Skeletal Muscular System PDF

Mechanism of Muscle Contraction Cross bridge attachment ○ Myosin head Power stroke Cross bridge detachment Myosin reactivation Resting sarcomere Myosin head back ATP + P bound to myosin head - energized position Myosin is not bound to actin because tropomyosin is bl...

Mechanism of Muscle Contraction Cross bridge attachment ○ Myosin head Power stroke Cross bridge detachment Myosin reactivation Resting sarcomere Myosin head back ATP + P bound to myosin head - energized position Myosin is not bound to actin because tropomyosin is blocking the binding How are muscles activated Motor neuron releases acetylcholine Acetylcholine bind ligand gated channels of muscle membrane - Action potential on muscle membrane Action potential travels through T-Tubule and causes release of Ca2+ from nearby sarcoplasmic reticulum Ca+ binds troponin to move tropomyosin  Sliding filament theory: Step 1 - cross-bridge attachment ○ Myosin will bind actin because tropomyosin moved ○ Myosin head is still back with ADP + P bound ○ Step 2 - Power Stroke ○ Myosin head swings forward while ADP + P removed Low energy ○ Myosin bound to actin  ○ Step 3 - cross-bridge detachment ○ ATP binds myosin head to release it from actin - myosin not longer bound to actin ○ Head forward ○ Step 4 - myosin reactivation ○ ATP is converted to ADP + P to cause myosin head back ○ Myosin is not bound to actin ○ Regulation of muscle contraction Ca ++ determines position of troponin/tropomyosin CA++ stored in the sarcoplasmic reticulum and is released in response to action potential carried by T-tubules Strength of contraction Motor unit: one motor neuron and all of the muscle fibers it innervates ○ Small motor unit: (4-10) Don’t use as much energy - allows more control over emotions/actions Small motor units with few muscle fibers Most abundant in the eyes ○ Larger motor unit: (50-100) Gives more strength - more muscle fibers = more strength Largest fibers in the legs Muscle tone: some motor neurons always active to maintain body position and posture Involuntary Energy production in Muscles Stored energy: ○ ATP - enough stored to last about 6 seconds ○ Creatine phosphate - transfers phosphate to ADP to make ATP - enough stored to last about 10 seconds ○ 10x more creatine phosphate can be stored than ATP Anaerobic respiration: without oxygen ○ Glucose only in 1st step (glycolysis) 2 ATPs Sustained for about 60 seconds Quick Produces lactic acid Aerobic respiration: with oxygen ○ Glucose need in all steps 36 ATP ○ Sustained for light to moderate activity ○ Fats also used for energy ○ Slower ○ Longer exercise fatty acids need to be used so blood glucose can be maintained  Types of muscle fibers Fast Twitch ○ Relies on anaerobic respiration ○ Lower blood supply and mitochondria ○ Activated for more intense exercise Slow Twitch ○ Relied on aerobic respiration ○ Higher bloody supply and mitochondria ○ Activated for light to moderate exercise Activation of different muscle fibers ○ Motor units only contain one type of muscle fibers ○ Muscles contain motor units with both slow and fast fibers ○ Slow fibers activated first ○ If needed, fast fibers will be activated