Physiology of Muscle contraction

Physiology of Muscle contraction

1. PHYSIOLOGY OF PHYSIOLOGY OF
MUSCLE MUSCLE
CONTRACTIONCONTRACTION

2. Types of muscle tissueTypes of muscle tissue
Striated – skeletal musclesStriated – skeletal muscles
Striated – cardiac muscleStriated – cardiac muscle
SmoothSmooth

3. Physiological properties of muscles Physiological properties of muscles
ExcitabilityExcitability
ConductivityConductivity
ContractilityContractility
Automaticity (smooth & cardiac Automaticity (smooth & cardiac
muscles)muscles)

4. Physical properties of musclesPhysical properties of muscles
ElasticityElasticity (for striated) (for striated)
PlasticityPlasticity (for smooth) (for smooth)

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6. Skeletal muscles functionsSkeletal muscles functions
1.1.Maintain body posture Maintain body posture
2.2.Body movement in spaceBody movement in space
3.3.Body parts movement with regards to Body parts movement with regards to
each othereach other
4.4.Enable thermogenesisEnable thermogenesis

7. SarcomereSarcomere is a structural & is a structural &
functional unit of skeletal functional unit of skeletal
musclemuscle
Is a part of muscle fiber between 2 Z-linesIs a part of muscle fiber between 2 Z-lines
Contains transverse tubuli (sarcoplasmic Contains transverse tubuli (sarcoplasmic
reticulum), myozin & actin fibers located in reticulum), myozin & actin fibers located in
orderorder

9. Relaxed
sarcomere
Sarcomere in the
state of contraction

10. Contractile elementsContractile elements
АctinАctin –– a double helical filament with –– a double helical filament with
tropomyosin tropomyosin & & troponin troponin attachedattached
МyosinМyosin – asymmetric hexamer with a – asymmetric hexamer with a
molecular mass 460 kDa. Myosin has a molecular mass 460 kDa. Myosin has a
fibrous tail made of 2 intertwined helices.fibrous tail made of 2 intertwined helices.
Each helix has a globularEach helix has a globular head portion, head portion,
which possesseswhich possesses АТP-аse activity, а АТP-аse activity, а
flexible segmentflexible segment connects head to the tail connects head to the tail

11. Motor unit structureMotor unit structure

12. MOTOR UNITMOTOR UNIT
Consists of motor neuron & a group of Consists of motor neuron & a group of
muscle fibers, which are supplied by axon muscle fibers, which are supplied by axon
of this motor neuronof this motor neuron
The number of muscle fibers in one motor The number of muscle fibers in one motor
unit depends on the function, which is unit depends on the function, which is
performed by this muscle ( from 10 tо performed by this muscle ( from 10 tо
30 000 fibers)30 000 fibers)

13. ADEQUATE STIMULIADEQUATE STIMULI
Nervous impulseNervous impulse is the only adequate is the only adequate
stimulus for skeletal muscle contractionstimulus for skeletal muscle contraction

14. NEURO-MUSCULAR SYNAPSENEURO-MUSCULAR SYNAPSE
Contact between motor neuron axon & Contact between motor neuron axon &
muscle fiber membrane:muscle fiber membrane:
Axon ending (pre-synaptic membrane)Axon ending (pre-synaptic membrane)
Motor endplate (postsynaptic Motor endplate (postsynaptic
membrane)membrane)
Synaptic cleftSynaptic cleft

15. AP
AP
AP
EPP
EPP
EPP
EPP
Ach

16. Аch
AP
Са
++
Са++
Аch
Аch-receptor
AP
Na
+
Na+
EPP
Cholinesterase
Na+
Na+
Chemical gated channels
Electrical gated channel

17. STAGES OF SYNAPTIC STAGES OF SYNAPTIC
TRANSMISSIONTRANSMISSION
1. Axon stimulation and
excitation of presynaptic
membrane.
2. Ca 2+ entry
3. Synaptic vesicles reach presy-
naptic membrane and rupture
4. Synaptic transmitter (Ach)
is released
5. Combination of Ach and the
receptor
6. Excitation of postsynaptic
membrane

18. Mechanism of neuro-muscular Mechanism of neuro-muscular
synapse worksynapse work
1.1.Discharge of motor neuron & AP Discharge of motor neuron & AP
spreading to axon endingspreading to axon ending
2.2.Opening of calcium voltage gated Opening of calcium voltage gated
channelschannels
3.3.Calcium entryCalcium entry
4.4.Acetylcholine release at motor endplateAcetylcholine release at motor endplate
5.5.Binding of acetylcholine to nicotinic Binding of acetylcholine to nicotinic
acetylcholine receptorsacetylcholine receptors

19. 5.5.Opening of sodium chemically gated Opening of sodium chemically gated
channels at endplatechannels at endplate
6.6.Increased sodium conductance in Increased sodium conductance in
endplate membraneendplate membrane
7.7.Generation of endplate potential (EPP)Generation of endplate potential (EPP)
8.8.Generation of action potential in muscle Generation of action potential in muscle
fibers (due to opening of voltage gated fibers (due to opening of voltage gated
sodium channels)sodium channels)

20. Cross-bridgesCross-bridges

21. Electro-chemical interactionElectro-chemical interaction
Inward spread of depolarization along T Inward spread of depolarization along T
tubulestubules
Charge movement of the slow calcium Charge movement of the slow calcium
voltage channel (dihydropyridine receptor) of voltage channel (dihydropyridine receptor) of
the transverse tubular membrane the transverse tubular membrane
Opening of calcium release channel Opening of calcium release channel
(ryanodine receptor) in sarcoplasmic (ryanodine receptor) in sarcoplasmic
reticulumreticulum
Calcium concentration in sarcoplasm Calcium concentration in sarcoplasm
increases 100 timesincreases 100 times

22. Са++ Са++Са++
SPR
triade
myosin
actin
Ζ Ζ
dehydropyridin ryanodin

23. Without AP calcium influx Without AP calcium influx
into cytoplasm is impossible!!into cytoplasm is impossible!!

24. Electro-mechanical couplingElectro-mechanical coupling
Calcium binds troponinCalcium binds troponin
Tropomyosin uncovers myosin binding Tropomyosin uncovers myosin binding
sites of actinsites of actin
Myosin heads get bound to these active Myosin heads get bound to these active
sites to form cross-bridgessites to form cross-bridges

25. The sliding filament cross-bridge The sliding filament cross-bridge
model model
Thin actin filaments slide along thick Thin actin filaments slide along thick
myosin ones due to cross-bridges myosin ones due to cross-bridges
formation formation
As a result sarcomere & muscle fiber As a result sarcomere & muscle fiber
length decreaseslength decreases

26. Chemo-mechanical interactionChemo-mechanical interaction
Myosin heads bend, allowing actin filaments Myosin heads bend, allowing actin filaments
to slide along myosin onesto slide along myosin ones
Sliding goes smoothly because myosin heads Sliding goes smoothly because myosin heads
get attached to the subsequent active centers get attached to the subsequent active centers
of actin.of actin.
The higher is cytoplasm calcium The higher is cytoplasm calcium
concentration, the more bridges can be concentration, the more bridges can be
formed and the stronger is contractionformed and the stronger is contraction

27. Mechanism of muscle relaxationMechanism of muscle relaxation
Calcium is pumped back into sarcoplasmic Calcium is pumped back into sarcoplasmic
reticulumreticulum
Calcium is released from troponinCalcium is released from troponin
Cessation of interaction between actin & Cessation of interaction between actin &
myosinmyosin

28. Energy expenditure during muscle Energy expenditure during muscle
contractioncontraction
Na/K pump workNa/K pump work
Sliding of myosin heads along actin filamentsSliding of myosin heads along actin filaments
Calcium pump workCalcium pump work
Most energy is spent for relaxationMost energy is spent for relaxation

29. Distribution of neuro-muscular Distribution of neuro-muscular
synapses in sceletal musclessynapses in sceletal muscles

30. «All or none» law«All or none» law
Single muscle fiber obeys this law:Single muscle fiber obeys this law:
Subthreshold irritation doesn’t cause Subthreshold irritation doesn’t cause
contraction, аnd threshold irritation causes contraction, аnd threshold irritation causes
maximal contraction, i.e. the amplitude of maximal contraction, i.e. the amplitude of
muscle contraction doesn’t depend upon muscle contraction doesn’t depend upon
the force of irritationthe force of irritation

31. «All or none» law«All or none» law
The whole muscle doesn’t obey this law The whole muscle doesn’t obey this law
because it consists of many motor units because it consists of many motor units
which all have different thresholds of which all have different thresholds of
depolarizationdepolarization

32. Types of contractionTypes of contraction
Isometric – tension increase without length Isometric – tension increase without length
increaseincrease
Isotonic – length decrease at the same Isotonic – length decrease at the same
tensiontension
Mixed - auxotonicMixed - auxotonic

33. Types of muscle contractionTypes of muscle contraction
TwitchTwitch
ТеtanusТеtanus
Тоnus Тоnus

34. Types of muscle irritation in Types of muscle irritation in
experimentexperiment
Indirect irritationIndirect irritation – impulse is applied to – impulse is applied to
the nervous ending of motor neuronthe nervous ending of motor neuron
Direct irritationDirect irritation– impulse is applied to the – impulse is applied to the
muscle directlymuscle directly

35. Single muscle contraction (twitch)Single muscle contraction (twitch)
CONTRACTION
PHASE
RELAXATION
PHASE
LATENT
PERIOD
TIME, 0,01 SEC

36. 1
2
3
4
5
Е
0
Е
кр
0
+30
А
В

37. TETANUSTETANUS
Strong & long lasting contraction in Strong & long lasting contraction in
response to series of irritations.response to series of irritations.
Develops due to summation of single Develops due to summation of single
muscle contractions as the result of muscle contractions as the result of
calcium concentration increasecalcium concentration increase

38. Summation of single contractionsSummation of single contractions
SUMMATION
TIME, 0,01 SEC
SINGLE
CONTRACTIONS

39. ““Toothed” tetanusToothed” tetanus
Develops when each subsequent Develops when each subsequent
stimulus gets into the period of muscle stimulus gets into the period of muscle
relaxationrelaxation so that so that
interval between two impulses is less than interval between two impulses is less than
the duration of single muscle contraction, the duration of single muscle contraction,
but longer than contraction phasebut longer than contraction phase

41. TOOTHED TETANUS

42. Smooth tetanusSmooth tetanus
Each subsequent stimulus is getting Each subsequent stimulus is getting
into contraction phase, i.e.into contraction phase, i.e. interval interval
between two subsequent stimuli is shorter between two subsequent stimuli is shorter
than contraction phase duration, but than contraction phase duration, but
longer than refractory period .longer than refractory period .

44. SMOOTH TETANUS

45. OPTIMUMOPTIMUM
Is frequency of irritation at which tetanus Is frequency of irritation at which tetanus
reaches its maximum amplitudereaches its maximum amplitude
Each subsequent stimulus gets into the Each subsequent stimulus gets into the
supernormal period, i.e. right after AP is oversupernormal period, i.e. right after AP is over
This leads to constant high concentration of This leads to constant high concentration of
calcium in cytoplasm (calcium pump has no calcium in cytoplasm (calcium pump has no
time to switch on)time to switch on)

46. PESSIMUMPESSIMUM
Is frequency of irritation at which there is no Is frequency of irritation at which there is no
summation of contractionssummation of contractions
Each subsequent stimulus gets into the Each subsequent stimulus gets into the
refractory period (during the AP refractory period (during the AP
development)development)
All the sodium channels stay inactivated & All the sodium channels stay inactivated &
new AP development is impossiblenew AP development is impossible

47. OPTIMUM
PESSIMUM
OPTIMUM
SMOOTH
TETANUS

48. 1
2
3
4
5
Е
0
Е
кр
0
+30
А
В

49. Muscle fibers classificationMuscle fibers classification
Each muscle fiber has just Each muscle fiber has just
one synapseone synapse

50. SlowSlow phasic fibers of oxydative phasic fibers of oxydative
typetype
rich in myoglobin & mitohondria rich in myoglobin & mitohondria
Red in colour Red in colour
Fatigue develops slowlyFatigue develops slowly
Very many fibers in one motor unit (up to Very many fibers in one motor unit (up to
30 000)30 000)
Compose muscles which maintain posture Compose muscles which maintain posture

51. FastFast phasic fibers of phasic fibers of oxydativeoxydative
typetype
Rich in mitohondriaRich in mitohondria
Able to synthesise АТP due to oxydative Able to synthesise АТP due to oxydative
phosphorylationphosphorylation
Perform fast contractionsPerform fast contractions
Develop fatigue slowlyDevelop fatigue slowly
Fewer fibers in one motor unit than in slow Fewer fibers in one motor unit than in slow
onesones

52. FastFast phasic with phasic with glucolitic glucolitic type of type of
oxydationoxydation
Few mitohondriaFew mitohondria
АТP is formed due to glucolisisАТP is formed due to glucolisis
No myoglobin (white in colour)No myoglobin (white in colour)
Quickly contract & develop fatigue quicklyQuickly contract & develop fatigue quickly
Little number of fibers in one motor unitLittle number of fibers in one motor unit

53. Tonic fibersTonic fibers
Motor neuron axon forms many synapsesMotor neuron axon forms many synapses
Slowly contract & slowly relaxSlowly contract & slowly relax
Low АТP-ase activity of myosinLow АТP-ase activity of myosin
Form external muscles of the eyeForm external muscles of the eye

54. Muscle strengthMuscle strength
Depends on muscle thickness & Depends on muscle thickness &
physiological cross sectionphysiological cross section

55. Muscle workMuscle work
Is energy spent on body movement with a Is energy spent on body movement with a
certain force to a certain distanse:certain force to a certain distanse:
A = F x SA = F x S
If F=0, then А=0If F=0, then А=0
If S=0, then А=0If S=0, then А=0
Maximum work is performed at middle Maximum work is performed at middle
loadsloads
Amax= Fmed x SmaxAmax= Fmed x Smax

56. FATIGUEFATIGUE
A process of temporal decrease of muscle A process of temporal decrease of muscle
workability.workability.
Develops due to the decrease of ATP in Develops due to the decrease of ATP in
muscle fiber or mediator in neuro-muscle fiber or mediator in neuro-
muscular synapsemuscular synapse
In neuro-muscular preparation fatigue In neuro-muscular preparation fatigue
develops first of all in the synapse!develops first of all in the synapse!

57. nerve
muscle
stimulator stimulator
Muscle at fatigue
Muscle at fatigue
Non-fatigued
muscle

58. Orbelli- Genetzynsky phenomenonOrbelli- Genetzynsky phenomenon
Myograme
myogramme

59. FATIGUE IN THE BODYFATIGUE IN THE BODY
Fatigue first develops in the nervous centers Fatigue first develops in the nervous centers
– it’s a defense mechanism– it’s a defense mechanism
Muscles still have reserve of energyMuscles still have reserve of energy
proof – Sechenov’s experiments with active proof – Sechenov’s experiments with active
restrest

60. ErgographyErgography
A method of muscle work registrationA method of muscle work registration
Ergogramme curve can show signs of Ergogramme curve can show signs of
fatigue:fatigue:
Decreased magnitude of contractionDecreased magnitude of contraction
Prolonged phase of relaxationProlonged phase of relaxation
Decreased frequency of contractionDecreased frequency of contraction

61. SMOOTH MUSCLESSMOOTH MUSCLES

62. Single unit (visceral) smooth Single unit (visceral) smooth
musclesmuscles
All internal organsAll internal organs
Lots of necsuses Lots of necsuses
(coloured red)(coloured red)
Few nervous endings Few nervous endings
(coloured green)(coloured green)

63. Multiunit smooth musclesMultiunit smooth muscles
Ciliary muscle & Ciliary muscle &
musculus dilator pupilimusculus dilator pupili
Have high density of Have high density of
neuro-muscular neuro-muscular
synapses (coloured synapses (coloured
green)green)

64. Smooth muscles nervous supplySmooth muscles nervous supply
Muscle cells
with nervous
supply
Muscle cells
without nervous
supply

65. Peculiarities of smooth musclesPeculiarities of smooth muscles
Spindle like cells lie close to each otherSpindle like cells lie close to each other
Tight contacts between the cells – Tight contacts between the cells –
necsusesnecsuses
Actin & myosin don’t have regular locationActin & myosin don’t have regular location
Sarcoplasmic reticulum is developed less Sarcoplasmic reticulum is developed less
than in skeletal musclesthan in skeletal muscles

66. Nervous supply of smooth muscles Nervous supply of smooth muscles
Supplied by sympathetic & Supplied by sympathetic &
parasympathetic nervesparasympathetic nerves
No synapses, nervous endings form No synapses, nervous endings form
varicosesvaricoses
Mediator is released into the intracellular Mediator is released into the intracellular
fluidfluid
After one cell is excited AP spreads to After one cell is excited AP spreads to
other cells along necsuses (electrical other cells along necsuses (electrical
synapses)synapses)
The whole muscle contracts The whole muscle contracts
simultaneously (functional syncytium)simultaneously (functional syncytium)

67. Adequate stimuliAdequate stimuli
Nervous impulseNervous impulse
Mechanical stretchingMechanical stretching
Chemical substances (hormones) Chemical substances (hormones)

68. Peculiarities of excitabilityPeculiarities of excitability
Threshold of depolarization is lower than Threshold of depolarization is lower than
in striated musclesin striated muscles
Membrane is more permeable for sodium, Membrane is more permeable for sodium,
that is why MP is lower (-50, -60 mV)that is why MP is lower (-50, -60 mV)
AP amplitude is lower and its duration is AP amplitude is lower and its duration is
longerlonger
Depolarization opens up voltage-gated Depolarization opens up voltage-gated
calcium channels, calcium influx slows calcium channels, calcium influx slows
down repolarizationdown repolarization

69. AUTOMATICITYAUTOMATICITY
The ability of cell to generate AP without The ability of cell to generate AP without
any external stimuliany external stimuli
Smooth muscle cell at the state of rest is Smooth muscle cell at the state of rest is
permeable to sodium, which slowly permeable to sodium, which slowly
depolarizes the cell to the critical level & depolarizes the cell to the critical level &
AP developsAP develops

70. Electrochemical coupling in smooth Electrochemical coupling in smooth
musclesmuscles
AP opens up calcium channels, calcium AP opens up calcium channels, calcium
enters the cell.enters the cell.
Ligands activate phospholipaze С on the Ligands activate phospholipaze С on the
cell membrane, activation of inositol-3P & cell membrane, activation of inositol-3P &
diacylglicerol.diacylglicerol.
inositol-3P releases calcium from EPS, inositol-3P releases calcium from EPS,
which starts contractionwhich starts contraction

71. Mechanism of calcium level Mechanism of calcium level
regulation in smooth musclesregulation in smooth muscles
in EPS
channel
pump
inositol
-3P
receptor
ligand

72. Peculiarities of smooth muscles Peculiarities of smooth muscles
contractioncontraction
In cytoplasm calcium binds with calmoduline In cytoplasm calcium binds with calmoduline
& activates proteinkinase . & activates proteinkinase .
Proteinkinase phosphorilates myosin head. Proteinkinase phosphorilates myosin head.
Actin-myosin cross-bridges are formedActin-myosin cross-bridges are formed
Drop of calcium concentration in myoplasm Drop of calcium concentration in myoplasm
causes dephosphorilation of myosin head & causes dephosphorilation of myosin head &
cross-bridges are destroyed cross-bridges are destroyed
Muscle relaxesMuscle relaxes