The Muscular System

1. The Muscular System

2. Muscle Types • Skeletal – attached to skeleton by tendons; during development individual cells fuse to form protein fibers and nuclei are pushed to the side; striated; under voluntary control

3. Muscle Types • Cardiac – forms the heart, cells fuse (intercalated discs) into a branching pattern; striated; involuntary control

4. Muscle Types • Smooth – located mostly in the walls of hollow organs; 1 nucleus/cell; not striated; involuntary control

5. Functions • Move body parts as muscle contracts • Muscles usually attach to 2 different bones • Insertion point – at moving bone • Origin point – at stable bone

6. Functions (con’t) • Move body parts as muscle contracts (con’t) • Muscles work in groups • Prime mover – one muscle that is mainly responsible for movement • Synergists – other muscles that help movement • Antagonists – produce movement in opposite direction

7. Functions (con’t) • Posture and Stability • Tonic contraction – only a few muscle fibers contract, therefore muscle as a whole doesn’t shorten - creates muscle tone - favors best function of other body parts

8. Functions (con’t) • Heat production – only 25% of energy produced by respiration is used for metabolic processes, the rest is lost as heat

9. Oxygen Debt • During rest or moderate exercise, O2 is supplied to muscles in sufficient concentration to support aerobic respiration • Strenuous exercise causes deficiency and lactic acid accumulates as a result of anaerobic respiration • C6H12O6 6CO2 + lactic acid + 2ATP = heat • Muscle fatigue – muscle loses ability to contract because of strenuous exercise for prolonged periods of time • Usually caused by lactic acid buildup • May result from decreased blood supply • Rarely from decreased acetylcholine from motor neuron

10. Oxygen Debt • Oxygen Debt.  This term describes how the body pays back its debt incurred after the exercise is over.  You will notice that even after you are done racing you will continue to breath hard.  At this point your body is still trying to repay the oxygen debt that was created when you were working hard.  Technically, it is excessive post-exercise oxygen consumption.  That's it.

11. Structure of Skeletal MuscleFig. 7-3 • Each muscle is composed of many muscle fibers • Each muscle fiber is composed of many myofibrils • Each myofibril is composed of actin (thin) & myosin (thick) filaments • Sarcomere – functional contractile unit (Z line to Z line)

12. Structure of Skeletal MuscleFig. 7-3

13. Structure of Skeletal MuscleFig. 7-3

14. Neuromuscular Junction • Connection point of motor neuron to muscle fiber; • Synaptic vesicles that release neurotransmitters (usually acetylcholine) stimulate muscle to contract

15. Neuromuscular Junction

16. Neuromuscular Junction • http://www.youtube.com/watch?v=ZscXOvDgCmQ

17. Major Events of muscle contraction and relaxation • Sliding Filament Model • Muscle fiber contraction • Muscle fiber relaxation • Threshold stimulus

18. Muscle Fiber Contraction • Actylcholine is released from the distal end of a motor neuron • Acetylcholine diffuses across the gap at the neuromuscular junction • The sarcolemma is stimulated, and a muscle impulse travels over the surface of the muscle fiber and deep into the fiber through the transverse tubules and reaches the sarcoplasmic reticulum

19. Muscle Fiber Contraction • Calcium ions diffuse from the sarcoplasmic reticulum into the sarcoplasm and bind to troponin molecules • Tropomyosin molecules move and expose specific sites on actin filaments • Linkages form between actin and myosin filaments • Actin filaments slide inward along the myosin filaments • Muscle fiber shortens as a contraction occurs

20. Muscle Fiber Contraction • http://www.youtube.com/watch?v=EdHzKYDxrKc • http://www.youtube.com/watch?v=WRxsOMenNQM • http://www.youtube.com/watch?v=0kFmbrRJq4w • http://www.youtube.com/watch?v=70DyJwwFnkU&NR=1

21. Muscle Fiber Relaxation • Cholinesterase causes acetylcholine to decompose and the muscle fiber membrane is no longer stimulated • Calcium ions are actively transported into the sarcoplasmic reticulum • Linkages between actin and myosin filaments are broken • Troponin and tropomyosin molecules inhibit the interaction between myosin and actin filaments • Actin and myosin filaments slide apart • Muscle fiber lengthens as it relaxes and its resting state is reestablished

22. Threshold Stimulus • Threshold stimulus is an all or none response – the minimal level of stimulation required to cause a fiber to contract; therefore not necessarily all muscle fibers in muscle contract

23. Types of Muscle Contractions • Tonic contraction – only a few fibers at a time contract – maintain muscle tone • Twitch contraction – single contraction that only lasts a fraction of a second; muscle fiber is able to • relax between stimuli • Tetanic contraction – a rapid series of stimuli produce a sustained contraction (summation of twitches); muscle does not relax before next contraction • Isotonic contraction – Fig. 7-5A – produce movement of joint; tension remains fairly constant and muscle shortens • Isometric contraction – Fig. 7-5B – tension increases with no shortening of the muscle

24. Tonic vs Twitch Contraction

25. Movements produced by skeletal muscle contraction • Flexion – makes angle between two bones smaller • Extenion – angle between two bones becomes larger; straighten

26. Movements produced by skeletal muscle contraction • Abduction – movement away from midline • Adduction – movement toward the midline

27. Movements produced by skeletal muscle contraction • Rotation – movement around a longitudinal axis

28. Movements produced by skeletal muscle contraction • Supination – hand position with palm turned to anterior position (anatomical position) • Pronation – hand position with palm turned posteriorly

29. Movements produced by skeletal muscle contraction • Dorisflexion – dorsum (top) of foot is elevated with toes pointing upward • Plantar flexion – bottom of the foot is directed downward (stranding on toes)

30. Web Links • Facial Muscle Video http://www.gustrength.com/forum/t-283781