Advanced Motor Control Flashcards
What is motor control
The ability to regulate or direct mechanisms essential to movement
Why do we have brains?
They allow muscle contraction letting us interact with world around us
Sea squirts used as evidence (digest brain when no longer move)
What is a degree of freedom
The number of parameters in a system that may vary independently (how many things that can change)
1 variable = 1 degree of freedom
Name bernsteins stages of motor learning
Stage 1 Freezing
Stage 2 Releasing and reorganising
Stage 3 Exploiting mechanical properties
Describe stage 1 of Bernsteins stages of motor learning
Freezing- you restrict the independence of body parts to reduce the number of degrees of freedom. Allows increased chance of success as less variables to control
Methods of ‘Freezing’
Freeze the joint by locking it out
Coupling joints together so that when 1 joint does something, the other one does the same
Describe stage 2 of Bernsteins stages of motor learning
Releasing and reorganising- as you get more proficient in a skill, you release previously frozen movements to improve power/speed/accuracy etc
Describe stage 3 of Bernsteins stages of motor learning
The motor system takes advantage of inherent mechanical properties allowing for better performance and energy use.
Eg Proximal to distal weighting
Define action potential
A change in electrical potential associated with the passage of an impulse along the membrane of a muscle or nerve cell
Define resting potential
The difference in ions across a membrane at rest, inside the cell is negative
How is resting potential maintained?
Na+/K+ pump 3Na are pumped out and 2K pumped in by active translocation which requires ATP
What is the all or nothing threshold
Threshold sits at -55mv if it is reached an action potential will fire, if not reached there is no action potential
Define refractory period
Brief period following an AP where another one cannot be fired, membrane is typically hyperpolarised. Means that the AP will only propagate in 1 direction
Define Temporal summation
The effect of multiple impulses received in the same place an add up to reach the threshold if received in quick enough succession
Define Spatial summation
Inputs from multiple neurons can trigger an AP
How is an AP propagated
- Depolarisation - voltage-gated Na+ channels open so inside of cell becomes more positive
- This causes voltage gated K+ channels to open + K+ to leave the cell
- Myelin increases the spread of electrical conduction by increasing membrane resistance and decreasing membrane capacitance.
- Therefore spread is rapid between each node of ranvier where more depolarisation occurs (Saltatory conduction)
Describe stochastic resonance
Noise lowers the threshold to maximise transfer of info. (Noise causes oscillation so easier to reach threshold)
Potential risk of stochastic resonance
If too much noise, may always be over the threshold
What is a motor unit
Smallest functional unit of motor system
Motor neuron + muscle fibres it innervates
How does a motor unit improve control
Cannot stimulate individual muscle fibres, by grouping them together it improves control as have less degrees of freedom
Why is there a delay between input and twitch contraction
Need time for Ca2+ to be released and initiate the sliding filament theory
Describe the sliding filament theory
- Ca2+ binds to troponin C which changes conformation
- This causes movement of tropomyosin away from myosin binding sites on the actin
- Cross bridge forms
- Power stroke occurs pulling actin towards the M line
- New ATP binds to myosin head breaking the cross bridge between actin +myosin
- Myosin head hydrolyses ATP to ADP + P ion, previous steps repeat until Ca2+ actively pumped back to sarcoplasmic reticulum
Define Tetanic contraction
Repeated stimuli at short intervals lead to motor unit being maximally activated + therefore maximum force output is reached
Name 3 types of motor unit
Slow twitch
Fast, Fatigue resistant
Fast twitch
What is the size principle
Small motor units in a muscle are recruited first
Benefits of size principle
Recruitment can stop when desired force reached
Large forces are not produced if not required
Orderly recruitment reduces complexity
Which motor units are typically smaller
Slow twitch are smaller as have smaller motor neurones, so therefore have a slightly lower threshold
How do you annotate excitation
Open circle
How do you annotate inhibition
Closed circle
What is a renshaw cell
Interneuron in the spinal cord, stimulated by alpha motor neurons
Uses negative feedback and reccurant inhibition to limit firing of motor neurons
Benefits of renshaw cells
Allow increased sensitivity and control as allow in increment of the input to be used.
(The muscle is simultaneously being excited by the same motor neuron that is stimulating the renshaw cell to cause inhibition)
Define muscle spindle
Stretch receptor that signal length/ changes in length of muscles
Muscle spindle position
Intrafused so sits within the muscle fibre and runs parallel to it
Describe bag fibre
Part of muscle spindle, senses change in velocity
Describe chain fibre
Part of muscle spindle, senses changes in length
Describe monosynaptic reflex arc
Muscle is stretched - muscle spindle detects stretch
Causes AP to be fired by 1a afferent fibres
Synapses in spinal cord with alpha motor neurons, which innnervate extrafusal fibres
Agonist muscle contracts
Describe difference between monosynaptic and polysynaptic reflex arc
Mono 1 synapse - only agonist muscle stimulated
Poly -multiple synapses - allows inhibition of anatagonist as well as contraction of agonist
What is the H-reflex
Artificially created stretch receptor, can be better controlled allowing you to assess response in a lab setting
Describe reciprocal inhibition
Used in polysynaptic reflexes
Interneurons form a second synapse that sends signals to a heterogenic muscle, typically inhibiting it
Benefits of reciprocal inhibition
Allows second muscle to do the opposite action to the agonist, allowing the agonist to have greater effect
What is Golgi tendon organ
Sensory receptor located near junction of muscle and tendon, detects change in muscle tension
Lies in series with extrafusal fibres
Golgi tendon organ role
Signals 1b afferent neurones
If muscle force exceeds threshold, GTO inputs inhibit alpha motor neurones, lowering the force produced
What are central control mechanisms
Allows a pattern of excitation and inhibition to be formed in various muscles, meaning that cyclical movements don’t need to be under voluntary control
What is electromyography
Records changes in muscle electrical potential, estimating muscle excitation
Electromyography methods
Indwelling - Needle, Fine wire
Surface EMG - Bipolar surface (used in sport)
Benefits of indwelling EMG
More localised pick up
More accurate
Surface EMG pros
Good for surface muscles
Global muscle pick up
Inexpensive + easy to apply (relative to other EMG methods
Non invasive
Can be kept on during sport
Surface EMG cons
Work poorly for deep muscles - hard to detect, also pick up signals from surface muscles
Can’t pick up individual motor unit signals
Other components (noise) included in signal
Doesn’t measure muscle force
EMG positioning - electrode separation
10mm separation has best signal to noise ratio across all levels of crosstalk
EMG positioning - crosstalk
Try to avoid positioning too close to other muscles to avoid interference
Where on a muscle should you put the electrode for an EMG
The belly
Thickest part of muscle has the biggest signal
In what direction should the electrode be
Parallel to muscle fibres
How to prepare skin for EMG
want as little stuff between muscle and electrode as possible
Shave hair
Sandpaper off any dead skin
Use alcohol wipe to remove oils
What is an analogue to digital converter
Converts continuous signals to finite numbers
Eg electrical potential continuously changing but measurements are taken at distinct time points
Analogue to digital converter limitations
Potential for errors as may not take measurements at right time
What is ADC amplitude resolution
The amplitude resolution of the analogue to digital converter measurements
Measured in BITs (2 to the power of the number)
What is time resolution
How often measurements are taken
Problems with time resolution
Sample frequency too low - risk of alias - measurement don’t reflect actual signal
Sample frequency high - lots of data to interpret may be difficult to handle
Describe EMG signal
APs from whole muscle add up to produce signal
The deeper the muscle the weaker the signal + has greater delay - takes longer to reach surface
What is in a raw EMG signal
Quiet time, bursts of muscle excitation
Lots of noise - want to remove
What is sampled signal
True signal + measurement errors + noise
What do you do in Full wave recitification
Flip any negative values to make whole signal positive
What is a low pass filter
It allows any low frequencies through but removes high frequency signals from data
Are methods to be able to remove specific frequencies too
How to work out how much force an individual muscle contributes?
Compare signal to % of maximum voluntary contraction
How to identify when a change in muscle excitation occurs
Work out mean and standard deviation of baseline
When it changes more than 3 standard deviations classed as something happening
EMG applications
Clinical practice
Resistance training
Research
Simulation
Biofeedback
Define neuroplasticity
Ability of the brain to form + recognise synaptic connections, particularly in response to learning or following an injury
Define EPSP
Excitatory post synaptic potential
Describe habituation
It can briefly mute a reflex if you repeat a stimulus frequently
Eg touching Siphon
1st time big response in EPSP + gill reaction
Repeated several times both responses decrease as realise stimuli not a threat.
Change only lasts brief period of time
Describe sensitisation
Also causes a brief change in response
Involves presynaptic facilitation of synaptic transmission
Applying noxious stimuli to another part of at similar time to touch stimuli, excites interneuron forming synapse on pre-synapse terminals of sensory neurons.
Describe classical conditioning
Paired pathway - stimulate siphon immediately prior to painful stimuli
Siphon sensory neurons therefore primed to be more responsive to input from interneurons
EPSP is therefore increased and thus increased Gill response
Hippocampus role
Helps convert ST memories to LT memories, particularly active at night.
Function of place cells
In hippocampus
Responsible for knowing where you are in space
Describe trisynaptic circuit of hippocampus
Long term potentiation is observed at 3 synaptic connections in hippocampus
1. Perforant path - granule cell
2. Mossy fibres - CA3 pyramidal cell
3. Schaffer collateral fibres - CA1 pyramidal cell
What is LT potentiation
Changes that remain for a longer period of time, >1yr
Especially if given boosts at various points
Describe induction of LT potentiation of Schaffer collateral - CA1 synapse
- Stimulate Schafer collateral - rise in EPSP
- Give 4 sets of 200Hz pulses through same stimulating electrode - produces tetanus
- Causes increased response to same initial stimulus
How does pairing post synaptic +pre synaptic activity cause LTP
Single stimulus applied to Schaffer collateral - evokes EPSP in post synaptic CA1 neurone
This alone doesn’t elicit any change in synaptic strength
Brief polarisation of CA1 neurons membrane potential alongside the Schaffer stimuli causes persistent increase in EPSP
How to induce LT depression
Low frequency 1Hz stimulation of Schaffer collaterals
Describe specifity LTP
Strong activity induces LTP at active synapse without impacting LTP at nearby inactive synapses
Describe associativity
If pathway 2 is weakly stimulated this alone has no impact on LPT
But if activated together with pathway 1s stronger stimulus both sets of synapses are strengthened
Describe Hebbian learning
Neurones form connections and strength when activated simultaneously
Which muscles are most active in EMG
the muscle with the highest mV
What do you need to know, to know which muscle produced the most force
Muscle activity
How long muscles maintained excitation
Type of contraction
Describe the Dewhurst experiment
Place sensor on belly of biceps brachii
Measure maximal voluntary contraction (hand under table + push up)
Hold forearm parallel to floor, don’t tense
Drop chain on arm - stop arm dropping.
Repeat but let arm drop
M1 textbook reflex latency
<40ms
M2 textbook reflex latency
50 - 100ms
M3 textbook latency
> 100ms
What does the homunculous show
The amount of cortical area devoted to a particular function
What does the homunculous show
The amount of cortical area devoted to a particular function
How was the homunculous discovered/mapped
By wilder Penfield
Doing awake brain stimulation
How was the homunculous discovered/mapped
By wilder Penfield
Doing awake brain stimulation
Describe the make up of the homunculous
Hands and face have largest proportion compared to actual size as need fine sensory / motor function in these areas
What did the merzenich experiments do
Used owl monkey to map sensation in the body to the specific part of the brain
Put a recorder on a specific part of brain, then touched areas of body until got a big response in the receptor.
Allowed them to create a detailed map, including specific reigons of each digit
How did the merzenich experiments test if the brain can retire + remap
Chopped off digit 3 - left monkey for 3 months - retested - digits 2+4 had taken over 3s area
Sutured digits 3+4 together - left 3 months - cortical reigons at the border between 3+4 became responsive to both digits
Can you train the somatosensory system
Yes
Monkeys were trained to spin a can with braille on it with digits 2+3+4 after 3 months their cortical areas had enlarged
How was the motor cortex mapping done
Merzenichs student used squirrel monkeys
Stimulate motor cortex - saw which muscle responded
How motor rewiring tested
Trained monkey to pick up food out of a well
Induced neuronal death in 1 part of brain (affecting dominant hand)
Monkey 1 - no input - retested 3 months later - decreased digit representation, Inc shoulder + elbow representation (learned none use, as just used other hand)
Monkey 2 - intense rehab 3 months unable to use good hand 95% of day, progressively challenging tasks. Digit representation increased
What is learnt none use
Phenomenon commonly seen in stroke pts
The damaged side isn’t used therefore brain wires and representation of damaged areas is reduced
Why is making intensive rehab progressively challenging important
If don’t Inc challenge, recovery plateaus
How does learning a motor skill change the motor map
Area of map used for that skill is increased in representation
Impact of high frequency repetitive transcranial magnetic stimulation
10Hz
Long term potentiation like cortical plasticity
Impact of repetitive low frequency transcraniel magnetic stimulation
1Hz
Long term depression like cortical plasticity
List 10 principles of neuroplasticity
Use it or lose it
Use it + improve it
Specificity
Salience
Transference
Interference
Time
Age
Repetition
Intensity
Describe use it or lose it
Neural connections in brain only stay strong if used
If don’t use they fade and weaken
Describe use it and improve it
Practice a skill often to strengthen neural connections
Describe specificity
Need to target parts of brain in a specific way which is specific to the skill you want to improve
Describe salience
Needs to be meaningful- motivation helps facilitate neuroplastic changes
Describe transference
Learning a skill in 1 situation can be transferred to another similar situation
Describe interference
When you practice and improve skills in 1 area it can interfere with your ability to improve skills in another area
Describe time
Start ASAP after injury -faster rate of improvement
Describe age (neuroplasticity)
Neuroplasticity is greater when young so easy for kids to pick things up but still very much possible when older
Describe repetition
Practicing frequently and consistently is key, Inc frequency = Inc improvement
Describe intensity
Need to keep increasing the level of challenge or improvement will plateau
Describe none-brain based control of movement
Studies removed brain activity meaning they had no voluntary control of movement
We’re able to induce + somewhat control movement.
Eg cat able to walk and change gait pattern to running when treadmill speed up. Demonstrating complexity
Effect of afferent feedback on motor control
Afferent feedback from proprioceptors + exteroceptors can modify ongoing locomotor pattern
What is a stable state
A consistent pattern of movement where nothing changes eg walking
Or remaining stationary
Define attractor
In a dynamic system
Set of states to which a system tends to evolve
What can an attractor be
Can range from simple to very complex
Single point, finite set of points, curve, manifold, strange attractor
What is a strange attractor
The point the systems returns to is never repeated
Stable and unstable patterns of human movements
Both are present if try to inc speed will often revert back to stable patttern
Describe a limit cycle
Cyclical patterns that change course but have some sort of attractor that always pulls it back to the same start point
Describe complexity
Can arise from simplicity, as a few things can accumulate/interact to lead to 1000s of possibilities
Define approximate entropy
Quantifys amount of regularity and the unpredictability of fluctuations in time series data
Define detrended fluctuation analysis
Determines statistical self efficacy of a signal, analysing time series data with long memory processes
Define Lyapunov exponent
Characteristes rule of separation of infinitismally close trajectories as in a lorenz attractor
Define motor skill
Ability to bring about end result with maximum capacity and minimum outlay of energy
Causes of variability
Increasing degrees of freedom
Kinematic movement variations
- motor system noise
-planning errors
- feedback corrections
- abundance/redundant covariation
Define Co variation
Correlated variation between 2 things - 1 things changing causes other thing to change
Define abundance
Having more degrees of freedom than you need
Define redundancy
Have degrees of freedom that are not needed / used
List types of variability
Outcome variability
Execution variability
Define outcome variability
Variability in the results
How the effect of movement is varied
Define execution variability
Kinematic variability
How movement is varied
Describe traditional approach to variability
Want outcome variability to be low therefore want a consistent movement pattern
Motor learning involves reducing variability
Sources of noise in variability
Central - motor commands
Peripheral- sensorimotor system
Potential causes of error/variability in a system
Initialisation error
Planning error
Execution error
Define initilisation error
Starting in a slightly different position requires slightly different movement
Define execution error
How it is completed
Define planning error
Variability in how they move
Types of noise that exist in execution error
Signal dependant - noise is proportional to movement
Signal independent- same amount of noise each time
Temporal - error in timing
Describe dynamical system approach to variability
Variation has a functional role
Adapt to external variables
Covariation
Feedback corrections
Reduce loading in repeatitive actions
Describe tolerance cost
Deviation from tolerant region
How much can movement vary and still be good
Define noise cost
Dispersion in execution variables
Overall level of variation
High bar variability study
Mechanically important factors had less variation in elite athletes
Mechanically unimportant factors had less variation in non-elite athletes
How can we measure variability
Discrete measures - parametric = standard deviation + coefficient of variation
Non parametric = interquartile range, median absolute deviation
Continuous measures - continuous relative phase (phase angles)
Describe dynamical systems theory
Task, environmental and individual constraints affect perception of options available to you, in turn effect the action you do, perception of the action leads to physical performance
Define coordination
Function that constrains degrees of freedom into behavioural unit
Define control
Process of parameterising, scaling or tuning the coordination function
Define performance outcome
The product or result of an action
List 4 coordination patterns
Inphase
Anti-phase
Proximal dominancy
Distal dominancy
Describe inphase
Both segments rotate in same direction
Describe anti-phase
Both segments rotate in opposite directions
Describe proximal dominancy
Proximal segment is the dominant contributor to a relative movement
Describe distal dominancy
Distal segment is the dominant contributor to a relative movement
How to assess coordination
Angle-angle diagram = qualitative
Vector coding - quantitative
Describe angle angle diagram
Proximal segment angle (x) vs distal segment angle (y)
Segment that varies more = dominant segment
1 angle Inc one angle dec = anti phase
Describe vector coding
Vector orientation between 2 adjacent data points on an angle angle diagram relative to the right horizontal
Outcome measure = coupling angle - angle at which the 2 things are coupled together
Describe coordination pattern
Coupling angles from vector coding are assigned different colours and mapped
Dominant segment - changes the most
What is a segmental dominancy profile
Provides info on coupling angle distribution within a coordination pattern classification
What is an inter data point ROM
Provides info on patterns of control
Eg dominant segment ROM at each instant in time
Describe continuous relative phase
Step 1 - phase plane - Plots 1 joint/ segment at a time on a graph of normalised angular displacement (x) vs normalised angular velocity (y).
Step 2 = phase angle - measures angle at centre 0 to the point
Step 3 = calculate difference between phase angles for 2 segments
0 degrees = complete inphase
180 degrees = complete antiphase
Define synergy
Interaction or cooperation of 2 or more things to produce a combined effect greater than the sum of their separate effects
Define motor synergy
2+ parts of the neuromuscular system, controlled by the CNS + that have intention, working together towards a common goal
3 types of motor synergy
Anatomical- move joint in same direction eg elbow flexors
Joint movement synergists- generate a moment in a particular direction-can build to complete task
Task synergist- action assists or resists task performance
What does a synergy do
Reduces dimensionality- so fewer controls are needed for many degrees of freedom
May decrease CNS demands, may decrease errors in performance
What is the uncontrolled manifold hypothesis
Relates to task specific variability in a redundant system
System acts in a multidimensional space where 1 dimension = 1 degree of freedom
The UCM is a sub space where desired performance occurs for a task specific variable
Use covarience to ensure variance stays within UCM
What is a kinematic synergy
Occurs at a movement level
Kinematic variables eg joint angles, are viewed as the elemental variable
How do multi joint synergies work
VUCM > VORTH
Helps stabilise performance by decreasing variability in key joints but not in unimportant ones
Can use covariance as using multiple joints to complete task
Describe kinetic synergies
Kinetic variance eg force/moment is viewed as the elemental variable
Uses central strategies to solve tasks, VUCM>VORTH
Describe muscle synergies
Muscle activations viewed as elemental variables
But hard to create link between activations and mechanics
Eg if walking each muscle group (knee flexors etc) form a synergy
To complete task each muscle within that synergy is activated in the same way - easier to control as only 1 input for multiple outputs.
How does practicing a movement effect UCM
As you practice - get better so variance reduces
Therefore can briefly increase variability of less important variables to allow for refinement and further improvement.
As you increase efficiency UCM gets smaller
