VIEWS: 18 PAGES: 44 POSTED ON: 9/17/2011
Muscular System Chapter 8 What are functions of the muscular system? 1. Gross body movement 2. Stabilizing body positions – “Tone” 3. Generate heartbeat 4. Movement substances within the body 5. Regulating organ volumes 6. Producing body heat Properties of Muscle Tissue 1. Electrical Excitability – able to respond to stimuli and send an impulse 2. Contractility – ability to contract forcefully, muscle body shortens 3. Extensibility – ability to stretch 4. Elasticity – ability to return to original length or shape What are the 3 types of muscle tissue? Skeletal Smooth Cardiac Skeletal Muscle Characteristics: * Multinucleated * Striated * Voluntary control Appearance: Smooth Muscle •Location: Internal organs, blood vessels •“Peristalsis” movement of digestive tract Uninucleated cells •Usually organized into two sheet-like layers: longitudinal and circular Involuntary •Two types: Visceral and Multiunit No striations Cardiac • Striated and uni- nucleated • Branching cells • Intercalated discs separate cells • Rhythmicity • Only found in wall of heart • Self-exciting tissue • Large transverse tubules Aponeurosis, Fascia and Tendons • Fascia – “gift wrap” around muscle body or found under skin (spider webs) • Tendons - connect muscle to bone • Aponeurosis – flat and sheet- like tendon connects muscle to CT Skeletal Muscle Anatomy The Muscle Fiber Structure • Sarcolemma • Sarcoplasm • Nucleus(i) • Sarcoplasmic reticulum • Mitochondria • Myofibrils 1. Actin (thin) 2. Myosin (thick) Skeletal Muscle Fiber Structure Anatomy of a Myofibril The Sarcomere! Sarcomere: Single contracting unit within a myofibril. Striation pattern is caused by the organization of the myofilaments • Length = Z line to Z line • I band = only actin region Contraction: Z-line • A band = myosin and actin region moves towards M line • H zone = only myosin region • M line = center of H zone Muscle Body Fascicles Largest to Muscle Fibers Smallest Myofibrils Myofilaments Now that you are familiar with muscle anatomy, what is the physiology of contraction? How does muscle contraction happen? Section 8.3 Structures Involved in Contraction Motor Unit: One neuron and all the muscle fibers it connects with. Stronger contractions have more motor units activated. The Neuromuscular Junction: where the neuron meets with the muscle fiber. Sarcomere – smallest contracting unit The Sliding Filament Theory Video: “Sarcomere shortening” Now, look at how this process really works… Muscle Contraction 1. Impulse reaches synaptic bulb. 2. Calcium channels open and calcium enters. 3. Ca causes vesicles to migrate to cell membrane to release neurotransmitter (Acetylcholine = Ach). 4. Vesicles fuse with membrane and release Ach Video into synaptic cleft (gap). 5. Ach diffuses across the cleft. 6. Ach binds with receptor proteins on motor end plate. 7. Motor end plate depolarizes. 8. Action potential is generated in muscle cell. 9. Action Potential moves: • along the sarcolemma •down the transverse tubules Animation •into the sarcoplasmic reticulum 10. Calcium is released from the sarcoplasmic reticulum. Binding site before and after calcium reaches myofilaments. VIDEO Troponin/tropomyosin complex pulled away by calcium so myosin can bind! 12. VIDEO 1 Video 2 13. 11. Relaxation phase… 1. Acetylcholine esterase decomposes Ach and removes it from synaptic gap. 2. ATP binds to myosin causing linkage to release from actin. 3. Actin and myosin filaments slide apart. 4. Calcium ions are actively transported back into the sarcoplasmic reticulum. 5. Muscle fiber relaxes. Section 8.4 How does the muscle fiber get ATP for the contraction? • Cell Storage • Creatine phosphate • Cellular respiration or fermentation Creatine Phosphate • Used when current cell supply of ATP runs out. (within 6 sec.) • Cannot be used directly as an energy source. • Purpose: to transfer stored energy to ADP to make ATP. • Creatine supply is exhausted in 30 sec. • Activities that benefit: 100 meter dash and weight lifting Aerobic Respiration • With oxygen available, glucose is converted into the max amount of ATP! Myoglobin: Oxygen-binding pigment found only in muscle cells. What if you run out of oxygen? Anaerobic respiration occurs by fermentation. Fermentation produces Lactic Acid. Lactic acid is carried to liver to be converted back to glucose. Low intensity or moderate exercise can recycle the lactic acid immediately. (not a lot is produced) Good energy source for “stop and go” sports. (soccer, tennis, short-term swimming) Oxygen Debt • The amount of O2 liver cells require to convert the lactic acid into glucose + the O2 muscle cells require to restore stored ATP and creatine phosphate. • Training can speed up the process. O2 Muscle need + O2 Liver need = Oxygen Debt For most activities, all systems are used. It’s just the percentages differ based on the intensity of the activity. % Creatine % Lactic % Aerobic Activity Phosphate Acid Respiration Sprint 95 3 2 Mile 15 55 30 Marathon 5 5 90 Muscle Fiber Types Slow Twitch Fast Twitch • Not easily fatigued • Easily fatigued • Myoglobin – “red” • Little myoglobin – “white” • Use in low intensity • Used in high intensity activities – Anaerobic activities – Endurance! Power! • Not a lot of growth – Lean • Increase filaments with • Lots of mitochondria use – Hypertrophy! • Can be irreversibly changed into slow twitch! Slow Fast Genetically, most people are 50% slow, 50% fast twitch What if the muscle cannot contract anymore? Muscle Fatigue • Loss of the ability to contract • Causes: 1. Lactic acid buildup, pH drops 2. Blood supply interruption 3. Lack of acetylcholine 4. Lack of ATP • Cramps: sudden, involuntary contractions or spasms in one or more of your muscles. Possible causes: lack of ATP, dehydration or electrolyte imbalance Muscular Responses • Threshold stimulus – minimum amount of stimulus (Ach) needed to cause a contraction. • All-or-None Response – a muscle fiber will always fully contract no matter the strength of the stimulus. If the minimum amount of stimulus is not met, no contraction will occur. Muscle contractions can be measured and recorded by: The Myogram Twitch: A single contraction of a muscle fiber. Myogram Recording (Latent) a) Shows a series of twitches with complete relaxation before the next stimulus. b) Summation another stimulus comes before complete relaxation can occur, thus increasing the contraction force. c) Tetanus: Stimulus is held constant, where there is no relaxation. Recruitment • Stimulating more motor units in a muscle body to contract. • A greater force applied to the muscle or increase the frequency of stimuli will cause this. Muscle Tone • Skeletal muscle fibers constantly being stimulated by brain. (involuntary) • Stretch receptors in muscles monitor muscle health. • Loss of posture tone = collapse How Do I Hypertrophy My 1. Muscles? Do high intensity activities. 2. Use the fast-twitch muscles. 3. Eat protein for building material. 4. Maintain activity or else: atrophy By age 80, there is a 50% decrease in muscle strength!
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