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Muscle Cell Function

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Three Types of Muscle. Cardiac Muscle. Found in the heart only. Involuntary ... like myofibrils that run in parallel fashion and extend the entire length of the ... – PowerPoint PPT presentation

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Title: Muscle Cell Function


1
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
  • Stomach, intestines, etc.
  • Involuntary
  • Unconscious control

4
Three Types of Muscle
  • Cardiac Muscle
  • Found in the heart only
  • Involuntary
  • Has its 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 thats not all.
  • Remember
  • 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)
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