Suzanne D'Anna1 Muscular Responses

Suzanne D'Anna2 Threshold Stimulus l any stimulus strong enough to initiate action potential l minimal strength of stimulation needed to cause a contraction

Suzanne D'Anna3 All-Or-None Response l individual muscle cells contract to their fullest extent when exposed to stimulus of threshold strength l muscle fibers do not partially contract l if stimulus is strong enough to initiate an action potential, a nerve impulse is transmitted along entire neuron at a constant strength

Suzanne D'Anna4 Twitch Contraction l brief contraction of all the muscle fibers in a motor unit l lasts only a fraction of a second l response to a single action potential in its motor unit l myogram is a record of a muscle contraction

Suzanne D'Anna5 Myogram (single muscle twitch)

Suzanne D'Anna6 Myogram l latent period - delay between the time that the stimulus was applied and the time that the muscle responded l period of contraction - muscle pulls at its attachments l period of relaxation - muscle returns to its former length

Suzanne D'Anna7 Tetanus or Tetanic Contraction l state of smooth sustained muscle contraction l muscle is stimulated very rapidly l no evidence of relaxation l point at which the muscle is unable to relax before next stimulus l results from the addition of Ca +2 released from sarcoplasmic reticulum

Suzanne D'Anna8 Twitch l brief muscular contraction followed by relaxation

Suzanne D'Anna9 Muscle Tone (tonus) l state of continuous partial contraction l muscles are never totally relaxed l important in maintaining posture l loss of tone - body will collapse

Suzanne D'Anna10 Types of Muscle Contractions

Suzanne D'Anna11 Isotonic Contractions l same as tone or tension l myofilaments slide freely l muscles shorten - movement occurs l Example: - bending, rotating arms, smiling

Suzanne D'Anna12 Isometric Contractions l muscles do not shorten l myofilaments do not move freely “skidding their wheels” l muscles are unable to slide because they are trying to move something more or less immovable l Example: - pushing against a wall

Suzanne D'Anna13 Types of Exercise

Suzanne D'Anna14 Effect of Exercise on Muscles l amount of work done by a muscle is reflected in the muscle itself l inactivity leads to weakness of muscle

Suzanne D'Anna15 Aerobic or Endurance l results in stronger, more flexible muscles l greater resistance to fatigue due to increased blood supply to muscles l benefits body metabolism l improves digestion, elimination

Suzanne D'Anna16 Aerobic or Endurance (cont.) l strengthens skeleton l heart enlarges - more blood pumped l gas exchange in lungs more efficient l no increase in muscle size

Suzanne D'Anna17 Weight Resistance Exercises l increase muscle mass l the use of immovable or slightly movable objects l requires little time, every other day l increase muscle size - increase strength l weight lifting will not increase endurance l will increase muscle definition