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Muscular Responses Suzanne D'Anna 1 Threshold Stimulus any stimulus strong enough to initiate action potential minimal strength of stimulation needed to cause a contraction Suzanne D'Anna 2 All-Or-None Response individual muscle cells contract to their fullest extent when exposed to stimulus of threshold strength muscle fibers do not partially contract if stimulus is strong enough to initiate an action potential, a nerve impulse is transmitted along entire neuron at a constant strength Suzanne D'Anna 3 Twitch Contraction brief contraction of all the muscle fibers in a motor unit lasts only a fraction of a second response to a single action potential in its motor unit myogram is a record of a muscle contraction Suzanne D'Anna 4 Myogram (single muscle twitch) Suzanne D'Anna 5 Myogram latent period - delay between the time that the stimulus was applied and the time that the muscle responded period of contraction - muscle pulls at its attachments period of relaxation - muscle returns to its former length Suzanne D'Anna 6 Tetanus or Tetanic Contraction state of smooth sustained muscle contraction muscle is stimulated very rapidly no evidence of relaxation point at which the muscle is unable to relax before next stimulus results from the addition of Ca+2 released from sarcoplasmic reticulum Suzanne D'Anna 7 Twitch brief muscular contraction followed by relaxation Suzanne D'Anna 8 Muscle Tone (tonus) state of continuous partial contraction muscles are never totally relaxed important in maintaining posture loss of tone - body will collapse Suzanne D'Anna 9 Types of Muscle Contractions Suzanne D'Anna 10 Isotonic Contractions same as tone or tension myofilaments slide freely muscles shorten - movement occurs Example: - bending, rotating arms, smiling Suzanne D'Anna 11 Isometric Contractions muscles do not shorten myofilaments do not move freely “skidding their wheels” muscles are unable to slide because they are trying to move something more or less immovable Example: - pushing against a wall Suzanne D'Anna 12 Types of Exercise Suzanne D'Anna 13 Effect of Exercise on Muscles amount of work done by a muscle is reflected in the muscle itself inactivity leads to weakness of muscle Suzanne D'Anna 14 Aerobic or Endurance results in stronger, more flexible muscles greater resistance to fatigue due to increased blood supply to muscles benefits body metabolism improves digestion, elimination Suzanne D'Anna 15 Aerobic or Endurance (cont.) strengthens skeleton heart enlarges - more blood pumped gas exchange in lungs more efficient no increase in muscle size Suzanne D'Anna 16 Weight Resistance Exercises increase muscle mass the use of immovable or slightly movable objects requires little time, every other day increase muscle size - increase strength weight lifting will not increase endurance will increase muscle definition Suzanne D'Anna 17