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. Myofilaments are 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. acetylcholine
The actual synapse

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

51. Contraction of smooth muscle

52. Skeletal Smooth Diameter 10 - 100 m 3 - 8 m Connective tissue
Epi-, Peri- & Endomysium
Endomysium only SR
Yes, complex
Barely, simple
T - tubules
yes no
Sarcomeres
Gap Junctions
voluntary
Neurotransmitters
Acetylcholine (Ach)
Ach, epinephrine, norepinephrine, et al
Regeneration
Very little
Lots, for muscle

53. Future governors of Califorina?