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Single contraction produced in a muscle fiber in response to a single action potential
3 phases of a twitch
- latent period
- contraction phase
- relaxation phase
phase of twitch in which calcium is relased; time from action potential in muscle cell to onset of contraction (few msec) (ie the time it takes for Ca to be released)
phase of twitch in which force is produced (10-100 msec) and crossbridge cycling occurs
phase of twich in which force decreases back to zero and Ca is re-uptake; longest phase
type of contraction in which there is constant tension but muscle length changes
type of contraction in which there is constant muscle length and tension changes, as in the case when u add weight w/out moving
shortening of muscle during isotonic contraction
lengthening of muscle during isotonic contraction (as is the case when holding weight downward after shortening)
Types of contractions due to load
Force produced by a muscle > load (muscle shortens)
Force produced by a muscle = load (length stays same)
Force produced by a muscle < load (muscle lengthens)
Worst type of contraction b/c can cause damage due to not being able to hold weight
the more crossbridges are made, the more ___ is produced
3 factors affect number of crossbridges
- frequency of stimulation
- fiber diameter
- fiber length
2 factors which affect frequency of stimulation
- treppe (over & over action potential cause response to build over time)
- summation (several action potentials happen at once to sum)
Occurs when repeated action potentials cause response to build over time & contraction occurs
several weak action potentials happen at once to sum, causing contraction
sustained contraction caused by summation of action potentials
Larger diameter of fiber = more filaments = more ___
(b/c there are more crossbridges; more sarcomeres in parallel which makes more ___)
How does fiber length at oonset of contractoin affect the amt of force generated?
The more myosin & actin are overlapping, the more force that can be generated; if there is no overlap, there is no force made
Max force is b/w:
How does the recruitment of motor units increase force?
Activating a motor neuron activates all of the muscle fibers in that motor unit, so there are more motor units activated when more force is needed
Small motor units ---> ____ fibers
Large motor units ---> ___ fibers
Explain the motor unit size principle
The order in which motor units are recruited is based on their size. Small units recruited before large units.
As the load the muscle is required to lift decreases, contraction velocity _____
2 ways in which muscle fibers are classified
- By their speed of contraction (fast or slow twitch fibers)
- By their primary mode of ATP production (glycolytic or oxidative fibers)
What is the rate-limiting step of cycle?
Fast fibers = ____ myosin ATPase
Slow fibers = ____ myosin ATPase
___ fibers contract 2-3x faster than ___ fibers
___ fibers relax more rapidly than ___ fibers
Why do fast fibers relax more rapidly?
Rate of Ca re-uptake is faster
Three types of skeletal muscle fiber types based on energy production
- slow oxidative = type 1
- fast oxidative = type 2A
- fast glycolytic = type 2B/X
Which type of muscle fiber utilizes myoglobin to carry oxygen so they appear red, and which type does not, so they appear white?
- Slow & fast oxidative: myoglobin
- Fast glycolytic: no myoglobin
____ fibers have high myosin ATPase activity, myglobin high glycogen stores, large diameter (greater force), and fatigue rapidly
Fast glycolytic fibers
___ fibers have low myosin ATPase activity, lots mitochondria, rich blood supply, small diameter and small diffusion barrier (so little force), and fatigue slowly
Slow oxidative fibers
____ fibers have high myosin ATPase activity, myoglobin intermediate diameter, moderately slow to fatigue
Fast oxidative fibers
(T/F) All muscle fibers in a motor unit are same type
In what order are the energy-classified recruited?
(fast glycolytic, fast oxidative, slow oxidative)
- 1.) Slow oxidative fibers
- 2.) Fast oxidative fibers
- 3.) Fast glycolytic fibers
Decline in a muscle's ability to maintain a constant force of contraction during repetitive stimulation
During high-intensity exercises, what are potential causes of muscle fatigue?
- Build up of H ions (which were formerly lactic acid)
- Depletion of acetylcholine (neuromuscular fatigue)
- Compression of blood vessels
During low-intensity exercises, what are potential causes of muscle fatigue?
Depletion of energy reserves
During high and low intensity exercises, what are other potential causes of muscle fatigue?
- Build up of inorganic phosphates
- Changes in ion distribution
Decrease in size from loss of myofibrils
Age-related loss of muscle
When muscle size increases due to adaption to use, it is due to ____
changes in size of individual cells (not cell division)