4 Skeletal muscle

4 Skeletal muscle - SKELETAL MUSCLE page 1 AC Brown A7a...

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SKELETAL MUSCLE AC Brown page 1 A7a CONTRACTION PATTERNS A. Contraction Terms and Contraction Twitch 1. Contraction: activation of muscle fiber to cause either increase tension (T, force) or shortening (decreasing length, L) or both a. isometric constant length (tension ) b. isotonic constant tension (length ) c. intermediate length and tension Note: Muscles can only contract (“pull”); they cannot extend with force (“push”). To move in both directions about a joint requires two sets of muscles; e.g. flexors and extensors. 2. Twitch: contraction following a single, brief stimulus either to the muscle itself or to the motor nerve innervating the muscle a. force or shortening pattern b. skeletal muscle twitch duration ranges from about 40 msec (1/25 sec) for fast muscles to 500 msec (1/2 sec) for slow muscles
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SKELETAL MUSCLE AC Brown page 2 A7a CONTRACTION PATTERNS (continued) B: Response to Multiple Stimuli (Summation) Two stimuli; second stimulus delivered while the muscle is still contracting A series (“train”) of stimuli 1. Phenomenon: since the electrical refractory period of nerve and muscle is much less than the twitch duration, a second stimulus can be given during the twitch 2. Characteristics a. second twitch begins before the first twitch is complete (contraction is not all-or-none) b. peak tension is greater than with a single twitch (mechanical summation) c. the smaller the delay between the two stimuli, the greater the peak tension (up to a certain point) C. Fusion and Tetanus 1. Apply continuous train of stimuli 2. Result Low frequency Series of separate twitches Intermediate frequency Summation but incomplete fusion (a & b) above High frequency Complete fusion and maximum tension (Tetanus)
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SKELETAL MUSCLE AC Brown page 3 A7a MECHANISM OF CONTRACTION A. Functional Anatomy of Skeletal Muscle 1. Muscle fiber (muscle cell, myocyte) a. excitable membrane (sarcolema); generates and propagates action potentials, similar to neuron axon (conduction velocity in order of 5 m/sec) b. composed of myofibrils, sarcoplasmic reticulum system, mitochondria, etc. 2. Myofibril
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This note was uploaded on 01/03/2012 for the course BIO 308 taught by Professor Acbrown during the Spring '10 term at Portland.

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4 Skeletal muscle - SKELETAL MUSCLE page 1 AC Brown A7a...

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