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Concepts of biological (BIOL116) - Dr. S.G. Saupe; biology Department, college of St. Benedict/St. John"s University, Collegeville, MN 56321; ssaupe

Muscles: structure & Function

I. Muscle Structure muscle are comprised of majority (fascicles) the muscle fibers (actually cells). The muscle fibersare surrounding by connective tissue.

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A. Muscle Fiber (cells)

lengthy (can run whole length of muscle) cylindrical multi-nucleate sarcolemma (=plasma membrane), sarcoplasmic delusion (=endoplasmic reticulum), sarcoplasm (= cytoplasm) T-tubules – inward extensions of the sarcolemma contains bundles of myofibrils company summary: muscle (tissue) � yarn (cells) � myofibrils � myofilaments

B. Myofibrils

threads the run with the muscle fibers made of actin and also myosin myofilaments (or just filaments) myosin filaments – thick; myosin (contractile protein); head and tail region; look prefer golf clubs actin filaments – thin; actin (contractile protein; globular units, dubbed G-actin, linked together to kind a chain, dubbed F actin; 2 chains intertwined); linked with regulatory protein (tropomyosin, troponin complex) attached in ~ intervals actin and also myosin filaments overlap to form a sarcomere many sarcomeres are joined end-to-end to type a myofibril

C. Sarcomeres

contractile units thick myosin filaments in middle region thin actin filaments toward exterior Z-line (region where adjacent sarcomeres are attached through by authorized their slim filaments); ns band (lighter area with just thin filaments) H zone (central ar with just thick filaments) M line - dark area in the H zone, region where myosin tails room joined A band (regions wherein thick and thin filaments overlap)

II. Muscle Contraction muscle contract as the actin and also myosin filaments slide previous oneanother. Keep in mind that the filaments execute not diminish in length. Slide requires energy thatis offered by ATP. The myosin head the the thick filaments is the "business" endof the process and contracts moving (like a ratchet) the thin filaments towards the middleof the sarcomere. This is referred to as the "Sliding Filament Model".Let"s check out howit works: ATP binding to the myosin head at a particular binding site; publication myosin indigenous the actin filament Myosin hydrolyzes the ATP into ADP & Pi. (note the the myosin is an ATPase). Some of the power is used to change the position of the myosin from a "bent" low-energy state, to an "open" high-energy state Energized myosin binds to a site on the actin filament ADP & Pi are released from the myosin head and also this causes the head to "spring back" to its original bent configuration relocating the actin filament towards the sarcomere center. III. Muscle Relaxation The muscle fibers go back to their initial position

IV. Regulation/Control bones muscles only contract when stimulated by a engine neuron.Muscle yarn don"t normally contract due to the fact that the myosin binding web page are usually blocked by regulatory proteins(troponin/tropomyosin complex). For contraction to occur, thetropomyosin/troponincomplex should be moved out that the way. How does this work? motor neurons extend to every skeletal muscle One engine neuron may activate native a dozen to plenty of muscle yarn The motor neuron doesn"t attach directly come the fiber, but there is a tiny gap (synapse) The electrical signal native the neuron get the end of the neuron (axon) stimulating the relax of a chemical (acetylcholine) neurotransmitter Acetylcholine diffuses throughout the synapse and also activates chemical-gated potassium channels in the post-synaptic membrane in the sarcolemma of the muscle fiber Potassium enters the muscle yarn which reasons a depolarization that the membrane (switches polarity). The tide of depolarization sweeps down the muscle fiber (= action potential) The action potential spreads v the T (transverse) tubules (I"ll bet you to be wondering what those to be for!) and into the sarcoplasmic reticulum. The SR publication calcium ion in an answer into the myofilaments Calcium binding to the troponin facility which alters the shape of the tropomyosin/troponin complex causing them come pull away from the binding web page on the actin thin filaments The exposed energetic sites can now bind through the myosin because that contraction Calcium pumps, via active transport, continually move calcium indigenous the sarcoplasm right into the SR.V. Energy source for Contraction ATP – this is the readily available energy source. It"s choose the money in your pocket. Favor your cash, the ATP go fast and there is normally only sufficient for a couple of contractions. ATP is created by the mitochondria – thus lots of huge ones in muscle fibers. This is likewise why numerous oxygen is compelled for muscles. Creatine phosphate – a backup energy resource that gives phosphate because that ATP. Favor ATP the is also quickly used up. Maybe analogous to a traveler"s check the you have the right to easily convert to cash. Glycogen – a polymer the glucose; a storage kind of energy. This is like having money in the bank. Girlfriend can accessibility these funds v a credit card or check. The is used for repeated contractions and also can be "used up". VI. Graded Contraction Here"s a paradox – we understand that we deserve to voluntarily transform theextent and strength that a contraction (a graded response), but at the cellular level theresponse is all-or-nothing. How are graded contractions generated? that is managed by thenervous device that: deserve to vary the variety of action potentials in the motor neurons. A single action potential reasons a solitary "muscle twitch". If a 2nd action potential arrives before the an initial one ends, then the responses add up further stimulating the muscle. If enough action potentials are obtained the muscle mirrors one smooth continual contraction (tetanus – not the same as disease). deserve to vary the variety of muscle yarn that room activated

VII. Cell kind - a refresher Muscle cells: (a) are elongated; (b) excitable; and also (c) cancontract. There space three significant types of muscle cells/tissue:

Skeletal. Responsible because that voluntary movements. These cells space long and also cylindrical, and when bundled together kind fibers, which in turn are sheathed right into a muscle. Skeleton muscle is striated and multi-nucleated. Smooth. Associated in involuntary movements. These cells are tapered (spindle shaped) and also are important in blood vessels, stomach, bladder, and internal organs. Smooth muscle is not striated because actin and also myosin space not regularly arranged together in bones muscle. There is only a single nucleus. The cells occur in sheets; electrical synapses (gap junctions) Cardiac. Involuntary contractions. Uncovered in the wall surface of the heart (where else?). Striated. The cells space branched (withstand pressure and resist tearing) and also are fused (intercalated disks) for intimate contact. Electric synapses. Single nucleus

VII. Cool Stuff

slow-moving twitch yarn – longer sustained responses, enriched v myoglobin (pigment like hemoglobin) and mitochondria. fast twitch fibers - couple of mitochondria, little myoglobin, rapid bursts Muscles deserve to only contract - thus, come move earlier and forth calls for two muscles acting oppositely the one another. Forexample, once the biceps contract the arm bends; as soon as the triceps contracts, the armextends.

Study Tips: The material explained in this section is uncovered in chapter47. Noþeles in this notes are "fair game" for the exam. If it"s inthe chapter but not in the notes, disregard it because that the exam.

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How to Study? come to class and get a great set the notes. Read the webnotes. Check out the particular sections in the chapter concerned the product inclass and in the net notes. Go v the pertinent section of the internet site/CDROM. Now,make a summary set of notes, combining the important elements from the foursources of information (class, web, text, CD). So far, you haven"t done any kind of studying� you"ve merely gathered information. Now, it"s time come study! Go with thesummary collection of notes questioning yourself the "W" concerns � what, why,when, where, "w"how? could you define the product to someone else?Could you teach this to someone who has actually never had actually the course? Test yourself bygoing v the inquiries at the finish of the chapter and in the CD-ROM. Do alist of terms. Make a principle map. Together an aside, as a rule-of-thumb you need to bestudying about 2 hrs for every hour in class.