Chapter 9: Skeletal Muscle PDF

Chapter 9 Skeletal Muscle Prefixes that refer to muscles : 1) Myo- refers to : muscles...

Chapter 9 Skeletal Muscle Prefixes that refer to muscles : 1) Myo- refers to : muscles or muscle tissue - example myocardium : - the muscular tissue of the heart 2) Sarco- refers to : muscle , and is often used in terms of the structure of muscle cells - example Sarcoplasm : - the cytoplasm of a muscle cell Skeletal Muscle Function: 1) generate movement 2) maintain posture 3) Stabilize joints 4) generate heat We think about muscles at many levels of organization from proteins to the muscle as an organ Muscle fiber the : individual muscle cell Muscles: Terms : stationary vointment represent the origin Stationary bone [ on - : attachment of - insertion : on moveable bone a muscle action of a muscle : the movement that occurs and where it occurs - ex : flexion of forearm (at the elbow Synergist : 2 or more muscles that have the same action - eX : biceps ferorus/Seritendinosur both flex at kne Antagonist : 2 or more muscles With opposite actions - eX : biceps brachil and triceps brachii Prime mover (PM)/agonist "boss" : of an action ; when more than one muscle contributes to an action ,the one that contributes the most is the PM Naming Skeletal muscles: 1) direction of fibers 2) Size 3) location 4) # of Origins 5) location of attachment brachii biceps rectus parallel to midline maximue (2) insertion - origin - + - - - : - Oblique angle to midline : - minimus - femoral - triceps (3) - Sternocleoidomastoid 6) Shape 7) action - deltoid : triangle - adductor longus adduction of femur : - trapezius trapezoid : Muscle fibers : an individual cell of skeletal muscle - they are multinucleated cells - One is wrapped w/ a CT called endomysium (Which bundles the cell) multiple are wrapped by perimysium - - epimysium wraps a group of fasicles /bundles of fibers) - all come together to form a tendon , then the tendon inserts on the bone - Sarcolemma : the plasma membrane of the muscle fiber - have a lot of mitochondria (organelle - have many myofibrils /organelle Connective tissueSheaths Support : each cell and reinforce and hold together the muscle, preventing the bulging muscles from bursting during exceptionally strong contractions 1) Epimysium (outside the muscle) : CT that surrounds the whole muscle 2) Perimysium : CT that surrounds fascicles 3) Endomysium (within the muscle) : CT that surrounds each individual muscle fiber -how it relates to the muscle fiber: each muscle fiber is wrapped by endomysium , providing individual support and housins capillaries and nerves -how it relates to the fascicle (bundle of muscle fibers) wrapped by : perimysium -how it relates to the muscle as an organ : Surrounded by the epimysium Myofibrils : muscle fibers are filled with myofibrils (hundreds to thousands /sell) - - each myofibril contains many sarcomeres Sarcomere the functional : unit of muscle contraction - contains all the necessary components needed for contraction  * read pg. 284 Myofibrils : have thin actin filaments and thick myosin filaments - z-disc : connects thin filaments ; defines the sarcomere - Sarcowere : contains all of the structures required for a muscle to contract ; known as "the basic unit of muscle contraction" - z-disc to 2-disc - A-band the length : of the thick filament , but contains both filaments l-band - : only contains thin filaments - H-zone : Only contains parts of thick filaments and a protein that acts as a connection , which defines the M-line - M-line : runs through the center of the H-zone Myofibrils : - made of thin and thick filaments - arrangement of filaments : - during contraction the , globular heads link the thick and thin filaments together forming , a cross bridge myosin Splits ATP and uses the released energy to - drive movement - thin filament proteins actin troponin (TnF, TnC : , , ThT) , and tropomyosin - ThI : binds to actin - TnC : binds to Cat - ThT : binds to tropomyosin - thick filament protein myosin : sarcoplasmic reticulum releases Cat (b/c of AP) Since tropomyosin is in the way of actin and myosin from binding Ca , binds to In Ca2+ binding to ThC results in conformational change in troponin. Bic troponin is bound to tropomyosin changing the , shape of troponin causes tropomyosin to move away from actin. Actin and myosin bind. Muscle fibers : - have a highly specialized plasma membrane called the sarcolemma - the Smooth ER(SER) is also specialized and is called the Sarcoplasmic reticulum (SR) - the triad is made up of the T-tubule and the terminal cisternae of the sarcolemna The sliding filament theory of muscle contraction : during contraction, the thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree The filaments don't change length as the muscle contracts (Shortens) , the sarcomere shortens How Shortening occurs: 1) actin and myosin bind(cross bridge formation).The formation of the cross bridge is stimulated by an action potential that causes the release of cat from the SR 2) the working stroke 3) cross bridge detachment 4Cocking of the myosin head Excitation - contraction coupling the sequence : of events by which transmission of an action potential along the sarcolemma causes myofilaments to slide look at figure 9 2 -. - ATP binding causes detachment - between ternas > Contraction thin filaments touch (thick filaments : do not move) - Sarcomere Shortens Shortening length The thin filamen of the sarconere occurs , but neither the thin nor thick filaments change. and thick slide past eachother. The sliding filament theory of muscle contraction Motor neurons : cells of the nervous system that activate muscles - Signal goes from brain - > Spinal cord - muscle cell of the nervous is a single system - Motor unit : one motor neuron and all the muscle fibers that that motor neuron innervates (acts on - are different sizes - When a motor neuron Sends info(AP) , it causes all of the muscle fibers in that motor unit to contract - is made up of one neuron (Cells of Ns) + a variety of muscle fibers (cells muscle of - size+ number activated determine the strength of the contraction - can contain few to many muscle fibers - muscles that have fine control (fingers movement , of eyeball) have small motor units - if more motor units in a muscle are activated, the strength of the contraction increase b1c more muscle fibers will contract ; this is called multiple motor unit summation or recruitment A muscle wifew motor units allow for less control than a muscle we many motor units (muscles of fingers Multiple motor unit summations , the more motor units that are active the stronger the force of the contraction , The size of motor units in any given muscle Corgan) determines how precise the movements of that muscle are - example : the fingers have small motor units and can therefore make very precise movements Muscle twitch : a lab phenomenon where a single electrical stimulus is given to the muscle - 3 phases : Ilatent period the first few milliseconds following stimulation when excitation : - contraction coupling is occurring ; cross bridges begin to cycle but muscle tension is not yet measurable so the myogram doesn't show a response - calcium release from SR , Ca + binding to troponin preparation for , cross bridge formation 2) period of contraction : Cross bridges are active - cross bridge formation , power stroke , recycling of ATP 3) period of relaxation : due to the pumping of Cat back into the SR ; contractile force declines ; muscle tension decreases to 0 - ca" uptake tropomyosin , recoves binding sites , resting state - considered a single verky contraction (not the way muscles normally work-which is usually smooth). In order to generate a smooth contraction , Stimulus frequency needs to increase. When more than one stimulus is given before the muscle can fully relax , wave summation occurs /greater the frequency greater , the wave summation * read pg. 299 Wave summation : leads to smooth sustained contraction and some increase in contraction strength - unfused tetanus there : is some relaxation fused tetanus the stimulus higher; only at maxtension development which frequency is even occurs is rare - : ,  Muscles at the organ level : 1 muscle twitch % : of tension is measured in graph allatent period : no tension in muscle , but the steps before actin + myosin binding are happening 3) contraction tension : increases to a maximum C) relaxation : muscle tension decreases involves SingleStimulus a - E 2) temporal summation : Stiruli are applied before the · C 3) muscle contracts Unfused tetanus : increase in Stimulus frequency ; the muscle reaches max tension wh some tension ; decrease · between Stimuli 4) fused tetanus : even greater stimulus frequency ; no relation between Stimuli generates a smooth contraction we some increase in - muscle tension as Stimulus frequency increases Multiple motor unit summation leads to stronger contraction Wave summation leads to smoother contraction w/ Some increase in contractile Strength (force Types of contractions require energy-ATP : 1) Isotonic contraction tension development and : movement generated a) concentric contraction : muscle Shortens + does work b) eccentric contraction : muscle tension + muscle stretching; lead to the most muscle invury 2) Isometric contraction tension : developes and no movement occurs (like a wall sit) Muscle fibers : cells Skeletal muscle response to exercise : there types of muscle fibers force by causing are 3 regular resistance exercise increases muscle muscle - - 1) Slow oxidative fibers cells to hypertrophy (increase in Size 2) Fast oxidative fibers 3) Fast glycolytic fibers - each muscle contains all 3 fiber types