Cell Physiolgy By: Dr. Foadoddini Department of Physiology & - - PowerPoint PPT Presentation

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Cell Physiolgy By: Dr. Foadoddini Department of Physiology & - - PowerPoint PPT Presentation

Jan 07, 2023 404 likes •834 views

Chapt. 6,7,8 Cell Physiolgy By: Dr. Foadoddini Department of Physiology & Pharmacology Birjand University of Medical Sciences Dr. Foadoddini Contraction of Skeletal Muscle Dr. Foadoddini Dr. Foadoddini Dr. Foadoddini T

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Cell Physiolgy

By: Dr. Foadoddini

Department of Physiology & Pharmacology Birjand 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: Sliding Ion Pumps Sources of Energy:

  • 1. Phosphocreatine
  • 2. glycolysis" of glycogen
  • 3. Oxidatjve 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 asynchronously Thus providing smooth contraction Frequency summation: tetanization The Staircase Effect (Treppe) muscle tone Muscle Fatigue

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Coactivation

  • f Antagonit

Msuscles Remodeling of Muscle to Match Function Hypertrophy the number of actin and myosin filaments in each muscle fiber Atrophy Hyperplasia actual number of muscle fibers Effects of Muscle Denervation Atrophy, degenerative changes, replaced by fibrous and fatty tissue, contracture

Adjustment of Muscle Length

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Excitation of Skeletal Muscle: Neuromuscular Transmission and Excitation-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 muscle Heart

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Calsequestrin

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Excitation‐Contraction Coupling

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Smooth Muscle

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Syncytial smooth muscle Visceral 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 another many 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-bridges

So, 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 kinase Ca Cm 4

ATP ADP

Mg2+

myosin phosphatase P

myosin light chain kinase (MLCK) Ca Cm 4 4 Ca2+ Calmodulin, Cm

contraction

relaxation

regulatory light chain

Cross-bridge activation in smooth muscle

Ca2+-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 Substances Ach NE Type of receptor

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slow wave rhythm pacemaker waves

Excitation of Visceral Smooth Muscle by Muscle Stretch

voltage-gated calcium channels self-excitatory

Excitation or Inhibition Hormones and Local Tissue Factor

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