The nerve impulse

• The nerve impulse is carried when there is a temporary reversal of charges across the fibre membrane
• Nerve impulses are self-propagating waves of electrical disturbance that travels along the cell-surface membrane of the neurone
• The outside of the axon has a positive potential in relation to the inside, which has a negative potential
• The resting potential is around -70mV and in this, the axon is said to be polarised
• What is the function of the sodium-potassium pump in resting potential?

  Pumps three sodium ions out and two potassium ions in
• What creates the electrochemical gradient in resting potential?

  More sodium ions in tissue fluid and more potassium ions in cytoplasm
• Why can't sodium ions easily diffuse back into the axon during resting potential?

  Most voltage-gated sodium ion channels are closed
• How do potassium ions move in relation to sodium ions during resting potential?

  Potassium ions diffuse out faster than sodium ions can diffuse in
• What effect does the outward diffusion of potassium ions have on the axon and tissue fluid?

  Tissue fluid becomes positively polarized, cytoplasm negatively polarized
• What happens to potassium ions due to the positive charge in the tissue fluid?

  Some potassium ions diffuse back into the cytoplasm
• When is equilibrium reached in the context of resting potential?

  When there is no net movement of ions
• If the stimulation of a neurone is above the threshold value, this causes an action potential
• The membrane potential during an action potential is about +40mV
• An action potential occurs in one section of the axon, this depolarises the next small section of the axon
• What initiates an action potential?

  Strong enough stimulus energy
• What happens when the threshold value is reached?

  Voltage-gated sodium channels open
• What occurs to sodium ions during an action potential?

  Sodium ions diffuse into the axon
• What is the effect of sodium ions diffusing into the axon?

  More voltage-gated sodium channels open
• What is depolarization in the context of action potential?

  Reversal in potential difference across the membrane
• What happens to voltage-gated sodium channels after action potential is established?

  They close
• What begins to open after the sodium channels close?

  Voltage-gated potassium ion channels
• What is the result of potassium ions diffusing out of the axon?

  Temporary overshoot and hyperpolarization
• What is hyperpolarization in the context of an action potential?

  Inside of the axon becomes more negative
• What happens to voltage-gated potassium channels after hyperpolarization?

  They close
• What role does the sodium-potassium pump play after an action potential?

  Moves 3 sodium ions in and 2 potassium ions out
• What is re-established by the sodium-potassium pump?

  Resting potential
• What does repolarization refer to in the context of an axon?

  Restoration of the axon's resting potential