Sliding Filament Theory: How Muscles Contract through Actin-Myosin Interaction, Slides of Physiology

Download Sliding Filament Theory: How Muscles Contract through Actin-Myosin Interaction and more Slides Physiology in PDF only on Docsity! Sliding Filament Theory  how do muscles work to move loads  muscles can only “pull” not “push” Actin’s Key Proteins 1. Tropomysin • Strand-like protein wrapped around the actin filament that blocks the myosin binding sites on the actin 2. Troponin • Globular shaped molecules that sit at top the tropomysin • Have calcium ion (Ca2+) binding sites In order for our muscles to contract, the myosin and actin myofilaments must slide overtop of each other. The filaments do not change their lengths. “Sliding Filament Theory” Problems to overcome: - the sites on the actin filament for the myosin to bind to are blocked by tropomyosin - myosin needs energy to bind and move the actin “Un-blocking” Actin - Calcium ions bind to the troponin causing the tropomyosin to move and reveal the binding sites - Calcium ions are regulatory molecules for muscular contractions - Calcium ions are released by the muscle cell (from the sarcoplasmic reticulum) when the cell becomes “depolarized” - A resting muscle cell is “polarized” - The action potential from the motor neuron arrives at the sacrolemma via acetylcholine - The cell becomes “depolarized” - The depolarization is carried into the fibre through the transverse tubules (T-tubules) - Terminal cisternae carry the depolarization into the filaments Relaxed Muscle : 2 Sacromeres 1 H zone I band Aband Z discs ; Thick filaments Thin filaments Partially Contracted Muscle : ' ' ' Saintly Z discs Mline Thin filaments Thick filaments Fully Contracted Muscle : Mline Z discs tS LLL LL LLL ater RR Sinblibobcolalolailh emery Thin filaments Sacromere Sacromere IvyRose Ltd. 2005, Online at www.lvyRose.co.uk Thick filaments Excitation-Contraction Coupling across the synaptic cleft and attaches to ACh receptors on the sarcolemma Neurotransmitter released diffuses  Steps to the Excitation-Contraction Coupling 1 Brain releases a nerve impulse to initiate a movement 2 Nerve impulse travels down the neuron to the neuromuscular junction (axon terminal) 3 The axon terminal releases the neurotransmitter acetylcholine 4 Acetylcholine crosses the synaptic cleft and binds to the receptors on the sarcolemma 5 The sarcolemma becomes depolarized 6 The action potential is transported to the interior of the muscle via T-tubules 7 The sarcoplasmic reticulum releases Ca2+ ions 8 Ca2+ binds to troponin 9 Tropomyosin slides revealing myosin binding sites on actin 10 ATP attaches to the head of myosin 11 Myosin attaches to actin 12 ATP splits to ADP + P and energy 13 Power stroke occurs causing actin to slide over myosin