Nerves work by sending electrical signals along specialized cells called neurons, then converting those signals into chemical messages that jump between cells. This two-step process, electrical then chemical, is how your brain knows you’ve touched a hot pan, and how it tells your hand to pull away, all within a fraction of a second. The human brain contains somewhere between 62 and 94 billion neurons, and each one can connect to thousands of others, creating an extraordinarily dense communication network.
Parts of a Nerve Cell
A neuron has three main parts, each with a distinct job. Dendrites are branch-like extensions that receive incoming signals from other neurons or from sensory receptors in your skin, eyes, ears, and other organs. They funnel information toward the cell body, or soma, which houses the nucleus and the machinery that keeps the cell alive and functioning.
The axon is the long, cable-like projection that carries signals away from the cell body toward the next neuron, muscle, or gland. Some axons are only a fraction of a millimeter long. Others, like the ones running from your spinal cord to your toes, can stretch over a meter. At the very end of the axon sits the axon terminal, where the electrical signal gets converted into a chemical one so it can cross the tiny gap between cells.
How Electrical Signals Travel
When a neuron is resting, the inside of the cell carries a slight negative charge compared to the outside. Think of this as a loaded spring: energy is stored in that charge difference, ready to be released. When the neuron receives enough stimulation from its dendrites, channels in the cell membrane snap open and allow positively charged sodium ions to rush in. This sudden inflow flips the local charge from negative to positive, a process called depolarization. It happens fast, lasting about one millisecond.
That burst of positive charge triggers the next stretch of membrane to open its own sodium channels, and so on down the length of the axon. The signal doesn’t fade as it travels because each section regenerates the full electrical impulse on its own, like a chain of dominoes where each one stands back up before knocking over the next.
Right behind the advancing wave, the neuron resets itself. Potassium channels open (they respond to the same voltage change but react more slowly), allowing positively charged potassium ions to flow out. This restores the negative interior charge. The potassium channels linger open a beat longer than necessary, briefly making the cell slightly more negative than its usual resting state. This brief overshoot prevents the signal from traveling backward and gives the neuron a tiny refractory window before it can fire again.
Why Some Signals Travel Faster
Nerve signals don’t all move at the same speed. Conduction velocities range from less than 0.1 meters per second (slower than a casual walk) to 200 meters per second (roughly 450 miles per hour). The difference comes down to two factors: the diameter of the axon and whether it’s wrapped in myelin.
Myelin is a fatty insulating layer that certain support cells wrap around axons in tight spirals. Instead of the electrical signal having to regenerate continuously along every segment of the axon, it effectively jumps from one small gap in the myelin to the next. These gaps, called nodes of Ranvier, are the only spots where ion channels cluster and the signal gets refreshed. Research shows that only about 16 layers of myelin wrapping are needed to fully optimize speed, mostly by reducing the electrical capacitance of the membrane so charge builds up faster at each node. The result is dramatically faster conduction with less energy spent.
Thicker axons also conduct faster. In unmyelinated fibers, diameter is the primary factor determining speed. This is why the nerves controlling your skeletal muscles (which need rapid responses) tend to be both thick and heavily myelinated, while the nerves carrying dull, aching pain signals are thin and unmyelinated.
Crossing the Gap Between Cells
Neurons don’t physically touch each other. A tiny gap called a synapse separates the axon terminal of one neuron from the dendrite of the next. When the electrical signal reaches the axon terminal, it triggers the release of chemical messengers called neurotransmitters, which are stored in small bubble-like packages. These molecules drift across the gap, bind to receptors on the receiving cell, and either encourage or discourage that cell from firing its own electrical signal.
The body uses several different neurotransmitters for different purposes. Glutamate is the brain’s primary excitatory messenger, meaning it pushes receiving neurons toward firing. GABA is the main inhibitory messenger, responsible for roughly 40% of the brain’s inhibitory signaling, and it pushes neurons away from firing. Others you may have heard of, like dopamine, serotonin, and norepinephrine, play more specialized roles in mood, motivation, alertness, and movement. Acetylcholine is the key messenger at the junction between motor neurons and muscles, translating a nerve impulse into a muscle contraction.
This chemical step might seem like an unnecessary complication, but it gives the nervous system enormous flexibility. A single neuron can receive thousands of excitatory and inhibitory signals simultaneously, and whether it fires depends on the net sum of all those inputs. That calculation, repeated billions of times per second across the brain, is the foundation of everything from reflexes to abstract thought.
Sensory and Motor Pathways
Nerve signals travel in two directions through the body. Sensory (afferent) neurons carry information inward, from receptors in your skin, organs, and sense organs up to the brain and spinal cord. When you step on a sharp rock, pressure and pain receptors in your foot generate signals that travel up sensory neurons to your spinal cord and brain for processing.
Motor (efferent) neurons carry commands outward, from the brain and spinal cord to muscles and glands. After your brain registers the sharp rock, motor neurons fire to adjust your foot, shift your weight, and tense nearby muscles. In many reflexes, the spinal cord handles this loop without waiting for input from the brain, which is why you can jerk your hand off a hot surface before you consciously feel the pain.
Voluntary and Involuntary Control
Your nervous system divides into two broad territories. The central nervous system is the brain and spinal cord, where information gets processed and decisions get made. The peripheral nervous system is everything else: the nerves branching out to your limbs, organs, skin, and sensory organs.
Within the peripheral nervous system, some nerves are under your conscious control. You decide to pick up a cup, and motor neurons in your arm execute that command. But a large portion of your nervous system operates without any conscious input. This autonomic division constantly regulates your heart rate, breathing, digestion, bladder function, and dozens of other processes. It receives signals from the brain and relays them to organs, but it also sends information back, letting your brain know how fast your heart is beating or whether your stomach is full. You never have to think about any of it.
How the Body Protects Its Nerves
Given how critical nerves are, the body invests heavily in protecting them. Peripheral nerves are surrounded by a barrier system similar in principle to the blood-brain barrier. Specialized cells lining the tiny blood vessels inside nerves form tight seals that restrict which molecules can pass through. Large proteins like antibodies and albumin are blocked, while essential substances like insulin and growth factors get selectively transported in.
On top of this chemical barrier, nerves are physically cushioned by dense bundles of collagen fibers arranged lengthwise along the nerve, absorbing mechanical stress from movement and compression. When this barrier system breaks down, whether from injury, autoimmune disease, or metabolic conditions like diabetes, the internal environment of the nerve becomes disrupted. That disruption is one of the earliest events in many forms of peripheral neuropathy, the tingling, numbness, and pain that result from nerve damage.