MUSCLE TISSUE

1. MUSCLE TISSUE Dr. Michael P. Gillespie

2. POSTURE / MOVEMENT • Stable posture results from a balance of competing forces. • Movement occurs when competing forces are unbalanced. • Force generated by muscles is the primary means for controlling the balance between posture and movement.

3. MUSCLE AS A SKELETAL STABILIZER • Muscle generates force to stabilize the skeletal system. • Muscle tissue is coupled to the external environment and internal control mechanisms provided by the nervous system allow it to respond to changes in the external environment. • Whole muscles consist of many individual muscle fibers. • Muscle adapts to the immediate (acute) and repeated long-term (chronic) external forces that can destabilize the body. • Fine control – surgery • Large forces – dead-lift

4. Types of Muscle Tissue • Skeletal muscle tissue • Cardiac muscle tissue • Autorhythmicity - pacemaker • Smooth muscle tissue Dr. Michael P. Gillespie

5. Functions of Muscle Tissue • Producing body movements • Stabilizing body positions • Storing and moving substances within the body • Sphincters – sustained contractions of ringlike bands prevent outflow of the contents of a hollow organ • Cardiac muscle pumps nutrients and wastes through • Smooth muscle moves food, bile, gametes, and urine • Skeletal muscle contractions promote flow of lymph and return blood to the heart • Generating heat - thermogenesis Dr. Michael P. Gillespie

6. Properties of Muscle Tissue • Electrical excitability • Produces electrical signals – action potentials • Contractility • Isometric contraction – tension without muscle shortening • Isotonic contraction – constant tension with muscle shortening Dr. Michael P. Gillespie

7. Properties of Muscle Tissue • Extensibility – ability of a muscle to stretch without being damaged • Elasticity • Ability of a muscle to return to its original length Dr. Michael P. Gillespie

8. Connective Tissue Components • Fascia – a sheet of fibrous CT that supports or surrounds muscles and other organs • Superficial fascia (subcutaneous layer) – separates muscle from skin • Deep fascia – holds muscles with similar functions together • Epimysium – outermost layer – encircles whole muscles • Perimysium • Surrounds groups of 10 – 100 individual muscle fibers separating them into bundles called fascicles Dr. Michael P. Gillespie

9. Connective Tissue Components • Endomysium • Separates individual muscle fibers within the fascicle • Tendon • All 3 CT layers may extend beyond the muscle to form a cord of dense regular CT that attaches muscle to the periosteum of bone • Aponeurosis • A broad, flat layer of CT Dr. Michael P. Gillespie

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11. BASIC COMPONENTS OF MUSCLE Dr. Michael P. Gillespie

12. MUSCLE SIZE • Whole muscles are made up of many individual muscle fibers. • These fibers range in thickness from 10 to 100 μm and in length from 1 to 50 cm. • Each muscle fiber is an individual muscle cell with many nuclei. • The individual muscle fibers contract, which will ultimately result in contraction of the entire muscle. Dr. Michael P. Gillespie

13. Nerve and Blood Supply • Skeletal muscles are well supplied with nerves and blood vessels • Neuromuscular junction – the structural point of contact and the functional site of communication between a nerve and the muscle fiber • Capillaries are abundant – each muscle fiber comes into contact with 1 or more Dr. Michael P. Gillespie

14. TWO TYPES OF PROTEINS IN MUSCLE • Contractile proteins • Actin and myosin • Shorten the muscle fiber and generate active force • Referred to as “active proteins” • Noncontractile proteins • Titan and desmin • Titan provides tensile strength • Desmin stabilizes adjacent sarcomeres • Make up the cytoskeleton within and between muscle fibers • Referred to as “structural” proteins Dr. Michael P. Gillespie

15. Sarcolemma, T Tubules, and Sarcoplasm • Sarcolemma – the plasma membrane of a muscle cell • T (transverse) tubules – Propogate action potentials – extend to the outside of the muscle fiber • Sarcoplasm – cytoplasm of the muscle fiber • Contains myoglobin – protein that binds with oxygen Dr. Michael P. Gillespie

16. Myofibrils and Sarcoplasmic Reticulum • Myofibril – the contractile elements of skeletal muscle • Sarcoplasmic reticulum (SR) – encircles each myofibril – stores CA2+ (its release triggers muscle contractions) Dr. Michael P. Gillespie

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18. Atrophy and Hypertrophy • Muscular atrophy – wasting away of muscles • Disuse • Denervation • Muscular hypertrophy – an excessive increase in the diameter of muscle fibers Dr. Michael P. Gillespie

19. Filaments and the Sarcomere • Filaments – structures within the myofibril • Thin • Thick • Sarcomere – basic functional unit of a myofibril • Z discs – separate one sarcomere from the next Dr. Michael P. Gillespie

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21. MYOFIBRIL ELECTRON MICROGRAPH Dr. Michael P. Gillespie

22. Filaments and the Sarcomere • A band – predominantly thick filaments • Zone of overlap at the ends of the A bands • H zone – contains thick, but no thin filaments • I band – thin filaments • M-line – middle of the sarcomere Dr. Michael P. Gillespie

23. Muscle Proteins • Contractile proteins – generate force • Myosin • Actin • Regulatory proteins – switch contraction on and off • Structural proteins Dr. Michael P. Gillespie

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25. Sliding Filament Mechanism • Muscle contraction occurs because myosin heads attach to the thin filaments at both ends of the sarcomere and pull them toward the M line. • The length of the filaments does not change; However, the sarcomeres shorten, thereby shortening the entire muscle. Dr. Michael P. Gillespie

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27. RELAXED & CONTRACTED MYOFIBRILS Dr. Michael P. Gillespie

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29. POWER STROKE OF CROSSBRIDGE CYCLING Dr. Michael P. Gillespie

30. Role of Ca2+ in Contraction • An increase in calcium ion concentration in the cytosol initiates muscle contraction and a decrease in calcium ions stops it. Dr. Michael P. Gillespie

31. Dr. Michael P. Gillespie

32. MAJOR SEQUENCE OF EVENTS UNDERLYING MUSCLE FIBER ACTIVATION • 1. Action potential is initiated and propagated down a motor axon. • 2. Acetylcholine is released from axon terminals at neuromuscular junction. • 3. Acetylcholine is bound to receptor sites on the motor endplate. • 4. Sodium and potassium ions enter and depolarize the muscle membrane. • 5. Muscle action potential is propagated over membrane surface. • 6. Transverse tubules are depolarized, leading to release of calcium ions surrounding the myofibrils. • 7. Calcium ions bind to troponin, which leads to the release of inhibition of actin and myosin binding. The crossbridge between actin and myosin heads is created. • 8. Actin combines with myosin adenosine triphosphate (ATP), an energy-providing molecule. • 9. Energy is released to produce movement of myosin heads. • 10. Myosin and actin slide relative to each other. • 11. Actin and myosin bond (crossbridge) is broken and reestablished if calcium concentration remains sufficiently high. Dr. Michael P. Gillespie

33. Rigor Mortis • After death the cellular membranes become leaky. • Calcium ions are released and cause muscular contraction. • The muscles are in a state of rigidity called rigor mortis. • It begins 3-4 hours after death and lasts about 24 hours, until proteolytic enzymes break down (digest) the cross-bridges. Dr. Michael P. Gillespie

34. Neuromuscular Junction (NMJ) • Muscle action potentials arise at the NMJ. • The NMJ is the site at which the motor neuron contacts the skeletal muscle fiber. • A synapse is the region where communication occurs. Dr. Michael P. Gillespie

35. Neuromuscular Juntcion (NMJ) • The neuron cell communicates with the second by releasing a chemical called a neurotransmitter. • Synaptic vesicles containing the neurotransmitter acetylcholine (ach) are released at the NMJ. • The motor end plate is the muscular part of the NMJ. It contains acetylcholine receptors. • The enzyme acetlycholineesterase (AChE) breaks down ACh. Dr. Michael P. Gillespie

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37. Production of ATP • 1. From creatine phosphate. • When muscle fibers are relaxed they produce more ATP than they need. This excess is used to synthesize creatine phosphate (an energy rich compound). Dr. Michael P. Gillespie

38. Production of ATP • 2. Anaerobic cellular respiration. • Glucose undergoes glycolysis, yielding ATP and 2 molecules of pyruvic acid. • Does not require oxygen. Dr. Michael P. Gillespie

39. Production of ATP • 3. Aerobic cellular respiration. • The pyruvic acid enters the mitochondria where it is broken down to form more ATP. • Slower than anaerobic respiration, but yields more ATP. • Utilizes oxygen. • 2 sources of oxygen. • Diffuses from bloodstream. • Oxygen released from myoglobin. Dr. Michael P. Gillespie

40. Muscle Fatigue • Muscle fatigue is the inability of a muscle to contract forcefully after prolonged activity. • Central fatigue – a person may develop feelings of tiredness before actual muscle fatigue. Dr. Michael P. Gillespie

41. Oxygen Debt or Recovery Oxygen Uptake • Added oxygen, over and above resting oxygen consumption, taken in after exercise. • Used to restore metabolic conditions. • 1. To convert lactic acid back into glycogen stores in the liver. • 2. To resynthesize creatine phosphate and ATP in muscle fibers. • 3. To replace the oxygen removed from hemoglobin. Dr. Michael P. Gillespie

42. Motor Units • A motor unit consists of the somatic motor neuron and all the skeletal muscle fibers it stimulates. • A single motor neuron makes contact with an average of 150 muscle fibers. • All muscle fibers in one motor unit contract in unison. Dr. Michael P. Gillespie

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44. MOTOR UNIT Dr. Michael P. Gillespie

45. Twitch Contraction • A twitch contraction is the brief contraction of all the muscle fibers in a motor unit in response to a single action potential. • A myogram is a record of a muscle contraction and illustrates the phases of contraction. Dr. Michael P. Gillespie

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47. Refractory Period • A period of lost excitability during which a muscle fiber cannot respond to stimulation. Dr. Michael P. Gillespie

48. Motor Unit Recruitment • The process in which the number of active motor units increases. • The weakest motor units are recruited first, with progressively stronger units being added if the task requires more force. Dr. Michael P. Gillespie

49. Muscle Tone • Even at rest a muscle exhibits a small amount of muscle tone – tension or tautness. • Flaccid – when motor units serving a muscle are damaged or cut. • Spastic – when motor units are over-stimulated. Dr. Michael P. Gillespie

50. Isotonic and Isometric Contractions • Concentric isotonic activation (contraction) – a muscle shortens and pulls on another structure. • Eccentric isotonic activation – the length of a muscle increases during contraction. • Isometric activation – muscle tension is created; However, the muscle doesn’t shorten or lengthen. Dr. Michael P. Gillespie