1. CHAPTER 8: MUSCULAR SYSTEM

2. 3 Types of Muscles 1. Skeletal 2. Smooth 3. cardiac

3. bone tendon fascia muscle fiber myofibril filaments Structure of a Skeletal Muscle muscle fascicle

4. 1. Tendon – holds the muscle to the bone

5. 2. Fascia - connective tissue that covers and separates muscles

6. 3. Muscle fiber = the muscle cell

7. 4. Myofibril – the contractile fibers in a muscle fiber

8. 2 Types a) actin - thin b) myosin - thick 5. Filaments

9. Muscle Fiber Structure

10. 1. Sarcoplasmic Reticulum - tubes run parallel to the myofibrils - stores calcium & functions as the ER

11. 2. Transverse Tubules - run at right angles to myofibrils - activate muscle contraction when stimulated

12. 3. Sarcolemma - the “cell membrane”

13. Myofibril Structure

14. Neuromuscular Junction - place where nerve fiber & muscle fiber meet

15. - each muscle fiber is connected to a motor neuron - nerve fiber meets at the motor end plate

16. - end of motor neurons contains synaptic vesicles that have neurotransmitters in them - one motor neuron can control many muscle fibers  motor unit

17. The myogram

18. Skeletal Muscle Contraction  a specific sequence of events needs to occur in order for a muscle fiber to contract - it starts with a nerve impulse traveling down a motor neuron axon - the nerve impulse causes the synaptic vesicles to release the neurotransmitter ACh - the ACh attaches to ACh receptors on sarcolemma then is broken down by acetylcholinesterase Neurotransmitter release

19. - the nerve impulse travels through the muscle fiber which causes the sarcoplasmic reticulum to release Ca 2+ ions - the calcium attaches to the troponin protein which will then move the tropomyosin proteins to uncover the active site on the actin

20. - the myosin heads attach to the active site on the actin filament - ATP is used, and the myosin pulls on the actin by the myosin cross-bridges - the muscle shortens as a contraction occurs Muscle contraction - the muscle will stay contracted until the Ca 2+ is reabsorbed by the SR - the active site will be covered up - actin slides back into its original position Muscle contraction 1

22. Energy Sources for Contraction - ATP supplies the energy - ADP needs to be regenerated into ATP - can borrow a phosphate from creatine phosphate - regenerate through the process of cell respiration

24. - myoglobin - can store O 2 in muscles for cell respiration - if O 2 levels are low and oxygen debt occurs glucose  pyruvic acid  lactic acid  cramps

25. - can lead to muscle fatigue  muscle loses ability to contract

26. Muscular Response Threshold Stimulus - minimal strength needed to start a contraction All - or - None Response - a muscle fiber will contract or it will not - no partial contractions Recruitment - the greater the stimulus, the more motor units will be activated, more muscle fibers will contract

27. The myogram latent period contraction period relaxation period recovery period

28. latent period - time between stimulus and contraction contraction period - time for the muscle to contract relaxation period - actin slides back into place recovery period - O 2 resupplied to muscles

29. Muscular hypertrophy - muscles get larger due to increased use Muscular atrophy - muscles get smaller due to less use

30. Smooth Muscle - thin - contains actin and myosin - are randomly arranged  no striations 2 Types a) Multiunit - found in eye and blood vessels - contracts only after receives a nerve impulse

31. b) Visceral - found in internal organs - displays rhythmic patterns - muscles able to stimulate each other - no continuous stimulus needed - Contraction is almost the same as in skeletal muscles - besides ACh, can be stimulated by norepinephrin - contraction occurs more slowly - muscles are able to stretch

32. Cardiac Muscles - only found in the heart - has actin and myosin - contains many mitochondria

33. Muscular Dystrophy  caused by a defective gene  the muscle fibers are unusually susceptible to damage  muscles become weaker and may be replaced by fat and connective tissue  there are over 40 types of MD  there is no cure

35. Anabolic Steroids Anabolic steroids change muscle mass and strength by three processes. 1. Increases the production of proteins 2. Blocks the hormone cortisol , which decreases muscle breakdown 3. Leads cells to differentiate into muscle more readily than fat