1. Threshold stimulus: minimal stimulus required to elicit a muscular contraction.
- Threshold -> generate AP -> muscle impulse -> Ca+ release -> fiber contraction
2. Recording a muscle contraction
a. Myogram: recording of an electrically stimulated isolated muscle
b. A twitch: single, short contraction reflecting muscle fiber stimulation
- Contraction + relaxation in one period
myogram of a series of twitch
c. The latent period + the time between stimulus and responding muscle contraction -> period of contraction + period of relaxation.
3. Summation
a. Summation: A rapid series of stimuli (at frequency that it cannot relax completely before next stimulus).
myogram of a summation
b. Tetanic contraction: forceful, sustained contraction without relaxation
myogram of a tetanic contraction
4. Recruitment of motor units
a. A whole muscle is composed of many motor units controlled by different motor neurons – respond to different thresholds of stimulation.
b. At a low intensity of stimulation, small numbers of motor units contract.
c. Stimulation intensity increase, other motor units are recruited until the muscle contracts with maximal tension.
5. Sustained contractions
a. Summation + recruitment = sustained contraction (strength increase)
b. Even when a muscle is at rest, its fibers usually remain partially contracted
Muscular & Digestive System 