Understanding Membrane Potentials in Neurons

Apr 9, 2025

Lecture on Membrane Potentials

Resting Membrane Potential

  • Definition: Separation of charges across the plasma membrane.
  • Charge Distribution: More negative charge inside the cell than outside.
  • Contributing Ions: Chloride, sodium, potassium, and proteins.
  • Neurons: Unlike other cells, neurons can rapidly change their resting membrane potential in response to stimuli.

Voltage and Potential

  • Voltage: Measure of potential energy due to separated charges.
  • Resting Membrane Voltage: Potential difference across the membrane when the neuron is not transmitting signals.
  • Factors:
    • Greater charge difference leads to higher voltage.

Current and Resistance

  • Current: Flow of electrical charge (ions) between two points.
  • Resistance: Hindrance to charge flow (e.g., myelin sheath as insulator).
  • Ohm’s Law: Current (I) = Voltage (V) / Resistance (R)
    • Current is directly proportional to voltage and inversely proportional to resistance.

Membrane Ion Channels

  • Role: Establish and change resting membrane potential.
  • Types of Channels:
    • Leaking Channels: Always open.
    • Gated Channels: Open and close in response to signals (chemical, voltage, or mechanical).
  • Examples:
    • Chemically Gated: Open in response to neurotransmitters.
    • Voltage-Gated: Open in response to voltage changes.
    • Mechanically Gated: Open in response to physical deformation.

Ion Movement and Electrochemical Gradients

  • Electrochemical Gradient: Combination of electrical and chemical gradients.
  • Ion Flow and Voltage: Ion flow creates current and voltage changes across membranes.
  • Measurement: Voltage measured using a voltmeter.

Resting Membrane Potential (RMP)

  • Typical RMP: -70 millivolts.
  • Factors Influencing RMP:
    • Ionic composition differences between intracellular fluid (ICF) and extracellular fluid (ECF).
    • Plasma membrane permeability.
  • Key Ions:
    • Potassium (K+): Primary role due to its permeability.
    • Sodium (Na+): Balanced by chloride ions outside.
  • Sodium-Potassium Pump: Maintains concentration gradients by active transport.

Dynamic Changes in Membrane Potential

  • Graded Potentials: Short-distance signals that decrease over time and distance.
  • Action Potentials: Long-distance signals that maintain size.
  • Depolarization vs Hyperpolarization:
    • Depolarization: Voltage becomes less negative, increasing action potential likelihood.
    • Hyperpolarization: Voltage becomes more negative, decreasing action potential likelihood.
  • Summary: Resting membrane potential driven by ion concentration and permeability, with sodium and potassium leakage channels playing significant roles.