Supra-spinal Control 1 - Cortical Motor Control Flashcards
Name the 4 main descending motor pathways.
- Corticospinal Tracts
- Rubrospinal Tract
- Reticulospinal Tract
- Vestibulospinal Tract
Where in the spinal cord is the reticular formation’s reticulospinal tract found?
- Medial Pathway
- Lateral Pathway
What is the reticulospinal tract (reticular formation) important for?
- Important in modulating locomotion patterns
What occurs in corticospinal tract damage?
- Loss of voluntary movement control
- Restored due to take-over by other systems
What pathway usually takes over if there is damage in the corticospinal tract?
- Rubrospinal Tract
From where does the vestibulospinal tract get its information from?
- Vestibular System
- Head
- Semi-Circular Canals
It measures translational movements in these systems
What is the function of the vestibulospinal function?
- Detects Translational Movement
- Sends information down to the spinal cord
- Maintains balance as a function of head movements deviations
Important in posture & head movements
Name the 2 lateral pathways.
- Corticospinal Tract
- Rubrospinal Tract
What are the functions of the lateral pathways?
- Fine & fractionated movements of the limbs & fingers
Name the 4 ventromedial pathways.
- Vestibulospinal Tract
- Tectospinal Tract
- Pontine Tract
- Medullary Reticulospinal Tracts
What are the functions of the vestibulospinal & tectospinal tracts?
- Control Posture of the Head & Neck
What are the functions of the pontine & medullary reticulospinal tracts?
- Control posture of the trunk & antigravity muscles of the limbs
Which area if Primary Motor Cortex (M1)?
Area 4
Which broddman area is premotor cortex?
Area 6
What 2 regions does the premotor cortex contain?
- Premotor Area (PM)
- Supplementary Motor Area (SMA)
Where is the Supplementary Motor Area (SMA)?
- Medial to the Premotor Area
Where are the motor areas located?
How did broddman divide up parts of the brains?
- Based on shape and neuronal patterns from histological sections
They were functionally accurate areas
Why are electrodes used on the brain surface?
- Stimulate Parts of the Cortex
- Check for residual function (e.g. after removing tumour)
- Used commonly after/before procedures
Which area has the lowest threshold for stimulation? (i.e. easiest to get movement if you stimulate)
- Primary Motor Cortex (M1)
What are 2 other places that if stimulated can cause movement (but need more than M1)?
- Premotor Cortex
- Somatosensory Cortex (S1)
However these need much more stimulation –> they can do this due to rich connections & some descending projections
Where is the SMA found?
- Dorsal Side
- Medial Face of the Cortex
- It is medial to the premotor area (which runs up to the midline before SMA starts)
What are the parietal regions involved in?
- Movement Control
- Set up visual space in which out moves are made
- Give us a sense of allocentric & egocentric space
What is allocentric space?
Pointing to places relative to you as a whole
What is egocentric space?
- This is the concept of own space
- Where movements have to be created around yourself and relative to yourself (own personal space)
(e.g. touching your nose)
From where in the thalamus does most of the input to the primary motor cortex (M1) come from?
- Ventral Lateral Nucleus (thalamus)
From where do most of the input in the thalamus come from going to the Premotor Cortex (PM + SMA)?
- Ventral Anterior Nucleus (thalamus)
Where does the lateral geniculate body of the thalamus project out to?
- Visual Cortex
Where does the medial geniculate body of the thalamus project out to?
- Auditory Cortex
How can we distinguish between the cortices?
- Thalamic projections to the cerebral cortex allows us to distinguish
What is the problem distinguishing between the Ventral Anterior & Ventral Lateral nuclei of the thalamus?
- Difficult to find the division at the thalamus
- Thus cannot trace it back very easily
Describe the pathways of the corticospinal system.
How is the primary motor cortex arranged?
-
Somatotopic Arrangement
i. e. a motor map which means certain parts are for certain movements (found using electrodes & fMRI)
What passes through the Posterior Limb of the Internal Capsule?
- Motor Projections
- Sensory Projections
- Visual Pathways
- Auditory Pathwys
What is the vascular supply to the motor cortex?
Where does it arise from?
-
Lenticula-Striate Arteries
- These penetrate the brain (modest perfusion)
- Arises from the middle cerebral artery
What can cause a stroke in the posterior limb of the internal capsule?
- Middle Cerebral Stroke
(commonly gets damaged in cortical strokes)
What is te difference between a cortical and capsular stroke?
- Cortical Stroke (rarer) –> unlikely to lose the whole territory –> may just lose a branch (e.g. loss of nerves of the hand/arm in one region)
- Capsular Stroke (common) –> complete hemiplegia
What is a hemiplegia?
- Paralyses of the one whole side of the body
One side of face | Contralateral side of the body
What usually causes a complete hemiplegia?
- Stroke affecting the Internal Capsule (capsular stroke)
Describe the corticospinal fibre pathway.
- Converges –> runs through posterior limb
- Gives off fibres to cranial nerve nuclei on ipsilateral side (e.g. voluntary eye movements)
- Descends to lower medulla –> pyramidal decussation
- Takes up either a lateral or dorsal (small) position
- Supplies muscles on contralateral side
How is the motor cortex mapped?
- Not a simple 1:1 projection (it is many-to-1)
- Pyramidal cells in M1 –> converge onto motoneurone/interneurone –> which then goes to muscle
How are the different parts of the body mapped in the cortex
- There are distinctions
- However there is some overlap (spread)
- However, once they converge –> it is mostly that one part
Describe the conversion of neurones in the motor cortex.
- Many cortical neurones –> converge –> then project down
- Not a strict map
- Map of best fit (not precise)
- This is called principal convergence
How are M1 pyramidal neurones from the cortex distributed?
- Project to several motoneurones & interneurone pools
A single corticospinal axos projects widely in the interneurone & motoneurone region of the spinal cord
- There is divergence of M1 pyramidal neurone inputs upon spinal motoneurones
How does a single motor corticospinal neurone distribute itself?
- Corticospinal neurones diverges to lots of differnet motor & interneurone pools (not just individual motor neurones)
- Controls a range of different motor neurones
What 2 important points must be remembered in relation to motor neurones & pyramidal neurones?
- No privileged communication line (i.e. no single corticospinal neurone synapses a single motoneurone)
- Many corticospinal neurones can communicate with one motor/interneurone pool (different corticospinal neurones can communicate various things)
What happens in terms of M1 distribution after cutting a nerve (e.g. facial nerve)?
- Cut –> thus no longer has any motor neurone
- Thus cannot carry out function –> die back & dissapear (movement no longer possible)
- Motor Cortex (M1) –> Somatotomic Map is remapped
-
Adjacent regions now take over (infiltrate)
*
What 2 reasons can explain the redistribution of parts of the motor cortex?
- Adjacent Regions were already present in the lost area (no sharp borders)
- Adjacent regions have grown into the area
(Probably a mixture of both - it is just a mixture and somthing dominates/wins out)
There is a lot of plasticity –> which is optimistic for stroke recovery
What 3 ways can primary motor cortex neurones code for in terms of muscle force?
- Code for dynamic aspects of force
- Code for dynamic & static aspects of force
- Code for static aspects of force
What causes an increase in force for a motor unit?
- Increased Firing Frequency
What does static aspect coding mean?
- Code for the Force (when taking place)
- Not active when force is low
What does dynapic phase aspect coding of movement mean?
- The differential
- The changing from a rest position
- Responsive to change
What does mixture of dynamic & static aspect coding of movement mean?
- 65% of neurones are like this
- Mixture of dynamic & static types
- This is how most motor & somatosensory system coding is managed
How are the 3 different types of neurones distributed? (percentages)
- Dynamic Aspect –> 10%
- Mixture (dynamic + static) –> 65%
- Static Aspect –> 25%
When is M1 active?
- Before Movement (thinking about movement you are about to execute)
- During Movement
When is M1 active?
- Before Movement (thinking about movement you are about to execute)
- During Movement
What else does the Primary Motor Cortex (M1) code for?
- Directionality
Coarse coding for direction –> by individual neurones
What does primary motor cortex code for?
- Direction of Movement
- Coding is coarse –> the neurone will fire in a range of movement directions
What is the mechanism called for accurately coding for directionality?
- Population Coding
How does the motor cortex code for accurate directions?
- Vector sum of all motor cortex neuronal activity –> gives a close approximation of the direction of movement
How does population coding work for M1?
- Firing rate of lots of different neurones are recorded
- Take the vector sum of the magnitudes & directions of each neurone
- Look at entire population (population coding) –> look at their vector sums –> and see the overall direction
- This is very similar to direction the arm took
What is population coding an example of?
- Higher Level Aspects of coding
- Population coding
What occurs if you use trains of microstimulation on the Premotor cortex & M1?
- Complex Movements
(e. g. causes hand movement to the mouth from any point)
This is an example of egocentric movements (defined point on the body where you move to regardless of starting posiiton - M1 is a lot more complex than initially thought)
What are the 2 parts of the premotor cortex?
Where are they found?
- Premotor Area (PM) –> Lateral
- *Supplementary Motor Area (SMA)** –> Medial
Where do the premotor area (PM) and supplementary motor area (SMA) project to?
- Primary Motor Cortex (M1)
What does the Premotor Area (PM) have strong inputs from?
- Cerebellum (via the thalamus)
What does the Supplementary Motor Area (SMA) have strong inputs from?
- Basal Ganglia (via the thalamus)
What is the function of the Premotor Area (PM)?
- Planning Movements (before movement)
- Based on External (especially) visual cues
(e.g. picking up something infront of you)
What is the function of the Supplementary Motor Area (SMA)?
- Planning Movements
- Based on internally generated strategies (e.g. learning sequences of movements)
(e.g. drawing a question mark in mid-air - as you already know the shape & movement so you are bringing it from memory store)
Where are PM & SMA relative to M1 in hierarchy?
- PM & SMA –> are higher in hierarchy of coding
(but M1 is not lower than we thought - it is slightly more complex)
What is responsible for planning movements for external & internal cues?
- Premotor Area (PM) –> External Cues
- Supplementary Motor Area (SMA) –> Internal Cues
What occurs if there is a lesion in the Premotor Area (PM)?
- Severe impairement on visual conditional motor task
(e. g. pulling handle if light is blue and twisting if light is red)
What occurs if there is a lesion in the Supplementary Motor Area (SMA)?
- Severe impairement on motor sequence learning task
(e. g. learning to open a lid by pushing, twisting & then lifting)
When is M1 active?
- During all tasks (whether internal or external/visual cue)
Which neurones are active during preparation to move in a visually cued task?
- Set-related neurones in the dorsal Premotor Area
Active during instruction-movement interval
When is supplementary motor area active?
- During sequenced movement tasks (e.g. learning to play sequence on piano)
- During mental rehearsal of tasks (e.g. mentally playing it in your head)
Involved in movement planning
What is active during visually cued behaviour movements?
- Premotor Areas
- M1 (for everything!)
What is active during movement (e.g. wriggling finger)?
- M1 (hand area)
- Somatosensory Cortex (propioceptive information coming back + information from skin)
When is the SMA active?
- Planning movements based on internally generated strategies (e.g. learned patterns)
