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15 Cards in this Set

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Define myograph
an input transducer (or “force transducer”) commonly used to record muscle contraction
Define myogram
a physiological recording of muscle contraction
Define muscle twitch
a rapid, jerky, contractile response of a skeletal muscle when given a single stimulus of sufficient strength
Define threshold stimulus
the smallest stimulus that first causes contraction
Define maximal stimulus
minimal stimulus that first causes a maximal contractile response
Define motor unit
a motor neuron plus all the muscle fibers (muscle cells) it innervates

motor units vary in # of muscle fibers and the size of the fibers

smaller motor units: have finer fibers; more easily stimulated

larger motor units: have thicker fibers, respond later, producing a more forceful contraction
Define motor unit summation
(recruitment): increasing the number of motor units contracting simultaneously producing a stronger contraction.

(Induced experimentally by increasing the amplitude of electrical stimulation).
Define mechanical summation
Mechanical Summation (wave summation): increasing the frequency of stimulation, thereby increasing the rapidity of contraction producing a stronger contraction.

Allows for smooth continuous contraction).

Both types of summation occur together in the grading of contractile responses.
Define tetanus
Tetanus: complete fusion of individual twitches, resulting in a continued state of contraction
Define fatigue
the decline in muscle tension as a result of previous contractile activity

Neuromuscular fatigue: caused by shortage of neurotransmitter (not likely to occur in our frog gastrocnemius lab exercise)

Mechanical fatigue: actual mechanism not totally clear.

May be caused by: - build-up of lactic acid, lowering pH and interfering with enzymatic activity - from a relative deficit of ATP which somehow affects the excitation- contraction coupling mechanism
Define muscle tone
a sustained partial contraction of portions of a skeletal muscle in response to activation of stretch receptors (due to asynchronous motor unit stimulation)

• stabilizes the position of bones and joints

• allows the skeletal muscles to act as a shock absorbers that cushion sudden bumps
Define treppe
when a skeletal muscle contracts more forcibly in response to the same strength of stimulation after it has contracted many times (not summation, relaxation occurs between each stimulation); May be caused by:

• priming the external cytosol with Ca++

• tightens up the slack due to the elastic series component (ESC)

• increase in temperature, increases enzymatic activity
Define an isotonic contraction
- in isotonic contractions, cross-bridge activity leads to a shortening of the sarcomeresIsotonic Contraction

1. Muscle shortens

2. Tension is constant

3. Energy is expended

4. Graph: Distance vs. Time
Define an isometric contraction
- in isometric contractions, cross-bridge activity leads to development of tension in the sarcomeresIsometric Contraction

1. Muscle does not shorten (change length)

2. Tension increases

3. Energy is expended

4. Graph: Tension vs. Time
Describe the function of the myograph transducer and how it was calibrated.
an input transducer used to record movement during muscle contraction

used a weight to calibrate