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40 Cards in this Set
- Front
- Back
muscle fiber |
a bundle of myofibrils
a muscle fiber is a multinucleated muscle cell
muscle fiber = muscle cell |
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sarcolemma |
plasma membrane around a muscle fiber |
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T tubules (location) |
extend across the sarcolemma |
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sarcoplasmic reticulum (SR) [Facts] |
-specialized smooth ER |
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triad |
one T tubule between two cisternae |
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myofibrils |
bundle of myofilaments
Actin & Myosin |
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myosin |
thick filaments; golf-club shaped |
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actin |
thin filaments; look like beads on a string |
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actin and myosin are? |
proteins |
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two other important proteins in muscle? |
troponin and tropomyosin |
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troponin and tropomyosin |
-both are attached to actin |
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sarcomere |
-the contractile unit of a muscle |
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synapse |
place where a nerve and its target meet |
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NMJ |
a synapse consisting of a motor nerve meeting a muscle |
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synaptic knob |
at end of motor nerve; rests on motor end plate of the sarcolemma |
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synaptic cleft |
small space between the synaptic- knob & motor end plate |
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acetylcholine (ACh) |
a neurotransmitter released from synaptic vesicles of the synaptic knob motor end plate |
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acetylcholinesterase |
enzyme that destroys ACh, thus ending a muscle contraction
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Excitation Step 1 |
1) nerve signal arrives at synaptic knob |
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Excitation Step 2 |
2) Voltage-gated Ca+2 channels (in synaptic knob) open; Ca+2 enters knob |
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Excitation Step 3 |
3) acetylcholine is released, travels across synaptic cleft, binds to its receptors on the sarcolemma of the muscle fiber |
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Excitation Step 4 |
4) other ion channels in sarcolemma open, and ions move in and out of the sarcolemma
produces an electrical signal called the end plate potential (EPP) |
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Excitation Step 5 |
5) this EPP starts an action potential that travels through the sarcolemma |
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the connection between action potential in the sarcolemma, and activation of myosin |
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1) action potential spreads across sarcolemma, then down T tubules, then into sarcoplasm |
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Excitation-Contraction Coupling Step 2 |
2) sarcoplasmic reticulum releases calcium ion
calcium ion enters the cytosol |
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Excitation-Contraction Coupling Step 3 |
3) calcium ion binds to troponin on actin (troponin looks like little spheres) |
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Excitation-Contraction Coupling Step 4 |
4) tropomyosin twists to reveal the myosin binding sites of actin |
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Contraction Step 1 |
1) myosin head “cocks” |
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Contraction Step 2 |
2) cocked myosin binds to actin at myosin binding site |
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Contraction Step 3 |
3) power stroke |
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Contraction Step 4 |
4) recovery stroke |
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Contraction Step 5 |
5) final result: |
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1) nerve signal traveling to the NMJ stops |
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Relaxation Step 1 |
1) nerve signal traveling to the NMJ stops |
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Relaxation Step 2 |
2) ACh dissociates from its receptors and ACh-ase breaks down ACh |
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Relaxation Step 3 |
3) calcium ion is pumped back into the SR cisternae from the cytosol |
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Relaxation Step 4 |
4) calcium ions come off troponin and return to SR |
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Relaxation Step 5 |
5) tropomyosin moves back into place and binding sites are covered |
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Relaxation Step 6 |
6) muscle returns to its resting length |