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Lecture 24+quiz

Terms in this set (25)

A single stimulus (AP on muscle fiber) will generate a single contraction
twitch
The twitch graph shows
• The latent period during which an AP is sent down the sarcolemma, into the T-tubles and calcium is released from the SR
• The contraction phase of the twitch graph is when actin & myosin can interact (crossbridge formation)
• The relaxation phase occurs as Ca++ is pumped back into the SR away from the troponin and the tropomyosin recovers the actin binding site
The force generated during a twitch is
1/10th the maximal force the fiber can generate
If you generate APs more frequently on a muscle fiber
muscle force increases as stimulus frequency increases
Wave summation
the successive building of contractions before the fiber can completely relax; force increases with time
Incomplete tetanus
sustained contraction, but with brief decreases in force as the fiber starts to relax before it is again stimulated to contract
Complete tetanus
sustained contraction with no relaxation between successive stimuli; generates the maximal force possible in a fiber
When a muscle cell receives a signal from a motor neuron, are all the sarcomeres activated?
yes
What is the relationship between number of crossbridges (or crossbridge cycles) formed and the amount of tension a muscle cell can generate at a given time?
The more cross bridges, the more contraction which = more tension
How does your body vary force production in a fiber?
The amount of motor units activated
What is a muscle fiber twitch?
contraction or how quick or often a muscle moves
What happens to the amount of tension in a muscle fiber as you vary the frequency of stimulation?
depends on the cross-sectional area of the muscle fiber and the frequency of neural stimulation
What is going on in a muscle fiber in terms of the amount of calcium present in the sarcoplasm during a twitch relative to wave summation/incomplete tetanus and complete tetanus?
-the more tension there is in the contraction, more calcium will be needed in the sarcolemma as oppose to the SR
In which response (twitch, incomplete tetanus, complete tetanus) is the most Ca2+ released?
-complete tetanus because there is no relaxation, the contraction must be sustained.
In which type of response do you develop the most tension in the muscle fiber?
complete tetanus
Why don't you always see a muscle twitch (when you look in the mirror), although you feel it beneath your skin?
underlying symptoms
When peak force is generated, the SR Ca++ channels are
open
Before the stimulus was applied, the SR Ca++ channels were
closed
What (physiologically) might explain why the period of relaxation is longer than the period of contraction?
longer period because it is passive, the result of recoil due to the series elastic elements of the muscle
During the latent period, the SR Ca++ channels are
open
Which type of stimulation frequency results in the greatest force production in the myofiber?
eccentric contraction
During wave summation, what do you think would happen to force production if there was more time between successive stimuli?
Wave summation releases more calcium and increases the force of contraction by increasing the firing rate of motor neurons using one muscle fiber. Recruitment use multiple motor units, in order to increase the force of contraction
During a twitch in a skeletal muscle fiber, what is happening in the latent period?
Calcium is flowing through mechanically gated channels
In which of the following conditions would you most reasonably expect to generate the most tension in a single muscle fiber? Assume otherwise equal conditions.
When a motor neuron generates a high frequency of action potentials. (greater than 80/s).
Which of the following will increase force production in a skeletal muscle?
Decreasing the time between successive neural stimulations
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