Mechanics of Muscle Contractions Flashcards
(32 cards)
What are the periods of a muscle twitch?
Latent period
Period of contraction
Period of relaxation
What is a muscle twitch?
A mechanical response to a single stimulation
Describe the latent period in a muscle twitch
- time between stimulus and initiation of a contraction (2-4 seconds)
- when the process associated with EC coupling occur
EC coupling occurs during what period of the muscle twitch?
the latent period
Describe the period of contraction
When actin and myosin interact so the muscle actively develops tension
During the period of contraction, if tension > load resistance, what type of contraction do you have?
isotonic
During the period of contraction, if tension < load resistance, what type of contraction do you have?
isometric contraction
Describe the period of relaxation in a skeletal muscle twitch
[Ca2+]_i returns to normal and tension diminishes
What does twitch duration depend on? What are factors influcing twitch duration?
Depends on Muscle type!
Factors including twitch duration include:
1) rates of hydrolysis of ATP by myosin produces different rates of contraction
2) differences in rate of Ca2+ uptake into SR
2)
Does fast twitch skeletal muscle fibers have a short or long twitch duration?
Short twitch duration
Do slow twitch fibers have fast or long twitch durations?
long twitch durations
How do the rates of Ca pumps in fast twitch fibers compare to slow twitch fibers?
Fast twitch fibers have faster Ca2+ uptake than slow twitch fibers, resulting in quicker Ca uptake and faster relaxation
What is summation in regards to skeletal muscle?
The adding of force to the first action potential if a subsequent action potential occurs before an activated muscle has time to fully relax
What is tetanus in regards to skeletal muscle contraction?
when action potentials occur repeatedly and rapidly creating a sustained contraction
What is tetanus fusion frequency?
the rate at which the action potentials occur so rapidly that no relaxation occur creating smooth or fused rise in tension to a pleateau
Applying the tetanic fusion frequency to stimulate the muscle results is what size tension?
The maximum tension that the muscle can produce.
What is the relationship between the tension the muscle can produce during tetanus and during a single twitch?
The tension produced during the plateau of a fused tetanus is 3 to 8 times that of a single twitch
What three factors influence the development of tension in a skeletal muscle?
Internal Ca2+ concentration
Series elastic elements
Muscle length
How does internal Ca2+ concentration influence the development of tension?
The Ca2+ released from a single action potential is nearly saturating. However, Ca2+ uptake begins as soon as the muscle is stimulated, so the elevated Ca2+ concentration is brief compared to the development of tension.
What is needed to maintain saturating levels of Ca2+?
multiple stimuli
What are series elastic elements?
structures in a muscle that are stretched when the muscle actively contractions. Exact structures unknown.
What is the effect of series elastic elements on twitch tension?
Much of the tension in a twitch tension must be used to stretch the series elastic elements before tension is transmitted to the load. Therefore, less than the full tension is transmitted to the load.
How does tetanus affect the series elastic elements?
because of the tetanic contraction, the series elastic elements remain stretched and more internal tension is applied to the load
What is a motor unit?
a motor neuron and all the muscle fibers it innervates
