1. Skeletal Muscular Contraction
Physiology
Skeletal Muscular Contraction

2. http://www. youtube. com/watch

4. Connective Tissue Endomysium Perimysium Epimysium
Surrounds each muscle fiber (cell)
Attaches to Z-lines in each sarcomere
Perimysium
Surrounds bundles (fascicles) of muscle fibers
Attaches to endomysium
Epimysium
Attaches to the Perimysium
Continuous with tendon

6. Sarcomere Repeating Patterns within the myofibrils Myofibrils
Proteins within the myofibers
Myosin
Actin

7. Muscle Anatomy Sarcolemma Myofibrils Muscle fiber cell membrane
Highly organized bundles of contractile and elastic proteins
Carries out the work of contraction

8. Contain 6 types of protein:
Myofibrils = Contractile Organelles of Myofiber
Contain 6 types of protein:
Actin
Myosin
Tropomyosin
Troponin
Titin
Nebulin
Contractile
Regulatory
Accessory

10. Titin and Nebulin Titin: biggest protein known (25,000 aa); elastic!
Stabilizes position of contractile filaments
Return to relaxed location
Nebulin: inelastic giant protein
Alignment of A & M

11. Changes in a Sarcomere during Contraction

14. Myosin Myo- muscle Motor protein of the myofibril Thick filament
Attaches to the M-line
Heads point towards Z-lines
Myosin heads are clustered at the ends of the filament
Myosin tails are bundled together

16. Actin Thin Filament Globular protein Attached to Z-lines G-Actin
Has binding site for myosin head
Forms a Cross-Bridge when myosin binds to G-actin
Five Actin proteins surround the myosin in 3-D pattern

19. Actin filament Binding sites Strong Weak binding binding
Myosin head group
S2 link
Stretching of the link generates tension
Myosin filament

21. Equal and opposite force
Why do thin filaments move?
Net force
Net force
Equal and opposite force
on thick filament

22. Actin
Tropomyosin
Protein that covers over the myosin binding site on G-Actin
Myosin head can’t bind to G-Actin, muscle relaxes
If the binding site on G-Actin is uncovered by removing Tropomyosin then myosin and actin bind, muscle contracts

23. Actin Troponin C Protein attached to Tropomyosin
When Troponin C changes shape it pulls on Tropomyosin
Calcium binding to Troponin C causes this protein to change shape
Tropomyosin moves and uncovers the binding site on G-Actin, so Actin and Myosin can bind
Contraction

24. Regulation of Contraction by Troponin and Tropomyosin
Tropomyosin blocks myosin binding site (weak binding possible but no powerstroke)
Troponin controls position of tropomyosin and has Ca2+ binding site
Ca2+ present: binding of A & M
Ca2+ absent: relaxation

26. Muscle Anatomy Sarcoplasmic Reticulum Terminal Cisternae
Modified endoplasmic reticulum
Wraps around each myofibril like a piece of lace
Stores Calcium
Terminal Cisternae
Longitudinal tubules
Transverse tubules (T-tubules)
Triad-two flanking terminal cisternae and one t-tubule
T-tubules are continuous with cell membrane

27. Role of calcium Troponin and Tropomyosin bind to actin
Troponin complex
Troponin and Tropomyosin bind to actin
block the actin – myosin binding sites
Troponin is a calcium binding protein

28. When Troponin binds calcium it moves Tropomyosin away from the actin-myosin binding site

29. Where does Calcium come from?
Intracellular storage called Sarcoplasmic Reticulum
Surround each myofibril of the whole muscle
Contains high concentration of calcium
Transverse Tubules connects plasma membrane to deep inside muscle

30. T-Tubules
Rapidly moves action potentials that originate at the neuromuscular junction on the cell surface

31. Membrane depolarization or APs carried deep into the muscle by T-tubules
Motor nerve
T-tubule +
Neurotransmitter receptors SR

32. My SR
Ryanodine Receptor
Dihydropyridine receptor
T-tubule SR
myoplasm

33. _ + _ + + + + _ _ + _ + _ + _ + _ + + Ca++ Ca++ Ca++ SR Ca++ pump
Myoplasm
(intracellular) _ _ _ _ + _ + + + _ + + _ _ + _ +
T-tubule
(extracellular) _ + _ + _ + +

35. Sliding Filament Theory
When myosin binds to the binding site on G-actin muscular contraction occurs.
The more myosin that bind to G-actin the greater the force of contraction
Calcium must be present

38. Sliding Filament Theory
Cross Bridge
Myosin in the High Energy Configuration binds to G-Actin
ADP + Pi are bonded to the myosin head when the cross bridge forms
Power Stroke
When the myosin and actin bind the myosin head changes shape
Myosin pulls the actin and pulls on the Z-line
Sarcomere shortens
ADP+Pi no longer binds to myosin head

39. Sliding Filament Theory
ATP binds to the myosin head
Myosin changes to its Low Energy Confirmation
In the Low Energy Confirmation Myosin breaks its bonds with Actin
Rigor Mortis
Lack of ATP
Build up of Lactic Acid

40. Sliding Filament Theory
ATPase
ATP is hydrolyzed to ADP + Pi
ATPase is on the myosin head
Myosin changes shape back to its High Energy Confirmation

41. Sliding Filament Theory
Some Myosin heads detach from Actin while other heads continue to keep their attachments
No slipping of the Z-lines
Contraction is held in place

42. What if we don’t have this?
ATP X
Actin + myosin  Actomyosin complex
Rigor mortis

44. Events at Neuromuscular Junction
Converts a chemical signal from a somatic motor neuron into an electrical signal in the muscle fiber

45. Events at Neuromuscular Junction
Acetylcholine (Ach) is released from the somatic motor neuron
Ach initiates an action potential in the muscle fiber
The muscle action potential triggers calcium release from the sarcoplasmic reticulum
Calcium combines with troponin C and initiates contractions

46. Events at Neuromuscular Junction
Ach binds to cholinergic receptors on the motor end plate
Na+ channels open
Na+ influx exceeds K+ efflux across the membrane
End-Plate Potential (EPP)
EPP reaches threshold and initiates a muscle action potential

47. Events at Neuromuscular Junction
Action Potentials move down the membrane
K+ builds up in the t-tubules
Depolarization occurs
Calcium gates on the SR opens
Calcium diffuses into the cytoplasm of the cell

48. Excitation-Contraction Coupling
The process where muscle action potentials initiate calcium signals that in turn activates a contraction-relaxation cycle

49. Initiation of Contraction
Excitation-Contraction Coupling explains how you get from AP in axon to contraction in sarcomere
ACh released from somatic motor neuron at the Motor End Plate
AP in sarcolemma and T-Tubules
Ca2+ release from sarcoplasmic reticulum
Ca2+ binds to troponin

50.  Net Na+ entry creates EPSP  AP to T-tubules
Details of E/C Coupling
Nicotinic cholinergic receptors on motor end plate = Na+ /K+ channels
 Net Na+ entry creates EPSP
 AP to T-tubules
 DHP (dihydropyridine) receptors in T-tubules sense depolarization

51. Nicotinic Cholinergic Receptors

52. DHP (dihydropyridine) receptors open Ca2+ channels in t-tubules
Intracytosolic [Ca2+] 
Contraction
Ca2+ re-uptake into SR
Relaxation

53. Excitation-Contraction Coupling
High cytosolic Calcium levels binds to Troponin C
Tropomyosin moves to the “on” position and contraction occurs
Calcium-ATPase pumps Calcium back into the SR
The more myosin heads that binds to actin to stronger the force of contraction

54. Summary of events
Synaptic Depolarization of the plasma membrane is carried into the muscle by T-Tubules
Conformational change of dihydropyridine receptor directly opens the ryanodine receptor calcium channel
Calcium flows into myoplasm where it binds troponin
Calcium pumped back into SR

56. Neuromuscular Junction
The more terminal boutons to attach to myofibers the greater the control of the muscle.
Recruitment
The greater the number of terminal boutons attached to myofibers there is more fine control of the muscle

58. Excitation-Contraction Coupling
Twitch
A single contraction-relaxation cycle in a skeletal muscle fiber
A single action potential in a muscle fiber
Latent Period
Between the muscle action potential
Time required for excitation-contraction coupling to take place

59. Is There Truth In Advertising?
Is the banana company telling the truth when they claim that bananas being high in Potassium actually prevents or relieves muscle cramps?
If so, how does this increase in Potassium relieve muscle cramps?
If not, why not and how do we actually relieve muscle cramps?

61. Muscle Contraction and ATP Supply
Phosphocreatine
Backup energy source
Quick energy used up in approx. 15 minutes

62. Causes of Fatigue Central Fatigue Subjective feelings of tiredness
Arises in the CNS
Psychological fatigue precedes physiological fatigue in the muscles
Low pH may cause fatigue

63. Muscle Fiber Classification
Oxidative only
Oxidative or glycolytic
Muscle Fiber Classification

64. Muscle Adaptation to Exercise
Endurance training:
More & bigger mitochondria
More enzymes for aerobic respiration
More myoglobin
no hypertrophy
Resistance training:
More actin & myosin proteins & more sarcomeres
More myofibrils
muscle hypertrophy

65. Causes of Fatigue Peripheral Fatigue
Arises between the neuromuscular junction and the contractile elements of the muscle
Ach depletion, neuromuscular junction receptor loss
Myasthenia Gravis

66. Skeletal Muscle Types Fast-twitch muscle fibers (type II) White Fibers
Low Myoglobin
Develops tension two to three times faster than slow-twitch fibers
Splits ATP more rapidly to complete contraction faster
Fatigues quickly

67. Skeletal Muscle Types Slow-twitch Muscle Fibers (Type I) Red
High Myoglobin levels
Slow to Fatigue

68. Contractions Isometric Contractions Isotonic Contractions
Creates force without movement
Isotonic Contractions
Moves loads