Action potentials

• What is an action potential in neurons?

  Voltage increase beyond resting potential
• What is the resting potential of a neuron?

  -70 millivolts
• What causes depolarization in a neuron?

  Increased permeability to sodium ions
• What happens when the action potential is generated at one position?

  It triggers the next node of Ranvier
• What maintains the resting potential in a neuron?

  Sodium-potassium pump and ion channels
• What is the threshold potential for generating an action potential?

  -55 millivolts
• What occurs when the threshold is reached?

  More voltage-gated sodium channels open
• What is the peak voltage of an action potential?

  +40 millivolts
• What happens to sodium channels at +40 millivolts?

  They close
• What causes repolarization in a neuron?

  Opening of potassium ion channels
• What is hyperpolarization?

  Voltage drops below resting potential
• What is the refractory period?

  Time when neuron cannot fire another action potential
• Why is the refractory period important?

  Prevents overlap of action potentials
• How does the refractory period affect impulse direction?

  Ensures action potential travels forwards only
• What does the all-or-nothing principle state?

  Action potential occurs fully or not at all
• What happens with larger stimuli?

  Higher frequency of action potentials occurs
• Why is it important for animals to respond to large stimuli?

  Prevents overwhelming the senses
• What is the role of sodium channels during the refractory period?

  They are recovering and cannot open
• What are the key stages of an action potential?

  1. Resting potential: -70 mV
  2. Depolarization: Sodium ions enter
  3. Threshold: -55 mV
  4. Peak: +40 mV
  5. Repolarization: Potassium ions exit
  6. Hyperpolarization: Below -70 mV
  7. Refractory period: Cannot fire again
• What are the implications of the all-or-nothing principle?

  • Action potential is either fully generated or not
  • All action potentials peak at +40 mV
  • Larger stimuli increase firing frequency, not amplitude
• What are the functions of the refractory period?

  • Ensures discrete impulses
  • Prevents backward propagation
  • Limits action potential frequency
• How does the Mexican wave analogy relate to action potentials?

  • Action potentials propagate like a wave
  • Each node of Ranvier triggers the next
  • Discrete events occur along the axon
• What are the three key factors affecting the speed of conductance in an axon?

  • Myelination of the axon
  • Diameter of the axon
  • Temperature
• What is the effect of myelination on action potential conduction?

  It results in saltatory conduction
• What are the myelin sheaths made of?

  Lipids
• What do Schwann cells do?

  They wrap around the axon to form myelin sheath
• What are the gaps between myelin sheaths called?

  Nodes of Ranvier
• How does saltatory conduction speed up action potential movement?

  It allows action potentials to jump between nodes
• What happens in an unmyelinated axon regarding action potentials?

  Every part must generate an action potential
• How does the diameter of the axon affect conductance speed?

  A wider diameter increases conductance speed
• Why does a wider axon diameter reduce resistance?

  It allows fewer ions to leak out
• What is the threshold potential for action potentials?

  -55 mV
• How does temperature affect the speed of conductance?

  Higher temperature increases speed up to a limit
• What role does facilitated diffusion play in action potential generation?

  It increases ion movement at higher temperatures
• How does temperature influence ATP production?

  Higher temperatures increase ATP production
• What is the relationship between respiration and active transport?

  Respiration generates ATP for active transport
• What is the optimum temperature for enzyme activity related to action potentials?

  Typically body temperature
• What are the factors affecting the speed of conductance along an axon?

  • Myelination: Saltatory conduction
  • Diameter: Wider = faster conductance
  • Temperature: Higher = faster conduction
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