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Muscle Tension

force exerted by a contracting muscle on an object


opposing force exerted on the muscle by the weight of the object to be moved

motor unit

consists of a motor neuron and all the muscle fiber it supplies. when a motor neuron fires(transmits action potential) all the muscle fibers it innervates contract

Latent period

first few milliseconds following stimulation when excitation-contraction coupling is occurring. During this period, muscle tension is beginning to increase but no response is seen on the myogram

Period of contraction

when cross-bridges are active, from the onset to the peak of tension development,

Period of relaxation

relaxation, reentry of Ca2+ into the SR

graded muscle response

muscle contraction graded in 2 ways
1) by changing the frequency of stimulation
2) changing the strength of stimulation

Temporal or wave summation

occurs because the second contraction occur before the muscle has completely relaxed.

unfused or incomplete tetanus

stimulus strength is held constant and the muscle is stimulated at an increasingly faster rate. sustained but quivering contraction

fused or complete tetanus

all evidence of muscle relaxation disappears and contractions fuse in a smooth sustained contraction plateau

Subthreshold stimuli

stimuli that produce no observable contraction

Threshold stimulus

the stimulus at which the first observable contraction occurs

maximal stimulus

strongest stimulus that produces increased contractile force.

isotonic contraction

(same tension) muscle length changes and moves the load

Isotonic-Concentric contractions

muscle shortens and does work (picking up a book or kicking a ball)

Isotonic-Eccentric contractions

muscle generates force as it lengthen. important for coordination and poseful movements. (walking up a heal...calf muscle)

Isometric contraction

tension may build up but muscle neither shortens or lengthens. load that is trying to be lifted is too heavy (trying to lift a piano)

aerobic respiration

requires oxygen and involves a sequence of chemical reactions in which the bonds of fuel molecules are broken and the energy released is used to make ATP

aerobic endurance

length of time a muscle can continue to contract using aerobic pathways

anaerobic threshold

the point at which muscle metabolism convertss to anaerobic glycolysis.

muscle fatigue

physiological inability to contract even though muscle is receiving stimuli


continuous contraction because cross bridges are unable to detach

Oxygen deficit

extra amount of oxygen for totally aerobic muscle activity and the amount actually used

force of muscle contraction affected by

1) number of muscle fibers stimulated
2) relative size of fibers
3) frequency of stimulation
4) degree of muscle stretch


release neurotransmitter into a wide synaptic cleft.


pouchlike foldings that sequester bits of extracellular fluid containing a high concentration of Ca2+ close to the membrane

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