Key components of a joint: bones, cartilage, ligaments, tendons, and fluid

Anatomy of a healthy knee joint

To understand arthritis, study a normal joint. Where two bones come together, each is lined by a cartilage cap. These bones are linked together by strong ligaments. The inner juncture is lined by a joint capsule (synovial membrane) containing lubricating joint fluid between the two surfaces, allowing for near-frictionless motion.

Breaking down the knee's anatomy

The human knee is a remarkably complex structure carrying the full weight of the body throughout a person’s life while allowing a number of complex twists, flexes, and extensions. It's also one of the body's biggest weaknesses—the location of chronic pain and replacement surgeries for millions of Americans.

Real surgical footage reveals what arthritis looks like up close

Arthritis is a painful condition of human joints that often results from the loss or breakdown of the soft cartilage padding that naturally exists between bones. This video shows footage from an actual knee surgery that beautifully demonstrates the difference between normal cartilage and the degenerative cartilage seen in osteoarthritis.

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.

Adhesion molecules and intercellular junctions allow cells to connect together

While some organic structures are mostly composed of non-cellular components (e.g., collagen and calcium phosphate minerals in bones), tissues and organs composed of connected cells rely on specialized proteins and connections to create watertight seals that protect cells within the interior from environmental molecules.

Arthritis explained, with Dr. Nick Golinvaux

Arthritis, a condition affecting millions globally, is more than just joint pain—it’s a breakdown of cartilage that cushions bones, leading to stiffness, swelling, and discomfort. While often associated with aging, arthritis can affect people of all ages, especially after injuries. Though there’s no cure yet, treatments range from medication and physical therapy to surgical interventions like joint replacements.

The collapse of gas bubbles in the joint synovial fluid causes 'cracking' knuckles

The human population can be divided into two categories: those who crack their knuckles and those who don't. Do you know the technical term for this phenomenon is "tribonucleation?" What actually happens inside a knuckle when it pops? This visual explainer breaks down finger joint popping in real time.

Learn about the basic anatomy of mosquitoes

This short explainer video breaks down the mosquito's general body components, highlighting how mosquitoes breathe, fly, and more. It also touches on how experts can tell different mosquito species apart.

Seven things you might not know about blood

The red stuff currently pumping throughout your body is a type of connective tissue that is both a solid and a liquid. The liquid portion—plasma—acts as a carrier for the solid portion, which includes blood cells and their biological brethren. Your body is constantly refreshing its supply of blood, creating new cells to replace those that have expired or died. This article overviews some lesser-known facts about blood (and why it's not always red).

Manholes connect underground sewer and water drain pipes

Wherever a portion of sewer is connected to another, a manhole is built. These serve both as access points for maintenance and as connectors for the system. This video shows how crucial manholes are for proper sewer functioning.

What's the point of pain?

It's notoriously hard to define pain, though everyone knows what it is. From day to day aches to the worst pains imaginable, this video goes into what researchers know about the purpose of pain. An estimated quarter of all adults live with chronic pain, which is defined as at least three months of pain.

Aging is a complex biological process affecting our cells, tissues, and organs

With each passing decade, researchers uncover additional causes and effects of this seemingly unstoppable process. This visually stimulating video dives into our current understanding of aging, complete with the biological hallmarks researchers use to study aging at the cellular level (biological age).

We hear because soundwaves are converted into electrochemical signals in our ears

This science teacher video systematically walks through the biology of the outer, middle, and inner ear. The explanation starts with the auricle, an external part that funnels sound through the auditory canal, and the tympanic membrane (the ear drum), which vibrates when sounds hit it. Beyond that, as the video details, is the eustachian tube, which is connected to the back of our throats and allows air to pass in and out to equalize ear pressure.

What are the universal human rights?

This video outlines what basic human rights are, who gets to pick them, who enforces them, and how. The basic idea of human rights states that each of us is entitled to the same basic rights and freedoms, no matter who we are or where we are born....

Vitamins are micronutrients human bodies need but don't naturally produce

Each vitamin is found in specific portions of a normal human diet and supports normal human functioning in distinct ways. Vitamin A is found in red meat, carrots, and potatoes and supports vision and skin health, while Vitamin D (common in fish and mushrooms) helps absorb calcium. See sources and uses of each vitamin with this chart.

Myokines are molecules that facilitate some of the benefits of exercise

When muscles contract, they release ‘hope molecules’ (myokines) such as IL-6 and irisin. These proteins then travel through the bloodstream to reduce inflammation, improve insulin sensitivity, and even support brain repair. This piece illustrates how movement triggers a systemic healing cascade throughout the human body.

A primer on human tears

Tears are one of the many behaviors that differentiate humans from the rest of the animal kingdom. Why do we cry? This comprehensive and well-written essay explores various theories about why we cry, observes tear fluid as the only one that does not elicit disgust, and attempts to interpret the meaning of tears in different circumstances. See what all the fuss is about here.

Visualize the components of fireworks

This article provides animated diagrams depicting how different parts of fireworks function. The elements work together through timed mechanisms to produce desired effects.

Minerals, crystals, rocks, and gems explained

Have you ever wondered what differentiates a mineral from a rock or a crystal from a gem? This three-minute video from the American Museum of Natural History elaborates on the unique properties and compositions that separate minerals, rocks,...

Snakes move around by coordinating hundreds of muscles

These muscles connect to their vertebrae, and allow the creature to move in various unique ways. Snakes can slither, move in a straight line, swim, jump and even "fly."

Friction is the force that resists the sliding of surfaces along one another

Friction always acts to resist movement and is determined by how rough the surfaces are and how hard they are pressed together. In the case of fluids, friction arises from the relative motion between adjacent fluid layers, which act like sliding surfaces.

How solar systems form

Learn how our sun, the planets, and other solar system bodies came to be with these videos and an infographic from NASA. Use this resource to visualize how the solar system formed and to model and describe the process.

Jam and jelly differ in texture because of how fruit is processed

Jam contains crushed fruit with preserved pulp and fibers for a thicker, spreadable texture. Jelly is made from filtered fruit juice and produces a smooth, translucent gel. The distinction reflects preservation methods developed to extend fruit shelf life while tailoring texture and appearance.

See how Stonehenge was built

This short animation shows how human beings managed to lug 30-ton stones over miles of prehistoric English countryside and stand them up The Stone Age engineering involved using giant wooden rollers and carving precisely interlocking tongue-and-groove joints to hold the heavy stones in place.

How fighter jet ejections work

One of the most complex pieces of equipment in a fighter jet is the pilot's ejection apparatus, and the process of ejecting is far more challenging and violent than its depicted in film. This six-minute video breaks down the protocol step-by-step.

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

About 2,000 US babies are born annually without some portion of their limbs, potentially leading to a lifetime of pricey prosthetics.

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.

Explore an interactive map built from more than 100,000 survey responses on where people find joy in their lives

Watch this video that uses Lego bricks to explain how venture capital works.

Firework or sparkler burns, even if they cover a relatively small area of skin, can significantly affect our range of motion.

Watch how viruses like Ebola can spill over from animals to humans—and vice-versa.

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

After 25 people used virtual reality headsets to practice flying with virtual wings—flapping their arms—their visual cortex responded to the wings almost as if they were real arms, treating them as body parts.

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.

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.

Alzheimer's can lead to brain shrinkage, with an average of around 2% of volume reduction per year

Legendary architect Frank Lloyd Wright designed the SC Johnson headquarters in Wisconsin, aiming to make a cathedral-like workplace

The word 'jazz' evolved from 'jasm,' 19th-century American slang for 'energy'

Explore chaos in this simulation of two double pendulums, where small differences in the release angles produce wildly different outcomes.

Corals are themselves not coral reefs—the term refers to the tiny marine invertebrates that build the rigid reef.

Take a 3D tour of the Hajj, Islam's annual pilgrimage to Mecca, undertaken by over 1.5 million Muslims.

While atoms are normally made of protons, neutrons, and electrons, exotic ones have been built with antimatter—alternate versions of normal matter that live for fractions of a second and are about a billion times as rare.

Fear or disgust related to clusters of holes and cracks, called trypophobia, may stem from evolutionary processes to help us avoid pathogens.

Watch how algorithms can be designed to train themselves and self-improve without human input, to the point where the optimized code is too complex for programmers to understand.

Hear 50 years of iconic hip-hop samples, the genre's foundational looped tracks

Objects can be 3D printed with light by projecting 2D computerized tomography (CT) scans onto rotating cylinders of resin, which solidify upon exposure.

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

The first steps to rebuilding your credit score include getting to know exactly what's on your credit report and figuring out how far you are from the '700 club,' or 'good score' range.

To reduce wrinkles in clothing, research recommends gentle wash cycles with more water and tumble drying with smaller loads and longer times.