Neuroscience Lecture Notes: Resting Potential

Introduction

• Previous discussions: Gross anatomy of neurons, glial cells, comparison of neuron size, shape, parts
• Today's goals: Understand the ionic basis of excitable cells, primarily focusing on:
  • The resting potential
  • Neurons at rest: Majority of time
  • Action potential: To be covered later
• Resources: PDFs of slides and practice games on Canvas (Materia)

Sub-Discipline

• Neurophysiology: Study of how electrical and chemical processes within cells govern signaling.

Resting Potential vs. Action Potential

• Resting potential: Neuron's state when not signaling (~ -65 mV on average)
• Action potential: Rapid electrical signal & chemical message transmission via synapse
• Analogy: Neurons store and release electrical charge like little batteries.

Importance of Ions

• Ionic concentrations:
  • Intracellular fluid: Negatively charged proteins, potassium, and low sodium
  • Extracellular fluid: Sodium, calcium, chloride, few negative proteins
  • Key ions: Sodium ( ), Potassium (K+), Chloride (Cl-), Calcium (Ca2+)

Phospholipid Membrane & Ion Channels

• Membrane composition: Hydrophilic heads, hydrophobic tails forming a bilayer
• Ion channels: Membrane-spanning proteins forming gates for ion flow
  • Types: Voltage-gated, chemically gated (ligand-gated), mechanically gated
• Special Channels:
  • Leak potassium channels: Always open
  • Sodium-potassium pump: Uses ATP to pump K+ in, Na+ out

Electrical Concepts

• Electricity in neurons:
  • Current (I): Movement of charged particles (measured in amperes)
  • Voltage/Potential: Force exerted on a particle (measured in volts)
  • Conductance (G): Ability to move charge (measured in Siemens)
  • Resistance: Inability to move charge (measured in ohms)
• Ohm's Law: Current (I) = Conductance (G) × Voltage (V)

Ionic Movements

• Diffusion: Ions move from high to low concentration
• Electrostatic Pressure: Opposites attract, likes repel
• Sodium-Potassium Pump:
  • Pumps 3 Na+ out for every 2 K+ into cell
• Membrane Potential Variation
  • Ranges from -50 to -80 mV, averages to -65 mV

Equilibrium Potential

• Potassium Equilibrium Potential (E_K): Balance point for potassium ion flow
• Nernst Equation: Calculates equilibrium potential for single ions
• Goldman Equation: Calculates permeability for multiple ions

Importance of Potassium

• Potassium Channels: Critical in maintaining resting potential
  • Mutations: Alter kinetics (e.g., Weaver Mouse, epilepsy)
• Extracellular Potassium:
  • Regulated by blood-brain barrier, astrocytes, and spatial buffering
  • Excess potassium can disrupt resting potential, causing severe issues

Conclusion

• Next Lecture: Action Potential
• Review Tasks:
  • Define and discuss diffusion and electrostatic pressure
  • Explain how they interact and how the sodium-potassium pump and leak channels contribute to the resting potential