Synapse

A synapse isn't actually a physical connection—it's a microscopic gap, typically just 20-40 nanometers wide, where neurons almost touch but never quite do. This space revolutionized neuroscience because it meant the brain works through chemistry, not just electricity. When Sherrington coined the term from the Greek "synapsis" (to clasp together), he was describing the ultimate paradox: connection through separation, where neurotransmitters leap across the void like molecular messengers.

Your brain contains roughly 100 trillion synapses—that's about 1,000 synapses for every star in the Milky Way galaxy. A single pyramidal neuron in your cortex can receive input from 10,000 different synapses simultaneously, integrating a symphony of signals every millisecond. This staggering density means that the number of possible neural connection patterns in your brain exceeds the number of atoms in the known universe, making each human brain more complex than anything else we've discovered.

Every time you learn something new, you're literally rewiring your synapses—they strengthen, weaken, or even disappear based on use, a phenomenon called synaptic plasticity. This is why practice makes perfect: repeatedly firing the same neural pathways physically enlarges and strengthens those synapses, making the signal transmission faster and more reliable. The phrase "neurons that fire together, wire together" captures how your experiences sculpt your brain's architecture, meaning your biography becomes your biology.

Each neuron doesn't simply relay messages—it's a biological voting machine that tallies excitatory and inhibitory signals from thousands of synapses before deciding whether to fire. Some synapses shout "go!" while others whisper "stop," and only when the combined input crosses a specific threshold does the neuron cast its electrochemical ballot. This means every thought, memory, and movement emerges from countless microscopic elections happening simultaneously, making consciousness a democracy of trillions.

Synaptic transmission adds a tiny delay—about 0.5 milliseconds per synapse—which means signals traveling through multiple synapses can lag significantly behind direct pathways. This is why reflexes bypass most synapses entirely, shooting signals straight to the spinal cord before your conscious brain even knows what happened. Your awareness of touching a hot stove arrives after your hand has already jerked away, revealing that much of what you experience as "now" is actually a carefully constructed memory played back milliseconds later.

Many neurological and psychiatric conditions are fundamentally synaptic disorders: Parkinson's involves dopamine synapses, depression relates to serotonin synapses, and Alzheimer's destroys synapses en masse before killing neurons. This insight has transformed treatment approaches—modern medications don't fix broken neurons but rather adjust the chemical conversations happening in the synaptic gaps. Understanding that mental illness often lives in these microscopic spaces helps destigmatize conditions by revealing their physical, biological nature.