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Nerve Impulses and Action Potentials

Jun 13, 2024

Nerve Impulses and Action Potentials

Introduction to Neuronal Response

  • Scenario: Catching a ball, recognizing the trajectory, and positioning to catch
  • Key Question: How does the brain process sensory information so quickly?

Transference of Information

  • Environmental information (e.g., eye signal about ball's movement) is converted into electrical signals by neurons
  • These signals, called action potentials or nerve impulses, allow rapid detection and response
  • Examples of quick response:
    • Recognizing a favorite song
    • Pulling foot away from a pin upon stepping

Neuron Structure

  • Human brain: tens of billions of neurons, interconnected
  • *Components:
    • Cell body with branches:
      • Dendrites: Receive signals
      • Axon: Longest branch transmitting signals
  • Nerve impulses travel like electricity through wires

Ionic Environment and Gradients

  • Extracellular (outside) surface: Salty solution, positive Sodium (Na+) and negative Chloride (Cl-) ions
  • Intracellular (inside): Positive Potassium (K+) ions and negatively charged proteins, making inside negative compared to outside
  • Electrical Gradient: Inner surface more negative
  • Diffusion Gradient: Higher K+ concentration inside, forcing them outside
  • Electrochemical Gradient: Combination of both
  • Resting Potential: Approximately -70mV

Ion Channels and Membrane Potential

  • Ion Channels: Pores allowing specific ions to pass through
  • Voltage-gated Ion Channels: Open/close at specific voltages
  • Graded Potentials: Small fluctuations, not enough to fire neuron
  • Threshold Potential: -55mV, required to fire neuron

Action Potential Process

  1. Resting Potential: ~-70mV
  2. Threshold Crossing: -55mV triggers voltage-gated Sodium channels
  3. Depolarization: Sodium ions rush in, inner surface becomes positive
  4. Peak Voltage: 30mV opens Potassium channels
  5. Repolarization: Potassium exits, restoring negative voltage
  6. Hyperpolarization: Voltage drops below -70mV
  7. Restoration: Pumps restore resting potential by exchanging Na+ and K+

Rules of Nerve Impulses

  1. All-or-None Principle: Action potentials occur fully or not at all
  2. Unidirectional Transmission: Signal moves forward due to refractory period
  3. Speed Factors: Myelinated axons use saltatory conduction, speeding up transmission via Nodes of Ranvier

Sensory and Response Mechanism

  • *Sense Organs Trigger Impulses:
    • E.g., light in eyes, smell, taste, touch, sound
  • Nerve Impulse Transmission: From sensory organs to brain/spinal cord
  • Reflex Actions: E.g., Pulling leg away from pin
  • Brain's Role: Interprets impulse patterns and commands appropriate responses
  • Digital Language: Nerve impulses are the brain's communication mode

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