Lecture 03, 4

• What are the two types of electrical signalling in nerve cells?

  Graded potentials and action potentials

  
• What is depolarisation in terms of membrane potential?

  Change to a more positive membrane potential

  
• What is repolarisation?

  Return to resting membrane potential after depolarisation

  
• What is hyperpolarisation?

  Change to a more negative membrane potential

  
• What effect does hyperpolarisation have on a neuron?

  Makes it less excitable
• How does the size of the stimulus affect graded potentials?

  Bigger stimulus results in bigger change
• What are the characteristics of graded potentials in a neuron?

  • Can be hyperpolarising or depolarising
  • Vary with stimulus strength
  • Can summate
  • Alter neuron sensitivity

  
• What stimulates graded potentials?

  Neurotransmitters, mechanical, and thermal forces
• Do all ligand-gated ion channels produce depolarising graded potentials?

  No, it depends on ion flow
• Where do graded potentials mainly occur in neurons?

  Dendrites or cell body
• What is the axon hillock's role in action potentials?

  Site of initiation of action potential

  
• What does it mean that graded potentials are decremental?

  They weaken as they move away from origin
• What are the two types of summation for graded potentials?

  • Temporal summation: Same stimulus, repeated quickly
  • Spatial summation: Different stimuli, applied simultaneously
• What triggers action potentials?

  Graded potentials, drugs, and neurotransmitters
• What is the nature of action potentials?

  Rapid large depolarisation for communication
• What are the three phases of action potentials?

  Depolarisation, repolarisation, after-hyperpolarisation

  
• What happens during the depolarisation phase of an action potential?

  Sodium channels open, Na+ rushes into cell

  
• What are the two gating mechanisms of voltage-gated sodium channels?

  Activation gate and inactivation gate

  
• What is the summary of membrane permeability during resting potential and action potential?

  • Resting potential: K+ channels open, K+ > Na+
  • Action potential: Na+ and K+ permeability changes, Na+ > K+
• What occurs during the repolarisation phase of an action potential?

  Potassium ions rush out of neuron
• What is the role of potassium channels during hyperpolarisation?

  They stay open longer than sodium channels
• What is tetrodotoxin (TTX) and its effect?

  Neurotoxin that blocks sodium channels
• What is the effect of tetraethylammonium (TEA)?

  Blocks voltage-gated potassium channels
• What are the key differences between graded potentials and action potentials?

  • Graded potentials: Local, variable, can summate
  • Action potentials: All-or-nothing, propagate without loss
• What is the all-or-nothing principle in action potentials?

  Threshold stimuli elicit action potentials

  
• What are the two types of refractory periods?

  Absolute and relative refractory periods

  
• What occurs during the absolute refractory period?

  No action potential possible due to inactivation

  
• What is the consequence of the relative refractory period?

  Action potential possible with stronger stimulus

  
• How do refractory periods affect action potential frequency?

  Limits frequency of action potentials generated

  
• What is frequency coding in relation to stimulus intensity?

  Stronger stimulus increases action potential frequency
• What influences the propagation velocity of action potentials?

  Axon diameter and myelination

  
• What is saltatory conduction?

  Action potential jumps between nodes of Ranvier

  
• What are the characteristics of conduction velocities in neurons?

  • Fast conduction: 100 m/s
  • Slow conduction: 0.5 m/s
  • Influenced by axon diameter and resistance
• What are the key points summarising action potentials?

  • All-or-nothing principle
  • Refractory periods encode firing frequency
  • Saltatory conduction allows rapid transmission

  
• What is the resting potential of a cell?

  Unequal distribution of ions across membrane

  
• What is the role of ion channels and pumps in membrane potential?

  Move ions across a membrane
• What forces act on ions moving across a membrane?

  Concentration and electrical gradients
• What is the upstroke of an action potential primarily due to?

  Inflow of Na+ ions
• What is the role of refractory periods in action potentials?

  Prevent immediate re-excitation of neuron

  
• What are the properties of action potentials?

  Rapid, large depolarisation, all-or-nothing