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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