VI. RESPONSES OF SKELETAL MUSCLE
A. Muscle twitch(100msec)
1. Latent period(10 msec)
Excitation-contraction coupling
2. Contraction period(40msec)
Tension/shortening
3. Relaxation period(50msec)
Returns to unstimulated tension/length
B. Graded contraction
1. All or none response
Refers to the myofiber
2. Multiple motor unit summation = Spatial
Individual motor units combine their activities to increase the contraction of the entire muscle.
3. Muscle tone
At any given time, some fibers are contracted which tightens muscle, but not enough to produce movement
4. Wave summation = Temporal
Summation in time, before complete relaxation
a. Incomplete tetanus
Contraction strength increases in amplitude with partial relaxation
b. Complete tetanus
Sustained contraction.
5. Asynchronous motor unit summation
Different motor units are activated at different times
6. Treppe
Stronger contractions after muscle has contracted several times. “Staircase” phenomenon
7. Isotonic & Isometric contractions
Isotonic – tension develops and it shortens
Isometric – tension develops and it doesn’t shorten