Q.What kind of contraction occurs in your neck muscles while you are reading your class assignment?

Electrically stimulated skeletal muscle shows several defining properties. A single muscle twitch, from one brief stimulus, passes through a latent period, a contraction period and a relaxation period. If a second stimulus arrives before the first twitch ends, the tensions add (summation), and repeated stimuli give a step-wise rise in contraction strength (the staircase phenomenon); if stimulation is rapid enough that the muscle never gets to relax, it stays continuously contracted (tetanus). Immediately after a stimulus there is a brief refractory period (about 0.02 s) during which the fibre cannot respond again. A muscle fibre only contracts once stimulus intensity reaches its threshold, and beyond threshold a fibre always contracts fully — never partially — regardless of how much stronger the stimulus becomes (the all-or-none principle), a rule obeyed b …