How the Nervous System Works

Every thought you have, every move you make, and every heartbeat that keeps you alive depends on electrical signals traveling through your nervous system. This network of specialized cells called neurons transmits information at speeds up to 120 meters per second, coordinating activities across your entire body. From the moment you decide to pick up a cup of coffee to the unconscious process of breathing while you sleep, your nervous system is constantly sending and receiving signals that keep you functioning.

The short answer

Your nervous system has two main parts. The central nervous system consists of your brain and spinal cord, which process information and generate responses. The peripheral nervous system contains all the nerves that connect your central nervous system to the rest of your body. Neurons communicate through electrical impulses called action potentials that travel along nerve fibers, then cross synapses using chemical messengers called neurotransmitters. This combination of electrical and chemical signaling allows you to process sensory information, control movement, and regulate involuntary functions like heart rate and digestion.

The full picture

The architecture: central and peripheral

Your nervous system divides into two functional parts that work together.

The central nervous system (CNS) is the processing hub. Your brain contains approximately 86 billion neurons that handle everything from conscious thought to regulating body temperature, according to research from the journal Neurobiology of Aging. Your spinal cord runs through your spine, transmitting signals between your brain and the rest of your body. Together, they form the command center where decisions are made and responses are coordinated.

The peripheral nervous system ( PNS) connects your central nervous system to every other part of your body. It includes all the nerves branching from your spinal cord to your organs, muscles, and skin. This network carries sensory information to your brain and motor commands back to your muscles. Without it, your brain would be isolated from the rest of your body.

How signals travel: action potentials

The fundamental unit of nervous system communication is the action potential, a brief electrical impulse that travels along a neuron.

A neuron has three main parts. The cell body contains the nucleus and most of the cell’s machinery. The axon is a long, thin fiber that conducts electrical impulses away from the cell body. The dendrites are branching structures that receive signals from other neurons.

When a neuron receives enough stimulation from neighboring neurons, it generates an action potential. This is a brief reversal of electrical charge that travels down the axon like a wave. The signal moves because ion channels in the axon membrane open and close in sequence, allowing sodium ions to rush in and then potassium ions to rush out. This creates a domino effect of charge reversal that propagates along the entire length of the axon.

The speed depends on axon thickness and whether it’s wrapped in myelin, a fatty insulation that speeds transmission. Unmyelinated axons conduct at about 1-2 meters per second. Myelinated axons can transmit at 10-120 meters per second, which is why reflexes that protect you from danger are so fast.

The connection: synapses

Neurons don’t actually touch each other. The gap between neurons is called a synapse, and signals cross it using chemicals.

When an action potential reaches the end of an axon, it triggers the release of neurotransmitters stored in synaptic vesicles. These chemicals diffuse across the synaptic cleft and bind to receptor sites on the neighboring neuron. Depending on the neurotransmitter and receptor, this can either excite the next neuron (making it more likely to fire) or inhibit it (making it less likely to fire).

The most common neurotransmitters are glutamate (excitatory), GABA (inhibitory), dopamine (reward and movement), serotonin (mood and sleep), and acetylcholine (muscle contraction and learning). The balance of excitation and inhibition across your entire nervous system determines your mental and physical state.

Two systems: voluntary and involuntary

Your nervous system controls both conscious and unconscious functions through different pathways.

The somatic nervous system handles voluntary actions. You decide to walk, reach for something, or speak, and your brain sends signals through this system to your skeletal muscles. These pathways are under your conscious control, which is why you can choose to move your hand or remain still.

The autonomic nervous system regulates involuntary functions that keep you alive without conscious thought: your heart beating, lungs breathing, food digesting, and pupils dilating. It divides into three parts. The sympathetic system activates your “fight or flight” response: it increases heart rate, dilates pupils, and diverts blood to muscles. The parasympathetic system handles “rest and digest”: it slows heart rate and promotes digestion. The enteric system controls your gastrointestinal tract independently, which is why stress affects your stomach.

Why it matters

Understanding your nervous system isn’t just academic. It explains why certain things happen to you.

When you’re scared and your heart races, that’s your sympathetic nervous system activating. When you can’t move a limb after sleeping on it wrong, that’s nerve compression. When you feel butterflies before a presentation, that’s your autonomic system responding to perceived threat.

For conditions like chronic pain, depression, and anxiety, understanding the nervous system is the first step toward treatment. Medications for many neurological and psychiatric conditions work by altering neurotransmitter levels or receptor activity in specific parts of your nervous system. SSRIs for depression, for example, increase serotonin availability in synaptic clefts, improving mood regulation.

Common misconceptions

“You only use 10% of your brain.” This is false. Brain imaging shows that virtually every part of your brain has a function, and you use most of it regularly. Different areas activate for different tasks, but no large unused reserves exist.

“Nerves are like electrical wires.” Not exactly. Both conduct signals, but nerves use ion movements and neurotransmitters, not electrons flowing through metal. Unlike wires, neurons can amplify signals, can be inhibited from firing, and fatigue with overuse. The analogy is useful but imprecise.

“Brain cells can’t regrow.” This is partially true for the central nervous system, but new discoveries are changing this view. The adult brain does generate new neurons in certain regions, particularly the hippocampus (involved in memory). Research continues on promoting regeneration after CNS injury.

Key terms

Action potential: A brief electrical impulse that travels along a neuron, caused by ion movements across the cell membrane.

Axon: The long fiber of a neuron that conducts electrical impulses away from the cell body toward other neurons or target tissues.

Dendrite: The branching structure of a neuron that receives signals from other neurons.

Myelin: A fatty substance that wraps around some axons, insulating them and dramatically increasing signal transmission speed.

Neurotransmitter: A chemical messenger released at synapses that transmits signals between neurons.

Synapse: The junction between two neurons where signals are transmitted chemically.