1. Vertebrate Anatomy – Ch. 9 AP Biology – Ch. 49
Muscle Cell Function
Vertebrate Anatomy – Ch. 9
AP Biology – Ch. 49

2. Functions of Muscle Maintain body posture Stabilize joints
Provide mobility
Generate heat

3. Three Types of Muscle Smooth muscle Found in the organs Involuntary
Stomach, intestines, etc.
Involuntary
Unconscious control

4. Three Types of Muscle Cardiac Muscle Found in the heart only
Involuntary
Has it’s own specialized electrical system allowing the heart to contract and relax on its own – no stimulus from the nervous system required
A single cardiac muscle cell, if left without input, will contract rhythmically at a steady rate; if two cardiac muscle cells are in contact, whichever one contracts first will stimulate the other to contract, and so on.

5. Skeletal Muscle Associated with the bones Allows for movement
Appears Striated (banding pattern)
VOLUNTARY

6. Muscle cell structure Long, cylindrical cell
Produced by union of many embryonic cells
Leads to huge cells
Up to 12 inches long
10x larger in diameter than avg. cell
Diagram

7. Muscle cell structure Many nuclei in each fiber
Arranged just below the plasma membrane
Again, indicates fusion of many cells
Nuclei pushed to periphery to make more room for unified contracting fibers
Diagram

8. Muscle cell structure Plasma membrane – sarcolemma
Cytoplasm – sarcoplasm
Lots of stored glycogen
Oxygen binding protein called myoglobin
Like hemoglobin

9. Muscle fiber - close up
Each muscle fiber contains a large number of rod-like myofibrils that run in parallel fashion and extend the entire length of the cell.
Myofibrils are densely packed.

10. Muscle fiber – close up Myofibrils appear banded
Banding is due to two types of smaller fibers
Thick filaments
Thin filaments

11. Myofibrils – thick and thin filaments
Thick filament
Myosin
Thin filament
Actin

12. Thick filament structure
Myosin
Myosin heads
Myosin heads can move and “stick to” actin at certain locations on the actin fiber

13. Thin filament structure
Actin
Twisted strings of pearls
Possess binding sites
Locations where myosin heads can bind
These remain hidden when the muscle is NOT contracting
Troponin and Tropomyosin
Molecules associated with the actin filaments
Troponin
Calcium binding sites on actin filaments
Tropomyosin
“rope” molecule that covers and hides myosin binding sites

14. The Sarcomere Z-line – anchor points for actin filaments
Sarcomere – from z-line to z-line
The sarcomere is the unit of contraction.

15. Interaction of Thick and Thin filaments – muscle contraction
Myosin head bound to ATP
In low energy state
Energy from ATP cannot be released until ATP is broken into ADP and Pi

16. Interaction of Thick and Thin filaments – muscle contraction
Myosin head hydrolyzes (breaks down) ATP to ADP and Pi.
Myosin head moves to its high energy position.

17. Interaction of Thick and Thin filaments – muscle contraction
Myosin head binds to actin forming a cross bridge
This occurs as long as the myosin binding sites on the actin filaments have been uncovered
Remember these were hiddin by the tropomyosin molecule

18. Interaction of Thick and Thin filaments – muscle contraction
Once the myosin head binds to actin, it releases ADP and Pi
Once ADP and Pi are released, myosin head returns to Low Energy State
REMEMBER: It is still hooked to the actin
THIS SLIDES THE THIN FILAMENT

19. Interaction of Thick and Thin filaments – muscle contraction
A new ATP binds to the myosin head
This causes a shape change in the myosin head that releases the myosin head from the actin molecule

20. Another Diagram

21. How it looks…
Contraction of a sarcomere

22. But that’s not all…. Remember Where do these chemicals fit it in?
Tropomyosin
Troponin
Calcium
Where do these chemicals fit it in?
CONTROL of the muscle contraction

23. Control of muscle contraction
Tropomyosin covers myosin head binding sites on actin filaments
Troponin – calcium binding sites

24. Control of muscle contraction
Calcium binds to troponin
Troponin bound by Calcium moves tropomyosin
Reveals myosin head binding sites
Allows binding to occur

25. Where does Calcium come from and WHY?
Calcium is stored in the Sarcoplasmic reticulum (fancy ER)
Nerve impulse releases calcium from SR into sarcoplasm (cytoplasm
Nerve impulse travels across synapse to sarcolemma
Down T-tubules
To SR
When nerve impulse reaches SR, Calcium is released
Allows muscle contraction to occur, ONLY when nerve impulse has told it to do so.

26. Links to animations How Muscles Work Sarcomere shortening
Sliding Filament Theory (includes nerve stimulation)