2. Striation Pattern of Sarcomere A band: Thick myofilaments extend across this band, but thin filaments extends only to H Zone I band: Contain only Thin myofilaments Z disc: Beginning of Sarcomere, anchor Thin Myofilam. H zone: Contains only thick Myofilaments M line: middle of Sarcomere Sarcomere Z Disc H Zone M Portion of a Myofibril I I A Band

Arrangement of the Filaments in a Sarcomere Longitudinal section within one sarcomere Figure 9.4d

Microscopic Anatomy Sarcomere Thick Myofilament Thin Myofilament

III. Physiology of Skeletal Muscle Fibers A III. Physiology of Skeletal Muscle Fibers A. OVERVIEW OF STEPS TO MUSCLE CONTRACTION * Brain: message to move  spinal cord  nerve  Axon Terminal 1. Events at Neuromuscular Junction: pp.286-288 Axon of Motor Neuron sends Action Potential to Sarcolemma 2. EXCITATION-CONTRACTION COUPLING: 289 A second Action Potential moves along sarcolemma Sarcoplasmic Reticulum releases Calcium Calcium binds to troponin and then Myosin Head binding site is uncovered Contraction begins 3. CROSS BRIDGE CYCLE: (Sliding Filament Model): Myosin Heads attach to Actin and pull it inward  Myofibrils shorten  Muscle fibers shortens = Muscle contracts

Major external ion = Na+ Major intracellular ion = K+ Physiology of Skeletal Muscle Fibers … B. Events at Neuromuscular Junction– Details Action Potential #1 travels down Axon to Terminals = Caused by ion movement Major external ion = Na+ Major intracellular ion = K+ a) Resting Membrane: initially inside of cell is negative due to having more negative Chemicals a) Na+ enters axon = Depolarization and inside of cell becomes positive b) K+ leaves axon = Repolarization and inside of cell goes back to negative Figure 9.7 (a-c)

2. Synaptic Vesicles release Ach via exocytosis 3. Ach diffuses across synapse 4. Ach binds with Ach receptors of motor end plate Axon Terminal Receptor

Run the Muscle Contraction Video- part 1

Initially Sarcolemma is in the Resting Membrane state Physiology of Skeletal Muscle Fibers … Binding of Ach to Receptors on Sarcolemma then triggers changes in Muscle Fibers and leads to C. Excitation-Contraction Coupling: events from transmission of action potential along sarcolemma to the beginning of contraction Initially Sarcolemma is in the Resting Membrane state 2. #2 Action Potential Receptors allow Na+ ions to enter and K+ ions to leave the muscle fiber; but more Na+ enters making the inside of the cell positive More Positive outside Negative inside Outside Cell Inside Cell Figure 9.8a

Initially Sarcolemma is in the Resting Membrane state Physiology of Skeletal Muscle Fibers … Binding of Ach to Receptors on Sarcolemma then triggers changes in Muscle Fibers and leads to C. Excitation-Contraction Coupling: events from transmission of action potential along sarcolemma to the beginning of contraction Initially Sarcolemma is in the Resting Membrane state 2. #2 Action Potential Receptors allow Na+ ions to enter and K+ ions to leave the muscle fiber; but more Na+ enters making the inside of the cell positive More Positive outside Negative inside Outside Cell Inside Cell Figure 9.8a

Excitation-Contraction Coupling … 2. #2 Action Potential … Charge inside cell changes from negative to positive If enough Na+ enters, an action potential travels down Sarcolemma It moves out in all directions via Depolarization and Repolarization Outside Cell + + + + + + + Inside Cell + Na++ K+ Figure 9.8b

Excitation-Contraction Coupling … 2. Action Potential … ©2007 Thomson Higher Education After Action Potential has ended, the Resting state is restored by the Na+-K+ pump Na+ Figure 9.8d

Excitation-Contraction Coupling … Action Potential … Action potential travels down the T-tubules The Sarcoplasmic Reticulum releases Ca+2 into the cell High Ca+ in the Sarcoplasm ultimately leads to muscle contraction Figure 9.8c

Run the Muscle Contraction Video-part 2

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