Neuronal Potentials and Action Potential

Types of Neuronal Potentials

• Resting Potential:
  • Maintained at -70 millivolts
  • Due to ion permeability differences and the sodium-potassium pump
  • Important ions:
    • Negatively charged proteins
    • Negatively charged chloride
    • Positively charged sodium
    • Positively charged potassium

Ion Channels

• Leaky Channels: Always open, allow ion flux.
• Voltage-Gated Channels: Open at specific voltages.

Ion Movement and Resting Potential

• Potassium:
  • Higher concentration inside the cell
  • Moves out due to chemical gradient
  • Stays due to electrical gradient
• Sodium:
  • Higher concentration outside the cell
  • Moves in due to electrochemical gradient
• Sodium-Potassium Pump:
  • Uses ATP to transfer 3 sodium out and 2 potassium in
  • Maintains resting potential

Graded Potentials

• Vary in size based on stimulus intensity
• Occur due to EPSPs (excitatory) and IPSPs (inhibitory)
• Dendrites receive signals; cell body integrates them
• Action potential triggered at -55 millivolts at axon hillock

Action Potentials

• All-or-Nothing: Not size-variable like graded potentials
• Initiation: Voltage-gated sodium channels open at -55 millivolts
• Depolarization: Sodium rushes in, voltage rises to +30 millivolts
• Repolarization: Potassium rushes out, brings voltage down
• Hyperpolarization: Temporary overshoot below -70 millivolts
• Restoration: Sodium-potassium pump restores resting potential
• Propagation:
  • Sodium diffusion causes adjacent depolarization
  • Refractory Period:
    • Absolute: No new action potential possible
    • Relative: Only strong stimulus can trigger a new action potential

Myelin and Propagation Speed

• Myelin Sheaths: Insulate axons, prevent ion leakage
  • Made by oligodendrocytes (CNS) and Schwann cells (PNS)
  • Enable saltatory conduction between nodes of Ranvier
• Axon Diameter: Larger diameter = faster transmission

Synaptic Transmission

• Terminal Buttons:
  • Depolarization opens voltage-gated calcium channels
  • Calcium influx triggers neurotransmitter release
• Neurotransmitter Action:
  • Cross synaptic cleft
  • Bind to post-synaptic receptors
  • Cause EPSPs or IPSPs, potentially triggering action potentials

• Additional Notes:
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