Muscular Physiology NewsletterRigor Mortis Rigor mortis is the process that your body goes through after you have died.It is the latin phrase for “stiffness of death”(1). It is where your skeletal musclesstiffen because the stimulation of muscle cells stop. And the muscle fibers mighthave been in mid-action at the time of death. And this may be when the crossbridges are still intact and your body needs ATP to release the cross bridges butbecause the ATP is used up when you die, so the cross bridges become “stuck” in aposition (1). This leaves the muscles in a dead body stiff because there was nomore ATP to “turn off” the contraction.4 Factors that Influence the Strength ofMuscle Contractions The muscle is capable of many different things. That helps us do things suchas lifting weights, to shaking hands, and writing. Sometimes we need a lot ofstrength and other times we don’t need a lot. Four factors that affect the strengthof muscle contractions are the number of cross bridges that can make contact, thelength of the fibers, and the frequency of the stimulation; summation andrecruitment (8.) The length influences the contraction because at a certain point itis the strongest. And the length affects the cross bridges contact, if its too long thecross bridges can’t reach, making contraction weak and if the muscle is too short, alot of cross bridges will be able to reach but it would get crowded and also makecontraction weak. (8.) The frequency of the stimulation impulses also affect thecontraction.
Phases of a Twitch Contraction There are 3 phases of a twitch contraction called the latent period,contraction phase, and relaxation phase. During the latent period the impulsetravels through the sarcolemma and T tubules into the SR where it triggers therelease of calcium ions (1). This calcium binding to troponin is what causes thecontraction to start, which is the contraction phase. After a few milliseconds thecontraction ceases and the relaxation phase begins.How the Treppe effects relates to Athletes The Treppe is a gradual, steplike increase in the strength of contraction. Thisrelates to the warm up of athletes because they use the principle of the staircasephenomenon when they warm up. A muscle contracts more forcefully after it hascontracted a few times then when it first contracts (1). This allows the warm up ofthe athletes to be more beneficial because it helps them get stronger and worktheir muscles more.
Skeletal Muscle FibersOne of the interesting things for Skeletal muscles is the a muscle organ iscomposed of bundles of contractile muscle fibers held together by connectivetissue. Closer magnification of a fiber shows another fiber, myofibrils, in thesarcoplasm, note sarcoplasm reticulum and t tubules forming a three part structurecalled a triad. A unique feature of the skeletal muscle cell is the t tubules, which areextensions of the plasma membrane, or sarcolemma, and the sarcoplasmicreticulum (SR), which forms networks of tubular canals and sacs. A triad is a tripletof adjacent tubules: a terminal sac of the sr, a t tubule, and another terminal sac ofthe sr. (1)First of there is four different type of Myofilaments which are myosin, actin,tropomyosin, and troponin. The thin filaments are made of a combination of threeproteins. The way they work is that the myosin head is chemically attracted to theactin molecules of the nearby thin filaments, so they angle the filaments. Whenthey bridge the gap between adjacent myofilaments, the myosin heads are usuallycalled cross bridges. (1)
Sliding Filament TheoryThe sliding filament theory is a muscle contraction. It allows for the shortening ofmuscle fibers because the myosin heads attach themselves to the thin filamentsand pull with a lot of force that moves the filament closer together, past them. Thisshortens the entire myrofibril and muscle fiber. (1) Ca++ in excitation, contraction, and relaxation of a muscle cellExtremely large protein complexes involved in the Ca2+-regulatory system of theexcitation-contraction-relaxation cycle have been identified in skeletal muscle, i.e.clusters of the Ca2+-binding protein calsequestrin, apparent tetramers of Ca2+-ATPase pump units and complexes between the transverse-tubular alpha1-dihydropyridine receptor and ryanodine receptor Ca2+-release channel tetramers ofthe sarcoplasmic reticulum. While receptor interactions appear to be crucial forsignal transduction during excitation-contraction coupling, avoidance of passivedisintegration of junctional complexes and stabilization of receptor interactions maybe mediated by disulfide-bonded clusters of triadin. Oligomerization of Ca2+-release, Ca2+-sequestration and Ca2+-uptake complexes appear to be an intrinsicproperty of these muscle membrane proteins. During chronic low-frequencystimulation, the expression of triad receptors is decreased while conditioning hasonly a marginal effect on Ca2+-binding proteins. In contrast, muscle stimulationinduces a switch from the fast-twitch Ca2+-ATPase to its slow-twitch/cardiacisoform. These alterations in Ca2+-handling might reflect early functionaladaptations to electrical stimulation. Studying Ca2+-homeostasis in transformedmuscles is important regarding the evaluation of new clinical applications such asdynamic cardiomyoplasty. Studies of Ca2+-handling in skeletal muscle fibers havenot only increased our understanding of muscle regulation, but have givenimportant insights into the molecular pathogenesis of malignant hyperthermia,hypokalemic periodic paralysis and Brody disease. (1)
Work a Muscle Until you "Feel the Burn"When you work out you are essentially tearing your muscle (actin) and when yourbody repairs your muscle it makes it bigger and stronger (more actin). Duringexcersise your muscles use up oxygen and tries to replenish it through anaerobicrespiration which results in the formation of lactic acid, which is what causes theburning sensation. (1) motor unitMost mature extrafusal skeletal muscle fibers in mammals are innervated by only asingle α motor neuron. Since there are more muscle fibers by far than motorneurons, individual motor axons branch within muscles to synapse on manydifferent fibers that are typically distributed over a relatively wide area within themuscle, presumably to ensure that the contractile force of the motor unit is spreadevenly (Figure 16.4). In addition, this arrangement reduces the chance thatdamage to one or a few α motor neurons will significantly alter a muscles action.Because an action potential generated by a motor neuron normally brings tothreshold all of the muscle fibers it contacts, a single α motor neuron and itsassociated muscle fibers together constitute the smallest unit of force that can beactivated to produce movement. Sherrington was the first to recognize thisfundamental relationship between an α motor neuron and the muscle fibers itinnervates, for which he coined the term motor unit. (1)
Unit of Combined Cells The cardiac muscle fiber does not taper like a skeletal muscle fiber. Cardiacfibers to form a continuous, electrically coupled mass called a SYNCYTIUM “unit ofcombined cells”. The Cardiac muscle forms a continuous, contractile band aroundthe heart chambers. It conducts a single impulse across a virtually continuoussarcolemma. These features are necessary for an efficient, coordinated pumpingaction. (1)
Skeletal Muscles Provide…Skeletal Muscles provide movement, heat production, and posture. Skeletal musclecontractions allow for the movement of the body as a whole. Skeletal muscle cellsare very active and numerous which allows for a huge amount of body heatbecause each cell goes through the process of catabolism to make heat. The musclecontractions also allow for people to stand, sit, and maintain posture throughoutthe day doing various activities. (1) Excitability, Contractility, and Extensibility Our body muscles are capable of many things. One of those things is theability to feel things or excitability which coincides with the nervous system becausethe muscle cells can respond to nerve signals. Contractility is the muscle being ableto contract or shorten, While extensibility is the muscles being able to extend orstretch.(1) These two things relate to agonist and antagonist because they are bothopposites and are the motions of what the agonist and antagonists do.