The number isn’t static. It’s growing.
🤔 What we’re actually asking
When someone asks “how many facts are there,” what they usually mean is: what’s worth knowing? And that’s a different question entirely. Because the nervous system isn’t just one thing—it’s this sprawling collection of neurons, synapses, chemicals, and electrical signals that somehow produces thought, movement, and every sensation you’ve ever felt.
Santiago Ramón y Cajal drew the first accurate pictures of individual neurons. Before that, scientists thought the brain was just continuous tissue, like a sponge. Cajal’s drawings changed everything. He won the Nobel Prize in 1906 for basically proving that neurons are discrete cells. That was one fact that opened the door to thousands more.
📊 The numbers that matter (and the ones that don’t)
Your nervous system contains roughly 86 billion neurons. That’s a number people like to throw around, but it’s almost meaningless by itself. What matters more: each neuron can connect to thousands of other neurons. The potential combinations are astronomical—more than the number of atoms in the universe, some estimates suggest.
But here’s where it gets interesting. Your brain weighs about 3 pounds (1.4 kg), which is only 2% of your body weight. Yet it uses 20% of your body’s energy. Your heart pumps about a fifth of your blood straight to your brain every minute. Those numbers tell you something about priorities.
Speed? Nerve signals travel at different speeds depending on the type of nerve. The fastest can hit 268 miles per hour (120 meters per second). That’s for things like reflexes—when you touch something hot and yank your hand back before you even consciously register the pain. Other signals, like dull aches, move much slower, around 2 mph. Your body’s basically running multiple communication networks at once.
✨ Things we learned recently
The Glymphatic System (2013)
Here’s a fact that wasn’t a fact until 2013: your brain has a waste-clearing system called the glymphatic system. Scientists discovered that while you sleep, your brain cells actually shrink, allowing cerebrospinal fluid to flush out toxic proteins. Before 2013, we didn’t know this happened. Now it’s in textbooks.
Or take gut neurons. Your digestive system contains about 500 million neurons—that’s more than your spinal cord has. People call it the “second brain,” though that’s a bit dramatic. These neurons can operate independently of your central nervous system, which is why you can digest food even if your spinal cord is severed. We’ve known about these neurons since the 1800s, but only recently understood how they communicate with the brain via the vagus nerve.
❓ The messy parts
Not everything we “know” is actually settled. Take memory formation. We know it involves strengthening synaptic connections (that’s called long-term potentiation, discovered in 1966). We know the hippocampus is crucial for forming new memories. We know that memories aren’t stored in one place but distributed across the cortex.
🎭 Facts that sound wrong but aren’t
Your brain doesn’t feel pain. Ironic, since it’s the organ that processes all pain signals. Brain surgeons can operate on awake patients, poking around in there while the patient talks. The skull and meninges (the brain’s protective layers) have pain receptors, but the brain tissue itself doesn’t.
You’re not using “only 10% of your brain.” That’s a myth that won’t die. Brain scans show activity throughout the brain even during simple tasks. Evolution wouldn’t have bothered giving you all that expensive, energy-hungry neural tissue if most of it sat idle.
Neurons can regenerate, but only in specific areas. The dentate gyrus in the hippocampus produces new neurons throughout your life—a process called neurogenesis. This was controversial when discovered in the 1990s because the old dogma was “you’re born with all the neurons you’ll ever have.” Sometimes science dogma is just wrong.
🔬 Where the facts come from
Different tools reveal different facts. EEG (electroencephalography) has been around since 1924 and measures electrical activity through the scalp. It’s great for timing but terrible for location. fMRI (functional magnetic resonance imaging), developed in the 1990s, shows which brain areas activate during tasks by measuring blood flow. It’s great for location but has poor time resolution—it takes seconds to capture changes.
Then there’s optogenetics, which came onto the scene around 2005. Scientists can now insert light-sensitive proteins into specific neurons, then use lasers to turn those neurons on or off. This lets researchers test cause-and-effect in ways that weren’t possible before. Each new technique adds layers to what we know.
📚 The accumulation problem
The 12 Cranial Nerves
Medical students have to memorize: olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, hypoglossal. That’s 12 pairs of nerves, each with multiple functions. The trigeminal nerve alone has three main branches that handle sensation for your face and motor control for chewing.
Multiply that level of detail across every structure, every neurotransmitter (there are over 100 identified), every pathway, every syndrome, every treatment… you see the problem. The facts pile up faster than anyone can organize them.
🏛️ Some facts are historical accidents
Broca’s area and Wernicke’s area—two regions critical for language—are named after the 19th-century doctors who studied patients with damage to those regions. Paul Broca examined a patient who could only say “tan.” After the patient died, autopsy revealed damage to what we now call Broca’s area. That’s how we learned that specific brain regions handle specific functions.
But here’s the thing: we now know language processing is way more distributed than those two areas. The simplified textbook version (Broca’s for speech production, Wernicke’s for comprehension) is outdated. Yet we still teach it because it’s a useful starting point. Some facts are scaffolding that we keep around even after building more complex structures.
🔄 What changes
Doctors performed frontal lobotomies on psychiatric patients, severing connections in the prefrontal cortex. Walter Freeman personally performed about 3,500 of them. He won awards. Now we recognize it as barbaric—destroying brain tissue to treat mental illness. That wasn’t ancient history; some patients who received lobotomies are still alive.
Our understanding shifts. Neuroplasticity—the brain’s ability to reorganize itself—was considered impossible until the late 20th century. Now it’s central to how we think about learning, recovery from injury, and even treating depression.
♾️ Why counting is futile
So how many facts exist about the nervous system? The question assumes facts are discrete, countable things. But they’re not. They’re provisional statements that get refined, contradicted, or confirmed. They’re nested inside each other—you can’t understand action potentials without understanding ion channels, can’t understand ion channels without understanding cell membranes, can’t understand membranes without chemistry.
The better question might be: what don’t we know? And that list is longer than what we do know. We’re still figuring out consciousness, how anesthesia actually works, why we dream, how chronic pain develops, what causes most psychiatric disorders at the cellular level.
The facts keep accumulating, but the mysteries aren’t shrinking proportionally. If anything, each answer generates new questions. That’s not a bug—it’s how science works. The map of the nervous system isn’t finished. It might never be.