Lecture on Neuron Communication and Action Potentials

Introduction

• Concept: Communicating everything through a simple, uniform signal
• Neurons communicate impulses responsible for actions, thoughts, and emotions
• Neurons fire impulses of uniform strength and speed; vary in frequency
• Brain translates signals like binary code
• Action potential: Fundamental for anatomy and physiology

Basics of Electricity in Biology

• Body: Electrically neutral overall, but localized charge differences
• Barriers (membranes) separate positive and negative charges to create potential
• Analogy: Neurons as small batteries
• Voltage: Potential energy from separated charges (measured in millivolts in the body)
• Current: Flow of electricity connected to voltage and resistance
• Resistance: Opposition to current (insulators vs. conductors)
• Ions: Positively or negatively charged particles crossing cell membranes

Resting Membrane Potential

• Resting neuron: Negative inside compared to outside (around -70 mV)
• Outside: Positive sodium ions; Inside: Positive potassium ions and negative proteins
• Creates negative charge inside the neuron
• Sodium-potassium pump: Moves ions to maintain charge difference
• Electrochemical gradient: Difference in charge and ion concentration

Ion Channels and Membrane Potential

• Membranes have ion channels for ions to pass through
• Types of ion channels:
  • Voltage-gated: Open at specific membrane potentials
  • Ligand-gated: Open when specific neurotransmitters/hormones bind
  • Mechanically gated: Open in response to physical stretching
• Movement of ions = electrical events in neurons

Action Potential

• Graded potential: Small change with few ion channels opening
• Action potential: Large change, depolarization triggering voltage-gated channels
• Threshold: -55 mV for action potential
• Depolarization: Sodium channels open, sodium enters, voltage becomes positive (~40 mV)
• Repolarization: Potassium channels open, potassium exits, voltage drops
• Hyperpolarization: Brief drop to ~-75 mV before returning to resting potential
• Refractory period: Neuron can't respond to new stimulus, prevents bidirectional signal

Frequency and Speed of Action Potentials

• Action potential strength is consistent; frequency varies with stimulus intensity
• Conductive velocity varies:
  • Faster in reflex pathways
  • Slower in glands, guts, and blood vessels
• Myelin sheath: Increases conduction speed via saltatory conduction (leaping between Nodes of Ranvier)

Summary and Future Topics

• Neurons use ion channels and electrochemistry to generate action potentials
• Phases: Resting state, depolarization, repolarization, hyperpolarization
• Next topic: What happens when action potential reaches the end of the axon

Additional Information

• Crash Course Kids: New educational content for younger audiences
• Standards for teachers to ensure helpful and accurate content

Credits

• Written by Kathleen Yale
• Edited by Blake de Pastino
• Consultant: Dr. Brandon Jackson
• Directed by Nicholas Jenkins and Michael Aranda
• Graphics by Thought Café