Catching a Falling Ruler: Reaction Time and Action Potentials

Introduction to Reaction Time Lab

• Popular lab involving catching a falling ruler
• Measures response time based on how quickly the ruler is caught
• Explores how the brain and muscles respond quickly

Action Potentials in Excitable Cells

• Key concept: Action potentials are electrical signals in excitable cells like neurons and skeletal muscle
• Excitable cells respond to stimuli by generating electrical signals

Cell Membranes and Ions

• Membranes control entry/exit of ions
• Ions (charged particles) use proteins to move through membranes
  • Passive movement through channels or active transport using pumps

Sodium-Potassium Pump

• Moves sodium (Na+) and potassium (K+) ions against their gradients with ATP
• Moves 3 Na+ out and 2 K+ in
• Creates more positive ions outside than inside
• Inside of cells has negative ions, making it more negative overall

Resting Membrane Potential

• Maintained by the sodium-potassium pump and leaky ion channels
• Sodium leaks in, potassium leaks out, maintaining a steady state
• Membrane potential: electric potential difference between inside and outside
  • Measured using microelectrodes

Neuron Membrane Potential

• At rest, neuron membrane potential is -70 mV (inside is more negative)

Action Potential Phases

1. Depolarization
   • Triggered by opening of gated sodium channels
   • Sodium rushes into the cell, making it more positive
   • Must reach threshold (-55 mV) to trigger an action potential (all-or-nothing principle)
2. Rising Phase
   • Sodium channels open, membrane potential becomes positive (~+30 mV)
3. Repolarization and Hyperpolarization
   • Sodium channels inactivate, potassium channels open
   • Potassium exits, membrane potential returns to resting state (-70 mV) with an overshoot (hyperpolarization)
   • Sodium-potassium pump restores resting potential

Gated Ion Channels

• Types
  • Ligand-gated: Open in response to ligand binding (e.g., neurotransmitters)
  • Mechanically-gated: Open in response to physical stimuli (e.g., touch)
  • Voltage-gated: Open in response to voltage changes
• Critical for initiating depolarization and action potentials

Propagation of Action Potentials

• Action potential spreads along neuron axons
• Initial depolarization triggers neighboring voltage-gated channels
• Previous axon segments repolarize and enter refractory periods
  • Important for unidirectional propagation and firing rate regulation
• Myelination affects action potential spread - further reading suggested

Relevance to Daily Life

• Action potentials are fundamental for activities like moving and thinking

Conclusion

• Understanding action potentials enhances comprehension of bodily responses and functions
• Encouragement to maintain curiosity about the biological processes

Amoeba Sisters Reminder: Stay curious!