Resting and Action Potentials

• what is resting potential?

  the potential difference or voltage across a membrane while the neurone is at rest, its is about -60mV inside the cell compared to the outside
• what is the generator potential?

  a small depolarisation caused by sodium ions entering the cell which has to be a big enough depolarisation to create an action potential
• what is the threshold potential?

  the potential difference across the membrane of about -50mV, if depolarisation doesn’t reach threshold no action potential is created, if threshold reached then action potential created
• what is an action potential?

  the depolarisation of a cell membrane so that the inside is more positive than the outside, with a potential difference across the membrane of +40mV, this can be transmitted along the axon
• What is the role of sensory receptors in the cell membrane?

  They generate nerve impulses in response to changes in the environment.
• How does sodium (Na) diffuse in the context of sensory receptors?

  Na diffuses into the cell down its concentration gradient.
• What happens when the stimulus is strong enough in sensory receptors?

  Sodium channels open, allowing Na to enter the cell.
• What is the significance of reaching the threshold potential in sensory receptors?

  It leads to the generation of an action potential.
• What is the term for the electrical signal generated by sensory receptors?

  Action potential.
• What is the relationship between the concentration gradient and the movement of Na in sensory receptors?

  Na moves into the cell due to the concentration gradient.
• If sodium channels open, what is the immediate effect on the cell's membrane potential?

  The membrane potential becomes more positive, leading to depolarization.
• How does the opening of sodium channels relate to the generation of nerve impulses?

  Opening sodium channels allows Na to enter, which depolarizes the membrane and generates a nerve impulse.
• What are the steps involved in the generation of an action potential in sensory receptors?

  1. Stimulus causes changes in the environment.
  2. Na diffuses into the cell down its concentration gradient.
  3. If the stimulus is strong enough, sodium channels open.
  4. Membrane potential reaches threshold.
  5. Action potential is generated.
• What is the state of a cell when it is polarised?

  The inside of a cell is negatively charged with respect to the outside.
• What does maintaining a resting potential mean?

  It means maintaining a difference in charge across the cell membrane.
• What does depolarisation refer to in a cell?

  It refers to a loss of polarisation across the membrane.
• What causes depolarisation in a cell?

  It occurs when sodium ions enter the cell.
• How does depolarisation affect the charge inside the cell?

  It makes the inside less negative with respect to the outside.
• What is repolarisation in the context of a cell membrane?

  It is when the membrane returns to a polarised state.
• What process restores the electrochemical gradient during repolarisation?

  Moving K+ ions out of the membrane.
• What effect does repolarisation have on the outside of the membrane?

  It makes the outside more positive with respect to the inside of the membrane.
• What are the stages of an action potential in a neuron?

  1. Polarisation: Inside is negatively charged.
  2. Depolarisation: Sodium ions enter, reducing negativity.
  3. Repolarisation: Potassium ions exit, restoring polarity.
• What is the function of the sodium-potassium pump?

  It returns ions to their original positions to maintain resting potential.
• What is the importance of maintaining resting potential in neurons?

  It is crucial for the generation of action potentials and proper neuronal function.
• What maintains the resting potential in a neurone?

  The Na+/K+ pump
• How does the Na+/K+ active transport pump function in maintaining resting potential?

  It uses ATP to transport ions across the membrane
• What is the difference between gated channels in the generator region and those further along the neurone?

  • Gated channels in the generator region open through different mechanisms.
  • They respond quickly to high pressure from a current.
  • Channels further along involve the dispersion of potassium.
  • They allow quicker entry and dispersion of ions.
• What is the overshoot voltage in a hyperpolarized neurone?

  • 70 mV or -80 mV
• Why is it harder to stimulate another action potential in a hyperpolarized cell membrane?

  Because a greater stimulus is needed to overcome the hyperpolarization
• What threshold voltage is required to initiate an action potential?

  • 60 mV
• What is the action potential peak voltage?

  +40 mV
• What are the voltage levels associated with different states of a neurone?

  • -70 mV: Resting potential
  • -80 mV: Hyperpolarization
  • -60 mV: Threshold
  • -50 mV: Increased potential
  • +40 mV: Action potential