【正文】 Ca channel (DHP receptor) junctional foot (ryanodine receptor) sarcoplasmic reticulum sarcolemma Ttubule The manifestation of muscle contraction force/tension and shortening The types of muscle contraction isotonic contraction isometric contraction single twitch tetanus Mechanics of Muscle Contraction Tension and Load ? The force exerted on an object by a contracting muscle is known as tension. ? The force exerted on the muscle by an object (usually its weight) is termed load. ? According to the time of effect exerted by the loads on the muscle contraction the load was divided into two forms, preload and afterload. Types of Contractions ? Twitch: a brief mechanical contraction of a single fiber produced by a single action potential at low frequency stimulation is known as single twitch. ? Tetanus: It means a summation of twitches that occurs at high frequency stimulation Effects of Repeated Stimulations Figure 1/sec 5/sec 10/sec 50/sec Isometric Contraction Length of muscle remains constant during contraction. A maximal active tension can be produced but no shortening occur. Isotonic Contraction Length of muscle changes. Tension fairly constant. Involves movement at joints Isotonic and Isometric Contractions Preload ? Preload is a load on the muscle before muscle contraction. ? Determines the initial length of the muscle before contraction. ? Initial length is the length of the muscle fiber before its contraction. ? It is positively proportional to the preload. The Effect of Sarere Length on Tension The Length – Tension Curve Concept of optimal length Afterload ? Afterload is a load on the muscle after the beginning of muscle contraction. ? The reverse force that oppose the contractile force caused by muscle contraction. ? The afterload does not change the initial length of the muscle, ? But it can prevent muscle from shortening because a part of force developed by contraction is used to overe the afterload. Resistance and Speed of Contraction Contractility is identified as an inner property of muscle, which determine the efficacy of muscle contraction. Effects of contractility on mechanics of muscle contraction Its potential acting site including calcium release, calcium sensitivity, crossbridge affinity, activity of ATPase, speed of crossbridge move, heatwork efficiency of ATP,etc. Thank you! See you next time. 。 regulates muscle contraction ?Tropomyosin ?Lies in groove of actin helix ?Blocks myosin binding ? sites in absence of Ca2+ ? Thick filament: Myosin (head and tail) ? Thin filament: Actin, Tropomyosin, Troponin (calcium binding site) THE CROSSBRIDGE CYCLE ATP ADP + Pi AlM A – M l ATP AlMlADPlPi A + M l ADP l Pi Relaxed state Crossbridge energised Crossbridge attachment Tension develops Crossbridge detachment Ca2+ present A, Actin。 (2) when ΔCK+ equal to E K+, of K+ flow bee 0, E K+ reaches to a equilibrium potential, that is resting potential. Identification: 1. Nernst formula Ek= Log [K+ ]o/[K+ ]i (mV) theoretic –87mV， actual –77mV 2. Change the concentration of K+ in extracellular fluid 3. Using TEA to block potassium channels Action Potential (AP) Action potential is a rapid, reversible, and conductive change of the membrane potential after the cell is stimulated. Successive Stages: (1) Resting Stage (2) Depolarization stage (3) Repolarization stage (4) Afterpotential stage (1) (2) (3) (4) The HodgkinHuxley Model of Action Potential Generation 1. Nernst formula ENa= Log [Na