Most Important Properties of Skeletal Muscles are as follows:
(a) Single muscle twitch is a single, quick isolated contraction of a muscle fibre to a single stimulus in the laboratory experiments.
The single isolated contraction of a muscle fibre caused by a single nerve impulse of artificial stimulus. Immediately after twitch, the muscle fibre relaxes.
(b) Latent period:
The brief period between the application of the muscle stimulus and the beginning of contraction t his is the time when Ca2+ is released from the sarcoplasmic reticulum, the filaments begin to exert force and shortening begins. The latent period for a striated muscle fibre may be as little as 2 milliseconds, from initiation of an action potential.
(c) Contracture or contraction phase is the extremely slow relaxation of muscles due to over stimulation. It is 0.04 sec. in skeletal muscle & upto 20 sec. in a visceral muscle.
(d) Relaxation period is the interval required for the contracted muscle to regains its original relaxed/elongated state. It is 0.05 sec. for a skeletal muscle & 2.3 sec. for visceral muscle.
(e) Refractory period is the interval during which a muscle fibre fails to respond to a second stimulus. It is 0.002 – 0.005 sec in skeletal muscle & 0.1 – 0.2 sec. in a cardiac muscle fibre.
(f) Threshold stimuli – Stimuli of certain intensity is strong enough to cause a response. The values differ from fibre to fibre. Stimuli stronger than the threshold one is called supraliminal/supralimited stimulus.
(g) Tetanus is a continued state of contraction caused by rapid succession of many stimuli. E.g., holding of book, pen, etc.
(h) Muscle tension is the force produced during contraction of muscle.
(i) Rigor mortis is the state of body stiffening after death due to nonseparation of actin and myosin filaments caused by nonavailability of ATP. Rigor mortis persists till decomposition starts.
(j) Tonicity is the maintenance of the health of muscles when few fibres in a relaxed muscle are always undergoing contraction alternately.
(k) Oxygen debt is the extra oxygen required during recovery phase of a muscle over the resting phase for regeneration of oxymyoglobin, restoration of depleted ATP and CP (creatine phosphate) & oxidation of lactic acid. Therefore deep breathing occurs.
(l) All or none principle is a minimal strength of a stimulus required to cause the contraction of a muscle fibre to brings about maximal contraction and no further contraction would occur by increasing the strength of the stimulus.
When a second stimulus is given to a muscle which is still contracting in response to the first stimulus, the second contraction is stronger than normal. This effect is called mechanical summation.
(n) Fatigue is the inability of a muscle to contract due to depletion of its chemicals and lactic acid accumulation by repeated contraction. A completely fatigued muscle refuses to respond to nervous stimuli.
The site of fatigue is the junction between nerve and muscle (neuromuscular junction). Extra oxygen available to a relaxing muscle due to faster breathing disposes of the lactic acid and the muscle fatigue disappear.
(o) In an isotonic contraction, tension rises and the skeletal muscle’s length changes. Lifting an object off a desk, walking, and running involve isotonic contractions.
(p) In an isometric contraction, the muscle as a whole does not change length, and the tension produced never exceeds the resistance.
(q) Treppe or stair case – The repeated stimulus of single muscle fiber in such a manner that the kymograph records a staircase like graph.