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Lecture 25 + quiz
Terms in this set (33)
Must muscles (muscle tendon units) change length to generate tension? When do you use isometric and isotonic contractions?
What ultimately determines the force of a contraction in a fiber or whole muscle?
What is the advantage of different fascicle orientations (pennation) and what effect does pennation have on a muscle's force potential?
What are isometric and isotonic contractions? Why doesn't length change in isometric contractions?
What are concentric and eccentric contractions?
Do myosin and actin form crossbridges in isometric contractions?
Are isometric contractions common? Are isotonic contractions common? Are eccentric and concentric muscle contractions common?
Consider the activation of your bicep brachii. When you pick an object up by flexing your elbow, is this an isometric or an isotonic contraction? Is it concentric or eccentric? When you lower something down by extending your elbow, is this an isometric or an isotonic contraction? Is it concentric or eccentric? When you hold something still in your hand, is this isometric or isotonic?
Muscle force is ultimately related to the amount of crossbridges that can be formed in a fiber or a whole muscle.
How can you vary the number of crossbridges formed in a single fiber to vary that fiber's force output?
How can you vary the number of crossbridges in a whole muscle to vary that muscle's force output?
Why does your body have 2 muscles that cross the same joint and perform the same actions (synergists), but are different in terms of fiber length or PCSA? (The example in class used the biceps brachii and brachialis.)
How does fascicle orientation (pennation) influence the amount a muscle can shorten and the amount of force it can create?
What is physiological cross sectional area (PCSA) and how does this relate to muscle force?
Given an equal muscle mass, which muscle shortens more: parallel or bipennate? Why? Which muscle has the greater PCSA?
Given an equal muscle mass, which muscle generates more force: parallel or bipennate? Why?
Why do some joints have pennate muscles with high PCSA and little shortening distances while other joints have muscles with parallel fibers, less PCSA and high shortening distances? (Consider the ankle compared to the elbow.)
Why might it be easier to hold a heavy load when your elbow angle is at 90° than at 170°?
After a trauma, you have ruptured your biceps brachii tendon and the muscle is no longer attached at its insertion. What symptoms would you expect? Can you still flex your elbow? What changes in functionality would you expect?
When attempting to reattach your muscle, your surgeon cuts the nerve serving the muscle. He still reattaches the insertion and closes the incision.
i. What functionality would you expect post-surgery?
ii. Should you be upset with your surgeon?
To develop most tension in a whole skeletal muscle
you must recruit all motor units to complete tetanus
Submaximal whole muscle contractions are due to asynchronous recruitment of motor units to incomplete tetanus
some motor units rest while other are active
Isometric contractions involve crossbridge formation that
tretches elastic elements in fiber, muscle but no over all length change in fiber or muscle-tendon unit
Isotonic contractions allow movement of the joint
oncentric contractions shorten the muscle, eccentric lengthen the muscle
Active muscle force is determined by the number of crossbridges formed in a muscle cell or whole muscle
more crossbridges, more force (tension)
What affects fiber's ability to generate force?
Sarcomere length (at time of activation), stimulus frequency, number of myofibrils
What factors affect force production in whole muscles?
Sarcomere length, stimulus frequency, number of motor units activated and PCSA
have larger PCSAs, can generate more force, but shorten less than same sized parallel fibered muscles
In extreme circumstance, contractions that recruit _____ motor units in a muscle to _____ are the most powerful, but they cannot be sustained for long periods of time.
All; Complete tetanus
Which will allow you to lift a heavier load?
Stimulating a muscle more frequently.
Which can pick up the heavier load? (Assume otherwise equal joint architecture.)
A short muscle with a large physiological cross sectional area.
During a sustained submaximal whole muscle contraction (like muscle activation that keeps your head upright throughout the day), what is happening in your neck muscles?
some motor units are activated to incomplete tetanus while others are resting
Which of the following will increase force production in a skeletal muscle?
Decreasing the time between successive neural stimulations
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