1. Muscle Physiology Dr Taha Sadig Ahmed 5/13/20151

2. 2 The Muscle Action Potential RMP = -90 mV ( same as in nerves ) RMP = -90 mV ( same as in nerves ) Duration of AP = 1-5 ms ( longer duration than nerve AP, which is usually about 1 ms ). Duration of AP = 1-5 ms ( longer duration than nerve AP, which is usually about 1 ms ). Conduction velocity (CV) in a muscle fiber ( cell) = 3-5 m/s ( slower than big nerves ). Conduction velocity (CV) in a muscle fiber ( cell) = 3-5 m/s ( slower than big nerves ). RMP= - 90 mV Amplitude إرتفاعه

3. 3 5/13/2015 Muscle Contraction There are 4 important muscle proteins : A/ two contractile proteins that slide upon each other during contraction : (1) Actin (2) Myosin B/ And two regulatory proteins : Troponin  excitatory to contraction Troponin  excitatory to contraction Tropomyosin  inhibitory to contraction Tropomyosin  inhibitory to contraction

4. 4 5/13/2015 The EPP at the motor end- plate triggers a muscle AP The EPP at the motor end- plate triggers a muscle AP The muscle AP spreads down inside the muscle through the Transverse Tubules The muscle AP spreads down inside the muscle through the Transverse Tubules ( T-tubules ) ( T-tubules ) to reach the Sarcoplasmic Reticulum (SR). to reach the Sarcoplasmic Reticulum (SR).  In the SR the muscle AP opens calcium channels ( in the walls of the SR)  calcium passively flows out ( in the walls of the SR)  calcium passively flows out ( by concentration gradient ) of the SR into muscle cytoplasm  Ca++ combines with Troponin  Tropomyosin gets moved  Myosin heads combines with Actin

5. Skeletal muscle is made up of many cylinderical,multinucleated muscle cells ( fibers) The fibers ( cell ) can be 10 to 100 ten micron in diameter, and can be hundreds of centimeters long. & is covered by a cell-membrane called Sarcolemma. 5/13/20155 One muscle cell ( fiber ) Sarcolemma

6. 5/13/20156 Each cell contains between few hundreds to a few thousands Myofibrils The myofibril is striated cand has dark bands  called A-bands) and light bands  called I-bands (I-bands). Each Myofibril Is made of 3000 Actin filaments And 1500 Myosin filaments.

7. Each myofibril is striated is striated It is made of Sarcomeres And each sarcomere is limited by two Z-lines (Z disk) The sarcomere contains both the  (i) A band and (i) A band and (ii) I band light (ii) I band light 5/13/20157 Z-lines

8. 8 5/13/2015

9. 9  A-bands consist mainly of thick filament  Myosin  The ends of Actin are Z-Discs(Z-lines ).  I-bands consist of thin filament  Actin.  The part of the Myofibril lying between two Z-discs is called Sarcomere.

10. 10 5/13/2015 Sliding Filament Mechanism When contraction takes place Actin & Myosin slide upon each other, & the distance between two z-discs decreases This is called Sliding Filament Mechanism. Z-line come closer together I-band gets smaller, and eventually may disappear A-band does not become smaller or bigger

11. 11 5/13/2015

12. 12 5/13/2015 Actin is made of globular protein callled G-actin G-actins are attached together to form F-actin strand ( chain ) Each two strands wind together to form double helix called Actin Filament Tropomyosin lies in the groove between the F-actin strands to cover the active sites on actin that bind the head of myosin Troponin is attached to tropomyosin and to actin Two Actin filaments Groove between the 2 F-actin strands Tropomyosin covering active sites on Actin

13. 13 5/13/2015 Attachment of Ca++ to Troponin initiates tcontraction and when is activated by Ca++ it will move the Tropomyosin away from the active sites on actinn & expose them for Myosin. > then myosin head will immediately attach to these actin active sites > when the myosin head attaches to actin it forms a “ cross- bridge” Attachment of Ca++ to Troponin initiates tcontraction and when is activated by Ca++ it will move the Tropomyosin away from the active sites on actinn & expose them for Myosin. > then myosin head will immediately attach to these actin active sites > when the myosin head attaches to actin it forms a “ cross- bridge”

14. Each 200 myosin molecules aggregate to form a myosin filament, from the sides of which project myosin heads in all directions. Myosin

15. Myosin Each Myosin molecule has (1) Head ( 2 ) Tail (3) Hinge (joint ) Furthermore, each myosin head contains  Furthermore, each myosin head contains  (1) ATP-binding site, & (2) ATP-ase enzyme.

16. 16 5/13/2015

17. 17 5/13/2015 Sliding Filaments

18. Attachment of Myosin to Actin activates the enzyme ATPase in the Myosin Head  Attachment of Myosin to Actin activates the enzyme ATPase in the Myosin Head  ATPase breaks down ATP releasing energy ATPase breaks down ATP releasing energy This energy is used in the “ Power Stroke ” to move the myosin head  leading to pulling & dragging of actin  This energy is used in the “ Power Stroke ” to move the myosin head  leading to pulling & dragging of actin   sliding of actin on myosin  sliding of actin on myosin The “ power stroke ” means tilting of the Myosin cross-bridge and dragging ( pulling ) of actin filament The “ power stroke ” means tilting of the Myosin cross-bridge and dragging ( pulling ) of actin filament 18 5/13/2015

19. 19 5/13/2015 A new ATP binding to Myosin head is essential for detachment of Myosin from Actin Then, on order to release the head of Myosin from Actin, a new ATP is needed to come and combine with the head of Myosin. Then, on order to release the head of Myosin from Actin, a new ATP is needed to come and combine with the head of Myosin.

20. The Cross-Bridge Cycle The Cross-Bridge Cycle 20 5/13/2015

21. Q: What is Rigor Mortis ? Q: What is Rigor Mortis ? Q: ATP is neede for 3 things : what are they ? Q: ATP is neede for 3 things : what are they ? Q: Is muscle relaxation a passive or active process ? Why ? Q: Is muscle relaxation a passive or active process ? Why ? Q: What happens to A-band and I-band during contraction ? Q: What happens to A-band and I-band during contraction ? Q: Ca++ is needed in nerve & muscle : when and where ? Q: Ca++ is needed in nerve & muscle : when and where ?

22. 22 5/13/2015 Why do we need the ATP in contraction ? ATP is needed for 3 things : ATP is needed for 3 things : (1) Power stroke. (1) Power stroke. (2) Detachment of myosin from actin active sites. (2) Detachment of myosin from actin active sites. (3) Pumping C++ back into the Sarcoplasmic reticulum (3) Pumping C++ back into the Sarcoplasmic reticulum