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Understanding Neurons and Action Potentials

Nov 18, 2024

Neurons and Action Potentials

Structure of Neurons

  • Dendrites: Branch-like structures that receive signals from other neurons via neurotransmitters.
  • Soma (Cell Body): Contains the neuron's main organelles like the nucleus.
  • Axon: Transmits electrical signals, wrapped in myelin.

Communication in Neurons

  • Neurotransmitters: Chemicals that transmit signals across a synapse to other neurons.
  • Action Potentials: Electrical signals that travel along the axon at speeds up to 100 meters per second.

Those dendrites receive signals from other neurons via neurotransmitters. which, when they bind to receptors on the dendrite, act as a chemical signal.

That binding opens ion channels that allow charged ions to flow in and out of the cell, converting the chemical signal into an electrical signal.

Resting Membrane Potential

  • Cells have a net negative charge due to ion distribution.
  • More Na+ (sodium), Cl- (chloride), and Ca2+ (calcium) ions outside the cell.
  • More K+ (potassium) ions and negatively charged anions inside.
  • Resting membrane potential: ~ -65 mV.

Signal Transmission

  • Ligand-Gated Ion Channels: Open in response to neurotransmitter binding.
    • Example: Sodium ion channels allow Na+ to enter, causing depolarization.
  • EPSP and IPSP
    • Excitatory Post-Synaptic Potential (EPSP): Net positive charge influx, depolarizes the cell.
    • Inhibitory Post-Synaptic Potential (IPSP): Net negative charge influx, hyperpolarizes the cell.

Action Potential Propagation

  • Threshold: EPSPs can reach a threshold (~ -55 mV) to open voltage-gated sodium channels.
  • Chain Reaction: Sodium influx causes depolarization, opening more sodium channels.
  • Depolarization Peak: Cell becomes positively charged (~ +40 mV).
  • Inactivation: Sodium channels stop inflow, enter an inactivated state.
  • Repolarization: Potassium channels open, potassium exits; Na-K pump restores balance.

Refractory Periods

  • Absolute Refractory Period: Sodium channels are inactivated, preventing immediate re-firing.
  • Relative Refractory Period: Sodium channels closed but can be opened with a stronger stimulus.

Role of Myelin

  • Saltatory Conduction: Rapid signal transmission across myelinated axons.
    • Nodes of Ranvier: Gaps in myelin where ion exchange occurs.

Conclusion

  • Action potentials enable rapid signaling across neurons.
  • Myelin enhances speed and efficiency of signal transmission.

Supporting the Learning

  • Support through Patreon, subscriptions, or social media sharing.

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