Muscle Physiology Muscle activity The muscle contraction is

Muscle Physiology

Muscle activity The muscle contraction is dependent of: l Electrical excitation of a muscle cell l Excitation-contraction coupling l Sliding of the myofilaments

Action potential l Resting membrane potential l Depolarization l Action potential l Repolarization ¡Absolute refractory period ¡Relative refractory period

Muscle contraction l Cyclic process beginning with calcium released from SR l Calcium binds to troponin l Changes in troponin shape l Tropomyosin uncovers active site on actin l Actin forms cross-bridges with myosin l Slinding of myosin and actin over each other

Muscle contraction l Muscle shortens l Ending of action potential l Calcium is reabsorbed by sarcoplasmic reticulum l Myosin detaches from actin l Muscle is in resting stage again

Muscle Contraction

Muscle contraction

Muscle Contraction

Muscle contraction l Twitch ¡Cycle of contraction, relaxation produced by a single stimulus ¡Phases l. Latent period l. Contraction phase l. Relaxation phase l Threshold stimulus ¡It is the voltage at which the first contractile response occurs

Muscle contraction l Subthreshold stimuli ¡All stimuli applied prior to the threshold stimulus l Graded potential ¡Graded muscle response to increased stimulus intensity l Maximus stimulus ¡Weakest stimulus at which all muscle cells are being stimulated

Muscle contraction l Treppe or staircase phenomenon ¡Stimulus is kept at same intensity ¡Height of individuals spikes increase in a stepwise manner ¡Repeated stimulation after relaxation phase has been completed ¡Subsequent contractions are more vigorous

Treppe Caused by: l Increased Ca levels from previous contractions l Increased heat generated by muscle work increases enzyme efficiency

Increased stimulus frequency Repeated stimulation before relaxation phase has been completed will cause: l Wave summation ¡one twitch is added to another ¡The intensity of the stimulus is kept the same ¡The frequency of the stimulus applied increases

Increased stimulus frequency l Incomplete tetanus ¡Muscle in peak tension. State of sustained fluttering contraction. l Complete tetanus ¡ Relaxation phase is eliminated ¡There is fusion of twitches

Effects of Repeated Stimulations

Muscle fatigue l Fatigue ¡Loss of the ability of a muscle to contract ¡Caused by deficit of ATP ¡Build up of lactic acid ¡Lower tissue p. H ¡Exhaustion of energy resources

Effect of the load on the skeletal muscle l Motor unit recruitment l Increased load beyond optimum level causes overstretch of the muscles : ¡The filaments do not overlap anymore ¡It will not allow contraction to happens