Iowa State University



Muscular System5 characteristics:Responsiveness: ability to respond to chemical signals, stretch and electrical changes across the plasma membraneConductivity: ability to pass an electric signal across the muscle fiberContractility: the ability to shorten when stimulatedExtensibility: the ability to be stretchedElasticity: returns to its resting length after being stretchedMuscle CharacterisiticsVoluntary, striated (light at dark bands) muscle attached to bone Muscle fibers=myofibersEpimysium: surrounds the entire muscle; Perimysium: wraps around one fascicle (group of muscle fibers); Endomysium: surrounds one individual muscle fiberSarcolemma- plasma membrane of sarcomereSarcoplasm- cytoplasm of a muscle cellSingle muscle fiber has hundreds of myofibrils that look spotty (because made of myofilaments, which make up sarcomeres)A bands: dark (both thin and thick filaments)I bands: lightH zone: thick filaments onlyI band: thin filaments onlySarcomere (smallest contractile unit of a muscle fiber, the functional unit) is from z disc to z discM line in middle just thick filamentsThick filaments: myosin, thin filaments: actinTropomyosin: rod shaped protein that spiral around actin and stabilize it, block myosin binding sites when contraction is not neededTroponinTnI- inhibitory subunit that binds to actinTnT- binds to tropomyosin and helps position it on actinTnC- binds calcium ionsSacrcolemma has tunnel like infoldings or transverse (T) tubules that carry electric current to cell interiorSarcoplasmic reticulum: network around each myofibril that stores calciumTriad- T tubule and 2 terminal cisternaeSliding of Filaments:Thick and thin filaments don’t change length during shortening, the overlap just changes as the sarcomeres shortenA band stays the same (makes sense, both thick and thin filaments)Actin filaments slide past myosinMotor Units:One motor neuron innervates many muscle fibersRecruitment:Always recruit the smaller motor units first (because if you just need a fine touch/pressure, then that will do it)Largest motor unit is the last one recruited (for extreme forces)Smallest motor units are type 1/slow for endurance running; dark meat and lots of fat for long exerciseLargest are type 2/fast for explosive motion; white turkey because not much mitochondria because use lactic acid that makes your muscles hurt after sprintingExercise increases recruitment of fast and large motor unitsMismatch- using wrong size of motor unit for a certain force neededMotor units die with age and you lose intricate control (loss of muscle as get older)Neuromuscular Junction:Connection between nerve fiber and muscle cell, ACh released from nerve fiber stimulates the muscle cell1. Local depolarization (end plate potential) ACh opens chemically gated ion channels, causes Na/K and depolarizes2. End plate potential spreads to adjacent membrane areas, voltage gated Na channels open, if threshold is reached, AP is generated3. From there, AP is propagated along the sarcomere to T tubules, where voltage sensitive proteins stimulate Ca2+ release from SR which is needed for contraction4. Calcium binds to troponin, which changes shape and moves tropomyosin away from the binding sites, allowing myosin to bind to actin5. When nervous stimulation ends, Ca2+ pumped back into the SR and binds to calequestrin- which neutralizes the charge so calcium can keep flooding in without the gradient having any effect on the flow of calciumCross Bridge Cycle:Continues as long as there is ATP and Calcium present1. Cross bridge forms as an energized myosin head binds to actin2. Power stroke occurs as ADP and P are released and the myosin head bends, causing the actin to slide toward the M line3. Cross bridge detachment occurs when ATP attaches to myosin4. Myosin head returns to high energy state, “cocking” and ATP is hydrolyzed to ADP and PRINSE AND REPEATRelaxation of a Muscle: Nerve stimulation ceases and acetylchlolinesterase removes ACh from the receptorsActive transport needed to pump calcium back into SR to bind to cal.Rigor Mortis: stiffening of the body beginning 3 to 4 hours after death-Happens because calcium will still be released, so myosin heads will attach to actin, but with no ATP, they will not detach from it so the muscles will stay contractedLength-Tension RelationshipAmount of tension generated depends on length of muscle before it was stimulated (textbook lifting experiment)Overly contracted beforehand- weak contraction results because the thick filaments are too close to the Z disc and can’t slideToo stretched beforehand- no actin/myosin interaction because they are too far apart to reach each otherMuscle Twitch (motor unit’s response to a single AP of its motor neuron)Latent period: first few milliseconds when EC coupling is occurringPeriod of contraction: cross bridges are active, if tension becomes great enough to overcome the resistance of the load, the muscle shortensPeriod of relaxation: final phase that is initiated by reentry of Ca2+ into the SR, muscle tension decreases to zeroMuscle CONTRACTS faster than RELAXESOther stuff:Myostatin: negative regulator of skeletal muscle mass, limits growth, also limits cardiac growthLoss of myostatin (deficiency) causes uncontrolled muscle mass growthGood for animals that need a lot of muscles (dogs that race), but more muscle means less fat which means less flavor for food and suchFused tetanus: when all evidence of relaxation disappears and the contractions fuse into a smooth, sustained contraction plateau; happens infrequently- superhuman strength to lift a car for ex.Wave/temporal summation: two stimuli delivered in succession, second twitch will be stronger because second contraction occurred before it relaxedIncomplete/unfused tetanus: when wave summation becomes greater and greater and end up with a sustained but quivering contractionIsotonic Contraction: Concentric/eccentric- shortening/lengtheningIsometric contraction: muscle tenses but doesn’t shorten/lengthen ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download