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Advanced Motor Control Flashcards

1
Q

What is motor control

A

The ability to regulate or direct mechanisms essential to movement

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2
Q

Why do we have brains?

A

They allow muscle contraction letting us interact with world around us

Sea squirts used as evidence (digest brain when no longer move)

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3
Q

What is a degree of freedom

A

The number of parameters in a system that may vary independently (how many things that can change)
1 variable = 1 degree of freedom

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4
Q

Name bernsteins stages of motor learning

A

Stage 1 Freezing
Stage 2 Releasing and reorganising
Stage 3 Exploiting mechanical properties

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5
Q

Describe stage 1 of Bernsteins stages of motor learning

A

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

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6
Q

Methods of ‘Freezing’

A

Freeze the joint by locking it out
Coupling joints together so that when 1 joint does something, the other one does the same

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7
Q

Describe stage 2 of Bernsteins stages of motor learning

A

Releasing and reorganising- as you get more proficient in a skill, you release previously frozen movements to improve power/speed/accuracy etc

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8
Q

Describe stage 3 of Bernsteins stages of motor learning

A

The motor system takes advantage of inherent mechanical properties allowing for better performance and energy use.
Eg Proximal to distal weighting

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9
Q

Define action potential

A

A change in electrical potential associated with the passage of an impulse along the membrane of a muscle or nerve cell

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10
Q

Define resting potential

A

The difference in ions across a membrane at rest, inside the cell is negative

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11
Q

How is resting potential maintained?

A

Na+/K+ pump 3Na are pumped out and 2K pumped in by active translocation which requires ATP

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12
Q

What is the all or nothing threshold

A

Threshold sits at -55mv if it is reached an action potential will fire, if not reached there is no action potential

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13
Q

Define refractory period

A

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

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14
Q

Define Temporal summation

A

The effect of multiple impulses received in the same place an add up to reach the threshold if received in quick enough succession

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15
Q

Define Spatial summation

A

Inputs from multiple neurons can trigger an AP

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16
Q

How is an AP propagated

A
  1. Depolarisation - voltage-gated Na+ channels open so inside of cell becomes more positive
  2. This causes voltage gated K+ channels to open + K+ to leave the cell
  3. Myelin increases the spread of electrical conduction by increasing membrane resistance and decreasing membrane capacitance.
  4. Therefore spread is rapid between each node of ranvier where more depolarisation occurs (Saltatory conduction)
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17
Q

Describe stochastic resonance

A

Noise lowers the threshold to maximise transfer of info. (Noise causes oscillation so easier to reach threshold)

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18
Q

Potential risk of stochastic resonance

A

If too much noise, may always be over the threshold

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19
Q

What is a motor unit

A

Smallest functional unit of motor system
Motor neuron + muscle fibres it innervates

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20
Q

How does a motor unit improve control

A

Cannot stimulate individual muscle fibres, by grouping them together it improves control as have less degrees of freedom

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21
Q

Why is there a delay between input and twitch contraction

A

Need time for Ca2+ to be released and initiate the sliding filament theory

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22
Q

Describe the sliding filament theory

A
  1. Ca2+ binds to troponin C which changes conformation
  2. This causes movement of tropomyosin away from myosin binding sites on the actin
  3. Cross bridge forms
  4. Power stroke occurs pulling actin towards the M line
  5. New ATP binds to myosin head breaking the cross bridge between actin +myosin
  6. Myosin head hydrolyses ATP to ADP + P ion, previous steps repeat until Ca2+ actively pumped back to sarcoplasmic reticulum
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23
Q

Define Tetanic contraction

A

Repeated stimuli at short intervals lead to motor unit being maximally activated + therefore maximum force output is reached

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24
Q

Name 3 types of motor unit

A

Slow twitch
Fast, Fatigue resistant
Fast twitch

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25
Q

What is the size principle

A

Small motor units in a muscle are recruited first

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26
Q

Benefits of size principle

A

Recruitment can stop when desired force reached
Large forces are not produced if not required
Orderly recruitment reduces complexity

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27
Q

Which motor units are typically smaller

A

Slow twitch are smaller as have smaller motor neurones, so therefore have a slightly lower threshold

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28
Q

How do you annotate excitation

A

Open circle

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29
Q

How do you annotate inhibition

A

Closed circle

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30
Q

What is a renshaw cell

A

Interneuron in the spinal cord, stimulated by alpha motor neurons
Uses negative feedback and reccurant inhibition to limit firing of motor neurons

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31
Q

Benefits of renshaw cells

A

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)

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32
Q

Define muscle spindle

A

Stretch receptor that signal length/ changes in length of muscles

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33
Q

Muscle spindle position

A

Intrafused so sits within the muscle fibre and runs parallel to it

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34
Q

Describe bag fibre

A

Part of muscle spindle, senses change in velocity

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35
Q

Describe chain fibre

A

Part of muscle spindle, senses changes in length

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36
Q

Describe monosynaptic reflex arc

A

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

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37
Q

Describe difference between monosynaptic and polysynaptic reflex arc

A

Mono 1 synapse - only agonist muscle stimulated

Poly -multiple synapses - allows inhibition of anatagonist as well as contraction of agonist

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38
Q

What is the H-reflex

A

Artificially created stretch receptor, can be better controlled allowing you to assess response in a lab setting

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39
Q

Describe reciprocal inhibition

A

Used in polysynaptic reflexes

Interneurons form a second synapse that sends signals to a heterogenic muscle, typically inhibiting it

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40
Q

Benefits of reciprocal inhibition

A

Allows second muscle to do the opposite action to the agonist, allowing the agonist to have greater effect

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41
Q

What is Golgi tendon organ

A

Sensory receptor located near junction of muscle and tendon, detects change in muscle tension

Lies in series with extrafusal fibres

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42
Q

Golgi tendon organ role

A

Signals 1b afferent neurones
If muscle force exceeds threshold, GTO inputs inhibit alpha motor neurones, lowering the force produced

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43
Q

What are central control mechanisms

A

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

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44
Q

What is electromyography

A

Records changes in muscle electrical potential, estimating muscle excitation

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45
Q

Electromyography methods

A

Indwelling - Needle, Fine wire
Surface EMG - Bipolar surface (used in sport)

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46
Q

Benefits of indwelling EMG

A

More localised pick up
More accurate

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47
Q

Surface EMG pros

A

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

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48
Q

Surface EMG cons

A

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

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49
Q

EMG positioning - electrode separation

A

10mm separation has best signal to noise ratio across all levels of crosstalk

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50
Q

EMG positioning - crosstalk

A

Try to avoid positioning too close to other muscles to avoid interference

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51
Q

Where on a muscle should you put the electrode for an EMG

A

The belly
Thickest part of muscle has the biggest signal

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52
Q

In what direction should the electrode be

A

Parallel to muscle fibres

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53
Q

How to prepare skin for EMG

A

want as little stuff between muscle and electrode as possible
Shave hair
Sandpaper off any dead skin
Use alcohol wipe to remove oils

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54
Q

What is an analogue to digital converter

A

Converts continuous signals to finite numbers
Eg electrical potential continuously changing but measurements are taken at distinct time points

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55
Q

Analogue to digital converter limitations

A

Potential for errors as may not take measurements at right time

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56
Q

What is ADC amplitude resolution

A

The amplitude resolution of the analogue to digital converter measurements
Measured in BITs (2 to the power of the number)

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57
Q

What is time resolution

A

How often measurements are taken

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58
Q

Problems with time resolution

A

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

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59
Q

Describe EMG signal

A

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

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60
Q

What is in a raw EMG signal

A

Quiet time, bursts of muscle excitation
Lots of noise - want to remove

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61
Q

What is sampled signal

A

True signal + measurement errors + noise

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62
Q

What do you do in Full wave recitification

A

Flip any negative values to make whole signal positive

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63
Q

What is a low pass filter

A

It allows any low frequencies through but removes high frequency signals from data

Are methods to be able to remove specific frequencies too

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64
Q

How to work out how much force an individual muscle contributes?

A

Compare signal to % of maximum voluntary contraction

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65
Q

How to identify when a change in muscle excitation occurs

A

Work out mean and standard deviation of baseline
When it changes more than 3 standard deviations classed as something happening

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66
Q

EMG applications

A

Clinical practice
Resistance training
Research
Simulation
Biofeedback

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67
Q

Define neuroplasticity

A

Ability of the brain to form + recognise synaptic connections, particularly in response to learning or following an injury

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68
Q

Define EPSP

A

Excitatory post synaptic potential

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69
Q

Describe habituation

A

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

70
Q

Describe sensitisation

A

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.

71
Q

Describe classical conditioning

A

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

72
Q

Hippocampus role

A

Helps convert ST memories to LT memories, particularly active at night.

73
Q

Function of place cells

A

In hippocampus
Responsible for knowing where you are in space

74
Q

Describe trisynaptic circuit of hippocampus

A

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

75
Q

What is LT potentiation

A

Changes that remain for a longer period of time, >1yr
Especially if given boosts at various points

76
Q

Describe induction of LT potentiation of Schaffer collateral - CA1 synapse

A
  1. Stimulate Schafer collateral - rise in EPSP
  2. Give 4 sets of 200Hz pulses through same stimulating electrode - produces tetanus
  3. Causes increased response to same initial stimulus
77
Q

How does pairing post synaptic +pre synaptic activity cause LTP

A

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

78
Q

How to induce LT depression

A

Low frequency 1Hz stimulation of Schaffer collaterals

79
Q

Describe specifity LTP

A

Strong activity induces LTP at active synapse without impacting LTP at nearby inactive synapses

80
Q

Describe associativity

A

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

81
Q

Describe Hebbian learning

A

Neurones form connections and strength when activated simultaneously

82
Q

Which muscles are most active in EMG

A

the muscle with the highest mV

83
Q

What do you need to know, to know which muscle produced the most force

A

Muscle activity
How long muscles maintained excitation
Type of contraction

84
Q

Describe the Dewhurst experiment

A

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

85
Q

M1 textbook reflex latency

A

<40ms

86
Q

M2 textbook reflex latency

A

50 - 100ms

87
Q

M3 textbook latency

A

> 100ms

88
Q

What does the homunculous show

A

The amount of cortical area devoted to a particular function

89
Q

What does the homunculous show

A

The amount of cortical area devoted to a particular function

90
Q

How was the homunculous discovered/mapped

A

By wilder Penfield
Doing awake brain stimulation

91
Q

How was the homunculous discovered/mapped

A

By wilder Penfield
Doing awake brain stimulation

92
Q

Describe the make up of the homunculous

A

Hands and face have largest proportion compared to actual size as need fine sensory / motor function in these areas

93
Q

What did the merzenich experiments do

A

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

94
Q

How did the merzenich experiments test if the brain can retire + remap

A

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

95
Q

Can you train the somatosensory system

A

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

96
Q

How was the motor cortex mapping done

A

Merzenichs student used squirrel monkeys
Stimulate motor cortex - saw which muscle responded

97
Q

How motor rewiring tested

A

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

98
Q

What is learnt none use

A

Phenomenon commonly seen in stroke pts
The damaged side isn’t used therefore brain wires and representation of damaged areas is reduced

99
Q

Why is making intensive rehab progressively challenging important

A

If don’t Inc challenge, recovery plateaus

100
Q

How does learning a motor skill change the motor map

A

Area of map used for that skill is increased in representation

101
Q

Impact of high frequency repetitive transcranial magnetic stimulation

A

10Hz
Long term potentiation like cortical plasticity

102
Q

Impact of repetitive low frequency transcraniel magnetic stimulation

A

1Hz
Long term depression like cortical plasticity

103
Q

List 10 principles of neuroplasticity

A

Use it or lose it
Use it + improve it
Specificity
Salience
Transference
Interference
Time
Age
Repetition
Intensity

104
Q

Describe use it or lose it

A

Neural connections in brain only stay strong if used
If don’t use they fade and weaken

105
Q

Describe use it and improve it

A

Practice a skill often to strengthen neural connections

106
Q

Describe specificity

A

Need to target parts of brain in a specific way which is specific to the skill you want to improve

107
Q

Describe salience

A

Needs to be meaningful- motivation helps facilitate neuroplastic changes

108
Q

Describe transference

A

Learning a skill in 1 situation can be transferred to another similar situation

109
Q

Describe interference

A

When you practice and improve skills in 1 area it can interfere with your ability to improve skills in another area

110
Q

Describe time

A

Start ASAP after injury -faster rate of improvement

111
Q

Describe age (neuroplasticity)

A

Neuroplasticity is greater when young so easy for kids to pick things up but still very much possible when older

112
Q

Describe repetition

A

Practicing frequently and consistently is key, Inc frequency = Inc improvement

113
Q

Describe intensity

A

Need to keep increasing the level of challenge or improvement will plateau

114
Q

Describe none-brain based control of movement

A

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

115
Q

Effect of afferent feedback on motor control

A

Afferent feedback from proprioceptors + exteroceptors can modify ongoing locomotor pattern

116
Q

What is a stable state

A

A consistent pattern of movement where nothing changes eg walking
Or remaining stationary

117
Q

Define attractor

A

In a dynamic system
Set of states to which a system tends to evolve

118
Q

What can an attractor be

A

Can range from simple to very complex
Single point, finite set of points, curve, manifold, strange attractor

119
Q

What is a strange attractor

A

The point the systems returns to is never repeated

120
Q

Stable and unstable patterns of human movements

A

Both are present if try to inc speed will often revert back to stable patttern

121
Q

Describe a limit cycle

A

Cyclical patterns that change course but have some sort of attractor that always pulls it back to the same start point

122
Q

Describe complexity

A

Can arise from simplicity, as a few things can accumulate/interact to lead to 1000s of possibilities

123
Q

Define approximate entropy

A

Quantifys amount of regularity and the unpredictability of fluctuations in time series data

124
Q

Define detrended fluctuation analysis

A

Determines statistical self efficacy of a signal, analysing time series data with long memory processes

125
Q

Define Lyapunov exponent

A

Characteristes rule of separation of infinitismally close trajectories as in a lorenz attractor

126
Q

Define motor skill

A

Ability to bring about end result with maximum capacity and minimum outlay of energy

127
Q

Causes of variability

A

Increasing degrees of freedom
Kinematic movement variations
- motor system noise
-planning errors
- feedback corrections
- abundance/redundant covariation

128
Q

Define Co variation

A

Correlated variation between 2 things - 1 things changing causes other thing to change

129
Q

Define abundance

A

Having more degrees of freedom than you need

130
Q

Define redundancy

A

Have degrees of freedom that are not needed / used

131
Q

List types of variability

A

Outcome variability
Execution variability

132
Q

Define outcome variability

A

Variability in the results
How the effect of movement is varied

133
Q

Define execution variability

A

Kinematic variability
How movement is varied

134
Q

Describe traditional approach to variability

A

Want outcome variability to be low therefore want a consistent movement pattern
Motor learning involves reducing variability

135
Q

Sources of noise in variability

A

Central - motor commands
Peripheral- sensorimotor system

136
Q

Potential causes of error/variability in a system

A

Initialisation error
Planning error
Execution error

137
Q

Define initilisation error

A

Starting in a slightly different position requires slightly different movement

138
Q

Define execution error

A

How it is completed

139
Q

Define planning error

A

Variability in how they move

140
Q

Types of noise that exist in execution error

A

Signal dependant - noise is proportional to movement
Signal independent- same amount of noise each time
Temporal - error in timing

141
Q

Describe dynamical system approach to variability

A

Variation has a functional role
Adapt to external variables
Covariation
Feedback corrections
Reduce loading in repeatitive actions

142
Q

Describe tolerance cost

A

Deviation from tolerant region
How much can movement vary and still be good

143
Q

Define noise cost

A

Dispersion in execution variables
Overall level of variation

144
Q

High bar variability study

A

Mechanically important factors had less variation in elite athletes
Mechanically unimportant factors had less variation in non-elite athletes

145
Q

How can we measure variability

A

Discrete measures - parametric = standard deviation + coefficient of variation
Non parametric = interquartile range, median absolute deviation

Continuous measures - continuous relative phase (phase angles)

146
Q

Describe dynamical systems theory

A

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

147
Q

Define coordination

A

Function that constrains degrees of freedom into behavioural unit

148
Q

Define control

A

Process of parameterising, scaling or tuning the coordination function

149
Q

Define performance outcome

A

The product or result of an action

150
Q

List 4 coordination patterns

A

Inphase
Anti-phase
Proximal dominancy
Distal dominancy

151
Q

Describe inphase

A

Both segments rotate in same direction

152
Q

Describe anti-phase

A

Both segments rotate in opposite directions

153
Q

Describe proximal dominancy

A

Proximal segment is the dominant contributor to a relative movement

154
Q

Describe distal dominancy

A

Distal segment is the dominant contributor to a relative movement

155
Q

How to assess coordination

A

Angle-angle diagram = qualitative
Vector coding - quantitative

156
Q

Describe angle angle diagram

A

Proximal segment angle (x) vs distal segment angle (y)
Segment that varies more = dominant segment
1 angle Inc one angle dec = anti phase

157
Q

Describe vector coding

A

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

158
Q

Describe coordination pattern

A

Coupling angles from vector coding are assigned different colours and mapped
Dominant segment - changes the most

159
Q

What is a segmental dominancy profile

A

Provides info on coupling angle distribution within a coordination pattern classification

160
Q

What is an inter data point ROM

A

Provides info on patterns of control
Eg dominant segment ROM at each instant in time

161
Q

Describe continuous relative phase

A

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

162
Q

Define synergy

A

Interaction or cooperation of 2 or more things to produce a combined effect greater than the sum of their separate effects

163
Q

Define motor synergy

A

2+ parts of the neuromuscular system, controlled by the CNS + that have intention, working together towards a common goal

164
Q

3 types of motor synergy

A

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

165
Q

What does a synergy do

A

Reduces dimensionality- so fewer controls are needed for many degrees of freedom
May decrease CNS demands, may decrease errors in performance

166
Q

What is the uncontrolled manifold hypothesis

A

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

167
Q

What is a kinematic synergy

A

Occurs at a movement level
Kinematic variables eg joint angles, are viewed as the elemental variable

168
Q

How do multi joint synergies work

A

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

169
Q

Describe kinetic synergies

A

Kinetic variance eg force/moment is viewed as the elemental variable
Uses central strategies to solve tasks, VUCM>VORTH

170
Q

Describe muscle synergies

A

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.

171
Q

How does practicing a movement effect UCM

A

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

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