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43 Cards in this Set

  • Front
  • Back
Describe the process of ECC coupling in skeletal muscle.
AP ->
Conducted to T-Tubule ->
opens DHPRs ->
mechanically opens RyRs in junctional SR ->
Calcium release ->
How is contraction terminated?
AP finishes.
Calcium in myoplasm is pumped back into SR by Calcium ATPase.
What is the total force developed by a muscle correlated with?
The number of cross bridges formed.
What two factors affect the number of cross bridges formed and therefore the total force developed by a muscle?
Concentration of calcium in the myofibril.
Length of muscle.
Tension = ?
Force pulling the two attachment points of the muscle toward each other.
Describe how Calcium affects contractile force.
Concentration of Calcium affects the extent of Troponin C binding and therefore how many cross-bridges can be formed.
Extent of Calcium release from SR is NOT the way that contraction is regulated in skeletal muscle.
Muscles can contract ___ or ___.
Isometrically or Isotonically.
Isometric force
Tension generation when muscle length is fixed. (no muscle shortening)
What is an example of isometric force?
pushing against a wall.
Isotonic Force
Contraction (shortening) against a constant load
Lifting a weight is an example of what type of force?
What is the length-tension relation?
Muscle length affects the amount of tension that can be developed.
What do the zero velocity on the load-velocity curve represent?
Zero velocity (zero shortening) is the veloicty at max load. You cant move your muscle any more but you can sustain the position you're in.
Different aspects of cross-bridge formation determine tension and velocity.
Tension development depends on?
Velocity depends on?
Tension development (no shortening) depends on the number of static cross-bridges formed.
Velocity (shortening) depends on the number of spare cross-bridges that can undergo cycling.
Why does the velocity of shortening decrease as shortening proceeds?
You have to use more and more cross-bridges to maintain a contraction as it proceeds. This leaves less open cross-bridges to participate in cycling.
Max Load (In terms of cross-bridges)
All cross bridges are used in resisting load so no shortening.
Lighter Loads (In terms of cross-bridges)
Small surplus of cross bridges so low shortening velocity
Almost zero load (In terms of cross-bridges)
Large surplus of cross bridges so max velocity.
What properties characterize Red Fibers?
Oxidative Metabolism
What are some examples of Red Fibers?
Postural Muscles and Upper/Lower Limbs
What are some properties that characterize White Fibers?
Low Myoglobin
Glycolytic Metabolism
Fatigue Easily
What are some examples of White Fibers?
Extraoccular muscles
Fine control of digits
Explain the mechanism by which red and white fibers differ in their velocity of contraction.
Velocity of contraction is correlated with myosin ATPase activity.
ATPase activity is determined by different myosin isoforms.
Muscle fiber type is not ___?
Name 2 conditions that might result in change of muscle type.
1) exercise training
2) Different patterns of neuronal stimulation
What is the influence of motor nerves on fiber type?
Small motor neurons- Red/ Slow twitch muscle
Large motor neurons- White/ Fast twitch muscle (large radius of axon means higher velocity)
Explain how muscles change during growth.
Sarcomeres added in series.
Increases velocity and extent of shortening.
Explain how muscles change during strength training.
Sarcomeres added in parallel.
What does strength training affect?
Increased Force!!
Doesnt change velocity or shortening capacity!
Name 3 conditions that lead to muscle atrophy.
Limbs in casts
How is the rate of atrophy different in fast vs. slow twitch muscle?
slow twich > fast twitch
How can reinnervation of a denervated muscle influence fiber type?
The size of the new motor neuron and the stimulation frequency can determine whether you get slow or fast twitch muscle.
How do single muscle fibers regulate contractile forces?
Force can be increased in a single muscle fiber by summation of twitches.
Why can force be increased in a single muscle fiber by summation of twitches?
Twitch duration is longer than AP duration.
Summation relies on the residual tension of fibers.
Summation depends on stimulation frequency. (High frequency means Calcium cannot decline before the next twitch causing tetanus.)
How do whole muscle regulate contractile force?
Force is increased by recruitment of multiple fibers.
Force varied by recruitment of neurons in motor neuron pool.
This type of contractile force regulation is important for smooth, fine motor control.
Whole muscle recruitment.
What is the order of recruitment for whole muscles?
small -> large
slow -> fast
Reversible deformation under stress
How is skeletal muscle elastic?
1) Stretchy
2) Relengthening after contraction
Why is elasticity of skeletal muscle important?
Prevents damage due to stretching.
What is the molecular basis of muscle elasticity?
Myofibrillar protein Titin.
CT's Tendons, etc...
Why do different muscles have different velocities of shortening?
Different myosin ATPase activities in muscles with different myosin isoforms.
Contractile force in a single skeltal muscle fiber is regulated physiologically by..?
The frequency of stimulation.