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Study Guide 1 - Skeletal Muscle Somatic Motor Division...

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Skeletal Muscle * Somatic Motor Division controls skeletal muscles with motor pathways of a single neuron that are always excitatory Neuromuscular Junction : synapse of a somatic motor neuron on a muscle fiber The junction contains Nicotonic receptors and chemically gated ion channels, and the opening of this channel is always excitatory because it allows monovalent cations to enter. Skeletal Muscle Structure Makes up the bulk of the muscle of the body and is 40% of total body weight. Most joint in the body are antagonistic muscle groups with flexor-extensor pairs. Muscle fibers are the largest cells in the body Made up of myofybrils with associated organelles. Myofibrils made with structural proteins that are in crystal arrays. Sarcomere : functional unit of muscle fiber: Contracts by sliding these filaments over one another. Muscle is elongated and as it contracts to get to bottom state it gets shorter and generates force. Sacroplasmic Reticulum : a modified form of the ER that wraps around each myofibril like a piece of lace and release Ca+ ions into the terminal cisternae T-Tubules : associated with terminal cisternae that makes the lumen of the t-tubule continuous with ECF. Rapidly move action potentianls that originate at the NMJ into the interior of the fiber. Without these tubules the action potential could reach the center of the fiber only by diffusion of positive charges and there would be much delay Cross Bridge Cylcing Actin: Thin filament: double helical arrangement of actin monomers. Thin filaments are arranged in hexaganol array around thick filaments. In skeletal muscle multiple G-actin molecules polymerize to form the filament. Myosin: Thick filaments are the, parallel bundles of myosin. In the bundles, these myosin heads stick out in all directions. The protruding heads have an elastic hinge where the heads join the rods. Interaction of myosin head with binding sites on actin thin filaments: cross-bridge cycle. Sarcomere Composition 2 Z disks: zig zag proteins that serve as the attachment sites for the the thin filaments I Band: lightest color of sarcomere because they are occupied by thin filaments. A Band: darkest as it encompasses entire length of a thick filament. At the outer edges the thick and thin filaments overlap. H Zone: Central region of the A band that is lighter than the outer regions of overlap M Line: Proteins that form attachment site for thick filaments. 1
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Cross-Bridge Cycling *Reactions here are going to be on the myosin head, which has an ATP binding site and ATPase activity. Actin molecule also has binding site. 1. Myosin head has no bound nucleotides, naked head. This configuration, proteins change their conformation based on what is bound. In this state the myosin head is attached to binding side and the neck forms a 45 degree angle with thick filament. In the absence of any ATP, the binding affinity to actin is very high.
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