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Understanding Neurons and Action Potentials

Apr 14, 2025

Anatomy and Physiology: Nervous System Lecture 3

Introduction

  • Course shifted to online format due to COVID-19
  • Current setup is crude; improvements planned
  • This is the third lecture in the series on the nervous system
  • Focus of the lecture: action potentials, ion channels, neuron conduction

Excitable Cells

  • Types of Excitable Cells:
    • Muscle cells (skeletal, smooth, cardiac)
    • Neurons
  • Function: Conduct action potentials and electrical currents

Neurons

  • Neurons have ion channels allowing ions to move through membranes, changing voltage
  • Understanding neuron function involves understanding ion flow

Ionic Concentration and Membrane Permeability

  • Electrolytes: Carry electrical charge (focus on sodium and potassium ions)
  • Sodium (Na):
    • Higher concentration outside the cell
    • Tendency to move inside the cell if membrane is permeable
  • Potassium (K):
    • Higher concentration inside the cell
    • Tendency to leak outside the cell

Ion Channels

  • Leaky Channels: Allow ions to passively flow across membranes
  • Role in Homeostasis:
    • Equilibrium is undesirable; homeostasis requires energy
    • Sodium-potassium pump maintains ionic imbalance using ATP

Sodium-Potassium Pump

  • Function:
    • Pumps 3 Na+ out, 2 K+ into the cell
    • Utilizes ATP (adenosine triphosphate) to function
  • Importance: Maintains resting membrane potential (RMP)
    • RMP ≈ -70 millivolts (inside relative to outside)

Action Potentials

  • Voltage Measurement: Using an oscilloscope
  • Depolarization:
    • Opening Na+ channels increases positivity (depolarizes)
    • Excites the neuron
  • Hyperpolarization:
    • Opening K+ channels increases negativity (hyperpolarizes)
    • Inhibits the neuron

Types of Gated Channels

  1. Chemically Gated Channels:
    • Open/close due to specific chemicals (e.g., neurotransmitters)
    • Example: Acetylcholine binding to receptors
  2. Voltage-Gated Channels:
    • Open in response to electrical changes
    • Example: Calcium channels in synaptic knobs
  3. Mechanically Gated Channels:
    • Open/close due to physical membrane distortion
    • Example: Channels opening due to pressure

Conclusion

  • Summary: Discussion on ion movement, resting membrane potential, and gated channels
  • Next Steps: Explore how action potentials spread in neurons and muscles

Lecture emphasized understanding ion channels and their role in neuron function; prepares for next lecture focusing on action potential propagation.

Full transcript