Muscular Responses Suzanne DAnna 1 Threshold Stimulus any

Muscular Responses Suzanne D'Anna 1

Threshold Stimulus any stimulus strong enough to initiate action potential l minimal strength of stimulation needed to cause a contraction l Suzanne D'Anna 2

All-Or-None Response 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 l Suzanne D'Anna 3

Twitch Contraction 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 l 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 l period of contraction - muscle pulls at its attachments l period of relaxation - muscle returns to its former length l Suzanne D'Anna 6

Tetanus or Tetanic Contraction 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 l Suzanne D'Anna 7

Twitch l brief muscular contraction followed by relaxation Suzanne D'Anna 8

Muscle Tone (tonus) state of continuous partial contraction l muscles are never totally relaxed l important in maintaining posture l loss of tone - body will collapse l Suzanne D'Anna 9

Types of Muscle Contractions Suzanne D'Anna 10

Isotonic Contractions same as tone or tension l myofilaments slide freely l muscles shorten - movement occurs l l Example: - bending, rotating arms, smiling Suzanne D'Anna 11

Isometric Contractions 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 l 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 l inactivity leads to weakness of muscle l Suzanne D'Anna 14

Aerobic or Endurance 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 l Suzanne D'Anna 15

Aerobic or Endurance (cont. ) strengthens skeleton l heart enlarges - more blood pumped l gas exchange in lungs more efficient l no increase in muscle size l Suzanne D'Anna 16

Weight Resistance Exercises 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 l Suzanne D'Anna 17