Nerve cells, also called neurons, are your body’s communication system. They generate electrical signals that carry information from one place to another, coordinating everything from pulling your hand off a hot stove to forming a memory of what you had for breakfast. The human brain alone contains roughly 86 billion of these cells, with estimates from different studies ranging between 61 and 99 billion. Billions more run through your spinal cord and branch out to every organ, muscle, and patch of skin.
How Nerve Cells Send Signals
Neurons aren’t naturally good electrical conductors. Instead, they’ve evolved a workaround: they move charged particles called ions back and forth across their outer membranes to create electrical signals. At rest, the inside of a nerve cell sits at a slightly negative voltage compared to the outside. When a signal fires, ions rush in and briefly flip that voltage to positive. This rapid flip is called an action potential, and it travels down the length of the cell like a wave, carrying information as it goes.
Signal speeds vary enormously depending on the type of nerve fiber. The fastest neurons transmit at around 200 meters per second (roughly 450 miles per hour), while the slowest creep along at less than 0.1 meters per second. The difference comes down largely to insulation. Many nerve fibers are wrapped in a fatty coating called myelin, which forces the electrical signal to jump from one gap in the coating to the next rather than traveling continuously. This jumping pattern dramatically accelerates transmission and is the reason you can jerk your hand away from danger in milliseconds.
Parts of a Nerve Cell and What Each Does
Every neuron has three main regions, each with a distinct job in the communication cycle.
- Dendrites are branching extensions that receive incoming signals from other neurons. Think of them as antennae, collecting information from the surrounding environment. They can also participate in local chemical signaling with neighboring cells.
- Cell body (soma) houses the nucleus and the machinery that keeps the cell alive. It integrates the signals arriving through the dendrites and determines whether to fire its own signal in response.
- Axon is a long, cable-like projection that carries the outgoing signal away from the cell body. At its tip, the axon converts the electrical impulse into a chemical message by releasing signaling molecules into the tiny gap between itself and the next cell.
How Neurons Talk to Each Other
Neurons don’t physically touch. A microscopic gap called a synapse separates the end of one neuron’s axon from the dendrites of the next. When an electrical signal reaches the axon tip, it triggers the release of chemical messengers (neurotransmitters) into that gap. These molecules drift across, latch onto receptors on the receiving cell, and generate a new electrical signal on the other side. The whole process takes just a fraction of a millisecond.
This electrical-to-chemical-to-electrical relay is how your entire nervous system operates. It lets signals branch, combine, and be fine-tuned at every junction. Some neurotransmitters excite the next cell, pushing it closer to firing. Others inhibit it, making it less likely to fire. The balance between excitation and inhibition at millions of synapses simultaneously is what produces coordinated movement, thought, and sensation.
Three Types of Nerve Cells
Not all neurons do the same job. They fall into three functional categories based on the direction they carry information.
Sensory neurons carry information toward the brain and spinal cord. They detect things like temperature, pressure, light, and sound, converting those physical stimuli into electrical signals the nervous system can interpret. When you step on a sharp object, sensory neurons in your foot are the first to fire.
Motor neurons carry signals in the opposite direction, from the brain and spinal cord out to muscles and glands. They’re the final command in any voluntary or reflexive movement. One group of motor neurons might tell your extensor muscles to contract while another group controls flexors, and the two work in opposition to produce smooth, coordinated motion.
Interneurons sit between the other two types, processing and relaying signals within the brain and spinal cord. They make up the vast majority of neurons in your body and are responsible for the complex processing behind decision-making, memory, and pattern recognition. In a simple reflex, interneurons can inhibit certain motor neurons while allowing others to fire, so the right muscles contract and the wrong ones stay relaxed.
How Nerve Cells Strengthen and Weaken Connections
Your nervous system isn’t static. Neurons change the strength of their connections based on how often and how intensely those connections are used. When two neurons fire together repeatedly, the synapse between them can become more efficient, a process researchers call long-term potentiation. This was first documented in the hippocampus, a brain region critical for forming new memories, and it’s one of the key biological mechanisms behind learning.
The reverse also happens. Synapses that are rarely activated can weaken over time through long-term depression, which is essentially a reversal of the strengthening process. Both changes depend on the flow of calcium into the receiving cell, and current evidence suggests they share overlapping molecular machinery, just triggered at different thresholds. This two-way flexibility is what allows your brain to rewire itself as you practice a skill, recover from an injury, or simply forget information you no longer need.
The Support Cells That Keep Neurons Working
Neurons can’t function alone. They rely on a supporting cast of non-neuronal cells called glia, which outnumber neurons in many parts of the brain. Three types do most of the heavy lifting.
Myelin-producing cells (oligodendrocytes in the brain and spinal cord, Schwann cells in the rest of the body) wrap layers of fatty membrane around axons. This insulation is what enables the fast, jumping style of signal transmission described earlier. A single oligodendrocyte can insulate segments of multiple axons at once.
Astrocytes are star-shaped cells that manage the chemical environment around neurons. They supply the raw materials neurons need to produce energy, help regulate ion concentrations after signals fire, and form part of the blood-brain barrier, the selective filter that controls which substances in your bloodstream can reach brain tissue.
Microglia act as the immune cells of the brain. They patrol for damaged cells, foreign material, and debris, engulfing and clearing anything that doesn’t belong. When the brain is injured or infected, microglia are the first responders.
Why Nerve Cells Need So Much Energy
Maintaining the electrical readiness of billions of neurons is expensive. After each signal, the ions that rushed in and out need to be pumped back to their starting positions to reset the cell for the next firing. This pumping mechanism alone accounts for an estimated 20 to 40 percent of the brain’s total energy consumption. It’s a major reason the brain, despite being only about 2 percent of your body weight, burns roughly 20 percent of the calories you consume at rest. Every thought, sensation, and movement you produce depends on this constant, energy-hungry cycle of charging, firing, and resetting across billions of nerve cells simultaneously.