M1-C2-:L17 --> Striated Muscle Cells
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- What is the functional unit of a myofibril?
- A sarcomere
- What is in H bands?
- Only thick MYOSIN
- What is in A bands?
- The OVERLAPPING region of myosin and actin
- What is in the I bands?
- Thin ACTIN filaments
- Where do the actin filaments anchor themselves?
- Z line
- During contraction, what happens to I band?
- Shortens
- During contraction, what happens to A band?
- No change
- During contraction, what happens to H band?
- Shortens until it disappears. (Thus the ends of actin filaments will overlap.)
- During contraction, what happens to Z disc?
- Comes closer together
- How many actin filaments per myosin chain?
- Six
- How many myosin motors per actin filament
- Three
- What is a myofilament composed of?
- The sarcomere is composed of only actin and myosin
- What chains are myosin composed of in skeletal muscle?
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4 LIGHT chains
2 HEAVY chains
0 - A thick filament has how many myosin molecules?
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200 myosin molecules
(Thus 400 motor heads) - What are the three proteins of actin filaments?
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Actin
Troponin
Tropomyosin - Describe the backbone of actin.
- Double stranded F-actin molecule wrapped in helix
- F-actin composed of what?
- Individual G-actin molecules
- What are the subunits of Troponin?
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Troponin T
Troponin I
Troponin C - What is involved in binding of Calcium during muscle contraction?
- Troponin C
- Describe the location of tropomyosin.
- Located in the groove of F-actin helix
- Describe the function of tropomyosin.
- Believed to block "active" sites on actin, thus prohibiting actin/myosin interaction
- Effects of Calcium on actin/myosin interaction.
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1. Calcium will bind to Troponin C.
2. Tropomyosin will move deeper into groove exposing active sites
3. This allows myosin heads to interact with actin active sites. ("Walk along" theory) - Describe the "walk along" theory of muscle contraction.
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1. Multiple myosin heads will contact single acting filament.
2. During contraction, some myosin heads will remain attached, holding the actin in place.
3. Others will release, straighten out to original position, and attach again for power stroke.
4. Repeat attach, ratchet, release all in concert over and over again. - Describe the mechanism of myosin head movement.
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1. ATP bound to head at rest
2. ATP hydrolyzed (ADP and Pi) changing conformation of myosin head.
3. Binding of myosin head to actin is what releases ADP and Pi.
4. Release of ADP and Pi will cause power stroke.
5. ATP will attach for release and "cocked" conformation. - What are t-tubules (transverse tubules)?
- Deep invaginations of plasma membrane in muscle cells
- Define motor unit.
- A muscle fiber innervated by a nerve
- What is the resting potential and why is it that number?
-
-90 mv
Because less [K] inside and more [Na] outside. - Describe actions of Action Potential in muscle contraction.
-
AP travels down sarcolemma (via Na pumps).
AP moves into T-tubules (via Na pumps)
T-tubules are close to sarcoplasmic reticulum which has Calcium channels on it.
Depolarization will cause the release of Calcium. - How many muscle fibers are innvervated by how many nerves?
- 98% of muscle fibers ar innvervated by 1 nerve located in the middle
- T/F - Nerve fibers penetrate muscle fibers.
- False - Separation via synaptic cleft.
- What is calsequestrin?
- Protein involved in sequestering Calcium for cessation of muscle contraction.
- What is a synaptic trough?
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Muscle fiber invagination at motor end plate - What is a subneural cleft?
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Smaller folds in synaptic trough. - Describe the actions of the Acetylcholine receptor.
- Binds acetylcholine, opens it (by increasing pore), and lets Na+ in.
- Describe the two methods of terminating muscle stimulation?
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1. Acetylcholinesterase (Primary)
2. Diffusion of acetylcholine from neuromuscular junction. - What are the general drugs X 3 that affect neuromuscular transmission?
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1. ACh antagonists (blockers)
2. ACh agonists (copy-cat compounds)
3. ACh inhibitors (similar to ACh agonists) - Name two types of ACh antagonists (blockers).
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1. Atropine
2. Curariform drugs - Name two types of ACh agonists (copy-cat compounds)
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1. Methacholine
2. Carbachol - Describe the effects of ACh inhibitors (also ACh agonists)
- Increases the length of time that the ACh molecule is present in the neuromuscular junction.
- What are some types of ACh inhibitors?
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1. Diisopropyl fluorophosphate
2. Neostigmine
3. Physostigmine