The nervous system operates like an incredibly fast electrical network — signals travel from one neuron to the next in a chain reaction that can cross your entire body in milliseconds:

Action potential: A stimulus causes sodium ions to rush into the neuron, creating a wave of electrical charge (about -70mV to +30mV) that races down the axon. This is an all-or-nothing event — the neuron either fires fully or not at all
Myelin sheath: Fatty insulation produced by special glial cells that wraps around axons like plastic coating on a wire. It speeds up signals dramatically — from 2 mph (unmyelinated) to over 250 mph (myelinated). Gaps between myelin segments called Nodes of Ranvier allow the signal to jump forward (saltatory conduction)
Synapse: The tiny gap (about 20 nanometers) between two neurons. When the electrical signal reaches the end of an axon, it triggers the release of neurotransmitters — chemical messengers like dopamine, serotonin, and acetylcholine — that float across the gap and bind to receptors on the next neuron, causing it to fire
Key neurotransmitters: Dopamine (reward, motivation), serotonin (mood, sleep), acetylcholine (muscle control, memory), GABA (calming, inhibitory), glutamate (excitatory, learning)
Reflexes: Spinal cord shortcuts that bypass the brain entirely — touch something hot, and a reflex arc pulls your hand back in ~50 milliseconds, BEFORE the pain signal even reaches your brain
Neuroplasticity: The brain physically rewires itself based on experience. Every time you practice a skill, the connections between those neurons strengthen (long-term potentiation). This is how learning works at the cellular level

💡 Your brain uses about 20% of your total energy — even though it's only 2% of your body weight. It contains ~86 billion neurons, each connected to thousands of others, forming ~100 trillion synapses.

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