1. “myo = muscle” The Muscular System

2. Muscular System There are 650 skeletal musclesThere are 650 skeletal muscles They make up 40-50% of our body weightThey make up 40-50% of our body weight Muscles play a crucial role in communicationMuscles play a crucial role in communication The smallest muscle in the body is the stapedius and controls the stapes (stirrup bone in the ear)The smallest muscle in the body is the stapedius and controls the stapes (stirrup bone in the ear) The largest muscle in the body???The largest muscle in the body??? –Gluteus maximus!

3. Important functions  Movement – both voluntary & involuntary  Maintaining posture  Supporting soft tissues within body cavities  Stabilizing joints  Guarding entrances & exits of the body  Maintaining body temperature

4. Characteristics Excitability (irritability)Excitability (irritability) Contractility (shrink) Contractility (shrink) Extensibility (stretch)Extensibility (stretch) Elasticity (recoil)Elasticity (recoil)

5. 5 Skeletal muscle – –Striated, has stripes – –Voluntary, multiple nuclei – –Attached to bones Cardiac muscle – –Striated, has stripes – –Involuntary – –Responsible for heart contractions Smooth muscle:Smooth muscle: –non-striated, no stripes –found in the digestive tract, walls of blood vessels, reproductive system –controlled by the autonomic nervous system Types of Muscles

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7. Anatomy of Muscles Muscle cells are called muscle fibers Nerve and blood supply Motor Unit – –Muscle fiber and neuron – –~150 fiber per neuron Neuromuscular Junction – –Communicate at synapse – –Ach (acetylcholine) – neurotransmitter in muscle contraction

8. Levels of Organization of a Muscle Muscle  Fascicles  Muscle Fibers (cells)  Myofibrils  Thick/Thin filaments

9. Connective Tissue Components Tendons – –Muscle to bone Aponeuroses – –Broad connection to bone (flat sheet between abs and dorsal muscles) Layers of connective tissue called fascia group muscles fibers together and give them strength

10. Connective Tissue Components Endomysium surrounds individual muscle fiber. Perimysium holds muscle cells together to form a fascicle. Epimysium surrounds groups of fasicles.

11. Sacromere Sacromere is the individual contractile unit of the muscle cell Sacromere is the individual contractile unit of the muscle cell Consists of: * Sarcolemma *Nuclei *Sarcoplasmic reticulum *Transverse tubules *Mitochondria

12. Myofibrils Myofibrils: protein strands inside of muscle cell Myofibrils: protein strands inside of muscle cell – Thin filaments: actin, troponin, tropomyosin – Thick filaments: myosin – Z line: boundary between sarcomeres

13. 13 2 Types of Myosin Filament Red (Type I) fibers (slow twitch) – –Fatigue resistant  endurance – –use aerobic metabolism White (Type II) fibers (fast twitch) – –participate in brief, powerful movements – –use anaerobic metabolism = slow twitch = fast twitch

14. 14 The Effects of Exercise on Muscle Muscles respond to damage by producing more actin and myosin filaments. This increases muscle size, but not number. Disuse of muscles reverses this process, as in space travel.

15. Shape, Size and Arrangement Skeletal muscles are considered organs Skeletal muscles are considered organs Muscle arrangement and shape are suited to their function Muscle arrangement and shape are suited to their function ParallelConvergentPennate Bipennate Sphincter

16. During contraction one bones usually stays stationary During contraction one bones usually stays stationary Skeletal muscles can only pull, not push Skeletal muscles can only pull, not push Origin is point of attachment that doesn’t move Origin is point of attachment that doesn’t move Insertion is point that does move with contraction Insertion is point that does move with contraction Origin and Insertion Points

17. Muscle Actions Agonist (Ex: biceps brachii) – Also called the prime mover – Contracts to produce movement Antagonist (Ex: triceps brachii) – Performs opposing action of agonist – Relaxes during contraction Synergists (Ex: bracioradialis) – Contract at same time of agonist – Makes prime movers action more efficient Fixator muscles – Stabilize joints – Help maintain posture during movement

18. Lever Systems First class levers –Work like seesaws Second class levers –Work like wheelbarrow Third class levers –Work like shovel –Most common type in body

19. How Muscles are Named Location –Brachialis(arm) & gluteus(buttocks) Action –Adductor brevis Direction of fibers –Rectus abdominis Shape –Deltoid (triangular) Number of heads/divisions –Biceps, triceps, quadriceps Origin and Insertion –Sternocleidomastoid (sternum, clavicle, mastoid) Relative Size of muscle –Gluteus maximus, medius and minimus

20. Quick Check 1.Connective tissue that covers individual muscle fibers? 2. Connective tissue that covers and connects fascicles? 3. Connective tissue that covers and connects groups of fascicles to form a whole muscle? 4. What connects muscle to bone.

21. Quick Check 5.Name three fiber arrangements? 6. What is the point of attachment that does not move with contraction? 7. What point does move with attachment? 8. Muscle action that contracts to performs a movement? 9. What is the most common type of lever system found in the body?

22. Thick and Thin Filaments A. Thin Filament Actin Troponin Tropomyosin B. Thick Filament Myosin

23. 23 Muscle Fiber Contraction #Sarcomere ShorteningSarcomere Shortening

24. 24 Muscle Fiber Contraction In the resting muscle, troponin prevents interactions between actin and myosin. the first step (response to stimulus) in the chain of events leading to contraction)The arrival of an action potential (the first step (response to stimulus) in the chain of events leading to contraction)triggers an internal release of calcium. Calcium binds with troponin and allows actin and myosin to interact. The myosin filaments slide past the actin filaments, shortening the sarcomeres and contracting the fiber. Calcium is taken up again into internal organelles, troponin prevents actin and myosin interaction, and the fiber relaxes. Sliding Filament Theory

25. 25 Copyright (c) Allyn & Bacon 2004 Muscle Fiber Contraction When stored Ca is released in the myofibril, it deactivates troponin, myosin interacts with actin by paddling. ATP then releases the myosin from the acitn. Role of ATP

26. 26 – –Neurons in spinal cord or cranial nerve nuclei control contraction of muscles Neural Control of Muscles

27. Action Potential 1. Threshold is met. 2. Brief hyperpolarization. Action Potential

28. 28 The Control of Muscle Contractions A single action potential may be sufficient to produce contraction (twitch contraction) Varying amounts of force may be supplied by: – –varying the firing rate of alpha motor neurons. – –recruitment (activating more motor units as more load is placed on a muscle).

29. Twitch Contraction Includes: – –1. Latent Period – –2. Contractile Phase – –3. Relaxation Phase

30. Wave Summation Muscle Twitch

31. 31 Control of Alpha Motor Neurons Alpha motor neurons receive input from: – –Muscle spindles – –Golgi tendon organs – –Brainstem and motor cortex neurons – –Spinal interneurons

32. 32 The Muscle Spindle Senses Stretch

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34. Muscle Disorders Muscle Atrophy: shrinkage of muscles due to lack of use. Muscle Spasms: uncontrolled tetanic contractions of a muscle group Muscle Cramp: painful muscle spasm usually due to ion and water imbalance. Rigor Mortis: no ATP so myosin head doesn’t release from actin. Role of ATPRole of ATP

35. Muscle Disorders Muscular Dystrophy: lack protein dystrophin which holds muscle fibers together. – –Death usually occurs ~21 from cardiac/respiratory muscle degeneration Myasthenia Graves: immune system attacks at neuromuscular junction  nerve can’t stimulate muscle contraction – –Death usually results from respiratory distress

36. Major Muscles of the Body