What is the peripheral nervous system?

A web of sensory neurons in the skin help filter out background sensations

The somatosensory system helps us organize and navigate our surroundings, enabling us to understand our bodies in relation to our environment and also filter out minor sensations that are basically background noise so they aren't overwhelming to our bodies. Meanwhile, viscerosensation—or internal sensation—refers to the internal sensory neuron system that conveys information from internal organs to the brain.

Human anatomy 101: the body's systems

Human life is made possible by the body's ten major systems, which maintain homeostasis by responding to incoming sensory and biochemical input. Each system must work independently and collaboratively for the body to maintain health and respond appropriately to its internal and external environments. The bones of the skeletal system, for example, give the body its shape and protect organs while also facilitating movement with the muscular system.

What is the muscular system?

The muscular system comprises three distinct types of muscle: smooth, cardiac, and skeletal. Cardiac muscles make up the heart, whereas smooth and skeletal muscles are found throughout the body. Smooth muscles line blood vessels and most organs, and skeletal muscles are responsible for moving the body or holding it stationary. All muscles are made of muscle cells or fibers, which give them the ability to contract.

A beginner’s guide to the brain

Small but powerful, the brain constitutes only about 2 percent of the human body. However, it runs jus about everything, day and night, all year round. Learn about the different parts of the human brain, as well as its unique defenses, like the blood brain barrier in this four-minute video.

Meet the 12 cranial nerves

Your cranial nerves are a set of 12 paired nerves in your brain. They help your brain and body communicate senses, movement or both.

Explore the heart in this interactive 3D model

The heart is the fleshy muscle at the heart (pun intended) of the circulatory system. The heart is segmented into four chambers: two for intake (the right side) and two for output (the left side). Controlled via the autonomic nervous system, also known as the involuntary nervous system, the heart typically beats 60 to 100 times per minute, sending nutrient- and oxygen-rich blood throughout the body.

An interactive dive into the immune system

Our bodies are equipped with an incredible system able to fight off invasive pathogens to protect us from illness. The complicated system includes lymph nodes, the spleen, bone marrow, and even the tonsils. But this same system can turn against itself, a condition known as autoimmune disorders. Follow along with this thorough, engaging explainer on the human body's defense system.

How humans breathe without thinking about it

We breathe without thinking about it thanks to the body’s respiratory system and autonomic nervous system, which controls vital functions. Breathing transports oxygen to the body’s cells to keep them working and clears the body of carbon...

Sleep disorders can exacerbate neurological and other health conditions

Brain regions that control sleep sit adjacent to those that regulate the autonomic nervous system, which controls involuntary bodily functions like heart and breathing rates. These neighbors influence each other, meaning poor sleep can impair or negatively impact the ANS, further disturbing sleep.

Nerve axons become damaged by leprosy, so patients may lose feeling in their skin

Infection of the peripheral nerves—nerves outside the brain and spinal cord—is a known complication of leprosy. That damage can cause patients to lose their sense of touch and the ability to feel pain or temperature in affected areas, leading to accidental injury.

The limbic system drives emotion, memory, and survival instincts in the brain.

This interconnected group of brain structures—including the amygdala, hippocampus, thalamus, and hypothalamus—processes emotional responses, regulates bodily functions, and plays a key role in memory and learning.

Scientists have unraveled new details about which nerve cells control goose bumps

Research in 2016 revealed that at least eight different types of neurons are associated with the sympathetic nervous system. One finding revealed that goose bumps and nipple erection are caused by neurons specialized to regulate these specific functions by controlling the erectile muscles in those tissues.

Neurons send signals through electrical impulses and chemical messengers

By converting electrical signals into chemical messages at synapses, neurons allow information to travel throughout the nervous system. With repeated use, synapses grow stronger, enhancing the associations between neurons.

The pancreas releases digestive enzymes and regulates blood sugar

The pancreas weighs about the same as a deck of cards and is smaller than the average adult human hand. This lopsided glandular organ controls blood sugar levels through insulin production and helps the body digest food by creating a neutralizing tonic filled with digestive enzymes.

The brain doesn't seem to massively rewire following amputation—upending earlier beliefs about phantom pain

The findings, published in 2025, traced three amputees' brain-body maps and how they respond to body part movements—both before and after scheduled arm amputations. The unexpected neural stability suggests that the unchanged pathways for the missing limbs may explain why people continue to feel them so acutely.

Nanoplastics can bypass the blood-brain barrier and may harm the nervous system

Nanoplastics are formed from the breakdown of microplastics and can breach cells. Their large surface area relative to size allows them to carry higher concentrations of forever chemicals than the surrounding environment into sensitive organs.

An explanation of TCP/IP, which helps transmit data across the internet like a club sandwich

The system consists of several layers—application, transport, internet, and network—each responsible for specific tasks. These include interacting with a web browser, checking for errors, sending packets of data across various networks to avoid congestion on their way to a destination address, and managing the transmission of information across hardware, such as an Ethernet cable.

Paralysis from polio occurs in under 1% of infections

About 1 in 200 cases of infection causes paralysis. For paralysis to occur, the virus travels from the throat, intestines, and gut to infect specific cells within the spinal cord and brain stem that control movements. Within hours of invading the nervous system, paralysis can occur. The virus can be present in bodily secretions and stool for multiple weeks post-infection.

Explore how the placenta acts as lungs, kidneys, and more in the womb

This temporary organ, formed from maternal and embryonic tissue, ultimately attaches to a fetus via the umbilical cord. It transports nutrients, oxygen, antibodies, and more from the mother to the developing fetus. It also carries carbon dioxide and waste away from the fetus. The placenta—which forms only during pregnancy—is expelled during childbirth, or it needs to be removed to prevent toxic maternal infections and extreme blood loss.

There are multiple types of multiple sclerosis—they differ by attack patterns

When your immune system targets the nervous system, this can cause new or worsening symptoms and the development of scarring or damage within the central nervous system. Relapsing-remitting MS is the most common type of the disease—it includes progressive bouts of attacks that occur months or years apart.

'Artificial embryos': The hidden steps in forming a spine

Somitogenesis is the process by which segmented body structures like vertebrae form in embryos. While the process is well understood in animals like mice or zebrafish it is difficult to study in humans. But now, researchers have created a model of somitogenesis, using pluripotent stem cells, called an axioloid.

Recent research found that the brain doesn't seem to massively rewire following amputation—upending earlier beliefs about the cause of phantom limb pain.

Not all public lands are part of the National Park System

The entire National Park System is located on public lands. There are four different land management agencies in the United States, including the National Park Service.

Central vestibular disease is another common cause of vertigo

Unlike peripheral vestibular disease that is caused by factors like inflammation in the inner ear, central vestibular disease involves dysfunction of one or more parts of the central nervous system. Vertigo of this type may last for seconds, hours, or even days. It's typically caused by issues with the brain stem and cerebellum and could be caused by stroke, tumor, and vestibular migraine, among other conditions.

US Customs and Border Protection traditionally operates at ports of entry and along US borders

CBP manages security at official border crossings and patrols areas between ports of entry to prevent unauthorized crossings. View details of the agency's mission, organizational structure, and approach to managing the United States' physical borders.

The Deep Space Network keeps NASA linked to spacecraft billions of miles away

NASA's DSN is a global system of giant radio antennas that receive data from faraway spacecraft like Voyager 1 and the James Webb Space Telescope. It is sensitive enough to detect a signal as weak as a single light bulb from billions of miles away.

The United States is one of only around two dozen countries with a fully federal system of government, in which power is divided between national and state governments.

While the sun's gravity keeps the planets in orbit, their gravity also pulls on the sun, causing it and everything else in the solar system to orbit around a mutual balance point called the barycenter—the true center of the solar system.

Learn how your body is, scientifically, like a firework with its own slow, controlled burn.

The syncytiotrophoblast is the outer layer of the placenta and the largest human cell, spanning an area about twice that of a king-sized bedsheet.

Planarian flatworms are small, aquatic worms with exceptional regenerative capabilities. When cut, the worms can regenerate multiple bodies in a matter of weeks.

Bone marrow (soft tissue found inside certain bones) generates roughly 500 billion new blood cells each day

Ebola infects and disables immune cells, triggering a cascade of events that leads to small blood clots throughout the body, weakening blood vessels and interrupting blood flow to key organs.

Read a deep dive on the 'all-purpose healing' peptide BPC-157.

According to the physics of black holes, our 4D reality may be a hologram—a projection of information coded on a 2D surface on the edge of the universe.

See how each of the more than two million known species relates to each other—and to common ancestors—in this zoomable tree of life.

Visualize how CRISPR-Cas9—a type of immune system used by single-celled organisms to attack invasive viruses—targets and makes precise changes to a gene's DNA.

The hormonal disorder PCOS was renamed PMOS in 2026, a move designed to improve care and research by shifting the focus to the hormonal causes of this condition that affects 1 in 8 women.

Lesser-known phobias include turophobia, or the fear of cheese, and nomophobia, the fear of being without your cell phone.

The animatronic shark from Steven Spielberg's 'Jaws,' the first modern blockbuster, was a complex underwater apparatus called 'Bruce.'

The Great Salt Lake's distinct dual coloration results from high-salinity organisms that only live in the northern portion and produce a purple protein.

This site reaches millions of visitors who are tired of AI chatbots and seeking human connection. Pretend to be an AI chatbot and ask questions, provide answers, and draw for people in real time.

Pure water does not conduct electricity because this flow of energy requires the movement of charged particles, and water is a neutral molecule.

Power lines are dotted with large, brightly colored balls to improve the visibility of these thin wires to helicopters and small planes and help prevent potential crashes.

Iran's Revolutionary Guard Corps is independent of Iran's regular army and is one of the most powerful and influential military-political organizations in the Middle East.

'Saturday Night Fever,' the 1977 film that introduced disco to the mainstream, was based on a fabricated magazine story.

While El Niño moves warm Pacific Ocean waters east along the equator, La Niña moves them west, shifting where rainfall will become more common for months.

Clever Hans was a 1900s horse that was believed to be able to solve math equations, tell time, and read and comprehend German, until a psychology student discovered how he got his answers.

For centuries, it was common to sleep in two shifts: a few hours at the beginning of the night, and a longer period beginning around midnight

The Nasdaq's 'Magnificent 7' companies are responsible for roughly 40% of the Nasdaq 100 index's gains, while the remaining 93 companies account for the other 60%.