These movements are under direct cortical control
Ventromedial pathways:
- These control posture and locomotion
- Under brainstem control
What are the contents of the Corticospinal tract? (CST)
2/3rds of the CST originates in areas 4 & 6 of the frontal motor cortex
The rest is somatosensory
Where do the axons contained within the CST synapse?
CST axons synapse on ventral horn motor neurones and interneurones to control muscles voluntarily
What other important tract is contained within the Lateral pathways of the spinal cord?
Rubrospinal tract (RST):
- Starts in the red nucleus of midbrain
- Receives inputs from same cortical areas as the CST (4 & 6)
What is the effect of lesions to the CST and/or RST?
fine movements of arms and hands are lost. Can’t move shoulders, elbows, wrist and fingers independently.
If only CST injured - RST can take over after a while so functions re-appear
Identify the labels innit
What are motor neuron pools?
A motor pool consists of all individual motor neurons that innervate a single muscle
As muscles often work in agonist-antagonist pairs, flexor motor pools are close to extensor pools etc
Describe the action of descending pathway axons (eg those of the CST) on motor neuron pools
They monosynaptically excite pools of agonist motoneurones
The same pyramidal neurones branch and via interneurons inhibit pools of antagonist motoneurones
(Similar to that of the crossed extensor reflex)
What is the purpose of the Vestibulospinal and tectospinal tracts?
Vestibulospinal:
- Stabilizes head and neck (think of a figure skater)
- Originates from Vestibular nucleus
Tectospinal:
- TST ensures eyes remain stable as the body moves
- Originates from superior colliculus
What is the purpose of the Pontine and Medullary Reticulospinal tracts?
These are ventromedial pathways controlling the trunk and antigravity muscles
Originate in the brainstem (pons & medulla) and use sensory information about balance, body position and vision to Reflexly maintain balance and body position
Innervates the trunk and anti-gravity muscles in the limbs
Identify the labels in the diagram of the pontine and medullary reticulospinal tracts
How does the motor cortex prevent reflexes from fucking up all the voluntary movements that we talked about
motor cortex can also free spinal neurones from reflex control - by interactions with the nuclei of the ventromedial pathways
eg Reticular nuclei, superior colliculus, vestibular nuclei
Lower motor neuron arrangement is described as being somatotopic
What does somatotopic mean?
point-for-point correspondence of an area of the body to a specific point on the central nervous system
What is the significance of area 6 in the brain?
Area 6 = Pre-motor and supplementary motor areas
Identify the functional areas of the brain in the diagram below
In order for us to do that voluntary movement stuff - what 3 things do we need to know for our motor cortex to plan the movement?
1) Where the body is in space
2) Where we want to go/move
3) The plan of action to get there
Epileptic seizures often ‘march’ across the body - starting with fingers and finishing at the face for example
What is the link between the motor homunculus and this?
The seizure will roughly move along the motor cortex’s somatotopic arrangement (motor homunculus)
However, the somatotopic map is not as simple as ‘this point in PMC = Bicep and this other point = yer toe muscle’
(more on that in a sec)
What are the 2 motor maps of area 6?
One of the Pre-motor area
One of the Supplementary motor area
Remember that both the PMA and SMA make up area 6
What do the PMA and SMA innervate?
SMA innervated distal motor units directly
PMA connects with reticulospinal neurones innervating proximal motor units
In what way is the somatotopic arrangement of the motor cortex not precise?
it does not represent upper motor neurones causing individual muscle movements
functional maps of the cortex appear to map movements – perhaps (in area 6) even the intention of a complete movement
So in reality, if you were to stick an electrode into specific areas of the motor cortex - what would happen?
Microstimulation of specific parts of area 4 elicits:
- Coordinated movements of hand or mouth
- Movements that bring hands into central space to inspect/manipulate objects
These are in the contralateral limb to the area being stimmed
Movements seem to follow 3 basic goals - to inspect, to manipulate or to defend
Identify the areas in the diagram and describe their role in body movements
Posterior parietal cortex (5 & 7):
- This is where the mental image of the body in space is generated
- The image is generated from somatosensory, proprioceptive and visual inputs
Prefrontal and parietal cortex are where decisions are taken:
- which actions/movements to take and their likely outcome
The Posterior parietal cortex and pre-frontal cortex must communicate with the rest of the brain obviously
How do they do this?
Axons (association fibres?) from PPC and PFC converge on area 6
Here signals encoding desired actions are converted into how to carry this out
What is meant by ‘mirror neurones’
Neurones in the PMA fire when we think about doing a movement (even if we dont do it)
However - they also fire when we watch another person do the same task
- Thus they are mirroring the PMA firing of the person doing the task
This is what allows us to understand other’s movement:
- It may also be the foundation of Empathy
- May be dysfunctional in those with autism
