Do muscles contrast faster if a larger electrically charge is applied?
I know about the whole concept of all or nothing in the nerve cells but a if an electrode is hooked up and a larger electrical charge is run through the muscle will it contract faster than normal?
- John TLv 54 years agoFavorite Answer
No. Not faster, but stronger.
The muscle force will increase until a maximum. Applying a larger voltage to the sarcolemma of the muscle increases the number of recruited motor units because the larger the voltage, the deeper the impulses go into the muscles. Through a process called summation, applying a larger stimulus increases the frequency of action potentials propagated through the muscle, and this causes faster propagation, but not faster contraction.
Note that motor units are defined as single motor neurons and all of their associated motor fibers. You are adding up the twitches of the individual fibers. Fibers come in at least 3 types: fast glycolytic (IIb), slow oxidative (I), and fast oxidative(IIa), and each human has different proportions of these fiber types due to genetic factors.
The force muscles generate depends on muscle length and shortening velocity. More frequent action potential propagation leads to more actin-myosin cross-bridges formed in sarcomeres, meaning higher force of contraction.
The electrical signal cannot generate any stronger contractile force if all motor units have been recruited, so you then switch to wave summation (repeated zaps of the muscle/repeated Ach binding nicotinic Ach Receptors) to increase contractile force until unfused tetanus (if muscles are allowed partial relaxation), fused tetanus (if muscles are forbidden from relaxing). At this point, muscles reach maximal tetanic tension and if held for longer time than normal will fatigue.