Skeletal muscle physiology Muscle contraction in the body
Skeletal muscle physiology • Muscle contraction in the body – Summation of muscle twitches – Motor units – Muscle contraction and loads • Friday: ch. 14 Cardiavascular Physiology (After ch. 14, we’ll cover smooth muscle located at the end of ch. 12)
A twitch is a single contraction/relaxation cycle
The muscle does not relax completely before the second stimulus occurs, resulting In a more powerful contraction: summation Stimulus
Motor unit • One somatic motor unit and the muscle fibers that it innervates
A muscle may have many motor units of many fiber types.
Recruitment of motor unit activity during muscle activity • Each motor neuron has its own threshold potential for firing action potentials • Each motor unit has its own threshold • A muscle’s activity varies with the number of motor units that are recruited • Recruitment is controlled by the nervous system
Recruitment • Weak stimulus activates low threshold neurons. These regulate slow fatigue resistant fibers. • Stronger stimuli fatigue resistant oxidative fast twitch fibers • Very strong stimuli glycolytic fast twitch fibers
Isotonic contraction – any contraction that creates a force and moves a load
Isometric contraction - Create force without movement
How can a muscle generate force without changing its length? • Each muscle elastic elements: – Tendons – Intracellular cytoskeletal proteins with elastic properties – Contractile proteins themselves can stretch • These are included in the term: series elastic elements.
- Slides: 14