Motor Control I - Role of the Motor Cortex and Spinal Reflexes Flashcards
What is the motor system made up of? x3
The cortex and voluntary movement - the motor cortex - sensory input / feedback Descending motor pathways - lateral (voluntary) - ventromedial (brainstem control) Spinal cord - motor neurones - sensory input - local reflexes
Draw the following structures in a diagram, with arrows showing how they influence each other
- Cerebral cortex (primary motor and supplemary/premotor
- thalamus
- basal ganglia
- cerebellum
- brain stem
- spinal cord
- muscle contraction and movements
- sensory receptors
see lecture
What are the 3 basic types of movement?
- reflex protective e.g. limb withdrawal
- closed loop confined to spinal cord - rhythmic motor patterns e.g chewing, walking
- a combination of reflex and voluntary - voluntary, purposeful, goal directed
- command originates for higher centres
- ‘open loop’
Spinal motorneurone activity is governed by inputs from:
1.
2.
3.
- Sensory input - local feedback control (via dorsal roots)
- Spinal interneurons - circuitry generating motor programmes
- Upper motor neurones - initiation and control
Which circuits are responsible for coordinated movements even when descending influences are severed?
central pattern generators in spinal cord
coordinated movements can still occur
What do lateral and medial motor neurones innervate?
Lateral motoneurons - fine motor muscles - distal (hands, feet, digits) Medial motoneurons - postural muscles - proximal (elbow, knee)
What are the two lateral motor pathways?
corticospinal and rubrospinal
Describe the corticospinal tract?
- a ‘direct line’ contralateral projection from cortex to lateral spinal motor neurones
- monosynaptic contact with alpha MNs
- majority of axons from neurones with cell bodies int he motor cortex (areas 4 and 6)
- innervate alpha motor neurones (and to a lesser extent intervneuones controlling distal muscles, particularly flexors
Describe the descending input from UMN
- adaptable patterns of movement
- in higher vertebrates
- input descending from the brain
- this is superimposed upon the intrinsic circuitry of the SC
Describe the rubrospinal tract
- originates in the Red Nucleus in the midbrain
- a much smaller component of the lateral pathway
- input from the same areas as the cotricospinal tract
- similar role to contricospinal tract
What is severing the lateral ascending spinal sensory pathways sometimes used for?
What can it lead to?
What is unaffected?
for intractable pain
- this can lead to a motor deficit –> voluntary movements are slower
- posture is unaffected as no damage to ventromedial tracts
-
- rubrospinal can compensate almost entirely for loss of corticospinal (except fine motor control)
- re-routing of cortical output via the rubropsinal tract
What is another name for the ventromedial motor pathway?
extra-pyramidal tracts
Where do the ventromedial motor tracts arise?
What is their function?
brain stem nuclei
- control of motor output to proximal and axial muscle s
- control of posture and locomotion
What are the two pairs of ventromedial pathways?
What are they both responsible for
- pontine reticulo-spinal and medullary reticulo-spinal
- vestriublo-spinal and tecto-spinal
Responsible for balance, body position, and visual input —-> modulate spinal reflexes and maintain body balance/posture
What is the role of the vestibulospinal tract?
- relays gravitational sensory information from vestibular labyrinth (inner ear) and stretch receptors in axial muscles
- maintains head and neck position and also legs
What is the role of the tectospinal tract?
- relays visual sensory information from retina and visual cortex
- orientates head and eyes to viral and auditory stimuli
Where are the cell bodies of the UMN for for the vestibulospinal tract?
- vestibular nucleus of medulla
Where are the cell bodies of the UMN for for the tectospinal tract?
superior colliculus of midbrain
Pontine reticulo-spinal tract:
- Where does it originate
- What is its role?
- originates from pons
- enhances antigravity reflexes of spinal cord
- facilitates leg extensors to maintain standing posture
Medially reticule-spinal tract:
- What is its role?
Has opposing effect
Frees antigravity muscles from reflex control
- allows voluntary override
Movement involves not just the execution, but also: - - - -
- sensory input
- planning
- deciding appropriate action
- holding plan in memory
What the main areas of the motor cortex?
What is each made up of?
Area 6 = supplementary motor area and premotor area
Area 4 = primary motor cortex (M1)
What is the role of area 4?
Primary motor cortex
Control of distal musculature (fine motor control)
What is the role of Area 6 (lateral)?
Premotor Cortex
- control of proximal musculature (posture and balance)
- control of movement sequencing
- preparation for movement, intitiation
What is the role of Area 6 (fronto/medial)?
Supplementary Motor Area
- role in planning and initiation
- bi-manual co-ordination
Primary Morot Cortical Output Neurones
- What are they also known as?
- What % of the corticospinal tact axons?
- What cells type are they? Where is their cell body?
- Do they activate small groups of muscle or single ones?
- Individually encode the …………/…………. of movement
- upper motor neurones
- 50%
- pyramidal (Betz cells), cell body in cortical layer
- small groups of muscles
- force/direction
Describe the basic circuitry of UMNs arranged in cortical columns
- invalids output neurone (Betz cell) and interneurones
- co-located with sensory inputs from muscles/joints influenced by output
- feedback on circuit (intracortical reflexes/learning)
What are the features of UMN damage?
- initial muscle weakness
- eventually spasticity (increase resistance to passive movement)
- increased muscle tone
- increased reflexes
- affects contralateral side to damage
- recovery possible as primary motor cortex shows adaptive alterations (also required for normal motor skills acquisition
