Skeletal Muscle Function PDF

Skeletal Muscle Function MEDI221/EXSC221  Objectives: Revise the microstructure of muscle Revise the sliding filament theory and excitation contraction coupling Describe the following: CNS and motor control Torque-angle relationship Length-tension relationship...

Skeletal Muscle Function MEDI221/EXSC221  Objectives: Revise the microstructure of muscle Revise the sliding filament theory and excitation contraction coupling Describe the following: CNS and motor control Torque-angle relationship Length-tension relationship Force-velocity relationship Muscle fiber type classification Reading Chapter 18: Skeletal Muscle Structure and Function (McArdle, Katch & Katch)  Microstructure of Skeletal Muscle Muscle is complex: At the cellular level: Fascicles→ muscle fibers→ myofibrils → sarcomere→ myofilaments (actin and myosin). Connective Tissue: Epimysium Perimysium Endomysium Sliding Filament Theory Internal Microstructure of a Myofibril  Excitation-Contraction Coupling Action potential → T-Tubule→ sarcoplasmic reticulum → release of Ca+ → Ca+ binds to troponin→ tropomyosin sheath unblocked → actin slides pass myosin → force production. Musculotendinous Unit = MTU Produce Transfer Sense Absorb CNS and Motor Control 1. Motor cortex Action potentials 2. Brainstem -descending systems 3. Spinal cord - interneurons Motor units CNS and Motor Units CNS varies muscular force 1. Recruitment of motor units 2. Firing frequency of motor units 3. Synchronisation of motor units Muscle spindles and Golgi Tendon Organs How do we measure strength? Torque-angle relationship of the knee extensors 16 Length-Tension Relationship Watch this video to understand the force-velocity relationship and its https://youtu.be/mEAii7IEtuo implications to training. MHC IIx MHCIIb MHC I White White/Red Red Large Med Small Low Med High Low Med High High High Low High Med/High Low High High Low Low Med/High High 3. Physiological Classification of Muscle Fibers Fast Fast slow Fast Fast slow High Mod/High Low High Mod Low Fiber type & Athletic Performance  Summary Sarcomere is the functional unit of skeletal muscle Myosin pulling past actin = force generation Tendons are actuators of force, MTU CNS integrates motor commands Torque varies at the angle we produce it and how fast we move Type I – slow twitch Type IIa – intermediate Type IIb – fast twitch