muscles and motor units Flashcards
what is EMG?
electromyography
during muscle contraction what is released over a neuromuscular junction?
neurotransmitter
what’s released from the sarcoplasmic reticulum during muscle contraction
?
calcium
what is a motor unit
one alpha neuron that activates muscle fibres
what does one action potential generate ?
singular twitch
what does multiple APs generate ?
continuous force
can lead to tetanic force
how do muscles generate extra force ?
recruits more motor units
increased firing frequency
what affects twitch properties ?
fatigue
temperature
how does the innervation number effect motor control
lower innervation leads to higher control
how does electromyography work ?
needle/electrode instead into the muscle or on surface of skin
records electric signals
what’s the relationship between muscle activity and force?
amplitude of EMG signal is proportional to force produced by the muscle
why do fast twitch fibres generate larger electrical responses ?
higher resting membrane potentials
higher sodium density
faster APs
do muscles produce more force eccentrically or concentrically ?
eccentrically
why do muscles produce less EMG during eccentric contraction ?
prevent damage
how does the NS know when to reduce firing rate ?
detection of metabolites and pain e.g. lactate
spinal suppression of motor neuron firing rates
changes in voluntary action
why does the NS reduce firing rate?
reduce neuronal fatigue
more likely to maintain fine motor control
explain high frequency fatigue
caused by continuous high frequency stimulation
recovers immediately
caused by failure of transmission along muscle membrane
explain low frequency fatigue
caused by intense exercise when not accustomed to it
takes hours/days to recover
caused by reduced calcium released from sarcoplasmic reticulum
what causes loss of force during fatiguing contraction
biochemical changes in the muscle
what does muscle stimulation during fatigue tell us ?
as fatigue develops, stimulation produces greater twitch force
shows neural drive to muscle is reduced - central fatigue
how can strength improvement early in training be explained by ?
increased neural drive to the muscle
what does acoustomyography measure (AMG) ?
produces sound of muscle contraction
represents muscle force
what does an ultrasound tell us about muscle contraction ?
if the muscle lengthens or shortens during contraction
