Topic 7.2 - Muscle Structure, Morphology and Contraction PDF

💪🏾 Topic 7.2 - Muscle: Structure, Morphology and Contraction Muscle Organisation (which 2 muscles are striated and which muscle is non-striated) What is the Structure of Skeletal Muscle Topic 7...

💪🏾 Topic 7.2 - Muscle: Structure, Morphology and Contraction Muscle Organisation (which 2 muscles are striated and which muscle is non-striated) What is the Structure of Skeletal Muscle Topic 7.2 - Muscle: Structure, Morphology and Contraction 1  Functional unit = Sarcomere → replicated down the length of muscle to form Myofibrils. Myofibrils are bundled together to give Muscle Fibres (a cell). Muscle Fibres are bundled and wrapped in connective tissue to form Fascicles. Fascicles are in turn bundled to form Muscle. What is Endomysium Connective Tissue Endomysium - Surrounds each individual muscle fibre What is Perimysium Connective Tissue Surrounds each Fascicle What is Epimysium Connective Tissue Surrounds entire muscle Topic 7.2 - Muscle: Structure, Morphology and Contraction 2  What are the different Sarcomere Bands During Contraction - A band stays the same width, H zone + I band becomes shorter What are the Thick and Thin Filaments Myosin forms thick filaments – Protein consisting of two identical subunits Actin is the main structural component of thin filaments – Interacts with the myosin cross bridge – tropomyosin and troponin, are associated with actin Topic 7.2 - Muscle: Structure, Morphology and Contraction 3  Myosin Structure myosin head an actin binding site + ATPAse Site Actin (Thin Filament) Structure actin filament forms a helix. Tropomyosin molecules → blocks Myosin Binding Site A troponin complex is attached to each tropomyosin molecule. What is the Power Stroke Bending of myosin heads pulls the actin filament toward the centre of the sarcomere What is the role of Calcium in Contraction Mechanism increasing amounts of calcium ions bind to TnC of Troponin Complex, a conformational change occurs which moves tropomyosin away from Topic 7.2 - Muscle: Structure, Morphology and Contraction 4  Myosin’s binding sites on Actin displacement allows myosin heads to bind to actin and contract. What is The Neuromuscular Junction + Explain Excitation-Contraction Coupling Neuromuscular Junction (NMJ): specialized synapse connecting motor neuron to skeletal muscle fiber. Action Potential (AP) at axon terminal opens Voltage-gated Calcium Channels. Release of Acetylcholine (ACh) into synaptic cleft. ACh activates Nicotinic ACh receptors (ligand-gated), causing influx of Sodium Ions. Activation of Voltage-gated Sodium Ions triggers AP in skeletal muscle. Depolarisation spreads over the sarcolemma and through the T tubules. Voltage sensitive proteins inside the T tubules change conformation. This opens the gated calcium channels, meaning calcium is released into the sarcoplasm Calcium binds to the troponin (subunit TnC), moving the troponin and tropomyosin away from the myosin binding site, and allowing muscle contraction interaction to occur Topic 7.2 - Muscle: Structure, Morphology and Contraction 5  Explain the Sliding Filament Theory 1. The myosin heads form a cross bridge with the actin filament. 2. The attached heads pull on the actin filament through a form of relaxation 3. ATP attaches to the myosin head, and this breaks the bond with the actin filament. Topic 7.2 - Muscle: Structure, Morphology and Contraction 6  4. The ATP hydrolyses and ‘cocks’ the myosin head back to the starting position (active movement). This movement slides the myosin filaments along the actin, causing the I band to shrink as the overlap increases. How do muscles relax Relaxation requires breaking the Cross-Bridge Cycle. In the absence of Motor Neurone firing, Calcium Channels close. ATPases in the Sarcoplasmic Reticulum (SR) quickly return Calcium to stores or expel it from the cell. Sarco/Endoplasmic Reticulum Calcium ATPases (SERCA) - Causes Troponin (TnC) to release Calcium, reversing the conformational change in Tropomyosin. Tropomyosin covers the Myosin binding site → muscle relaxes 2 components of a Motor Unit single motor neurone + Muscle fibres Topic 7.2 - Muscle: Structure, Morphology and Contraction 7  How does Smooth Muscle Contraction Work Depolarization opens L-type Voltage-gated Calcium channels, allowing Calcium influx. Intracellular Calcium binds to Calmodulin, activating Myosin Light Chain Kinase (MLCK). MLCK phosphorylates Myosin Heads through ATP Hydrolysis. Phosphorylated Myosin Heads can attach to Actin-Binding Sites. Thin Filaments anchored to dense bodies are pulled, causing muscle fiber contraction. Topic 7.2 - Muscle: Structure, Morphology and Contraction 8  Explain how contraction is controlled in Smooth Muscle involuntary. varicosities (swellings of axons) filled with neurotransmitters contact the sarcolemma. Smooth muscle can be spontaneously active, generating action potentials without external stimuli, often due to pacemaker cells in hollow organ walls. Topic 7.2 - Muscle: Structure, Morphology and Contraction 9