1. Muscle Physiology
PSK 4U1

2. Structure of Skeletal Muscle: Connective Tissue Coverings
Epimysium
Surrounds entire muscle
Perimysium
Surrounds bundles of muscle fibers
Endomysium
Surrounds individual muscle fibers

4. Structure of Skeletal Muscle:
Sarcolemma
Muscle cell membrane
Myofibrils
Threadlike strands
within muscle fibers
Actin (thin filament)
Troponin
Tropomyosin
Myosin (thick filament)

6. The Sarcomere
The sarcomere is a functional unit, of skeletal muscle.

8. The ‘Sliding Filament’ Theory of Muscular Contractions
Whenever we recruit muscles to cause movement, the following sequence of events occurs:
An electrical signal is sent along nerves from the central nervous system (CNS) to a neuromuscular junction at the target muscle.

9. The Neuromuscular Junction
Site where motor neuron meets the muscle fiber

10. Electrical nerve impulses become chemical
2) When an electrical nerve impulse reaches the axon, a neurotransmitter called Acetylcholine (Ach) is released.

11. Depolarization
3)Acetylcholine (Ach) triggers the muscle fiber to become permeable to sodium ions, which flow into the muscle from interstitial fluid, and cause the muscle to ‘depolarize’.

12. The Release of Calcium
4) A depolarized muscle fiber leads to the release of calcium ions (Ca++) from the sarcoplasmic reticulum, a.k.a. ‘Z-lines’.

14. Troponin & Tropomyosin
5)The thin filaments (actin), in a myofibril, have binding sites for the globular protein heads of the thick filaments (myosin). In a relaxed muscle, these binding sites are covered by the proteins, troponin and tropomyosin.
Calcium ions cause the troponin and tropomyosin to unwind, exposing the myosin binding sites on actin filaments.

15. Actin/Myosin Crossbridging
6)When the myosin binding sites are exposed, actin and myosin filaments bind, and the globular protein heads ‘cock’, pulling the actin filaments along.

16. Cross-Bridge Formation in Muscle Contraction

17. Muscular Contraction
7) Muscle shortening occurs due to the movement of the actin filament over the myosin filament because of a reduction in the distance between Z-lines in the sarcomere.

19. Energy for Muscle Contraction (ATP)
ATP is required for muscle contraction
It causes the protein heads on myosin to ‘cock’.
It is required to break the actomyosin bond.
Energy from the hydrolysis of ATP is used for active transport of calcium ions back into the sarcoplasmic reticulum.

20. Sources of ATP for Muscle Contraction

21. Motor Units
A motorunit is a single motorneuron & all the muscle fibers it innervates.
Eye muscles – 1:1 muscle/nerve ratio
Hamstrings – 300:1 muscle/nerve ratio

22. Clinical Physiology Rigor mortis Electrocution Parkinson’s Disease
Tetanus

23. The Sliding Filament Theory https://www. youtube. com/watch

24. The ‘All or None’ Principle

25. Optimal Muscle Length for a Maximal Strength Contraction

26. Muscle Fiber Types Fast Twitch fibers Slow Twitch fibers
Type IIb fibers
Fast-twitch fibers
Fast-glycolytic fibers
Type IIa fibers
Intermediate fibers
Fast-oxidative glycolytic fibers
Slow Twitch fibers
Type I fibers
Slow-twitch fibers
Slow-oxidative fibers

28. Comparison of Maximal Shortening Velocities Between Fiber Types

30. Fiber Types and Performance
Power athletes
Sprinters
Possess high percentage of fast fibers
Endurance athletes
Distance runners
Have high percentage of slow fibers
Others
Weight lifters and nonathletes
Have about 50% slow and 50% fast fibers

31. Alteration of Fiber Type by Training
Endurance and resistance training
Cannot change fast fibers to slow fibers
Can result in shift from Type IIb to IIa fibers
Toward more oxidative properties

32. Training-Induced Changes in Muscle Fiber Type

33. Getting Stronger Hypertrophy and Hyperplasia
Increase in size of muscle
Increase in number of motor units

34. Coordination
Intermuscular The ability to recruit the optimal balance of agonists, antagonists, synergists, and stabilizers to produce smooth, purposeful, and efficient movements
Intramuscular An untrained athlete can only recruit up to 60% of the motor units in a given muscle during maximal contraction, wheras a trained athlete can recruit up to 90%

35. Force Regulation in Muscle
Types and number of motor units recruited
More motor units = greater force
Fast motor units = greater force
Initial muscle length
“Ideal” length for force generation
The right balance of agonists, antagonists etc.

36. Proprioceptors 3) Pacinian corpuscles 1) Muscle spindles
Detect dynamic and static changes in muscle length
Stretch reflex
Stretch on muscle causes protective contraction
2) Golgi tendon organs (GTO)
Monitor tension developed in muscle
Prevents damage during excessive force generation
Stimulation results in protective relaxation of muscle
3) Pacinian corpuscles
Initiate protective contraction in response to excessive pressure and changes in temperature.

37. Muscle Spindle

38. Golgi Tendon Organ

39. Pacinian Corpuscles

40. Proprioceptive Neuromuscular Facilitation