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Dr. Foadoddini ١ Cell Physiolgy By: Dr. Foadoddini Department of Physiology & Pharmacology Birjand University of Medical Sciences Chapt. 6,7,8
Dr. Foadoddini١
Cell PhysiolgyBy: Dr. FoadoddiniDepartment of Physiology & PharmacologyBirjand University of Medical Sciences
Chapt. 6,7,8
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Contraction of Skeletal Muscle
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T‐
tubule
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Sliding Filament Mechanism
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active tension
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Tension
Length
N
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Energy for:SlidingIon Pumps
Sources of Energy:1. Phosphocreatine2. glycolysis" of glycogen3. Oxidative metabolism
Efficiency of Muscle Contraction:٢۵%Max at a moderate velocity
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muscle twitch:a single, sudden contraction lasting for a fraction of a second.
The characteristics of isotonic
contraction depend on the load and the
inertia of the load.However, the isometric system records strictly changes in force of muscle
contraction itself. Therefore, the isometric system is most often used when comparing the functional characteristics of different muscle types.
Latency
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Fast Versus Slow Muscle Fibers
Motor unit:All the muscle fibers innervated by a single
nerve fiber .
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Force Summation:Multiple fiber summation : (size principle)
are driven asynchronouslyThus providing smooth contraction
Frequency summation: tetanization
The Staircase Effect (Treppe)muscle tone
Muscle Fatigue
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Coactivation
of Antagonit
Msuscles
Remodeling of Muscle to Match FunctionHypertrophy the number of actin
and myosin filaments in each muscle
fiberAtrophyHyperplasia actual number of muscle fibers
Effects of Muscle DenervationAtrophy, degenerative changes, replaced by fibrous and fatty tissue, contracture
Adjustment of Muscle Length
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Excitation of Skeletal Muscle:Neuromuscular Transmission andExcitation-Contraction Coupling
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End- plate potential
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Ca
K
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Type of drugs:
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Curar
Botulinum
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In Frog muscleHeart
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Calsequestrin
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Excitation‐Contraction Coupling
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Smooth Muscle
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Syncytial
smooth muscleVisceral smooth muscle
gut, bile ducts, ureters, uterus, many blood vessels.
mass of hundreds to thousands of smooth muscle fibers that contract together as a single unit.adherent to one anothermany gap junctions
ciliary
muscle , iris muscle of the eye, piloerector
muscles that cause erection of the hairs
Control mainly by nerve signals By non-nervous stimuli
Depolar. Without action potenential
but junctional pot..
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dense bodies
A/M= 5 to 10/1 Vs, 2/1 in skletal
"side polar" cross-bridgesSo, contract as much as 80 per cent of their length
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Stress- relaxation
"Latch“ Mechanism for Prolonge Holding of Contraction of Smooth Muscle
Tonic contraction, sometimes lasting hours or even days
Slow Cycling of the Myosin Cross-Bridges far less ATPase
activity
Less Energy Ryequired
to Sustained Contraction
Slowness Of Onset Contraction and Relaxation
Force of Muscle Contraction
as the activation of the enzymes decreases, the cycling frequency decreases, allows the myosin heads to remain attached
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P
myosin light chain kinaseCa Cm4
ATP ADPMg2+
myosinphosphataseP
myosin light chain kinase (MLCK)Ca Cm4
4 Ca2+
Calmodulin, Cm
contractionrelaxation
regulatory light chain
Cross-bridge activation in smooth muscleCa2+-stimulated myosin phosphorylation
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Smooth muscle can maintain force with reduced energy expenditure
stimulation
force
[Ca2+]
velocity &crossbridge phosphorylation
Smooth muscle has the ability to maintain force development even when a high [Ca2+] and hence cross-bridge turnover is not maintained.
Maintained force development, but with reduced velocity of movement, confers a clear physiological advantage to smooth muscle and is absent from striated muscle.
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diffuse junctions contact junctions
Excitatory and Inhibitory Transmitter SubstancesAchNE
Type of receptor
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slow wave rhythmpacemaker waves
Excitation of Visceral Smooth Muscleby Muscle Stretch
voltage-gated calciumchannels
self-excitatory
Excitation or Inhibition Hormones and Local Tissue Factor
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