Module 4 Flashcards
Define motor unit
the neuron, and all muscle fibres activated by that neuron
Define innervation ratio
number of muscle fibres innervated by a motor neuron
define neuromuscular junction
what neurotransmitter does it use?
Where is this junction located on the muscle
synapse where motor neuron connects to muscle
ACh
located near middle of muscle fibre (so signal spread evenly
what are larger and smaller innervation ratios good for?
Larger - better for stronger muscles that don’t need as much fine control but need more contractile force (e.g. quadriceps
Smaller - better for smaller more controlled movements (e.g. eye)
what is the motor end plate
postsynaptic region of the muscle cell that receives signal from motor neuron
what is excitation contraction coupling
name steps
process causing action potential to cause contraction via actin myosin cross bridge.
- action potential arrive at motor end plate cause ACh release to synaptic cleft.
- action potential propagate in t-tubules depolarizing until reach sarcoplasmic reticulum.
- reaches sarcoplasmic reticulum and releases calcium into the fibre.
- ca2+ bind to troponin moving tropomyosin and exposing binding sites on actin.
- cross bridge cycle
- When finished signalling, ca2+ pumped back into sarcoplasmic reticulum or diffuse and cause muscle to relax.
temoral summation vs spatial summation
temporal - multiple signals from the same presynaptic neuron
spatial - multiple signals from different presynaptic neurons
describe EMG
describe 2 collection methods/equipment
records local electrical activity
could use surface electrodes or indwellings
Pros and cons of surface EMG compared to indwelling
surface:
Pros
- non-invasive
- good for general electric activity from muscle group contracting isometrically
Cons
- deeper motor units take longer to get to surface and must pass through more tissue causing to lose signal strength.
- cross talk from other muscles nearby
- movement artifacts from electrode movement/touching etc.
- can not record activity from deep muscles
- can not identify single motor unit using one differential EMG
indwelling:
Pros
- can record specific muscle and can eliminate cross talk
- can record deep muscles
- gold standard
Cons
- invasive
- records only small portion of muscle
-
Describe differential recording in surface EMG and indwellings
surface - place two electrodes on skin, common signals are subtracted out as noise.
indwelling - indwelling with two wires attached do the same things as above.
Regarding EMG, what is noise vs artifacts
Noise - non-muscle electric signals from nearby electronics (e.g. power lines), or body (not muscle being recorded)
Artifacts - False signals generated by electrodes or cables. Could be from movement or cables touching.
EMG-force relationship. Whats a simple way you could compare EMG activity to force.
What are problems with this relationship or EMG in general?
could keep muscle at same length and do isometric contraction and compare it at different forces.
- Not the best predictor of muscle force or tension (although correlates)
- not good for rapid muscle changes
- relationship will be different depending on muscle because of varying discharge rates and MU recruitment
- can be impacted by cross talk
- impacted by fat percentage
- impacted by unique anatomy (pennation angles, muscle shape, distribution of fibres etc.)
