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BIOA02 MODULE 2 Lec 16 Skeletal Miuscles

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Biological Sciences
Mary Olaveson

BIOA02 MODULE 2 Lec 16 Skeletal MusclesFebruary 14 2012NEUROMUSCULAR JUNCTIONalong the axon there is an action potential that triggers the release of a neurotransmitter from the synaptic terminal into the region of the synaptic cleft between one cell and another cellthe situation between a nerve and a musclethe nerve is called a motor nerve and the synapse is called the neuromuscular junctionthe action potential comes down and causes the neurotransmitter to be released into the synaptic cleft and in this particular situation the neurotransmitter is acetylcholineacetylcholine then goes into the synaptic cleft and interacts with receptors on the muscle cell membranethe receptors are also called nicotine receptors because they are stimulated by nicotinethese nicotine receptors are found in every nerve muscles and can be stimulated by nicotinemuscle cell membrane depolarizes and an action potential happens in the muscle membraneaction potentials spread through Ttubulesdeep in the muscles where its going to trigger the release of calcium from sarcoplasmic reticulum which is going to lead to a series of events that lead to muscle contractioninsert Slide 2 hereSKELETAL MUSCLE STRUCTUREthe basic units of the muscle is the muscle cell or the muscle fibresmuscle fibres are very long and run the entire length of the muscle and they are multinucleated multiple nucleidevelop from multiple cells fusing togetherlooking from a macroarrangement these muscle cells are bound into structures called fasciclefibres surrounded by connective tissuethe fascicle are bound together by more connective tissue and they form the muscle as a wholeon a microscopic levelrepeating unit that looks the same as the macrostructurebundles that are situated within the cellbundles run the entire length of the muscle and are called myofibrilmyofibril have two major components actin and myosin which are protein filaments which are called thick and thin filamentsmuscles contract because these actin and myosin filaments slide across each other causing the muscle to shorten and contractthere are other components of myofibrils insert slide 3 heresacrolemma is the plasma membrane of the muscle cell sarcoplasmic reticulum has calcium stored in itaction potential that is generated in the sarcolemma is going to travel down the T tubule which is going to cause calcium to be released from the sarcoplasmic reticulummitochondria which produce ATP ATP is hydrolyzed at the beginning of muscle contraction and is also needed for muscle relaxation thick filaments myosin and thin filaments actin form an overlapping pattern which repeats itself as you go down the length of a myofibrilrepeating pattern is called sacromerea contractile unitinsert slide 4 hereSARCOMERE STRUCTUREyellow rod coming out surrounded by six pink rodsthese are actin and myosin filamentsorientation is such that every myosin is surrounded by a circular arrangement of actin filamentsmyosin thick filaments have globular heads that protruding up outwards and interacts with actinbinding sites on globular site that bind to actin which also has binding sites and they come together to form cross bridgescross bridges can exert in a low energy state and a high energy stateas they go from low to high energy states they cause the actin to slide inwards and thats where the force for muscle contraction comes from seen in cross section sliding of these actin and mysocin filaments over one anothermediated by the interaction of the myosin globular heads on the actin filamentsinsert slide 5 hereSacromere Structure Z line to Z lineredpink fibres are the actin molecules and yellow are myosin molecules sacromere is the area between the two Z line anchors there is a region in the middle where the myosin molecules dont have globular heads and as it goes to the outside there are regions where myosin molecules do have globular headswhere the globular heads are on the myosin molecules there is a space of overlapwhere the myosin molecules are overlapping the actin molecules
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