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Chapter 6 The Muscular System I.Overview of Muscle Tissues • Differ in cell structure,location, and how they are stimulated to contract • Smooth and skeletal muscle cells are elongated and called ________________________ • Contraction-shortening-depends on 2 types of myofilaments • Terms myo-,sarco- and mys- refers to muscleexample-muscular cytoplasm is called ___________________. Muscle fibers sarcoplasm skeletal muscle – – – – – attach to skeleton and form smoother contours of body huge,cigar shaped and ______________________ largest of muscle fibers-as much as 30 cm in length __________________________with obvious stripes ___________________since only muscle subject to conscious control Voluntary muscle multinucleate striated – – – – However,subject to involuntary reflexes Tire easily and requires rest Fairly fragile Bound by ___________________________which provides strength and support Connective tissue – Each muscle fiber contained in a declicate connective tissue sheath called ___________________________ – _________________________-connective tissue wrapping a bundle of fibers called a _________________ perimysium endomysium fascicle – ___________________________= many fascicle bound together w/ this tough coat – Epimysia blend into the strong_,cordlike_________ or aponeurose(sheetlike) that connect muscle to bones,cartilages or connective tissue – Other functions of tendons-besides movementare durability and conservation of space epimysium tendons Smooth Muscle • • • • No striations and is involuntary Mainly in walls of hallow visceral organs such as ___________________________________________ _________________________________________ Propel substances on a definite tract or pathway Spindle shaped and uninucleate Stomach,bladder,and respiratory passages • Scant endomysium • Most often in 2 layers-one running circularily and one running longitudinallyalternately contract or relaxing changing size and shape of organ Cardiac Muscle • • • • Only in heart Forms most of heart walls ________________________but involuntary Cushioned in bundles w/ small amount of endomysium striated • When heart contracts,internal chambers get smaller,forcing blood into arteries leaving heart • Branching cells joined by junctions___________________________________These traits and spiral arrangement of bundles allow heart activity to be closely coordinated,giving steady contraction rate • ______________________can shift heart into “high gear” Nervous system Intercalated discs ****** We focus mostly on skeletal muscle here! Muscle Functions – – – – movement _______________________as a result of muscle contraction;quick response to environment Maintaining _____________-maintain erect posture despite gravity Stabilizing ________________-esp. w/ poorly fitting articulating surfaces as in shoulder _________________________________-by –product of muscle activity;ATP used for contractions and ~40% released as heat to mostly maintain normal body temp for at least 40% of body mass posture Generating heat joints II. Microscopic Anatomy of Skeletal Muscle » ________________________ = plasma membrane of muscle cells » Nuclei pushed aside by ________________-long ribbonlike organelles;have alternating light (I) and dark (D) bands along myofibrils-give striped appearance » I band has midline interruption darker__________________ sarcolemma myofibrils Z disc • » A band has lighter central area called _____________-Its M line contains tiny protein rods that hold thick filaments together » Myofibril actually chains of contractile units-_____________________-line up end –to- endalong myofibril length » 2 type of protein myofilaments-larger are ___________________ made of bundled myosin –extend length of A band H zone sarcomeres Thick flaments » Also contain ATP enzymes to generate ATP for energy» Ends studded w/ small projections____________________________ » Thin filaments composed of ______________-called actin filamentsanchored to z disc-do not extend into end of relaxed sarcomere,so central region-_________________is sometimes called bare zone cross bridges Contractile protein H zone Sarcoplasmic Reticulum » In a contraction,bare zone does not appear because actin and myosin completely overlapped » ______________________________(SR)specialized smooth ER-tubules and sacs surround every myofibril-picture a crocheted sleeve-Role is to________________________________ __________________________________ ________ Store calcium and release to stimulated muscle fiber on demand…contraction occurs III. Skeletal Muscle Activity • A)Stimulation and Contraction of Single Muscle Cells – Functional properties include 1)___________________(irritability/responsivenes s)-abilty to receive and respond to stimulus • 2) _______________________-ability to forcibly shorten when stimulated • 3) _________________________-ability of muscle cells to stretch • 4)__________________________-ability to recoil and resume resting length Excitability contractility extensibility elasticity Nerve stimulus and Action Potential: • Must receive nerve stimulus • May be a few or 100’s of muscles cells stimulated by a nerve cell______________________ • _____________________= 1 neuron and all skeletal muscles stimulated • __________-long extension of nerve cell-branches into axon terminals when it reaches muscle,each forming a junction w/sarcolemma=_________________junctions Motor unit neuron Nerve fiber or axon Neuromuscular junction • Nerve and muscle are close but do not totally meetforming ____________________(has interstitial fluid) • When nerve impulse reaches terminals___________________________is released-Ach________________________in the case of skeletal muscles neurotransmitter Synaptic cleft acetylcholine • Ach attaches to receptors(membrane proteins)part of sarcolemma.With enough Ach ,sarcolemma is more permeable to Na+ that diffuse out of cell….more Na enters than K+ leaves----creates a current called ___________________________-now unstoppable-result in muscle contraction • Ach is broken down into ____________________________by enzymes acetylcholinesterase-AChE-during action potential,so one impulse makes one contraction action potential Acetic acid and choline Returns to resting state by… – diffusion of ___________out of cell – operations of ________________pumping NA+ and K+ ions back to original position K+ Sodium potassium pump Mechanism of Muscle Contraction • • • • _________________________TheoryWhen muscle fibers are activated by nervous system,myosin heads attach to binding sites on thin filaments and sliding begins.Each cross bridge attach and detach several times during a contraction-pulling filaments towards center of sacromere and cell shortens The movement of myosin cross bridges is somewhat like that of a centipede The attachment of myosin cross bridges to actin requires Ca2+ ions,which come from inside the cell where action potentials stimulate sarcoplasmic retuiculum to release Ca2+ into cytoplasm.This triggers the binding of myosin to actin causing filaments sliding When action potential ends,Ca2+ ions are reabsorbed into SR storage areas and muscle cell relaxes Sliding filament theory Contraction of skeletal muscles as a whole • • • • Whole muscle responds to “all or none principle ”,but whole muscle reacts in _____________________ Can be changed by ________________________of muscle stimulation and by changing # muscle fibers stimulated ____________________________=brief jerky contractions Normally,nerve impulses are delivered at a very fast rate w/o much relaxation Graded responses Changing frequency Muscle twitches • Smooth,rapid sustained contractions called _____________or complete,tetanus • Until complete tetanus is reached,the muscle is said to be ______________________________tetanus • Muscle contractions can be slight or vigorous depending on work to be done and thus innervation • Energy for muscle contractions-needs to make ATP fused Unfused or incomplete • Energy for muscle contractions-needs to make ATP: • Direct phosphorylation of ADP by creatine phosphate(CP)-found in ______________but not other cell types.As ATP is used,reactions between CP and ADP generates more ATP.(CP supply quickly exhausted • ________________-for light to moderate exercise,95% ATP comes from aerobic-cellular respiration-from mitochondrion….the collection of chemical pathways are also called ______________________.Glucose broken down to CO2 and H2O 36 ATP/1 g glucose-fairly slow and requires continuous O2. Muscle fibers Oxidative phosphorylation Aerobic respiration • ____________________________- occurs to provide pyruvic acid for cell respiration---occurring in cytosol.After this ,w/o O2,fermentation via production of _______________________occurs5% of ATP from each glucose-promotes muscle fatigue and soreness glycolysis Lactic acid fermentation or anaerobic glycolysis • ___________________________occurs if muscle is unable to contract even though it is still innervated…usually caused from ___________________________________________ during prolonged muscle activity….alot dependent on muscle supply….breathing rapidly and deeply will generate more ATP Muscle fatigue O2 deficit Types of Muscle contractions: • ________________________________myofilaments are successful in sliding movements,muscle shortens and causes movement-eg. Knee bending • _______________________________________myosin myofilaments are “spinning their wheels”and tensions continually increases -trying to slide but you are attempting to move something immovable Isotonic contractions Isometric contraction – ____________________________--state of continuous partial contraction-firm and ready for action – ____________________-if muscle is not innervated and becomes soft and flabby – ___________wasting away of a muscle – Aerobic –or endurance-exercise-results in stronger,more flexible muscles and subjected to less fatigue(jogging,biking)-results partly because of greater blood supply-also enhances metabolism in general-improving digestion,elimination,coordination and cardiovascular system………..but does not increase muscle size much – Resistance –or ______________________exercises increases muscle size-increase individual muscle cell size(make more contractile filaments and increases connective tissue0 Muscle tone isometric flaccid atrophy IV.Muscle Movements,Types and names – Types of Body Movement • Every one of our 660+skeletal muscles is attached to bone or other connective tissue at no fewer than 2 points: – ____________attached to immovable or less movable bone – ______________attached to more movable bone • Muscle moves toward origin in contraction origin insertion flexion extension Most common movements : • ___________________movement mainly in sagittal plane that decreases < of joint and brings 2 bones closer together-eg.knee and elbow • ____________________opposite of flexion and increases >-eg straightening knee • ________________________movement of bone around longitudinal axis-eg in ball- and- socket joints • __________________________-moving limb away from midline • ___________________________opposite of abduction-toward bodyline • ___________________________-combination of flexion,extension,abduction,adduction commonly seen in ball-and socket-proximal end of limb is stationary,and its distal end moves in a circle-outlines a cone rotation abduction circumduction adduction Dorsiflexion and plantar flexion B.Special Movements – ____________________________-Up and Down movement of foot at ankle:pulled toward shin is dorsiflexion and pointing towards toe is plantar flexion – _____________________________invert turn sole medially and evert,turn sole laterally – ___________________________________-supination-turn backwards @ radius and ulna-forearm rotates laterally to turn palm anterior laterally-radius and ulna parallel/pronation when forearm rotates medially-palm faces posterior-radius and ulna form X. – ___________________________-opposition from saddle joint in hand-moves ththumb to touch other fingers Inversion and eversion Supination and pronation opposition C. Interactions of Skeletal Muscles in the Body • Muscles can only pull • ____________________________-major muscle responsible for designated movement • _________________________ -oppose or reverse a movement • __________________________-help prime movers by doing same movement or reducing undesirable movement-example:making a fist w/o moving wrist • Fixators-specialized synergists-hold a bone still or stabilize origin of prime mover so all tension used to move insertion bone Prime mover antagonists synergists Size of muscle Naming skeletal muscles # of origins – Direction of muscle fibers-in re to an imaginary lineexample-rectus(straight)-rectus femoris-straight muscle of thigh – _____________________________________maximus,minimus,longus – location of muscle-associated bone used in name often eg-temporalis muscle overlies temporal bone – _____________________________________-eg. Biceps-2 origins – Location of muscle’s origin and insertioneg.sternocleidomatstoid-origin in sternum and clavicle-inserts in mastoid process of temporal bone – _________________________________-eg.deltoid means triangular – _________________________________-eg-flexor Muscle shape Action of muscle convergent circular E. Arrangement of Fascicles – ________________-fascicles in concentric circles(spinchters – __________________-meet at a single insertiontriangular or fan shaped – ________________________-parallel to long axis of muscle – __________________________-spindle –shaped muscle w/expanded center(biceps brachii) – _____________________-short fascicles attach obliquely to a central tendon parallel fusiform pennate
