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BIOL 153
Robert Harris

Biology 153/155 May 30 , 2012 Muscle Physiology Muscle System Functions:  Body movement  Maintenance of posture: very important to humans as we walk on 2 feet (v.rare in mammals)  Respiration: use muscles to breath  Production of body heat: skeletal muscles account for 50% of body heat generated at rest, can be stepped up very dramatically, shivering: minute uncontrolled contractions of skeletal muscles that generate a lot of heat  Communication: not just for speaking but body language as well  Constriction of organs and vessels  Heart beat: muscles pump the blood around the body, cardiac muscle is unique Properties of Muscles :  Contractility: Ability of a muscle to shorten with force, this is actually a very big deal as this is relatively new in the evolutionary pathway  Excitablility: Capacity of muscle to respond to a stimulus  Extensibility: Muscle can be stretched to its normal resting length and beyond to a limited degree, beyond that degree they rip because the cells exoskeleton is not able to hold its shape- but it is VERY high degree of extensibility  Elasticity: Ability of muscle to recoil to original resting length after stretch, muscles are very good at this Read the English translation of the passage on the picture of Davinchi’s diagram. Muscle Tissue Types: 1. Skeletal - Attached almost always to bone (at least at one end) - Nuclei multiple and peripherally located - Striated (stripped appearance), voluntary and involuntary (reflexes) 2. Smooth - Walls of hollow organs, blood vessels, eye, glands, skin - Single nucleus centrally located - Not striated, involuntary, gap junctions in visceral smooth – allow action potentials to move across them without decreasing the strength 3. Cardiac - ONLY IN Heart - Single nucleus centrally located (usually – up to as many as 3 or 4) - Stiations, involuntary, intercalated disks Skeletal Muscle Structure  Muscle fibers or cells - Develop from myoblasts - Numbers remain constant  Connective tissues  Nerve and blood vessels  The striations of individual cells line up with those of other cells, this is not by accident during formation they communicate with other cells and match up their striations allowing them to be efficient.  Cells can be as large as cm in length – THAT’S why they need multiple nuclei, spaced out evenly in order for things like mRNA to be released and for control of cellular functions. Organization 1:  Tendon – a single unit that is attached  Muscle fascicle: Connective Tissue, Nerve, Blood Vessels  Connective Tissue - Externcal lamina - Endomysium - Perimysium - Fasciculus - Epimysium  Fascia  Nerve and blood vessels - Abundant Individual muscle cells are controlled by the motor neurons. Muscle Fiber = single skeletal muscle cell:  Myofibril: the part of the cell that forces the contraction  All of the rest is there to help with contractile activity Internal Organization  Single myofibril: you can actually  Z line: they are what helps the myofibril actually do what it does  Sarcomere: the Z lines together this is the functional unit of the muscle cell  T tubules: each T tubule is basically looks like a piece of lace going through the cell, gives a redundant appearance, they only go across the cell, they do not open up infront of behind, they stay in a single plane all the way across the cell. All of the openings will open into the outside at that level. They wrap around the myofibril at the level of the attachment to the sarcoplasmic reticulum  Sarcoplasmic reticulum: the fluid of the muscle tissues - does the functions of the ER Organization of myofilaments II:  Z line: more accurate description = Z plate – A network of crosslinked connections that act as anchoring for Tital and Filaments  I band: if you pick any titan fiber you will see 6 other filaments around it = arranged in a honey comb pattern = more efficient packing of protein  Zone of overlap: Sliding filament model II: The sarcomere is moving, but the actual filaments are just sliding past each other and not contrating, the sliding is casing the two Z lines to come closer together therefore we see the shortening of the sarcomere There is no change in the size of the thick/thin filaments = what we see is a change in the ratios of the different areas due to the thick/thin filaments sliding Stucture of Actin and Myosin: Each thick filament is made up of between 2-3 hundred myosin molecules. Myosin Molecule is basically a diamer (imagine if you took a pair of golf clubs, line them up and twist them together and at the end there is the heads sticking out). Where there is attachment of all these thick twisted areas = M line. It is the interactions between the thick and thin filaments = contraction. Structure of thin filament is very different. Actin basically forms balls = G actin molecules. These balls have the ability to stick together. When you have the
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