E109 Lecture 7: Muscles II PDF

E109 Lecture 7: Muscles II Extended Office Hours: Monday 12-2PM 351 Steinhaus Hall Sample questions will be Available later today...

E109 Lecture 7: Muscles II Extended Office Hours: Monday 12-2PM 351 Steinhaus Hall Sample questions will be Available later today on course website Contraction cycle crossbridgeformation Rigor state: Myosin bound to actin calciumis anecessity G-actin molecule ADP lost. The cross-bridge enters the ATP binds to myosin allowing transient Rigor state detachment. Myosin in low E state. Myosin binding sites 4 Myosin filament ADP ATP 3 5 Pi lost. Myosin forms strong bond with ATP hydrolyzed. Myosin assumes high actin and performs the power stroke. E state & forms weak bond with actin. Ca2+ ADP ATP Pi Pi 1 ADP 2 Contraction cycle ATP ADP crossbridge cycle Ca2+ Regulation airtight initiate its understandthe roles release ofcalcium will causeloss of iitenfa.fi tension cycle iii tissue T.fi peedtoletgo Review The neuromuscular junction is a synapse connecting motor neurons and muscle cells Excitation contraction coupling is the conversion of an electrical signal in the sarcolemma into a Ca+2 signal in the cytoplasm Calcium release from the SR is a critical regulatory step in contraction ATP is used for detachment of cross bridges and by Ca+2 pumps used to move calcium into the SR Learning Objectives Understand how force production is determined through the Intrinsic properties of the sarcomere controlled by the nervous system (Extrinsic control) Summary of Muscle Contraction sarcomereshortens when contractionhappens Zlinesgointowardsthemiddle duringcontration A band Z line notcontracted I band H zone Z line I contracted Figure 12-7 Length-tension Relationship Tension Isometric contractions looking musclesabilitytogenerate force a givenlength 0.5 x 1.0 x 1.5 x resting length resting length resting length length tensionrelationship Length-Tension Relationship at intermediatelengths yougeneratethemost overlapbetweenmyosin actin Relative Tension (% maximum) 100 80 60 7 bandMatt the 40 20 0 1.3μm 2.0μm 2.3μm 3.7μm not Sarcomere length Intrinsic property Force-velocity Relationship crossbridge more weight morecrossbridges needed 20 g 20 gg 100 Isotonic Contractions moreweight more length x velocity time Force-velocity Relationship The inability to detach quickly enough causes some cross bridges to oppose force i production fasteryougothequickercrossbridges are tryingtowork Review Sliding filament model provides mechanism responsible for the force-length relationship of skeletal muscle function The tradeoff between speed and force in skeletal muscle is driven by the time required for cross bridge detachment Neural control of muscle force Figure 12-7 Muscle Twitch actionpotential twitch Muscle fiber +30 Action potential Neuron from CNS membrane potential in mV -70 Motor Recording Time end plate electrodes +30 Muscle fiber membrane Muscle action potential potential in mV -70 2 msec Time Latent Contraction Relaxation period phase phase Tension Development of tension during one muscle twitch 10–100 msec Time Twitch Summation Skeletalmuscle Tension 0 100 200 300 400 500 Time (ms) stimulation puise 5471481 58 appliedinshorttime period Tension 0 100 200 300 400 500 Time (ms) Twitch Summation unfused tetanus Maximum tension fused tetanus Time (ms) Maximum tension single twitch tension Time (ms) Neural control of force Tension 0 100 200 300 400 500 Time (ms) The nervous system regulates muscle force: -Through changes in action potential frequency -Through changes in the number of muscle cells (motor units) activated Motor Unit Recruitment SPINAL CORD Neuron 1 Neuron 2 Neuron 3 Motor nerve KEY Muscle fibers Motor unit 1 A motor unit consists of Motor unit 2 one motor neuron and all the fibers it Motor unit 3 innervates Motor Unit Recruitment 100 50 Small MU Intermediate MU Large MU 0 0 25 50 75 100 % of Motor Units Recruited Order of motor unit recruitment Fiber Types Small Motor Unit Intermediate Motor Unit Large Motor Unit Fiber Types Slow Twitch Intermediate Twitch Fast Twitch Fiber Types Twitch tension Slow Intermediate Fast Time (ms) Velocity Vmax Cellular Metabolism Fiber Types Slow Oxidative Fast Oxidative Fast Glycolytic Fiber Type Comparison Fiber Type Characteristics Slow Oxidative Fast Oxidative Fast Glycolytic Twitch Speed Slow Intermediate Fast Myosin ATPase Slow Intermediate Fast Fiber Diameter Small Medium Large Ca2+ Pumps in SR Fewer Many Many Endurance Fatigue Resistant Fatigue Resistant Easily Fatigued Metabolism Oxidative Oxidative Glycolytic Capillary Density High Medium Low Mitochondria High Medium Low O2 storage Myoglobin Some myoglobin None