3 major muscle types
- Cardiac muscle
- Smooth muscle
- Skeletal muscle
Muscle - Structure of skeletal muscle
- A whole skeletal muscle is made up of individual muscle fibres
- Each runs the entire length of the muscle
Muscle Fibre - Structure of skeletal muscle
- Muscle fibres run parallel to each other and are surrounded by connective tissues
- A muscle fibre is a single muscle cell
Muscle cells
Cells are multinucleated and have large numbers of mitochondria
Myofibrils - Structure of skeletal muscle
Along the length of a muscle fibre the cell is divided into discrete contractile elements called myofibrils
Myofibrils (side view) - Structure of skeletal muscle
- When viewed from side using a light microscope a myofibril shows a pattern of light and dark bands
- Gives muscles a striated pattern
What are skeletal muscles also called?
Striated muscle
Myofibrils (Cross section) - Structure of skeletal muscle
- When looking at cross section, you can see an organized cytoskeletal pattern of thick and thin filaments
- These are myosin and actin filaments
A band - myofibrils
- Dark bands
- Made up of stacked thick and thin filaments that are aligned parallel to each other
- Boarders are defined by the length of thick filaments
Why is the middle of A band slightly lighter?
The thin filaments do not reach this far from the ends
What is the lighter portion in A band called?
H zone
I band - myofibrils
- Light bands
- Made up of a portion of the thin filaments that do not extend into the A band
What is the vertical line in the middle of the I band called?
Z line
H zone - myofibrils
- Lighter portion of A band
- Contains proteins that hold thick filaments and myosin together in a stack
- Only contains heavy chains of myosin
M line - myofibrils
- Runs down the centre of the H zone
- It’s the proteins that hold the thick filaments together in a stack
Z line - myofibrils
- Vertical line in the middle of the I band
- The distance from one Z line to the next is called a sarcomere
Sacromere
Functional unit of skeletal muscle
Sacromere - size and growing
- Relaxed is about 2.5 um in width
- When muscles are growing they extend the length of the muscle fibre by adding new sarcomeres onto the ends
What does the area in A band where thick and thin filaments overlap contain?
- Cross-bridges
- They extend from the thick filaments and form when thin filaments bind
What is thick filaments composed of?
- The motor protein myosin
- Two dimers come together in a tail-to-tail formation and these stack up with other myosin molecules
- The heads stick out
Myosin
- Uses ATP to move along actin filaments
- Each molecule of myosin is a dimer of 2 subunits
What happens when two dimers come together?
- The tails wrap around each other
Two important sites on heads of myosin
- An actin binding site
- A myosin ATPase binding site
Thin filaments
- Made up of 3 proteins: actin, tropomyosin, and troponin
- Main structural component is two actin filaments
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Module 1: Section 1 + 256
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Module 1: Section 316
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Module 1: Section 413
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Module 1: Section 531
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Module 2: Section 120
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Module 2: Section 216
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Module 2: Section 332
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Module 2: Section 451
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Module 2: Section 511
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Module 4: Section 127
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Module 4: Section 235
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Module 4: Section 333
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Module 4: Section 426
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Module 4: Section 59
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Module 4: Section 628
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Module 5: Section 115
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Module 5: Section 234
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Module 5: Section 352
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Module 5: Section 47
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Module 5: Section 533
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Module 5: Section 67
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Module 6: Section 121
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Module 6: Section 223
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Module 6: Section 344
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Module 6: Section 428
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Module 6: Section 512
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Module 6: Section 613
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Module 6: Section 743
