Anatomy and Physiology / Unit 5: The Muscular System
5.5 Muscle Contractions and Smooth and Cardiac Muscle
Notes
- Isotonic contraction: the muscle shortens and moves a load. Concentric (shortens) and eccentric (lengthens while resisting). Isometric contraction: tension rises without shortening (pushing against a wall).
- A single stimulus produces a twitch. Rapid repeated stimuli produce summation and tetanus (smooth sustained contraction). Recruiting more motor units increases force.
- Muscle tone: continuous slight contraction keeps muscles ready and maintains posture.
- Smooth muscle contracts slowly, can sustain contraction with little energy, and is regulated by the autonomic nervous system and hormones. Cardiac muscle beats on its own (autorhythmic) and has a long refractory period so it cannot be tetanized.
- Atrophy is shrinking of muscle from disuse; hypertrophy is enlargement from resistance exercise.
Practice
A person pushes against a wall that does not move. This is an example of:
Tension develops but the muscle does not shorten.
A muscle receiving rapid repeated stimulation develops smooth sustained contraction. This is:
Fused summation of twitches is tetanus.
Why can the heart not go into tetanus?
Cardiac muscle cannot be re-stimulated until it relaxes, which allows filling.
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