Neuromuscular Flashcards
draw the motor neuron and label its components
what is a ‘pool’ of MN’s?
an amount of MN;s in the spinal cord that control a given muscle or muscle group
what do motor neurons do ?
they receive and integrate excitatory and inhibitory inputs from neurons originating in the brain, spinal cord and periphery
what is the definition of a motor unit (MU)
a motor neuron and the muscle fibres it innervates
tension is inversely proportional to MU size - true or false
false- directly proportional
low innervation ratio ( small #) will do what
rely more on rate coding than recruitment to increase force output
what is the size of an action potential recorded by intramuscular EMG indicative of
( microphone analogy ) how close the active motor unit is to the recording site
higher innervation ratio ( large #) will do what
more coarse control ( e.g. trunk and proximal limb muscles )
type 1 (s) motor unit properties:
smallest
high oxidative
low glycolytic
slow twitch
low fatiguability
type IIa (FR) motor unit properties:
medium size - recruited second
medium oxidative
high glycolytic
fast twitch
low fatiguability
type IIb (FF) motor unit properties :
largest
low oxidative
high glycolytic
fast twitch
high fatiguability
what is the hennemans size principle?
excitatory input required to reach threshold increases with soma size (i.e. activation threshold increases with soma size)
- recruited smallest to largest because less energy required to recruit smaller first
functional consequences of hennemans size principle
-simplifies the task of modulating force
- ensures a smooth increase in force production
- minimizes fatigue as slow twitch, fatigue - resistant muscle fibres are activated first
how is force production controlled
-motor neuron pool controls force by :
-number of active motor units (recruitment)
-discharge rate of active motor units ( rate coding)
do all muscles use rate coding and rectuitment to the same extent? why or why not
no, control strategy varies by muscle due to:
-number of motor units
-force (% maximum) at which recruitment is complete
-maximal discharge rates
what is surface EMG
-non invasive way of measuring motor neuron output (listening to a convo through a door)
set-ups for voluntary surface EMG
-MONOPOLAR SET-UP (electrodes far apart)
- highly sensitive to ‘cross-talk’ (will pick up signals from other muscles)
-best for evoked responses
-BI-POLAR SET-UP (electrodes closer)
-most common set-up
-less sensitive to cross-talk
-willl have more phase cancellation and amplification (weird evoked responses like an M wave)
if you measure EMG across days.. what would you need to control?
-placement of electrodes
-environmental factors (humidity)
raw emg provides relatively little information - true or false
true
what are the common processing methods of surface EMG
- root mean square (RMS) amplitude
-full-wave rectification (rectified EMG)
-integration (integrated EMG ; iEMG)
what is the root mean square method (RMS)
calc works in reverse- S-M-R
1) square all amplitudes (to prevent + and - values from cancelling)
2) calculate mean of all amplitudes from part 1
3) take the square root of the mean from pt2
what is the full-wave rectification method
where absolute values are taken of each data point so the entire waveform is positive
what is the integrated EMG method (iEMG)
calculated as the area under the curve of rectified EMG signal (units change from mV to mV.s to reflect the inclusion of time)
what is the equation for force/what is force
F= ma
-a push or pull
-pulling forces are tensile forces
what is muscular force
measure of the tension developed by a muscle
what is torque/ equation for torque
turning effect caused by a force about an axis
T= Fr (r=momentum arm)
what is muscular torque
torque produced by muscles is responsible for movement of our limbs about our joints
where do slow-twitch fibres tend to be located
tend to be more centrally located
what is innervation ratio equal to
innervation ratio = # of muscle fibres/ MU
what is phase cancellation when looking at a surface emg ?
if the muscle fibers are misaligned or oriented in a way that produces signals with opposite phases, the EMG signals may cancel each other out, leading to a reduction or elimination of the recorded signal. This phenomenon is known as phase cancellation.
what are the limitations of surface emg
-gives limited insights into characteristics of the active MUs
-volume conduction (the action potentials are recorded a long way from their source)
- low pass filtering (adipose tissue and skin drastically alter the signal)
what is INTRAMUSCULAR EMG (IEMG)
(like inserting a microphone into a choir and trying to figure out which one is singing)
- electrode inserted into a muscle can record motor unit potentials (MUPs) at close range
-yields data about - discharge rates, recruitment and derecruitment and signal complexity
limitations of iEMG
- Reflects activity of a small number of MUs near the recording zone of the electrode
-challenging to track the same MUs
-invasive
-best suited to low-moderate intensity iso contractions
what are the different types of electrodes
-tungsten microelectrode
(0.125mm diameter)
-Fine wire
(0.05mm diameter/ inserted via a 25 gauge hypodermic needle
amplitude of MUP is NOT indicative of MU size (tension or innervation ratio) - true or false
-true
indicative of proximity to recording zone
what is the onion skin model
discharge rates decrease from earliest to latest recruited MUs (high motor unit firing rates with low threshold units)
what is the reverse onion skin model
discharge rates increase from earliest to latest recruited MUs. (matches contractile speed of muscle fibres to discharge rates)
when would the reverse onion skin model be superior for?
-high force contractions / brief tasks
true or false: derecruitment thresholds are often higher
false , lower
true or false: discharge rates are lower are derecruitment
true
what is the clinical applications for transcutaneous electrical stimulation (TES)
-diagnostics, disease progression, and treatment methods
-used in physio clinics to help reactivate muscle fibres (e.g. post surgery)
what does stimulation of the nervous system within a research setting enable us to do?
-assess responsiveness of multiple sites within the central and peripheral nervous systems & muscle fibres
-seperate the nervous and muscular systems (electrical and mechanical responses)
-can be compared to voluntary responses to quantify central fatigue
what are the common sites of stimulation? (TES)
-cortical
-spinal
-peripheral nerve
-muscle belly
draw the motor pathway (pg 8 of NM 3)
What does spinal stimulation produce?
produces a short-latency response termed the cervicomedullary motor evoked potential (CMEP)
What does peripheral stimulation produce?
stimulation applied to a peripheral nerve will evoke a compound muscle action potential (CMAP a.k.a M-wave)
what is a maximal M-wave
increase stimulus intensity with successive stimuli until wave size reaches a plateau (Mmax)
-when size doesn’t increase despite an increase in current, all motor units of a muscle have been activated
what is the vital importance of Mmax?
-expressing responses to cortical or spinal stem as a % Mmax enables us to assess a comparable portion of the motor pathway
-across individuals
-with different stimuli within an individual
what is a twitch
response to a single stimulus
what is a doublet
response to 2 stimuli 10ms apart (i.e., 2 pulses @ 100hz)
what is tetanus
-response to multiple stimuli at low, moderate, or high frequencies (e.g. 0.5s or 1s @ 10, 20, 50 or 100Hz)
what is a train
-multiple stimuli that will evoke tetanus
what is Hz?
unit of frequency (impulses per second
what do force/torque responses assess?
allow assessment of intrinsic contractile properties of muscle
-influence of central ns has been removed
How are twitches and tetani measured? (In terms of)
-peak force responses
-rate of force development/relaxation
-time to peak and half-relaxation
Can be used to estimate central fatigue using the interpolated twitch technique (ITT)
ADVANTAGES of peripheral nerve (i.e nerve trunk) stim
-depolarizers axons according to diameter, like how the muscle would naturally be activated (i.e., activated motor unites are randomly distributed through the muscle)
-easy to activate all axons
- evoke high forces with a relatively low stimulus intensity (i.e. requires less current than muscle belly)
DISADVANTAGES of peripheral nerve stim
-activates axons of other muscles innervated by that nerve (sometimes antagonists)
-can be difficult to maintain electrode position
-poor reducibility
-may not be accessible
ADVANTAGES of muscle belly stim
-easy to maintain electrode position
-high reproducibility
-hence, it is commercially available
DISADVANTAGES of muscle belly stim
-activates muscle fibres closest to skin
-fast-twitch fibres tend to be superficial so fatigue occurs rapidly
-can’t activate all nerve endings (muscle fibres)
-antagonist muscle will be stimulated if intensity is too high
-relative to nerve trunk stimulation, requires a higher stimulus intensity to evoke a given force (increased discomfort)
Cortical stim evokes which response
MEP (motor evoked potential)
Spinal stim evokes which response
CMEP/H-reflex (cervicomedullary motor evoked potential/ Hoffmann reflex)
Peripheral stim evokes which response
M-wave/Mmax
What physiological mechanisms contribute to sex-based differences
-muscle perfusion
-skeletal muscle metabolism
-fibre type properties
What non-physiological mechanisms that contribute to sex-based differences
Bias in sex-based research where males are researched more than females in both Human and animal models
What are the general sex-based differences
-anatomical and physiological differences between the sexes that often lead to functional differences in performance and fatiguability
-magnitude of sex differences (if they exist) are TASK DEPENDENT (duration, intensity, speed of contraction, muscle group involved, environmental factors .. etc)
General male differences
Typically have greater muscle mass and their whole muscles are often stronger and can produce more power compared to females
-faster contractile properties
-Greater reliance on anaerobic /glycolitic metabolism
General female sex-based differences
Generally have greater proportional area of type 1 muscle fibres, less fatiguable
-greater reliance on oxidative properties
-slower contractile properties
When intensity is lower and contractions /exercise is sustained, females often fatigue _______ than males
Less
How do we compare relative changes
Normalize
Explain the steps of EC coupling and explain what could happen if there is a problem with one of the steps
What are internal forces
-forces that act within the object or system (body)
What are external forces
-forces acting on an object or a system (non-contact force=gravity)
What are some internal factors which influence the maximal force developed by a muscle
-arrangement of fibres (muscle design)
-size (cross sectional area) of muscle fibres
-# of muscle fibres
-proportion of muscle fibre types
-intrinsic force of muscle fibers (strength per cross sectional area/specific strength)
Draw a parallel muscle
Draw a unipennate muscle
Draw a bipennate muscle
Draw a circular muscle
Length in muscle design
In series arrangement of fibres
-maximizes the range of motion and shortening velocity but does not affect strength
Width in muscle design
In parallel arrangement of fibers
-maximizes the force of the muscle (increases cross-sectional area)
Angular muscle design
Fibers at an angle to the line of pull maximize the number of fibers for a given volume of muscle
Whole muscle force is greater when fibers are on an angle because
There are more fibers
What are some external factors that influence the maximal force developed by muscles
-length
-velocity
-neural drive to the agonist/antagonist muscles (e.g., voluntary drive)
Maximal shortening velocity of a muscle fibre depends on :
-length (#of sarcomeres in series)
-fibre type (myosin ATPase control rate of cross bridge cycling)
Shortening contractions (less F more V)
-faster actin and myosin slide past each other, the more binding sites are missed
Lengthening contractions (F^ with V^)
-stretching of partially activated sarcomeres
-greater average force per cross bridge cycle
-faster cross bridge reattachment
Isokinetic contractions
Angular velocity is constant and maximal torque exerted is measured
Isotonic contractions
External load is “constant” and maximal velocity achieved is measured
What is muscle power?
The ability to generate maximal force as fast as possible
P=F x v
-more relevant than muscle strength (force)
-most activities are dynamic (not static)
-impacted by both force and velocity
Both III/IV afferents ‘sample’ the interstitial space within the muscle true or false
True
III/IV afferents send information back to the PNS true or false
False -CNS
How could we manipulate III/IV afferent feedback (I.e., attenuate and augment sensitivity) within a lab setting (I.e., increase feedback ?)
PECO (post exercise cuff occlusion)- because it traps metabolites which continues to stimulate the metaboreflex, without central command (voluntary drive)
How do we decrease III/IV afferent feedback
Fentanyl block will partially block III/IV afferent feedback from the lower limbs when injected at L3-L4
^peripheral fatigue - decreases central fatigue =feel no pain
What is cortical stimulation
Cortical stimulation can be done using -transcranial electric stimulation (TES)
-transcranial magnetic stimulation (tms) of the motor cortex is a commonly applied technique to investigate motor output
What is TMS?
Transcranial magnetic stim
- TMS utilizes electromagnetic induction to depolarize the axons of neurons within the primary motor cortex
What are the uses of TMS
- Diagnostic tool
Will indicate damage to motor pathway due to: - spiral cord injury (sci) - MS or amyotrophic lateral sclerosis - stroke - therapeutic technique
Repetitive TMS (rTMS) has been shown to alter resting membrane potentials (and excitability ) of targeted cites within the CNS - used to treat movement & psychiatric disorders - research (single / double pulse)
Age, sex - related differences, fatigue, environmental stress, etc.
What are the different coil types?
- Double (figure 8) coil
- single coil
- double cone coil
What is the double (figure 8 ) coil used for
- Most commonly used (most research is hand muscles)
- most focused (placement is critical)
- least powerful (useless for lower limbs)
What is the single coil used for
- 2nd most commonly used
- low locality
- moderately powerful (good for proximal arm muscles)
What is the double cone coil used for
- Least commonly used
- low locality (placement is forgiving)
- most powerful (needed for trunk and leg muscles)
What does a motor evoked potential represent (MEP)
Represents excitability of the motor pathway
What does the silent period represent
- Represents inhibitory reflexes (intracortical inhibition)
What does stimulation of the nervous system allow us to assess
- Assess the responsiveness of multiple sites within the central & peripheral nervous systems & the muscle fibers themselves
- separate the nervous & muscular systems (electrical & mechanical responses)
What we the advantages of TMS
- Less painful than electrical stim
- car stimulate deep cortical neurons noninvasively
- some types provide therapeutic treatments
What are the disadvantages of TMS
- Very expensive
- requires high trained individuals
- coil type matters
- not everyone can receive the stimulus
Which technique is commonly used to augment III/IV efferent feedback INDEPENDENTLY of voluntary drive
PECO
How will III/IV muscle afferent feedback influence the development of peripheral fatigue during exercise
-III/IV muscle afferents are responsible for the Afferent arm (i.e., the sensor) of the cardiovascular and ventilators reflex responses to exercise
- muscle perfusion and O2 delivery directly alter thefatiguability of skeletal muscle
- therefore, neural feedback from working muscles (I. E. Intact muscle afferent feedback) is VERY important for endurance exercise capacity
How will III/IV muscle afferent feedback influence the development of central fatigue during exercise
-III/IV afferent feedback from working muscles facilitates central fatigue by exerting inhibitory influences on central motor drive during exercise
- when these afferents are partially blocked, central motor drive (as measured by iEMG) is much higher early on during a time trial, contributing to greater fatigue
What is the advantages of blocking III/IV afferents
-highly reproducible responses
-less confounding variables than a single limb blockade
Disadvantages of blocking III/IV afferents
-can only partially block the afferents of the lower limb (can only partially blocked the afferents of the lower limb (without knowing by how much)
-requires highly skilled personnel
-very invasive
What might cause a rightward shift in a force-frequency curve?
-a faster muscle
-force needs a greater input to elicit same response
-sarcoplasmic reticulum (SR) quickly sequesters Ca2+
(Muscle requires a higher input to generate the same amount of force)
What might cause a leftward shift in a force-frequency curve
- slower muscle
-force will summate more quickly
-SR taking longer to sequester Ca2+
-mostly due to slowed relaxation time (movement of Ca2+ in and out of SR)
Right and leftward shifts in the force frequency relationship depend on …
How long it takes for force to summate. This happens because the contractile properties are faster or slower ( less to do with recruitment and everything to do with how much intracellular calcium is available to aid in cross-bridge cycling)
Which of the 2 EMG responses elicited by TMS represents intracortical inhibition and what are the units of the measurement
The silent period (milliseconds)
Which of the two EMG responses elicited by TMS represents the excitability of the motor partway and what are the units of the measurement
Motor evoked potential (MEP) (milivolts)
-normalized to Mmax
What is the relationship between MEP amplitude and TMS output in the biceps brachii
Sigmoidal relationship
What is the relationship between SP duration and TMS output in the biceps brachii
Linear relationship
Validity vs reliability
Validity: refers to the accuracy of a measurement
Reliability: refers to the reproducibility of the measurement/technique ( how many times can you get the same results from one person (intra-) or between individuals (inter-))
What are the common wearables in the fitness tracking world
-movement sensors (pedometers, accelerometers, GPS)
-Physiological sensors (HR monitors, sleep monitors, temp sensors or integrated systems)
(Sensors can be highly variable (use different technologies) and detect multiple parameters)
What is accelerometry
Small microelectromechanical devices that detect changes in acceleration (with reference to earths gravitational pull) as a mechanical disturbance which is then converted to an electrical signal.
This electrical signal is transmitted to an external device
What are the 2 common methods that wearables use to measure HR?
-peripheral pulse detected by photoplethysmography (i.e., optical sensing technology)
(Assuming light can easily penetrate a well perfused area)
-electrical activity from the heart when recorded by electrodes embedded within a chest strap monitor
Both detect events over time to get a rebate (changes in saturation to RR intervals)
Two common techniques wearables use to monitor temperature
-ingestible capsule that contains very small crystals that detect changes in the surrounding temperature (via vibration). This signal will be converted and transmitted to an external data log system
-wearable device (often an arm band) that will measure skin convective heat flux
How do devices measure oxygen saturation (wearables)
-pulse oximetry uses spectrophotometry to determine how much hemoglobin is saturated with oxygen by emitting and detecting light through biological tissues
-oxygenated and deoxygenated hemoglobin have different light absorption rates ( oxygenated hemoglobin will absorb more light)
How do sleep monitoring devices work?
will integrate multiple sensors that detect movement and physiological data
-accelerometry
-heart rate and or a strain gauge to detect chest wall movement
-O2 saturation
-nasal cannula to detect flow
Quality of sleep is often worse with the complexity of the devices
What are some advantages of wearables
-most are useful (to an extent) for improving sport performance
-most brands are accurate when measuring steps and heart rate (although the latter is more variable)
-likely improve adherence to physical activity
-have been able to detect, record, and alert local emergency services when a potentially life threatening event has occurred
Disadvantages of wearables
-expensive
-smartwatches often go for fashionable designs with less than optimal placements for accuracy (wrist is not well perfused)
-many claim to quantify sleep but will be using complex algorithms (with limited measurements) that over/under estimate sleep quality
-no brand accurately measures energy expenditure
-when measuring o2 saturation devices are highly susceptible to movement artifacts and not valid in all conditions ( extreme cold or peripheral perfusion is low/ poor validity at high altitude)
-inter-reliability (reproducibility between people) is often low because variation of skin colour & physical ability hasn’t been considered in product design
Vestibular organs are ________ across the head
Mirrored
What branch of the brain interprets the difference between firing rates as head motion
CNS
What is the vestibulo-ocular reflex
Function :stabilize gaze (finger infront of face example)
Vestibular organs —-> ocular muscles
What is the vestibulospinal reflex
Function: maintain upright balance
Vestibular organs—-> postural muscles
What is electrical vestibular stimulation
-small electrical currents activate vestibular afferents
-mimics activity we would have if vestibular organs were actually sensing head motion
-CNS interprets this afferent activity —> we are falling
What is the importance of the cathode/anode placement in electrical vestibular stimulation
CATHODE (-)
-Causes deploarization
-^ vestibular afferent firing rate (head will turn toward cathode)
ANODE (+)
-causes hyperpolarization
- decreases vestibular afferent firing rate
How do vestibulospinal reflexes act on muscles during electrical vestibular stim
-act on muscles involved in the postural task to elicit compensatory balance responses
-balance response always directed to the anode
-biphasic—> short and medium latency responses
-medium latency (ML) response corresponds with overall activity of the muscle
-positive ML—> vestibulospinal reflex increasing EMG
-negative ML—> vestibulospinal reflex decreasing EMG
Vestibulospinal reflexes are __________
Craniocentric
Stimulation/sensation of head motion is bound between…
The inner ears
Direction of balance responses dependant on head-on-feet posture —alters…
What muscle activation we see
What are some considerations when using EVS
When using EVS to investigate vestibulospinal reflexes, the direction/size of the responses can be influenced by
-anode/cathode position
-positional and angle
-other sensory input
