What Does the Nervous System Do?

The nervous system controls all body functions by sending electrical and chemical signals between your brain and body. It manages everything from voluntary movements like walking to involuntary processes like heartbeat and digestion through a network of billions of nerve cells.

The Three-Phase Communication System

Your nervous system operates as a continuous communication loop with three essential phases. Each phase serves a distinct purpose in keeping you alive and responsive to your environment.

Sensing (Input Phase): Specialized sensory neurons constantly gather information from inside and outside your body. These receptors detect light, sound, temperature, pressure, pain, and chemical changes. Your skin alone contains approximately 200 pain receptors per square centimeter, alongside receptors for pressure, cold, and warmth. This sensory data flows continuously to your central nervous system for processing.

Processing (Integration Phase): Your brain and spinal cord analyze incoming signals and decide how to respond. This integration happens at multiple levels—some responses occur in the spinal cord for quick reflexes, while complex decisions involve extensive brain processing. The brain contains roughly 100 billion neurons that form trillions of connections, enabling everything from simple pattern recognition to abstract thinking.

Responding (Output Phase): Motor neurons carry commands from your central nervous system to muscles and glands throughout your body. These signals travel at speeds up to 328 feet per second, enabling rapid responses to stimuli. When you touch something hot, the entire sense-process-respond cycle completes in milliseconds, pulling your hand away before conscious awareness catches up.

Two Operating Systems in One

The nervous system divides its labor between voluntary and involuntary control, each handling different aspects of body function.

Your somatic nervous system manages conscious movements and sensory perception. When you decide to move your arm, pick up an object, or turn your head, somatic motor neurons transmit those commands to skeletal muscles. This system also processes sensory information you’re aware of—the texture of fabric, the taste of food, the sound of music. You maintain direct control over these functions, though with practice many movements become automatic.

The autonomic nervous system regulates involuntary processes that keep you alive without conscious effort. This includes heart rate, blood pressure, digestion, breathing patterns, pupil dilation, sweating, and hormone release. The system operates through two complementary branches that work in opposition to maintain balance.

The sympathetic branch activates during stress or activity, increasing heart rate, dilating airways, releasing stored energy, and redirecting blood flow to muscles. This “fight or flight” response prepares your body for action, whether facing genuine danger or everyday stressors like public speaking or traffic jams.

The parasympathetic branch promotes “rest and digest” functions when you’re calm. It slows heart rate, stimulates digestion, conserves energy, and facilitates repair processes. After a stressful event ends, this system helps return your body to baseline functioning.

The Signal Transmission Process

Understanding how neurons communicate reveals the precision of nervous system function. Each neuron consists of a cell body, branching dendrites that receive signals, and a long axon that transmits signals to other cells.

Signals travel as electrical impulses along the neuron’s length. When an impulse reaches the axon terminal, it triggers the release of chemical messengers called neurotransmitters into the synapse—the microscopic gap between neurons. These chemicals drift across the synapse and bind to receptors on the next neuron, converting back to an electrical signal that continues the message chain.

The myelin sheath, a fatty coating around many axons, accelerates signal transmission by up to 15 times. This insulation allows long-distance communication within your body to happen nearly instantaneously. Damage to myelin, as occurs in multiple sclerosis, disrupts signal transmission and causes neurological symptoms.

Central Command and Distributed Networks

The central nervous system—your brain and spinal cord—serves as the primary processing center. The brain integrates sensory information, generates thoughts and emotions, stores memories, and coordinates complex behaviors. Different brain regions specialize in specific functions: the frontal lobe handles decision-making and planning, the temporal lobe processes sounds and language, the occipital lobe interprets visual information, and the parietal lobe manages sensory perception.

The spinal cord acts as a communication highway between brain and body. It contains approximately 13.5 million neurons that relay messages in both directions. The spinal cord also handles certain reflexes independently, enabling rapid protective responses without waiting for brain input.

The peripheral nervous system extends throughout your body as a network of nerves branching from the brain and spinal cord. These nerves reach every organ, muscle, and tissue, creating the physical infrastructure for body-wide communication. You have 12 pairs of cranial nerves directly connected to your brain and 31 pairs of spinal nerves.

Daily Life Applications

The nervous system’s functions become tangible when you consider everyday activities. Reading these words requires your visual system to detect light patterns, your brain to decode those patterns into letters and words, and your cognitive systems to extract meaning. Simultaneously, your autonomic system maintains your breathing rhythm, adjusts your posture, and manages countless other background processes.

During physical exercise, multiple nervous system components coordinate seamlessly. Your brain sends voluntary movement commands to skeletal muscles. Your autonomic system increases heart rate and breathing to supply more oxygen. Sensory feedback from muscles and joints helps maintain balance and adjust movement patterns. Your body temperature regulation activates sweating to prevent overheating.

Emotional responses demonstrate the nervous system’s integration of physical and psychological processes. When you feel anxious, your sympathetic system may cause a racing heart, sweaty palms, and shallow breathing—all physical manifestations of neural activity. Conversely, deep breathing exercises can activate the parasympathetic system, reducing anxiety through this mind-body connection.

The Global Impact of Nervous System Health

Recent research from the World Health Organization reveals the massive scale of neurological conditions worldwide. In 2021, more than 3 billion people—over one in three individuals globally—lived with a nervous system disorder. These conditions have become the leading cause of disability and illness worldwide, accounting for more disability-adjusted life years than any other health category.

The burden increased 18% between 1990 and 2021, driven primarily by population aging and growth rather than increasing disease rates. The most common conditions affecting nervous system function include stroke, neonatal brain injuries, migraine, dementia, diabetic neuropathy, meningitis, epilepsy, autism spectrum disorder, and nervous system cancers.

Diabetic neuropathy emerged as the fastest-growing neurological condition, with cases more than tripling since 1990 to reach 206 million in 2021. This highlights how metabolic diseases can damage nervous system function over time, affecting both sensory perception and autonomic control.

Protective Factors and Risk Reduction

Research identifies several modifiable risk factors that affect nervous system health. High blood pressure emerged as the most significant risk factor, contributing to 84% of preventable stroke cases. Ambient and household air pollution, lead exposure, high blood sugar levels, and smoking also significantly impact nervous system function.

Maintaining nervous system health involves several evidence-based practices. Regular physical activity improves blood flow to the brain and spinal cord while supporting overall nervous system function. Adequate sleep allows the brain to consolidate memories and clear metabolic waste products. Managing chronic conditions like diabetes and hypertension prevents nerve damage that accumulates over time.

Protecting your head and spine from injury remains critical, as nervous system tissue has limited regenerative capacity. Wearing helmets during activities with fall risk, using seatbelts, and taking precautions to prevent falls in older adults all reduce injury risk. Avoiding toxins like excessive alcohol and certain chemicals helps preserve nerve cell function.

Frequently Asked Questions

How fast does the nervous system transmit signals?

Nerve signals travel at different speeds depending on the type of neuron and whether it has myelin insulation. The fastest neurons in the body, called alpha motor neurons, transmit signals at approximately 328 feet (100 meters) per second. This speed allows your body to react to stimuli in milliseconds. Slower neurons without myelin coating transmit signals at around 3 feet per second, which is adequate for functions that don’t require split-second timing.

Can the nervous system repair itself after damage?

The nervous system has limited regenerative capacity compared to other body tissues. Peripheral nerves outside the brain and spinal cord can regrow slowly after injury, though recovery is often incomplete. The central nervous system—the brain and spinal cord—has minimal regenerative ability, making injuries to these structures particularly serious. However, the brain demonstrates neuroplasticity, the ability to form new neural connections and reorganize existing ones, which allows some functional recovery after injury through rehabilitation.

What’s the difference between the brain and the nervous system?

The brain is one component of the nervous system—the central processing unit—but not the entire system. The nervous system encompasses the brain, spinal cord, and all the nerves throughout your body. Your brain integrates information and coordinates responses, while the spinal cord relays signals and handles some reflexes. The peripheral nerves carry information between your central nervous system and the rest of your body. All three components work together as an integrated communication network.

Why do some body functions happen automatically while others require conscious control?

This division reflects evolutionary efficiency. Automatic functions handled by the autonomic nervous system—like heartbeat, digestion, and breathing—are too critical for survival to rely on conscious attention. You’d forget to breathe while sleeping if these processes required active thought. Meanwhile, voluntary functions controlled by the somatic nervous system—like walking, speaking, and manipulating objects—benefit from conscious control because they require flexible responses to changing environmental conditions. Some functions, like breathing, bridge both categories: normally automatic but overridable by conscious control when needed.

The Continuous Operation

Your nervous system never truly rests. Even during sleep, it maintains vital functions, processes memories, and monitors for threats. The autonomic nervous system adjusts heart rate and breathing throughout the night. The brain cycles through different sleep stages, each serving distinct purposes in memory consolidation and physical restoration. Sensory systems remain partially active, ready to rouse you if something requires attention.

This perpetual activity demands significant energy. The brain, despite comprising only 2% of body weight, consumes approximately 20% of your body’s energy at rest. Neurons require constant fuel to maintain the ion gradients that enable electrical signaling and to produce the neurotransmitters that facilitate communication between cells.

The nervous system’s complexity emerges from relatively simple building blocks—neurons and their connections—organized into elaborate networks through development and learning. Each experience you have, skill you learn, and memory you form reflects changes in these neural networks, demonstrating the system’s remarkable adaptability throughout life.

Sources:

1. World Health Organization (2024). Over 1 in 3 people affected by neurological conditions. https://www.who.int/news/item/14-03-2024
2. Cleveland Clinic (2023). Nervous System: What Does It Do? https://my.clevelandclinic.org/health/body/21202-nervous-system
3. Institute for Quality and Efficiency in Health Care (2023). How does the nervous system work? https://www.ncbi.nlm.nih.gov/books/NBK279390/
4. National Institute of Child Health and Human Development. What does the nervous system do? https://www.nichd.nih.gov/health/topics/neuro/conditioninfo/functions