Cell Physiolgy By: Dr. Foadoddini Department of Physiology & Pharmacology Birjand University of Medical Sciences

Transcription

1 Chapt. 6,7,8 Cell Physiolgy By: Department of Physiology & Pharmacology Birjand University of Medical Sciences ١

2 Contraction of Skeletal Muscle ٢

3 ٣

4 ٤

5 T tubule ٥

6 Sliding Filament Mechanism ٦

7 ٧

8 ٨

9 ٩

10 ١٠

11 ١١

12 ١٢

13 active tension ١٣

14 Tension N Length ١٤

15 ١٥

16 Energy for: Sliding Ion Pumps Sources of Energy: 1. Phosphocreatine 2. glycolysis" of glycogen 3. Oxidative metabolism Efficiency of Muscle Contraction: ٢۵% Max at a moderate velocity ١٦

17 muscle twitch: a single, sudden contraction lasting for a fraction of a second. Latency 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. ١٧

18 Fast Versus Slow Muscle Fibers Motor unit: All the muscle fibers innervated by a single nerve fiber. ١٨

19 Force Summation: Multiple fiber summation : (size principle) are driven asynchronously Thus providing smooth contraction Frequency summation: tetanization ١٩ The Staircase Effect (Treppe) muscle tone Muscle Fatigue

20 Coactivation of 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 Adjustment of Muscle Length ٢٠ Effects of Muscle Denervation Atrophy, degenerative changes, replaced by fibrous and fatty tissue, contracture

21 Excitation of Skeletal Muscle: Neuromuscular Transmission and Excitation-Contraction Coupling ٢١

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23 ٢٣

24 End- plate potential ٢٤

25 Ca K ٢٥

26 Type of drugs: ٢٦

27 Curar Botulinum ٢٧

28 In Frog muscle Heart ٢٨

29 Calsequestrin ٢٩

30 Excitation Contraction Coupling ٣٠

31 Smooth Muscle ٣١

32 Depolar. Without action potenential but junctional pot.. Control mainly by nerve signals mass of hundreds to thousands of smooth muscle fibers that contract together as a single unit. adherent to one another many gap junctions Syncytial smooth muscle Visceral smooth muscle By non-nervous stimuli ciliary muscle, iris muscle of the eye, piloerector muscles that cause erection of the hairs gut, bile ducts, ureters, uterus, many blood vessels. ٣٢

33 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 ٣٣

34 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 "Latch Mechanism for Prolonge Holding of Contraction of Smooth Muscle Stress- relaxation as the activation of the enzymes decreases, the cycling frequency decreases, allows the myosin heads to remain attached ٣٤

35 Cross-bridge activation in smooth muscle Ca 2+ -stimulated myosin phosphorylation 4 Ca 2+ Calmodulin, Cm Ca Cm 4 Ca Cm 4 myosin light chain kinase (MLCK) myosin light chain kinase regulatory light chain ATP Mg 2+ ADP P relaxation contraction ٣٥ P myosin phosphatase

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37 ٣٧

38 Smooth muscle can maintain force with reduced energy expenditure Smooth muscle has the ability to maintain force development even when a high [Ca 2+ ] 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. [Ca 2+ ] force velocity & crossbridge phosphorylation ٣٨ stimulation

39 diffuse junctions contact junctions Excitatory and Inhibitory Transmitter Substances Ach NE Type of receptor ٣٩

40 slow wave rhythm pacemaker waves self-excitatory voltage-gated calcium channels Excitation of Visceral Smooth Muscle by Muscle Stretch ٤٠ Excitation or Inhibition Hormones and Local Tissue Factor

41 ٤١