A concussion is an injury to the brain that can be caused by a hard hit to the head or violent shaking of the brain.

Diabetes is a condition in which the hormone insulin isn't released in sufficient amounts, or at all. Insulin is produced by cells in the pancreas and regulates levels of sugar in the blood.

The endocrine system in the body's regulator. It is composed of tissues and organs throughout the body that secrete hormones.

Glands are specific structures that make and release hormones. An example is the thyroid gland, which releases hormones that control the rate of metabolism in the body.

Glands, such as those in the neck, are specific structures that make and release hormones.

Hormones are chemicals carried in the blood responsible for triggering a wide variety of changes in different parts of the body.

A nerve cell, also called a neuron, is the primary cellular building block in the nervous system.

There are two main sections of the nervous system - the central nervous system and the peripheral nervous system - which work together.

The peripheral nervous system contains nerves that form a network throughout the body that directs voluntary and involuntary activities. The spinal cord connects the brain to nerves throughout the body.

The peripheral nervous system consists of all the body's nerves located outside of the spinal cord and brain.

Located at the base of the brain, the pituitary gland regulates other glands in the body and is sometimes referred to as the master gland.

A stroke is caused by a lack of blood flowing to a portion of the brain, causing brain tissue to become damaged. A stroke can cause paralysis and/or brain damage.

If the thyroid gland produces too little or too much hormone, a wide variety of problems can occur.

Cartilage is found at the end of bones and joints. It enables the ends of bones to move smoothly against each other.

Bones are living tissue made of cells. Cells in bones use energy and oxygen for growth and repair.

A contusion, also referred to as a bruise, occurs when muscle tissue is injured and blood vessels are broken, causing a discoloration under the skin.

A joint is the place where two bones come together. The knee is an example of a hinge joint.