In this issue:

Twitch contraction and the

treppe effect

1

Cardiac Muscle and rigor mortis 1

How skeletal muscles move 2

Story Title 2

A twitch contraction is a brief contraction of all the muscle fibers in a motor unit in response to a single action potential in its motor neuron. A muscle contraction, called a myogram, shows the variations of contractions. A brief delay, called the latent period, occurs between application of the stimulus (time zero on the graph) and the beginning of contraction. During the latent period, the muscle action potential sweeps over the sarcolemma and calcium ions are released from the sarcoplasmic reticulum. During the second phase, the contraction period (upward tracing), repetitive power strokes are occurring, generating tension or force of contraction. In the third phase, the relaxation period (downward tracing), power strokes cease because the level of Ca2+ in the sarcoplasm is decreasing to the resting level. The concept or phenomenon of "Treppe" occurs when a muscle contracts more forcefully after it has contracted a few times than when it first contracts. This is due to the fact that active muscles require decreasing degrees of succeeding stimuli to elicit maximal contractions. Returning to our example of the second set of squats feeling easier than the first, during the first set there was insufficient warm-up, and the second set felt easier because the first set actually served as a warm-up. The phenomenon in which the contraction strength of a muscle increases, due to increased Ca2+ availability and enzyme efficiency during the warm-up.

Tw i t ch Contract i on & Th e t r e p p e e f f e c t

Special points of interest:

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Group A1

Muscular physiology

0 1 / 1 4 / 1 3 V o l um e 1 , I s s u e 1

Graph depicting the treppe effect

Syncytium is cardiac muscle tissue contracts as a syncytium effects the autonomic nervous system. Rigor Mortis is a noticeable sign of death, caused by chemical changes in the muscles. When someone passes away the arms and legs become stiff and are hard to move around.

The four factors that influence the strength of muscle contractions:

1) the number of muscle fibers stimulated– muscle fiber contraction involves a number of cells.

2) The relative size of the fibers– it is a single a

motor neuron and all fibers are innervates.

3) Frequency of stimulation has high frequency.

4) The degree of muscle strength, strength test help you determine your current fitness level.

Card i ac mu sc l e and r i gor mort i s

The functions of a myofilament is to pull out every myofibril and the myofilaments and see all of the actins and mysins.

5. The sliding of a filament theory is how the muscles produce, when you have thin and thick filaments that slide past one another as you work out and that’s what makes your muscles eventually get stronger.

The structures that are unique to the skeletal muscle fibers are M-Line, A-Band, I-Band, and H-Zone.

- M-Line: Thin line all the way through

- A-Band: tells the length of the myosin (also stays the same when a muscle contracts)

- I-Band: Distance between the myosins

- H-Zone: Distance between Actin between same molecule. (Shrinks when muscle contacts)

The H-Zone and I-Band are contractile because they shorten.

The M-Line and A-Band are Excitability

S t r u c t u r e s u n i q u e t o t h e s k e l e t a l m u s c l e f i b e r s

Skeletal muscle moves bones by receiving acetylcholine from a

motor nerve that triggers an action potential across the

muscle fibers. Muscle fibers contain actin and myosin, which

are the function components of muscle contraction. Movement of

a bone occurs when the muscle attached is being shortened. The

chemical reactions that cause muscle contraction generate heat

- energy conversion always generates "useless" energy; entropy

increases.

How s k e l e ta l mu s c l e s mov e