Mechanics of Muscle Contraction Flashcards
What is the stimulation to twitch ratio?
1 stimulation → 1 twitch
What are the 3 muscle twitch phases?
- Latent phase
- Contraction phase
- Relaxation phase
What is the latent phase?
The period of time between the stimulation of the muscle and the onset of contraction
What is the contraction phase?
The period of time during which the muscle is actively contracting, from beginning to end of muscle tension
What is the relaxation phase?
The period of time during which the muscle is returning to its resting state (peak tension to no tension)
What happens during the latent phase of a muscle twitch?
The stimulus triggers an action potential (AP) which causes myosin to bind to the actin active site, beginning muscle contraction.
What happens during the contraction phase of a muscle twitch?
Myosin heads slide along the actin filaments, generating tension in the muscle which lasts from the beginning to the end of the phase.
What happens during the relaxation phase of a muscle twitch?
- Ca2+ ions are absorbed back into the cisternae
- tropomyosin moves back over actin binding site
- myosin head released from actin
- the filaments move back into resting position
Resulting in a decrease in muscle tension from peak to no tension.
What determines the speed at which different muscles contract?
Various muscles contract at different speeds due to differences in their composition of muscle fibers.
What are the implications of muscles having different types of muscle fibers?
The composition of muscle fibers in different muscles can affect their:
- strength
- endurance
- speed of contraction
What factors determine the tension generated in a skeletal muscle fiber?
The tension generated in a skeletal muscle fiber is dependent upon its sarcomere length.
What is sarcomere length?
Sarcomere length is the distance between two Z-lines in a muscle fiber
How does sarcomere length affect muscle tension?
- muscle tension is maximal when sarcomeres are at an optimal length
- too much or too little stretching will result in decreased tension
What happens to active tension in skeletal muscles when sarcomeres are too short or long?
When sarcomeres are too short
- active tension decreases
- because the myosin heads cannot reach the actin filaments effectively
What other factor affects the tension generated in a skeletal muscle fiber?
- the frequency of APs across the skeletal muscle fiber
- higher frequencies of APs result in greater tension
What factors determine the tension generated in a skeletal muscle as a whole?
- the frequency of action potentials transmitted along a somatic motor nerve
- recruitment
What is the frequency of action potentials transmitted along a somatic motor nerve?
the number of action potentials that occur per unit of time
- higher frequencies of APs result in greater muscle tension
What is recruitment in the context of muscle tension?
the activation of additional motor units in a muscle, resulting in an increase in muscle tension.
- used by the NS to regulate the amount of tension generated by a muscle
What is the effect of frequency of action potentials on wave summation in skeletal muscles?
Increasing the frequency of action potentials can lead to wave summation in skeletal muscles.
What is wave summation?
Refers to the
- increasing tension in a skeletal muscle
- due to summation of twitches
- caused by repeated stimulations (APs fired)
- before the end of the relaxation phase
When does wave summation occur?
Wave summation occurs when successive stimuli arrive before the relaxation phase has been completed.
What is the minimum stimulus frequency required to produce wave summation in skeletal muscles?
over 50/second
What is Treppe?
Treppe is an increase in peak tension with each successive stimulus delivered shortly after the completion of the relaxation phase of the preceding twitch.
When is Treppe observed in skeletal muscles?
Treppe is observed in skeletal muscles when successive stimuli are delivered shortly after the completion of the relaxation phase of the previous twitch.
When is a skeletal muscle fiber’s maximum potential tension reached?
A skeletal muscle fiber’s maximum potential tension is not reached until tetanus.
What is tetanus?
Tetanus is the maximum tension that a muscle can produce
What is incomplete tetanus?
Sustained contraction of the muscle in response to repeated stimuli (increased stimulation frequency), where muscle relaxes briefly between each stimuli
What is complete tetanus?
When a higher stimulation frequency (more, repeated stimuli) eliminates the relaxation phase, and the muscle is in continuous contraction
- does not relax between stimuli
What happens when there are greater fibers per neuron?
The greater the number of fibers per neuron, the finer the movement, requiring more brain power.
How is an increase in force made possible?
An increase in force is made possible by recruiting more motor units.
What happens if the motor stimulus is strong enough?
If the motor stimulus is strong enough, it will cause multiple motor units to respond.
What is the effect of the combined contractile force produced by motor units?
The combined contractile force produced by motor unit 1 and 2, and their combined 5 muscle fibers, is much greater than the force produced by either motor unit alone.
How are muscle fibres of different motor units in a skeletal muscle arranged?
Muscle fibers of different motor units are intermingled
What is the benefit of muscle fibers of different motor units being intermingled?
The benefit is that the forces applied to the tendon remain balanced regardless of which motor units are stimulated.
Does the tension applied to the tendon remain constant?
Yes, the tension applied to the tendon remains fairly constant, even though individual motor units cycle between contraction and relaxation.
What is an isotonic contraction?
A muscle contraction with movement
- concentric - muscle shortens
- eccentric - muscle elongates
What is an isometric contraction?
A muscle contraction without movement
Does a muscle shorten during an isometric contraction?
No, there is no muscle shortening during an isometric contraction.
Can you provide an example of an isometric contraction?
Pushing against a wall
