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Flashcards in Module 2 Deck (234)
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Force to cause the contraction

Power Stroke


Mutation in dystrophin in the heart

Dilated Cardiomyopathy


What is the distance achieved in each cross-bridge cycle?

10 nanometer


- Brief muscular contraction followed by relaxation
- due to a single action potential
- Starts 2 millisecond after depolarization of the membrane
- Duration: 7.5 ms in “Fast” Fibers; 100 ms in “Slow” Fibers

Muscle Twitch


- All muscle fibers innervated by a single motor nerve fiber
o Made up of alpha motor neuron, its axon and all muscle fibers it supplies
o Alpha motor neurons are also called “final common pathway”, “lower motor neuron”

- For movements that require rapid and exact control
o One motor nerve fiber would innervate few muscles

The Motor unit


Large amount of ATP are cleaved to form ADP during contraction process, and the greater the amount of work performed by the muscle, the greater the amount of ATP that is cleaved; this phenomenon is called _____

The Fenn Effect


Muscle contraction is said to be ___ when the muscle does not shorten during contraction



Muscle contraction is said to be ___ when the muscle does shorten but the tension on the muscle remains constant throughout the contraction



- means adding together of individual twitch contractions to increase intensity of overall muscle contraction



- Type of summation that occurs by increasing the number of motor units contracting simultaneously
- size principle is followed
- Motor units driven asynchronously by the spinal cord
- Contraction alternates among motor units one after the other

Multiple Fiber Summation (Spatial Summation)


Type of summation that occurs by increasing the frequency of contraction and sometimes can lead to TETANIZATION

Frequency Summation (Temporal Summation)


- Smaller motor units are recruited first before big motor units
- Basis: small motoneurons in the spinal cord are more excitable than large ones

Size Principle


When the frequency reaches a critical level, the successive contractions eventually become so rapid that they fuse together and the whole muscle contraction appears completely sooth and continuous. This process is called ___



- Each contraction occurs after complete relaxation, its initial strength of contraction may be as little as one half its strength
- Each contraction increases up to plateau
- Due to Ca++ accumulation, increase in temperature, ph changes
- Seen in warm-up exercise

Staircase Effect or Treppe


- Complete relaxation not given; subsequent stimuli done
Results in progressive increase in total contraction strength

Wave Summation


- no relaxation after contraction

Complete Tetany


incomplete relaxation after contraction

Incomplete Tetany


Which of the following tetanizes at lower stimulus frequency?

Slow-Twitch Fibers


Which of the following has a larger maximal force during tetany?

Fast-Twitch Fibers


Tension developed by stretching the muscle to different lengths

Passive Tension


The tension developed when the muscle is stimulated to contract at different lengths.

Active Tension


Active Tension + Passive Tension

Total Tension


If the resting muscle length is extended, the following will happen:

Passive Tension: Increases
Active Tension: Decreases
Force of Contraction: Increases


- With zero load, shortening velocity is maximal
Corresponds to the maximal cycling rate of the cross-bridge
- Increasing the load, decreases the velocity of the muscle shortening

Force-Velocity Relationship


- Reflects work done at each load
- Maximal rate of work done at a submaximal load (when force of contraction is approximately 30% of the maximal tetanic tension)

Power-Stress Curve


- Length is held constant
- No muscle shortening/lengthening
E.g. holding an Ipad in midair

Isometric Contraction


- Load is held constant
- With Muscle Shortening: CONCENTRIC CONTRACTION (e.g.pulling a weight up)
- with muscle lengthening: ECCENTRIC CONTRACTION (e.g. lowering a weight down)

Isotonic Contraction


- Remaining contractile activity of the muscle at rest
- Due to low levels of contractile activity in some motor units driven by reflex arcs from muscle spindles
- Helps maintain posture

Muscle Tone


- Protective mechanism to prevent muscle cell injury or death
- Directly proportional to rate of depletion of muscle glycogen and creatine phosphate stores and the accumulation of lactic acid
- Occurs earlier in fast-twitch fibers

Muscle Fatigue


- increase of the total mass of a muscle
- Maybe due to be due to fiber hypertrophy or sarcomere addition

Muscle Hypertrophy