Neuron Communication and Action Potentials

Communication in the Nervous System

Neurons communicate impulses responsible for actions, thoughts, and emotions using electrical impulses.
Only one type of signal is sent by neurons, which varies in frequency.
Brain deciphers these signals like binary code based on location, sensation, magnitude, and importance.
The nerve impulse is known as the action potential.

The body is electrically neutral overall but certain areas have more positive or negative charges.
Barriers (membranes) keep charges separated to build potential.
Voltage is the measure of potential energy, while current denotes the flow of electricity (ions) across membranes.
Resistance affects current flow: High resistance (insulators like plastic), Low resistance (conductors like metal).

A resting neuron's interior is more negative compared to its exterior (~ -70 mV).
Sodium ions (positive) outside the neuron, potassium ions (positive) + negatively charged proteins inside.
This creates a more negative interior, making the neuron polarized.
Maintained by the sodium-potassium pump which pumps out 3 sodium ions for every 2 potassium ions pumped in.

Membrane has ion channels which open based on specific triggers (voltage, ligands, mechanical stretch).
Voltage-gated channels: Open/close based on membrane potential.
Ligand-gated channels: Open when specific neurotransmitters or hormones bind.
Mechanically-gated channels: Open in response to physical stretching.

Graded Potential: Small, localized change in membrane potential (not enough to trigger full signal).
Action Potential: Large change triggering voltage-gated channels, leading to signal transmission down an axon.
To initiate: Resting neuron (all channels closed at -70 mV) receives stimulus, sodium channels open -> depolarization to -55 mV (threshold) -> full depolarization to +40 mV.
Depolarization leads to a chain reaction along the axon (voltage-gated sodium channels opening sequentially).
Once depolarization hits +40 mV, repolarization occurs (potassium channels open) dropping voltage below resting (~ -75 mV) -> hyperpolarization -> sodium-potassium pumps restore resting potential.
Refractory period: Axon part can't respond to stimuli to prevent reverse signal travel.

Frequency of action potentials indicates strength of stimulus or required response (e.g., delicate vs. forceful actions).
Conduction velocity varies: fastest in reflex pathways, slower in glands, guts, and blood vessels.
Myelinated axons (insulated) conduct signals faster than non-myelinated ones due to saltatory conduction via Nodes of Ranvier.

Neurons communicate using action potentials, from small graded potentials to large signals sending impulses down an axon.
Voltage in these processes mostly consistent - threshold at -55 mV and peak depolarization at +40 mV.
Next session will cover how action potentials jump to other neurons.

Crash Course Kids for younger audience, focusing initially on 5th-grade science with topics like food chains and gravity.