Lecture Notes on Threshold Potential

Introduction

• Topic: Threshold Potential
• Relation: Connected to depolarization and repolarization processes in neurons.

Situational Example

• Strong Stimulus: Strong touch on the wrist.
  • Generates an action potential.
  • Brain receives a signal indicating the sensation.
• Weak Stimulus: Tiny ant walking on the wrist.
  • No action potential generated.
  • No signal sent to the brain; sensation not felt.

Key Discussion Points

• Stimulus Strength and Response:
  • Strong stimuli can depolarize the axon to +30mV, generating action potentials.
  • Weak stimuli fail to reach the threshold potential, thus do not generate action potentials.
• Conservation of ATP:
  • It is advantageous not to generate action potentials for every minor stimulus.
  • Saves energy (ATP) by not responding to insignificant stimuli.

How the Body Differentiates Stimuli

• The Role of Threshold Potential:
  • Resting Membrane Potential: -70 mV.
  • Threshold Potential: -55 mV, the membrane potential needed to trigger an action potential.
• Mechanism:
  • In Weak Stimulus:
    • Few sodium ion channels open.
    • Insufficient sodium ions enter the axon.
    • Membrane doesn't reach -55 mV (threshold potential).
  • In Strong Stimulus:
    • Many sodium ion channels open.
    • Sufficient sodium ions enter the axon.
    • Membrane reaches or exceeds threshold potential.
    • Results in successful depolarization and action potential generation.

Conclusion

• Function of Threshold Potential:
  • Prevents unnecessary action potentials for weak stimuli.
  • Efficiently manages energy use by the nervous system.
  • Ensures only significant stimuli reach the brain.