Neuron Action Potentials and Synaptic Communication

Posted on Nov 17, 2024 in Biology

Action Potential Generation

An action potential is an electrical signal in a neuron, a change in membrane potential from negative to positive. Only excitable cells can generate action potentials, allowing communication through electrical currents.

An oscilloscope measures action potentials, amplifying and recording the electrical activity of cells.

Ion channels, proteins in the cell membrane, generate electrical signals. Their permeability determines action potential generation.

Active transport (Na+/K+ pump) moves ions against their gradient using ATP.

Types of Ion Channels

  • Ligand-gated channels: Activated by chemical stimuli (neurotransmitters).
  • Voltage-gated channels: Activated by changes in membrane potential.
  • Stimulus-gated channels: Activated by mechanical stimuli.
  • Phosphorylation-activated channels: Activated by enzymes adding phosphate groups.

Key Concepts

  • Agonist: Mimics neurotransmitter action, activating channels.
  • Antagonist: Blocks neurotransmitter action, preventing channel opening.

Membrane Potential and Equilibrium

Phosphate groups on proteins attract potassium ions, maintaining intracellular concentration.

Potassium equilibrium potential is when there is no net potassium movement (-92.3 mV).

Potassium leak channels keep membrane potential close to potassium equilibrium.

Stimulus and Refractory Periods

  • Suprathreshold stimulus: Generates action potentials.
  • Subthreshold stimulus: Does not generate action potentials.
  • Absolute refractory period: No action potential can be generated.
  • Relative refractory period: Action potential possible with a suprathreshold stimulus.

Action Potential Phases

  1. Threshold: Minimum stimulus to open sodium channels.
  2. Depolarization: Sodium influx, membrane potential becomes positive.
  3. Repolarization: Potassium efflux, membrane potential returns to negative.
  4. Hyperpolarization: Membrane potential becomes more negative than resting.

Signal Propagation and Synapses

Electrotonic propagation: Current decay in subthreshold stimuli.

Myelin loss can be fatal in humans.

Types of Synapses

  • Electrical synapses: Direct molecule transfer between cells.
  • Chemical synapses: Neurotransmitter release across synaptic cleft.

Synaptic Transmission

Calcium influx triggers neurotransmitter release via exocytosis. Neurotransmitters bind to postsynaptic receptors. Vesicles are recycled through endocytosis.