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Chapter 9 Muscle Anatomy

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Muscle Structure- connective tissue component 1. Endomysium- delicate connective tissue membrane that covers specialized skeletal muscle fibers. 2. Perimysium- tough connective tissue binding together fascicles 3. Epimysium-coarse sheath covering the muscle as a whole 4. These 3 fibrous components may become a tendon or an aponeurosis.

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Size Shape and fiber arrangement 1. Skeletal muscles vary considerably in size, shape, and fiber arrangement 2. Size- range from extremely small (muscles to bones in ear) to extremely large-(quadriceps) 3. Shape- variety of shapes, such as broad, narrow, long, tapering, short, blunt, triangular, quadrilateral, irregular, flat sheets, or bulky masses. 4. Arrangement- variety of arrangements, such a s parallel to long axis, converge to a narrow attachment, oblique, pennate, bipennate, or curved; the direction of fibers is significant due to its relationship to function

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Attachment of Muscles 1. Origin- point of attachment that does not move when the muscle contracts. 2. Insertion- point of attachment that moves when the muscle contracts

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Muscle Action Muscle movement is a coordinated action of several muscles; some muscles in the group contract while others relax PRIME MOVER (agonist)- a muscle or group of muscles that directly performs a specific movement ANTAGONIST- muscles that, when contracting, directly oppose prime movers; relax while prime mover (agonist) is contracting to produce movement; provide precision and control during contraction of prime movers.

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Muscle actions continued SYNERGISTS-muscles that contract at the same time as the prime movers; they facilitate prime mover actions to produce a more efficient movement FIXATOR MUSCLES- joint stabilizers

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LEVER- any rigid bar free to turn about a fixed point called a fulcrum In the body the bones act as a lever, joints serve as a fulcrum and the muscles applies a pulling force on a bone lever at the point of attachment to the bone.

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Levers (p284)

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Tips on Naming Skeletal Muscles Direction of Muscle Fibers rectus oblique Relative Size of Muscle Fibers maximus minimus longus Location of the Muscle temporalis frontalis

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Tips on Naming Muscle Number of Origins biceps triceps quadriceps Location of Origin and Insertion sterno cleido mastoid

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Naming Muscle Muscle Shape deltoid Muscle Action flexor extensor adductor

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Physiology of the Muscular System General Function of the Muscular system MOVEMENT HEAT PRODUCTION POSTURE Function of muscular tissue Excitability ( or irritability)- they can respond to regulatory mechanisms like nerve signals. Contractility- Ability to contract, pull on bones and produce movement Extensibility- Ability to extend or stretch to return to resting length.

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Muscle Cell overview Muscle cell are called fibers because they are threadlike in shape. Sarcolemma is the plasma membrane of the muscle cell. Sarcoplasmic Reticulum- Network of tubules and sacs found within mm fibers Membrane of the SR continually pumps calcium ions from the Sarcoplasm and stores the ions within its sacs. Muscle fibers contain many mitochondria and several nuclei. Myofibrils are numerous fine fibers packed close together in the sarcoplasm

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Sarcomere Segment of myofibril between two successive Z lines Each myofibril consists of many sarcomeres Contractile unit of the muscle fiber

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T tubules Transverse tubules extend across the sarcoplasm at right angles to the long axis of the muscle fiber. Membrane has ion pumps that continually transport Calcium ions inward from the sarcoplasm Allow electrical impulses traveling along the sarcolemma to move deeper into the cell.

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Triad A T-tubule sandwiched between 2 sacs of SR. Allows an electrical impulse traveling along T- tubule to stimulate the release of Ca++ causing a contraction of the mm cell.

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Myofilaments Each myofibril contains thousands of thick and thin myofilaments Four different proteins make up these myofilaments Myosin Makes up THICK filaments Heads are chemically attracted to actin molecules Myosin heads are known as cross bridges when attached to actin. Actin- globular protein that forms two fibrous strands twisted around each other to form the bulk of the THIN filament. Tropomyosin- protein that blocks the active sites on the actin molecules Troponin- protein that holds tropomyosin molecules in place

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Sliding Filament Theory The sliding filament theory states that when signaled the actin filament within each sarcomere slides toward one another, shortening the sarcomere in each fiber causing muscle contraction.

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Mechanism of contraction When a motor neuron sends and impulse to the muscle cell The neurotransmitter ACETYLCHOLINE is released and stimulates the T tubules and the impulse travels inward causing release of Ca++. Ca++ binds to troponin, causing the tropomyosin to shift and expose active sites on the actin.

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Relaxation of Muscle Immediately after Ca ions are released the SR begins pumping them back into the sacs. Ca++ ions are removed from the troponin and it shuts down the contraction. ATP is the energy source Muscle cells continually re-synthesize ATP from the breakdown of CREATINE PHOSPHATE Aerobic respiration- adequate levels of ATP because Oxygen is available. Anaerobic respiration- inadequate O2 levels in cell respiration result in lactic acid fermentation. See ACTIN-MYOSIN ppt

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The Motor Unit= Neuromuscular junctions (nerve meets muscle)

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Muscle fiber types Red-slow twitch fibers (dark meat) Thin, slow acting ATPases, red in color due to myoglobin Fat metabolism, fatigue resistant- aerobic pathways High endurance, not much power White-fast twitch (white meat) Little myoglobin, thicker, fast acting ATPases Large glycogen reserves, anaerobic, fatigable fibers Short term, rapid, intense movements Intermediate-fast twitch fibers Fast acting, fast acting myosin, oxygen dependent, less fatigable,

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Muscle fibers cont Muscles contain a mixture of muscle fibers Sprinting- white fast twitch Marathon- red slow twitch Posture- red slow twitch Weight lifters- balance between red and white.

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Physiology of Skeletal Muscle Contraction Energy Sources Breakdown of ATP ATP ADP + O2 + energy Energy comes from CELLULAR RESPIRATION Results depend on AMOUNT OF OXYGEN AVAILABLE Moderate activity- adequate amounts of oxygen Strenuous activity- not enough oxygen causing Pyruvic Acid (from the first step of Cell respiration) to be converted to LACTIC ACID OXYGEN DEBT-extra oxygen that must be taken in by the body for restorative process. Difference between the amount of oxygen needed for totally aerobic respiration during muscle activity and the amount actually used.

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Muscle tone Steady partial contraction present at all times State of tension when awake Enable muscle to react immediately Does not produce active movement Loss of muscle tone in paralysis, coma, atrophy, prolonged immobilization.

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Muscle fatigue Muscle unable to contract Tension drops Inability to generate enough ATP to power contraction Excessive accumulation of lactic acid and ionic imbalance Spasm- sudden involuntary contraction Clonic- alternating spasm with relaxation Tonic- sustained Tetanus-smooth sustained contraction Tetany-result of low calcium, increases excitability of neurons, convulsions may follow.

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Twitch Contraction A quick jerk of a muscle that is produced as a result of a single, brief threshold stimulus. 3 phases Latent: AP reaches sarcolemma; SR releases Ca 2+ ; 2ms Contraction: Cross-bridge formation; Ca 2+, troponin; 15ms Relaxation: Ca 2 + uptake; tropomyosin covers actin; 25ms All or None response- Once the muscle fiber has been stimulated to contract the muscle fiber will contract to its fullest extent.

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Twitch Contraction

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Twitch to full contraction How do twitches achieve whole muscle contraction? By building tension 1. Multiple motor units are stimulated (recruited) 2. Stimulus from nerve arrives more frequently

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Types of Muscle contraction- myography Single twitch contraction- seen in above slide Treppe Staircase phenomenon- strength of contraction builds after it has contracted a few times (stronger when you get warmed up) Tetanus Results from the coordinated contractions of different motor units within the muscle organ. These motor units fire in an overlapping time sequence to produces a relay team effect that results in a sustained contraction. This is the kind of contraction exhibited by normal skeletal muscle organs most of the time. (incomplete and complete tetanus)

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Muscle contraction cont Muscle tone Tonic contraction is a continual, partial contraction in a muscle organ. At any one moment a small number of the muscle fibers in a muscle contract, producing a tautness of the muscle rather than a recognizable contraction. Muscle tone. Allows muscle to always be ready to respond when stimulated immediately. Muscles with less tone than normal are FLACCID Muscles with excess tone are called SPASTIC. GRADED STRENGTH PRINCIPLE- basically the number of muscle fibers contracting are in response to the task. Ie. Heavy object, more myofibrils contract

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Isotonic vs. Isometric contraction Isotonic contraction is a contraction in which the tone or tension within a muscle remains the same as the length of the muscle changes. (P 328) There is actually movement- lifting weights Isometric contraction is a contraction where the length of the muscle stays the same while the muscle tension increases. Ie. Pulling up on an immovable object.

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Points of Interest Muscle fatigue- simply muscle exhaustion. Muscle runs out of ATP rendering myosin heads incapable of producing the force required for continued contraction Exercise effects on muscle: Disuse causes atrophy (wasting away). Overuse causes hypertrophy (overgrowth) Strength training- increases the number of myofilaments in each muscle fibers, increasing muscle mass. (muscle fibers stay the same myofilaments can increase.) Endurance training- lean muscle not hypertrophy. This increases the number of blood vessels to the tissue, increasing oxygen availability and efficiency along with increase in mitochondria for higher ATP production.

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Cardiac muscle Heart muscle Cells directly connected via intercalated discs (pores through which ions pass) Allows all connected cells to contract as one Cardiac muscle is autorhythmic (spontaneous generation of AP) Involuntary (influenced by hormones) Metabolism is always aerobic

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Smooth muscle Less actin & myosin, no sarcomeres Contracts slowly No O 2 debt Autorhythmic Involuntary control