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L26 - Muscle Physiology Nov 12 Week.docx

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Tracy Mc Donald

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Muscular System: Histology and Physiology Skeletal Muscle System Functions - Body movement – b/c attached to bone o Exception – muscle attached to sclera of eye o Skin in face - Maintenance of posture o Protect and stabilize joints o Maintain various body positions – standing, sitting o Muscles that maintain postures are always contracting - Respiration – diaphragm, intercostals muscles help us breathe - Production of body heat – main energy source is ATP, work out of it, majority of energy is lost as head – breakdown of ATP, muscles use so much ATP – main contributor to body temp – explains why you get hotter when you exercise - Communication – wouldn’t be able to write, speak, facial expression Properties of Muscle - Contractility: ability of a muscle to shorten forcefully o Muscle attached to 2 bones, when shortened, pulls on 2 bones, creates tension which causes muscle to move bone - Excitability: capacity of muscle to respond to a stimulus o Can it respond to electrical stimulus coming from NS? Yes! o Reason it has capability is b/c on its plasma membrane it contains voltage-gated channels o When axon synapses w/skeletal muscle, sends NT across which causes change in resting potential and propagate AP across membrane o Can respond to hormone, pH changes in addition to electrical impulses - Extensibility: muscle can be stretched beyond its resting length and still be able to contract o Normal resting position is anatomical position but can stretch muscles beyond normal resting position and still generate a force - Elasticity: ability of muscle to recoil to original resting length after its been stretched - Muscle tissue can only ever be contracted or not, cannot be inhibited – gravity has to take over and relax muscle, or opposing muscle group contracts while other relaxes Skeletal Muscle Structure - Composed of muscle cells (fibers), connective tissue, blood vessels (like bone), nerves - Fibers are long, cylindrical, multinucleated (tube type structure) o Cell is as long as the muscle – small muscles cell is short, large muscle cell is long o Nucleus is just under plasma membrane b/c we don’t want it to interfere w/muscle protein properties that allow for contraction - Striated appearance due to light and dark banding – striped appearance – bands created by proteins within muscle fiber Picture #1 - Outer layer – muscular fascia – fibrous sheath of CT surrounding muscle (very dense + thick) o Surrounds indiv. Muscles and sometimes groups w/similar functions - Epimysium – dense irregular CT and tightly adheres to fascia layer – deep to fasia – surrounds muscle too - Inside epimysium – bundles of muscle fibers – fasciculus (pl. fasciculi) - Each fasciculus is surrounded by perimysium - Btwn muscle fibers in fasciculus is endomysium (loose aereolar CT) - Muscles have a very extensive blood + nerve supply – every single muscle fiber is innervated by a nerve - Arteries + veins penetrate all 3 layers + fascia to get into level of muscle fibers where they reach muscle fibers and form extensive capillary bed around fiber – delivers nutrients + O 2 - As we train, more capillary beds are formed  receiving nutrients and O more suf2iciently, improves endurance - Single axon divides up and innervates several muscle fibers - Single motor neuron + associated fiber is motor unit – efficient way of signaling muscle fibers – send signal down 1 neuron causing reaction at several fibers - Every fiber has a synapse/neuromuscular junction - 1 axon/motor neuron goes to several fiber but each fiber only receives 1 branch – don’t wanna contract muscle fiber from diff ends at diff times – want coordinated contraction Picture #2 - Muscle fibers end where tendon is located - Tendon is continuation of 3 CT layers- attaches to bone (epimysium surrounds whole muscle, perimysium surrounds fasciculus, and endomysium surrounds muscle fibre in fasciculus) - Plasma membrane of muscle fiber – sarcolemma - Nuclei - # of them located on length of muscle fiber - Inside muscle fiber – transverse tubules (ttubules) – evaginations of sarcolemma – creates larger SA for AP to move along membrane – AP propogates along sarcolemma in little pore through ttubule – allows for faster response to the neural stimulation - Sarcoplasmic reticulum (SR) – smooth endoplasmic reticulum – stores calcium + when AP signals contraction, will release calcium into cytoplasm of muscle fibre - Sarcoplasm – cytoplasm of muscle fibre - Depending on fibre type, # of mitochondria located – endurance fibres have more mitochondria, less mitochondri
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