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Muscles &Muscle Tissue

Muscles &Muscle Tissue

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Muscles &Muscle Tissue

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  1. Muscles &Muscle Tissue Chapter 9

  2. Function of Muscles • Movement • Posture • Stabilization of Joints • Thermogenesis (heat production)

  3. Functional Characteristics of Muscle • Excitability (irritability) • Can receive and respond to stimuli. • Stimuli can include nerve impulses, stretch, hormones or changes in the chemical environment. • Contractility – the ability to shorten with increasing tension. • Extensibility – the ability to stretch. • Elasticity – the ability to snap back (recoil) to their resting length after being stretched.

  4. Three types of muscle Skeletal Smooth Cardiac

  5. Characteristics of Skeletal Muscle • Striated • Multinucleate (it is a syncytium) • Voluntary • Parallel fibers

  6. Arrangement of connective tissue in skeletal muscle

  7. Muscle microstructure

  8. Myosin

  9. A thick myofilament

  10. A thin myofilament Made of actin, troponin and tropomyosin

  11. Arrangement of myofilaments

  12. The sarcomere:the functional unit of skeletal muscle

  13. Anatomy of a myofibril

  14. Summary of skeletal muscle anatomy:muscles are made of fascicles

  15. Fascicles are made of fibers, fibers are made of myofibrils

  16. Fibrils are divided into sarcomeres,sarcomeres are made of myofilaments

  17. Myofilamentsare made of protein molecules

  18. Muscle Contraction:the Sliding Filament Theory • Muscle contraction requires: • Stimulus – the generation of an action potential. • Crossbridge formation – interaction between the thick and thin myofilaments. This is triggered by Ca++ ions released from the sarcoplasmic reticulum. • Energy – ATP to energize the myosin molecules.

  19. T- tubules supply the stimulus,Sarcoplasmic Reticulum supplies the Ca++,Mitochondria supply the ATP.

  20. The role of Calcium ions

  21. Muscle contraction

  22. Show the animation

  23. Excitation-Contraction coupling • Stimulus or excitation is required for muscles to contract. • In skeletal muscle, the stimulus is from a motor neuron. • The stimulus is in the form of an action potential. • This action potential starts at the neuromuscular junction (NMJ).

  24. A neuromuscular junction (NMJ).

  25. The actual synapse acetylcholine

  26. Excitation-contraction coupling

  27. Show NMJ animation

  28. Motor units

  29. Micrograph of an NMJ

  30. A Synapse Synaptic vesicles

  31. Myogram of a single muscle twitch

  32. Comparative speed of different muscles

  33. Graded Muscle Responses • The “twitch” describes just one fiber, it really isn’t how muscles normally work. • Muscles contract smoothly and respond to different levels of demand. • This is accomplished through “graded responses”. There are two ways muscle responses are “graded”

  34. Wave Summation • Wave summation is accomplished by repeated stimuli. • As the rate of stimulus delivery increases, there is less and less time for the fiber to relax between stimuli. • If the stimuli are rapid enough, the muscle fiber will contract completely and remain contracted until the stimulus stops of the muscle fatigues. • This is called tetanus (or tetany).

  35. Recruitment • Since action potentials are “all-or-none” responses, when a fiber is stimulated to tetany, it exerts maximum tension. • To respond to stronger stimuli and thus increase the amount of tension, muscles will recruit more motor units until they reach maximal stimulus and all the motor units are recruited • This continues until they either accomplish their task or fatigue.

  36. Treppe

  37. Types of contractions • Isometric – means “same length”. Force is developed without measurable movement. • Isotonic – means “same tension” movement is achieved with force or “tension” remaining constant.

  38. Isotonic contraction: Concentric

  39. Eccentric Contraction This refers to the tension that is applied on a muscle as it lengthens. Example: When you lower the dumbbell you just lifted, you don’t do so by allowing the muscle to just relax. Think about the consequences of that! Eccentric contractions are about 50% more forceful than concentric ones.

  40. Isometric Contraction

  41. Energy physiology in skeletal muscle

  42. Anaerobic Metabolism:a losing proposition

  43. Aerobic endurance

  44. Anaerobic endurance

  45. Fiber Types • Fast Glycolytic (fast twitch a or type IIB) • few mitochondria, adapted for fast, powerful contraction, large diameter, little myoglobin (white fibers), few capillaries, fatigues rapidly • Fast Oxidative (fast twitch b or type IIA) • many mitochondria, fast contraction, intermediate diameter, lots of myoglobin & capillaries (pink fibers), moderately fatigue resistant • Slow Oxidative (slow twitch or type I) • many mitochondria, slow contraction, smallest in diameter, don’t hypertrophy, lots of myoglobin & capillaries, very fatigue resistant, red fibers

  46. Stretch and tension

  47. Stretch/Tension

  48. The Effect of Load on Contraction

  49. Smooth Muscle

  50. Varicosities