exam qs

• Explain how the resting potential of -70mV is maintained in the sensory neurone when no pressure is applied (2)

  • Membrane more permeable to potassium ions and less permeable to sodium ions;
  • Sodium ions actively transported / pumped out and potassium ions in.
• The membrane potential of a neuron is the same whether medium or heavy pressure was applied at the finger tip. Explain why. (2)

  • Threshold has been reached;
  • Threshold or above causes maximal response / all or nothing principle.
• A myelinated axon conducts impulses faster than a non-myelinated axon. Explain this difference. (3)

  • In myelinated, nerve impulse jumps from node to node / saltatory conduction
  • In myelinated action potential / impulse does not travel along whole length
• Describe how the resting potential is established in an axon by the movement of ions across the membrane (2)

  • active transport of Na+ out of axon
  • diffusion of K+ out of axon
• Sodium and potassium ions can only cross the axon membrane through proteins. Explain why. (2)

  • can not pass through phospholipid bilayer
  • because water soluble / not lipid soluble / charged
• Only every other stimulus produced an action potential. Explain why (5)

  • refractory period
  • requires greater stimulation
  • K+ channels open
  • Na+ channels close
• When a neurone transmits a series of impulses, its rate of oxygen consumption increases. Explain why. (3)

  • more respiration
  • more energy / ATP supplied
  • for active transport of ions
• Explain how a resting potential is maintained in a neurone. (4)

  • membrane relatively impermeable / less permeable to Na+ / gated channels closed
  • Na+ pumped out
  • by sodium ion carrier
  • inside negative compared to outside