Neurons are one kind of nerve cell that transmit signals throughout the body.

The brain has three main parts-- the brain stem, the cerebellum, and the cerebrum. Let's start with the brain stem. It consists of the midbrain, pons, and medulla oblongata. Located just above the brainstem are the thalamus and hypothalamus.

When you respond involuntarily to a hot object, a reflex arc begins when sensory neurons in your hand detect pain. Sensory neurons then carry information in the form of a nerve impulse to the spinal cord.

The backbone encases the spinal cord, a bundle of nerves that play a key role in the central nervous system.

Nerve impulses move across spaces called "synapses" via specific chemical messengers referred to as "neurotransmitters." Special structures located on the ends of axons release neurotransmitters into the synapse when an impulse is received.

A black hole is created when an extremely large star has a supernova explosion and the remaining core is swallowed by its own gravity. The gravitational forces within a black hole are so strong light is not able to escape.

Temperatures can reach 15 million degrees Celsius at the center of the sun.

As a comet orbits the sun, solar wind pushes the gases outward in a trailing tail.

Giant stars have a diameter of 10 to 100 times the size of the sun. White dwarfs are smaller stars that can be smaller than Earth.

The sun is the center of the solar system around which Earth and the other planets orbit. The planets travel in an ellipse around the sun.

The sun is the center of the solar system around which Earth, the other plants, and their moons revolve. Inertia causes planets to remain in motion. The pull of gravity between the sun and planets keeps the planets from flying off into space.

A supernova is a huge explosion that results when a massive star has burned up most of its fuel and breaks apart. The resulting core can form a smaller, dense star called a neutron star.

This webpage includes information about the amendments to the U.S. Constitution and their role in the history of the United States of America.

Educators can use America From Scratch (and its discussion guides) to engage the most important issues of the day, and to encourage critical thinking and promote civic engagement with their students.

This primary source set includes documents and images from the lives of American authors in the 19th century. A teacher guide is included to assist educators in utilizing the primary sources in their instruction.

An article based on data and evidence that includes charts and information that can be analyzed statistically by students.

This annotated slideshow adapted from KET's Electronic Field Trip to the Forest illustrates how blight decimated the American chestnut tree and the methods scientists use to identify and pollinate the remaining trees to create blight-resistant trees.