Spinal nerves carry nerve impulses to and from the spinal cord through two nerve roots:
Motor (anterior) root: Located toward the front, this root carries impulses from the spinal cord to muscles to stimulate muscle movement.
Sensory (posterior) root: Located toward the back, this root carries sensory information about touch, position, pain, and temperature from the body to the spinal cord.
In the center of the spinal cord, a butterfly-shaped area of gray matter helps relay impulses to and from spinal nerves. The "wings" are called horns.
Motor (anterior) horns: These horns contain nerve cells that carry signals from the brain or spinal cord through the motor root to muscles.
Posterior (sensory) horns: These horns contain nerve cells that receive signals about pain, temperature, and other sensory information through the sensory root from nerve cells outside the spinal cord.
Impulses travel up (to the brain) or down (from the brain) the spinal cord through distinct pathways (tracts). Each tract carries a different type of nerve signal either going to or from the brain. The following are examples:
Lateral spinothalamic tract: Signals about pain and temperature, received by the sensory horn, travel through this tract to the brain.
Dorsal columns: Signals about the position of the arms and legs travel through the dorsal columns to the brain.
Corticospinal tracts: Signals to move a muscle travel from the brain through these tracts to the motor horn, which routes them to the muscle.