Controlling muscle contraction

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Controlling muscle contraction

  1. 1. Controlling Muscle Contraction & Muscle Response Chapter 8: Muscular System Unit 2: Support and Movement
  2. 2. Types of Muscle <ul><li>Recall there are three types of muscle </li></ul><ul><ul><li>Cardiac and Smooth muscle are considered involuntary </li></ul></ul><ul><ul><ul><li>You cannot consciously control these muscles </li></ul></ul></ul><ul><ul><li>Skeletal muscle is the only muscle tissue that is under voluntary control </li></ul></ul><ul><ul><ul><li>You think to move your skeletal muscle </li></ul></ul></ul><ul><ul><ul><li>You control your movements using your nervous system. </li></ul></ul></ul>
  3. 3. Nervous Signal <ul><li>When you want to move you big toe… </li></ul><ul><ul><li>You think about moving your big toe </li></ul></ul><ul><ul><li>Your brain generates an electrical signal </li></ul></ul><ul><ul><li>The signal is sent down your spine </li></ul></ul><ul><ul><li>The signal is sent down a nerve in your leg </li></ul></ul><ul><ul><li>The signal reaches the end of the nerve’s axon at the motor end plate </li></ul></ul>
  4. 4. Neuromuscular Junction
  5. 5. Acetylcholine <ul><li>A nerve impulse will be sent to the end of a motor neuron axon. </li></ul><ul><ul><li>This impulse will stimulate the release of acetylcholine into the synaptic cleft. </li></ul></ul><ul><ul><ul><li>Acetylcholine diffuses across synaptic cleft and react with receptors in motor plate of muscle. </li></ul></ul></ul><ul><ul><ul><ul><li>Once acetylcholine in the muscle fiber membrane associates with a receptor, a Muscle Impulse is stimulated. </li></ul></ul></ul></ul>
  6. 6. Muscle Impulse <ul><li>Muscle Impulse Animation </li></ul>
  7. 7. Muscle Impulse <ul><li>The muscle impulse travels through the transverse tubules, deep into the muscle fibers, and reaches the sarcoplasmic reticulum. </li></ul><ul><ul><li>The sarcoplasmic reticulum contains a high concentration of calcium ions. </li></ul></ul><ul><ul><li>Like a reservoir of calcium ready to burst </li></ul></ul>
  8. 8. Role of Calcium Ions <ul><li>In response to a muscle impulse, the SR opens gates that allows Ca2+ to move out. </li></ul><ul><ul><li>Ca2+ ions bind with troponin, which changes shape and moves tropomyosin off the actin binding sites. </li></ul></ul><ul><ul><ul><li>As a result, myosin is able to bind to actin and begin the contraction cycle described earlier </li></ul></ul></ul>
  9. 10. Muscle Relaxation <ul><li>When nerve impulses cease, two events lead to muscle relaxation: </li></ul><ul><ul><li>Acetylcholine is decomposed by </li></ul></ul><ul><ul><li>Acetylcholinesterase . </li></ul></ul><ul><ul><li>2. Calcium ions are actively pumped back into the sarcoplasmic reticulum. </li></ul></ul>
  10. 11. Threshold Stimulus <ul><li>When a muscle fiber is exposed to a series of nervous stimuli of increasing strength, the fiber remains unresponsive until certain strength of stimulation is applied. </li></ul><ul><ul><li>The minimum strength required to cause a contraction is called the Threshold Stimulus . </li></ul></ul>
  11. 12. All-or-None Response <ul><li>Muscle fiber exposed to a stimulus of threshold strength respond to its fullest extent. </li></ul><ul><ul><li>In other words, all the myosin heads react by binding and pulling on the actin </li></ul></ul><ul><ul><li>The extent of shortening depends on the resistance & the number of motor units that are recruited for the lift </li></ul></ul><ul><ul><ul><li>This phenomenon in which muscles always contracting fully is called the All-or None Response . </li></ul></ul></ul>
  12. 13. Recording a Muscle Contraction <ul><li>A muscle can be stimulated electrically, and when it contracts, its movement can be recorded. </li></ul><ul><ul><li>The resulting muscle contraction pattern is called a Myogram . </li></ul></ul>
  13. 14. Recording Contractions <ul><li>If a muscle is exposed to a single stimulus to activate some of its motor units, the muscle will contract and then relax. </li></ul><ul><ul><li>A single contraction that lasts only a fraction of a second is called a Twitch . </li></ul></ul><ul><ul><ul><li>The delay between the time the stimulus was applied and the time the muscle responded is the Latent Period . </li></ul></ul></ul>
  14. 16. Recording Contractions Continued <ul><li>The latent period lasts less than 0.001 seconds. </li></ul><ul><ul><li>This period is followed by a Period of Contraction when the muscle pulls at its attachments. </li></ul></ul><ul><ul><ul><li>A Period of Relaxation when it retunes to its former length. </li></ul></ul></ul>
  15. 18. Summation <ul><li>A muscle fiber exposed to a series of stimuli of increasing frequency reaches a point when it is unable to completely relax before the next stimulus in the series arrives. </li></ul><ul><ul><li>The force of individual twitches combines by the process of Summation . </li></ul></ul>
  16. 19. Series of Twitches
  17. 20. Summation
  18. 21. Tetanic Contraction <ul><li>When the resulting forceful, sustained contraction lacks even partial relaxation, it is called a Tetanic Contraction . </li></ul>
  19. 22. Use and Disuse of Skeletal Muscle <ul><li>Skeletal muscles are very responsive to use and disuse. </li></ul><ul><ul><li>Forcefully exercising muscles causes them to enlarge ( Muscular Hypertrophy ) </li></ul></ul><ul><ul><li>Unused muscle undergoes Atrophy decreasing their size and strength. </li></ul></ul>
  20. 23. Muscle Fibers <ul><li>There are two types of muscle fibers: </li></ul><ul><ul><ul><li>Slow Twitch Fibers </li></ul></ul></ul><ul><ul><ul><li>Fast Twitch Fibers </li></ul></ul></ul><ul><ul><ul><li>These fiber types respond differently to exercise/stress. </li></ul></ul></ul>
  21. 24. Slow Fibers <ul><li>A muscle contracting weakly activates a specialized group of muscle fibers called Slow Fibers . </li></ul><ul><ul><li>When stimulated, slow fibers produce more mitochondria, and a more extensive capillary network </li></ul></ul><ul><ul><ul><li>Mitochondria for extra ATP production </li></ul></ul></ul><ul><ul><ul><li>Capillaries to deliver more oxygen </li></ul></ul></ul><ul><ul><ul><li>*Their overall size does not change </li></ul></ul></ul>
  22. 25. Fast Fibers <ul><li>Forceful exercise, in which a muscle exerts more than 75% of its maximum force, utilizes specialized muscle fibers called Fast Fibers . </li></ul><ul><ul><li>In response to strenuous exercise, these fibers produce new filaments of actin and myosin. </li></ul></ul><ul><ul><ul><li>The diameter of the muscle fibers increase, and the entire muscle enlarges. </li></ul></ul></ul><ul><ul><ul><li>The extra myosin and actin fibers give the muscle more strength </li></ul></ul></ul>
  23. 26. Disuse <ul><li>If regular exercise stops: </li></ul><ul><ul><li>Capillary network shrink </li></ul></ul><ul><ul><li>Number of mitochondria within the muscle fibers drops </li></ul></ul><ul><ul><li>Number of actin and myosin filaments decrease </li></ul></ul><ul><ul><ul><li>Unused muscle may decrease to less than half its usual size within a few months. </li></ul></ul></ul>

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