Skeletal muscle action potential Membrane potential (mV) Cardiac contractile cell action potential Cardiac autorhythmic cell action potential Absolute refractory period Relative refractory period Depolarization (Na$^+$ enters) +30 -Action potential Repolarization (K$^+$ leaves) 2 1 mV Stimulus Stimulus After- hyperpolarization (undershoot) Threshold Resting membrane potential 3 Time (ms) -90 Absolute refractory period 100 Time (msec) 40 20 0 1 2 -20 Relative refractory period Voltage (mV) -40 200 300 -60 -80 -100 How long does 1 AP take? What is RMP? What ion flows in in phase 1? What ion flows out in phase 2? How long does 1 AP take? What is RMP? What ion flows in in phase 1? What ion flows in in phase 2? What ion flows out in phase 3? 0 100 200 300 400 500 Time (msec) How long does 1 AP take? What is RMP? Tricky, there is none. What do we have instead? What ion flows in in phase 1? What ion flows in in phase 2?
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- One action potential (AP) takes approximately 1-3 milliseconds. - The resting membrane potential (RMP) is approximately -70 mV. - In phase 1 (depolarization), sodium ions (Na+) flow into the cell. - In phase 2 (repolarization), potassium ions (K+) Show more…
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The contractile cardiac muscle action potential is: 1- unique due to its extended hyperpolarized state 2- similar to autorhythmic cardiac muscle action potentials 3- similar to skeletal muscle action potentials 4- unique due to its voltage-gated Cl- channels 5- unique due to its extended plateau phase
Adi S.
A) Starting with the action potential in the motor neuron, list in order the steps associated with excitation-contraction (EC) coupling – i.e. list the steps between depolarization of the neuromuscular junction and the binding of actin and myosin. Be specific. 1. Action potential is generated in the motor neuron. 2. The action potential travels down the motor neuron and reaches the neuromuscular junction. 3. Depolarization of the neuromuscular junction occurs. 4. Calcium channels on the T-tubules open. 5. Calcium ions enter the cytoplasm of the muscle fiber. 6. Calcium ions bind to troponin. 7. Troponin undergoes a conformational change. 8. Tropomyosin moves away from the binding site on actin. 9. Myosin heads bind to actin, forming cross-bridges. 10. Myosin ATPase hydrolyzes ATP, providing energy for the power stroke. 11. Myosin heads undergo a power stroke, pulling the actin filament towards the center of the sarcomere. 12. ATP binds to myosin, causing detachment from actin. 13. The cycle repeats as long as calcium ions are present and ATP is available. 1 b) Using the information from the previous part, tell where and how each of the following would affect EC coupling: a). Blocking calcium channels on T-tubules - This would prevent calcium ions from entering the cytoplasm of the muscle fiber, inhibiting EC coupling. b). Blocking calcium binding to troponin - This would prevent the conformational change of troponin, resulting in tropomyosin remaining in its blocking position and inhibiting the binding of actin and myosin. c). Inhibiting the active transport for calcium into the SR - This would decrease the concentration of calcium ions in the SR, reducing the availability of calcium for EC coupling. d). Inhibiting myosin ATPase - This would prevent the hydrolysis of ATP by myosin, impairing the power stroke and muscle contraction. e). "Turning off" genes in skeletal muscle that code for tropomyosin - This would result in the absence of tropomyosin, allowing actin and myosin to bind continuously without regulation, leading to uncontrolled muscle contraction.
Madhur L.
Q: The action potential that occurs in the sarcolemma of a skeletal muscle fiber propagates in a single direction and does not reverse itself. What property most ensures one-way propagation? Slow calcium channel opening during peak depolarization Rapid opening of sodium channels The sodium channel refractory period Potassium repolarization Q: When starting from rest, a progressive increase in the frequency of action potentials in the somatic motor neuron does all of the following, EXCEPT: Causes an increase in the concentration of calcium within the sarcoplasmic reticulum. Causes greater force production Leads to an increasing frequency of action potentials in the sarcolemma Increases the percentage of myosin that will cycle on actin.
Md.Daniyal A.
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