The nervous system is made up of the brain, spinal cord, and several kinds of nerves that are found throughout the body. These create complex circuits through which animals experience and respond to sensations.
A familiar type of nervous system circuit is a reflex. Reflexes are simple networks found in the nervous system of all animals. For example, when the eyelid is touched, it closes; when the toe is pinched, the foot pulls away “automatically.”
Many different types of diseases can affect the nervous system, including birth defects, infections, inflammatory conditions, poisoning, metabolic disorders, nutritional disorders, injuries, degenerative diseases, or cancer. Neurologic diseases are often more common in a particular breed or sex, or tend to occur at a certain age.