electromyography Flashcards
what is electromyography
recording of the action potential occurring in skeletal muscles
what is extra-cellular recording
both electrodes outside the muscle fibres
record the emf (potential) between 2 locations outside of cell
not invasive
examples of extra-cellular recording
ECG/EKG - electrocardiogram - record AP from heart - electrodes on limbs/chest
EEG - electroencephalogram - AP from brain - electrodes on scalp
what is intracellular recording
in wet lab
cell cultivated and fine electrode goes in cell
difference between voltage and out of the cell recorded - record membrane potential
at rest there is a separation of charge - mem potential =-70mV (more -ve in than out)
nobel work - Huxley and Hodgkin - understand how nerves transmit info from 1 end to other and signal doesn’t reduce
what happens in extra-cellular recording
measure difference between inside and outside the cell at 2 points and compare the 2 points
At rest V=0 - no difference between points
when AP generated at 1st point it is depolarised so V difference increases
signal goes back to 0 as AP moves along axon
when reach next electrode V decreases below 0
when it passes it goes back to 0
what happens when there is an electrical signal to the hand
the muscle is innervated and the sensory neuron carries the signal back to CNS - stimulate both axons (up sensory - feel signal, down motor - thumb moves)
where does the ulnar nerve serve
skin on hand and 1st 1 and a half fingers and muscles
if you stimulate nerves in the hand what are the different affects
nothing - done something wrong
feel the sensation - activated the large myelinated neurons
thumb moves - more stimulation required, stimulated small myelinated neurons
pain - stimulated small unmyelinated neurons
what happens in voluntary contraction
transducer converts the force from the thumb to line on graph
force and electrical activity increase and decrease at the same time
measure electrical activity of muscle
electromyography - physical representation of electrical events
what happens to the force (thumb movement) when you generate a single AP by putting electricity into a nerve on its path
small AP = twitch
signal larger = bigger twitch
what happens if the muscle is stimulated at different frequencies
low freq - individual twitches disappear before next one
higher frequency - faster than time for force to disappear, force adds onto previous one -summation, the force gradually increases and twitches are not distinct
even higher freq- fused/tetanic contraction, can’t see individual twitch, not pathological
difference between force in voluntary contraction and electrical stimulation
can make max smooth force voluntarily if send AP at the right time - frequency to cause fused contraction
nerve system is really well controlled
generate
send right number of impulse down fibres - max force almost indefinitely
experimentally - 20impulse per second
