KIN 100 1st Edition Lecture 3 Muscle Different subdisciplines study different aspects of a topic exercise physiology metabolism biomechanics morphology motor control activation Muscle anatomy Motor Unit a motor neuron and all of the muscle fibers it innervates each muscle fiber responds to only one motor neuron Neuromuscular junction NMJ connection between the neuron and the muscle Types of muscle fibers fast twitch high force short period of time easily fatigable type 2 anaerobic metabolism few capillaries appears white white muscle slow twitch low force long time fatigue resistant type 1 aerobic metabolism many capillaries appears red red muscle Motor Unit Morphology Muscle motor units Innervation ratio eye muscles 6 3000 10 gastrocnemius 600 2000 calf muscle Innervation ratio number of muscle fibers per motor neuron eye muscles have much more fine control many motor units each unit controls few muscle fibers Muscle biopsy small piece of muscle removed and stained for study studied for different reasons Physiology of muscles contraction time shorter in fast twitch longer in slow twitch Muscle contraction 1 2 3 4 5 6 7 8 Myosin and Actin proteins in muscle fibers Acetylcholine neurotransmitter released from vesicles in motor neuron and actives the muscle fiber by hitting the receptors Nerve action potential AP Acetylcholine ach released from vesicles Ach binds to muscle receptor sites Muscle fiber AP generation AP travels along muscle fibers Ca released in muscle fibers Ca causes actin proteins Muscle contraction shortening of muscle fibers Action potential electronic signal sent through cells myosin crossbridges pull actin filaments along Muscle Contraction Pathology Myasthenia gravis receptor sites are not fully developed harder to receive messages signals ALS Lou Gehrigs Disease number of motor neurons decrease impaired muscle contraction Types of Muscle Contraction Isometric static contraction no movement change in joint angle Isotonic dynamic muscles move Concentric muscle shortening Eccentric muscle lengthening Measuring Muscle Strength Isometric maximal force pushing against a wall Isotonic repetition maximum RM max weight you can lift a set number of times
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