1. Muscle Tissue

2. Summary General General Types of muscle tissue Types of muscle tissue Functional characteristics Functional characteristics Functions Functions Structural organization of skeletal muscle Structural organization of skeletal muscle Gross and microscopic anatomy Gross and microscopic anatomy Contraction sequence Contraction sequence Muscle metabolism Muscle metabolism

3. General Skeletal muscle represents about 40% of our body mass, including smooth and cardiac muscle the figure may be as high as 50% Skeletal muscle represents about 40% of our body mass, including smooth and cardiac muscle the figure may be as high as 50% Muscles transform chemical energy into mechanical energy, i.e. exert a force. Muscles transform chemical energy into mechanical energy, i.e. exert a force. Muscles pull they do not push. Muscles pull they do not push. Skeletal and smooth muscle cells are called fibers. Skeletal and smooth muscle cells are called fibers. Myo-, mys- and sarco- refer to muscles Myo-, mys- and sarco- refer to muscles

4. Muscle Types Skeletal Skeletal Smooth Smooth Cardiac Cardiac

5. Functional Characteristics Excitability (irritability) – receive and respond to stimuli. Excitability (irritability) – receive and respond to stimuli. – Stimuli = neurotransmitters, extracellular pH – Response = generation of an electrical impulse (AP) Contractility = ability to shorten, requires energy Contractility = ability to shorten, requires energy Extensibility = ability to stretch, does not require energy Extensibility = ability to stretch, does not require energy Elasticity = ability to recoil, i.e. return to resting length Elasticity = ability to recoil, i.e. return to resting length

6. Functions of Muscle Tissue Produces movement Produces movement – Locomotion – Propulsion – Manipulation Maintains posture Maintains posture Stabilizes joints Stabilizes joints Generates heat – primarily skeletal m. Generates heat – primarily skeletal m.

7. Structural Organization of Skeletal Muscle Muscle (Organ) Muscle (Organ) Fascicles Fascicles Fiber (Cell) Fiber (Cell) Myofibrils Myofibrils Myofilaments Myofilaments – Actin – Myosin

8. Skeletal Muscle Gross Anatomy Tissues: Tissues: – Blood vessels – Nerves – branches to each fiber – Connective Tissue Endomysium –wraps each fiber Endomysium –wraps each fiber Perimysium –wraps fibers into fascicles Perimysium –wraps fibers into fascicles Epimysium –wraps fascicles into a muscle Epimysium –wraps fascicles into a muscle All are continuous with each other and the tendons. All are continuous with each other and the tendons.

9. Skeletal Muscle Microscopic Anatomy

10. Myofibrils – hundreds to thousands per cell contain the contractile proteins = myofilaments Myofibrils – hundreds to thousands per cell contain the contractile proteins = myofilaments – Actin – thin filaments – Myosin – thick filaments

11. Contraction – Sliding Filament Model Sliding filament theory Sliding filament theory – Hugh Huxley 1950’s – Contraction (shortening) - the thin filaments slide past the thick filaments and overlap increases. – Relaxation (lengthening) - thin filaments return to their original position. – Occurs simultaneously in sarcomeres throughout the fiber = muscle shortening.

12. Brain  Spinal Cord  Motor Neuron  Muscle Motor = movement Neuron = nerve cell

13. Motor Neuron  Muscle Fiber Motor neuron releases neurotransmitter called acetylcholine (ACh). ACh causes muscle fiber to produce an electrical signal. Electrical signal causes actin & myosin to move, and this causes muscle to move.

14. A Myofibril at Rest

15. Recall: Section through a Muscle

16. A Myofibril at Rest “At rest” = fiber has not received message to move

17. A Myofibril at Rest “At rest” = fiber has not received message to move Actin (thin) attaches to Z-line. Myosin (thick) does not attach to actin or the Z-line. Myosin heads are bent back (cocked).

18. Contraction in the Myofibril 1. Signal from ACh to contract 2. Myosin attaches to actin 3. Pushes actin toward center of sarcomere. 4. Sarcomere gets shorter.

19. Contraction Let’s compare length of sarcomeres: Let’s compare length of sarcomeres:Relaxed:Contracted:

20. Contraction in the Myofibril If each sarcomere gets shorter, then the myofibril as a whole gets shorter. If each sarcomere gets shorter, then the myofibril as a whole gets shorter. Myofibrils shorten  fibers shorten Myofibrils shorten  fibers shorten Fibers shorten  Muscle contracts Fibers shorten  Muscle contracts

21. Contraction in the Myofibril After contraction, muscle relaxes (back to original length). After contraction, muscle relaxes (back to original length). –Myosin heads pick up ATP & break it apart. –This cocks the head, detaching it from actin. Now ready to contract again. Now ready to contract again. Head is Cocked ATP

22. Contraction

24. Types of muscular contraction Isometric Isometric –Muscular contraction where the tension developed occurs with no change in length –Otherwise known as static contraction or position. –Improves muscular strength at fixed joint angle –Does not develop aerobic fitness –Can be done anywhere –Examples; rugby scrum, tug of war.

25. Types of muscle contraction Isotonic Muscles contact at speed controlled by the performer Motor unit recruitment is at the speed required for the specific sports activity. Develops aerobic and anaerobic fitness Most physical activities are isotonic Can occur in two ways: concentric and eccentric.

26. Contraction Concentric contraction Concentric contraction –Muscle shortens under tension –Insertion moves towards origin –Occurs in agonist muscle –e.g. Chin-ups – use of bicep brachii in upward phase

27. Contraction Eccentric contraction Muscle lengthens under tension Insertion moves away from origin Occurs in antagonist muscle Only occurs if the antagonist is acting as a brake to help control the joint movement E.g. Chin-ups – use of biceps in downward phase.

28. Two major factors determine the capabilities of a particular skeletal muscle: 1) Types of muscle fibers within the muscle. 2) Physical conditioning or training.

29. Two contrasting types of skeletal muscles fibers in the human body: 1)fast fiber 2)slow fiber

30. Fast fiber large in diameter & use massive amounts of ATP. large in diameter & use massive amounts of ATP. contract in 0.01 sec or less following stimulation. contract in 0.01 sec or less following stimulation.

31. Slow fibers half the diameter of fast fibers half the diameter of fast fibers take three times as long to contract take three times as long to contract continue to contract for extended periods. continue to contract for extended periods.

32. Muscle Metabolism Stored ATP – 4-6 seconds but is regenerated by 3 mechanisms: Stored ATP – 4-6 seconds but is regenerated by 3 mechanisms: – Direct phosphorylation of ADP from creatine phosphate (CP) with the help of creatine kinase. SUPER FAST gives another 6-10 seconds of activity. – Anaerobic glycolysis – glucose is broken down into 2 pyruvate molecules and 2 ATP molecules. Fast but short term – supports another 30-40 seconds of activity. Problem - lactic acid build-up

33. Muscle Metabolism Energy Energy – Aerobic glycolysis (respiration) or Kreb’s Cycle Glucose + O2 yields CO2 + H 2 O + 30 ATP’s Glucose + O2 yields CO2 + H 2 O + 30 ATP’s Pyruvate, amino acids, and fatty acids can also enter this cycle. Slow process, more useful for endurance exercise. Pyruvate, amino acids, and fatty acids can also enter this cycle. Slow process, more useful for endurance exercise.

34. Muscle Fatigue

35. Fatigue Physiological inability of a muscle to contract – not enough ATP; different from psychological fatigue. ATP production lags behind use – contractures (no ATP to release cross bridges. Physiological inability of a muscle to contract – not enough ATP; different from psychological fatigue. ATP production lags behind use – contractures (no ATP to release cross bridges. Accumulation of lactic acid decreases pH and inhibits ATP production. Accumulation of lactic acid decreases pH and inhibits ATP production. Restoration of ionic balance of Na and K requires ATP also – impaired with intense exercise. Restoration of ionic balance of Na and K requires ATP also – impaired with intense exercise.

36. Fatigue Oxygen debt = amount of oxygen needed to restore muscle anaerobic fuel stores.

37. What is oxygen debt? Oxygen debt- is the temporary lack of oxygen availability. Oxygen debt- is the temporary lack of oxygen availability.

38. What causes it? It is caused by heavy exertion and the respiratory and circulatory systems not delivering enough oxygen to meet the demands of energy production It is caused by heavy exertion and the respiratory and circulatory systems not delivering enough oxygen to meet the demands of energy production

39. Oxygen debt leads to the build up of what in the muscles? Lactic acid Lactic acid  is the metabolic waste that builds up in the muscle fiber after prolonged exercise.

40. Heat 60% of the energy released by muscle contraction is in the form of heat – 40% is in the form of work. Shivering is muscle contraction used to warm a cold body. 60% of the energy released by muscle contraction is in the form of heat – 40% is in the form of work. Shivering is muscle contraction used to warm a cold body. When you exercise strenuously your body heats up. How is the heat dissipated????? When you exercise strenuously your body heats up. How is the heat dissipated?????