Muscular System Chapter 9 PDF

Chapter 9 Muscular System 3 Types of Muscles  Skeletal- Voluntary; muscles  Smooth (visceral)- Involuntary; walls of organs  Cardiac- Involuntary; heart Skeletal Muscle Structure  Connective Tissue Coverings - Fascia- layers of fibrous c.t. which surrounds muscles and holds...

Chapter 9 Muscular System 3 Types of Muscles  Skeletal- Voluntary; muscles  Smooth (visceral)- Involuntary; walls of organs  Cardiac- Involuntary; heart Skeletal Muscle Structure  Connective Tissue Coverings - Fascia- layers of fibrous c.t. which surrounds muscles and holds them in place * Tendon- fascia that projects beyond the end of the muscle fibers forming a cord that may attach to bone * Aponeuroses- broad, fibrous sheets which may attach to bone or muscles  Epimysium- layer of connective tissue that closely surrounds a whole muscle  Perimysium- inward extension of epimysium which surrounds bundles (fascicles) of muscles cells (fibers)  Endomysium- inward extension of perimysium which surrounds each muscle fiber  http://www.youtube.com/watch?v=M Gtq0eJshI8&feature=related Structure of a muscle fiber (cell) (fibers are elongated, multinucleated, striated)  Sarcolemma-cell membrane  Sarcoplasm-cytoplasm  Myofibrils-tightly packed bundles of muscle protein filaments taking up most of sarcoplasm - Nuclei and mitochondria are just under sarcolemma - Myofilaments-protein filaments * 2 types- they lie parallel to each other and overlap(appears as striations) 1. actin-thin filament 2. myosin-thick  Sarcoplasmic reticulum- endoplasmic reticulum  Transverse tubules (T-tubules)- formed from indention of sarcolemma and pass all the way through the fiber - Contains extracellular fluid  Cisterna-enlarged sac of Sarcoplasmic Reticulum on either side of T-tubules ++ Arrangement of myofilaments in a myofibril A band-length of MYOSIN; includes some actin where there is overlap  I band- between A bands; ACTIN only  H zone - center of A band where there is only myosin  Z line - runs down center of I band  Sarcomere - area from Z line to Z line; smallest unit of muscle contraction Structure of Myofilaments  Myosin-composed of the protein myosin-it has cross bridges  Actin-composed of 3 types of proteins: 1. Actin-main protein 2. Tropomyosin-covers the active site 3. Troponin-attached to the end of tropomyosin - Ca++ binds to it Neuromuscular Junction where a motor nerve fiber connects to a muscle fiber  Synaptic knob - end of motor neuron - Has vesicles containing chemicals called neurotransmitters  Motor end plate - highly folded, depressed area of sarcolemma that synaptic knob fits into - Has receptors that neurotransmitters bind to  Synaptic cleft - space between syn. knob and motor end plate - Neurotransmitters are released into it and then bind to receptors Motor Units A motor unit is one motor neuron and all the muscle fibers it forms junctions with - Small motor units- (those with fewer muscle fibers) allow a muscle to have finer, more precise movements. Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.  Stimulus/Steps for Contraction ACETYLCHOLINE (ACh) - nerve impulse causes release of acetylcholine (ACh) from synaptic vesicles - Acetylcholine (Ach) binds to acetylcholine (Ach) receptors on motor end plate - generates a muscle impulse - muscle impulse eventually reaches sarcoplasmic reticulum and the cisternae  Excitation Contraction Coupling muscle impulses cause sarcoplasmic reticulum to release calcium ions into sarcoplasm calcium binds to troponin to change its shape position of tropomyosin is altered binding sites on actin are animation  http:// www.viddler.com/embed/17b8f09e Sliding Filament Model of Muscle Contraction When sarcromeres shorten, thick and thin filaments slide past one another H zones and I bands narrow Z lines move closer together Steps for Muscle Relaxation 1. The enzyme acetylcholinesterase breaks down acetylcholine at the neuromuscular junction and the muscle fiber membrane is no longer stimulated. 2. Ca++ moves back into the cisternae by active transport. The active sites are now covered by tropomyosin and the cross bridges release.  http:// www.youtube.com/watch?v=jqy0i1K XUO4&list=EC3EED4C1D684D3ADF Energy Sources for Contraction  ATP-needed for cross bridge formation between the actin and myosin filaments  Creatinephosphate -as it is broken down, the energy it releases can be used to reform ATP from ADP and P  Glycogen - can be broken down into glucose for cell respiration Oxygen Supply  Hemoglobin (red pigment in red blood cells) – - Stores oxygen - As blood flows through capillaries in muscles, oxygen from Hemoglobin moves into muscle fibers - Oxygen then can be used for cellular respiration  Myoglobin (brownish red pigment in muscle cells) – - Has a higher attraction for O2 than hemoglobin - When capillaries are opened (relaxed muscle), myoglobin can trap oxygen that is not used immediately and store it - Used later when capillaries are closed (contracted muscle) - Reduces the muscle’s need for a constant blood supply Oxygen Debt  Develops as a muscle undergoes strenuous exercise (1-2 minutes)  When all oxygen is used up, muscle cells resort to anaerobic respiration to break down glucose (glucose-- >pyruvic acid ---> lactic acid)  Lactic acid builds up in muscle, lowers pH, and causes soreness.  When muscle relaxes, blood flow increases, and accumulated lactic acid is carried to liver and converted to glucose. Oxygen Debt  The amount of oxygen debt is equal to the amount of oxygen needed to convert all accumulated lactic acid to glucose and to return ATP and Creatine Phosphate levels to normal in muscle tissue.  In order for muscles to contract, they need ENERGY -Mostly from cellular respiration -Much of the energy is lost as heat. Types of Muscle Cells RED MUSCLE FIBERS WHITE MUSCLE FIBERS  “Slow contracting”  “Fast contracting”  Good supply of blood  Not as much (Hb) and lots of myoglobin and hemoglobin, mitochondria myoglobin, or  Can regenerate ATP mitochondria quickly   Contract long time with Have more Ca++ so little fatigue can contract quickly,  Ex: postural muscles but not for long without fatigue  Ex: hand and eye muscles Muscular Responses  Threshold Stimulus-the minimum amount of stimulus needed for a muscle fiber to contract  All-or-None Response-when a muscle fiber is stimulated, it contracts all the way or not at all; no PARTIAL contractions: - Subthreshold-no contraction - Threshold-full contraction - Suprathreshold-full contraction Muscle Twitch A muscle twitch is a single full contraction of a skeletal muscle fiber  Myogram-a recording of muscle responses  Periods during a muscle twitch: 1.Latent period-time after application of stimulus and beginning of contraction 2.Periods of contraction 3.Periods of relaxation 4.Refractory period -after contraction when muscle won’t respond to a normal stimulus  Sustained Contractions: 1. Summation-muscle does not have time to completely relax between contractions 2. Tetanus-stimuli are so close together that there is no relaxation  Muscle Tone-state of partial contraction of a whole skeletal muscle; some fibers are contracted and others are not Types of Muscle Contraction ISOTONIC ISOMETRIC  As muscle  As muscle contracts, it contracts, it does changes in length not change in  No change in length tension  Increase in tension  Bones move  No bone movement Skeletal Muscle Actions  Origin-end of muscle that does not move  Insertion-end of muscle that moves Interaction of Skeletal Muscles  Prime mover-muscle whose contraction is responsible for most of the movement  Synergists-muscles whose contractions aid the action of the prime mover  Antagonist-muscle whose contraction opposes the action of Comparison of Skeletal, Cardiac, and Smooth Muscle Tissues Skeletal Muscle Tissue  Cylindricalcells  Multinucleated  Striated  Voluntary  Each fiber has its own connection to a neuron Cardiac Muscle  Cylindrical, branched  Each fiber is not fibers  Single nucleus per connected to fiber neuron  Striated  Intercommunicat  Involuntary  Intercalated disks- ion-when one heavy striations contracts, all which occur at contract junctions between  Rhythmicity- self- ends of adjacent fibers exciting - gap junctions are located here Smooth (Visceral) Muscle Tissue  Tapered fibers, nonstriated  Single nucleus per fiber  Each fiber is not connected to a neuron  Involuntary  Gap junctions-intercommunication so that when one contracts, all in the “sheet” contract  Rhythmicity-self-exciting  Peristalsis-wavelike contractions of smooth muscle in walls of many tubular organs