ActionPotentialallornothing free science lessons

• What should you be able to describe by the end of the video on action potentials?

  The events taking place during the action potential and the All or Nothing principle
• What is the resting potential of a neuron?


  Approximately -65 mV
• What is the charge inside the axon membrane when a neuron is not transmitting an impulse?


  Negative compared to the outside
• What is the concentration of sodium ions inside and outside the axon?


  Higher concentration outside than inside
• What is the concentration of potassium ions inside and outside the axon?


  Higher concentration inside than outside
• What protein is found in the axon membrane that helps transport ions?


  The sodium-potassium pump
• How does the sodium-potassium pump function?


  It transports three sodium ions out and two potassium ions in using ATP
• What type of diffusion do sodium and potassium ions undergo through their channels?


  Facilitated diffusion down their concentration gradients
• Which ions diffuse more rapidly through their channels?

  Potassium ions
• What triggers the opening of voltage-gated ion channels?


  When the membrane potential reaches a certain value
• What happens to the membrane potential when sodium ions diffuse into the axon?


  The inside of the axon becomes less negative
• What is the maximum potential reached during an action potential?


  Approximately +40 mV
• What occurs when the membrane potential reaches +40 mV?


  Voltage-gated sodium channels close and voltage-gated potassium channels open
• What is repolarization in the context of an action potential?


  The process of the inside of the axon switching from positive to negative
• What is hyperpolarization?


  When the inside of the axon becomes more negative than the resting potential
• What restores the resting potential after an action potential?


  The sodium-potassium pump
• What is the All or Nothing principle in action potentials?


  An action potential is generated only if the stimulus exceeds a certain threshold
• What happens if the stimulus is below the threshold?


  No action potential is generated
• How does the size of the action potential relate to the strength of the stimulus?

  The size of the action potential does not depend on the strength of the stimulus
• What does a stronger stimulus produce in terms of action potentials?


  A greater frequency of action potentials
• What does a very strong stimulus produce?


  A high frequency of action potentials
• What are the key events during an action potential?


  1. Resting potential at -65 mV
  2. Stimulus detected, sodium channels open
  3. Sodium ions diffuse in, causing depolarization
  4. Membrane potential reaches +40 mV
  5. Sodium channels close, potassium channels open
  6. Potassium ions diffuse out, causing repolarization
  7. Hyperpolarization occurs
  8. Resting potential restored by sodium-potassium pump
• What are the two parts of the All or Nothing principle?


  1. Action potential generated only if stimulus exceeds threshold
  2. Size of action potential remains constant regardless of stimulus strength