Action potential

• What is an action potential?

  A rapid depolarization of a neuronal membrane that propagates along the membrane.
• How long does an action potential typically last?

  Approximately 1-3 milliseconds.
• What are the main structures of a neuron?

  • Dendrites
  • Axon
  • Soma
  • Axon terminal

  
• What usually initiates an action potential in a neuron?

  An electrical stimulus that pushes the membrane potential beyond threshold.
• What is the resting membrane potential (Em) of a neuron?

  Approximately -70 mV.
• What happens during depolarization in an action potential?

  Na+ channels open, allowing Na+ to enter the cell.

  
• What is the significance of the threshold in action potential initiation?

  It is the Em where the permeability of Na+ exceeds that of K+.
• What are the key phases of an action potential?

  1. Rising Phase: Na+ influx causes depolarization.
  2. Overshoot: Em exceeds 0 m, the Em approaches the Em of Na+
  3. Falling Phase: Na+ channels inactivate, K+ exits.
  4. Undershoot: Em approaches EK, leading to hyperpolarization.
  5. Return to resting value.
• What occurs during the falling phase of an action potential?

  Voltage-gated Na+ channels inactivate and K+ channels open, causing repolarization.

  
• What is the difference between absolute and relative refractory periods?

  Absolute: no further AP can occur; Relative: a stronger stimulus can initiate an AP.
• What role does the myelin sheath play in action potential propagation?

  It increases the speed of action potential conduction.
• How does the diameter of an axon affect conduction velocity?

  A larger diameter results in faster conduction velocity.
• What effect does cooling tissue have on action potentials?

  It slows down action potentials.
• What is tetrodotoxin and its effect on sodium channels?

  Tetrodotoxin is a potent Na+ channel blocker found in pufferfish.
• What are some symptoms of tetrodotoxin poisoning?

  Symptoms include tingling, weakness, and respiratory distress.
• What are the therapeutic applications of ion channel interventions?

  • Blocking sodium channels can prevent pain and reduce cardiac arrhythmias.
  • Local/regional anesthetics block sodium channels to inhibit nerve conduction.
• What is the effect of scorpion toxin on sodium channels?

  It increases the probability of sodium channel opening and inhibits inactivation.
• What is the effect of potassium channel openers?

  They relax smooth muscle and have been investigated as vasodilators.
• How do chemical agents affect action potentials?

  Chemical agents can block ion channels, affecting conduction.