TAILIEUCHUNG - Lecture Human anatomy and physiology - Chapter 9: Muscles and muscle tissue (part b)

This chapter presents the following content: Gross anatomy of a skeletal muscle, microscopic anatomy of a skeletal muscle fiber, sliding filament model of contraction, physiology of skeletal muscle fibers, contraction of a skeletal muscle, muscle metabolism, force of muscle contraction, velocity and duration of contraction, adaptations to exercise. | 9 Muscles and Muscle Tissue: Part B Review Principles of Muscle Mechanics Same principles apply to contraction of a single fiber and a whole muscle Contraction produces tension, the force exerted on the load or object to be moved Review Principles of Muscle Mechanics Contraction does not always shorten a muscle: Isometric contraction: no shortening; muscle tension increases but does not exceed the load Isotonic contraction: muscle changes in length and moves the load Isotonic Contractions Isotonic contractions are either concentric or eccentric: Concentric contractions: the muscle shortens and does work Eccentric contractions: the muscle lengthens as it contracts and does work Review Principles of Muscle Mechanics Force and duration of contraction vary in response to stimuli of different frequencies and intensities Motor Unit: The Nerve-Muscle Functional Unit Motor unit = a motor neuron and all (four to several hundred) muscle fibers it supplies Figure Spinal cord Motor neuron cell body Muscle Nerve Motor unit 1 Motor unit 2 Muscle fibers Motor neuron axon Axon terminals at neuromuscular junctions Axons of motor neurons extend from the spinal cord to the muscle. There each axon divides into a number of axon terminals that form neuromuscular junctions with muscle fibers scattered throughout the muscle. Motor Unit Small motor units in muscles that control fine movements (fingers, eyes) Large motor units in large weight-bearing muscles (thighs, hips) Motor Unit Muscle fibers from a motor unit are spread throughout the muscle so that a single motor unit causes weak contraction of entire muscle Motor units in a muscle usually contract asynchronously; helps prevent fatigue Muscle Twitch Response of a muscle to a single, brief threshold stimulus Simplest contraction observable in the lab (recorded as a myogram) Muscle Twitch Three phases of a twitch: Latent period: events of excitation-contraction coupling Period of contraction: cross bridge formation; tension .

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