brain, spinal cord, and nerve disorders
Overview of Spinal Cord Disorders
Anatomy of the Spinal Cord
The Spinal Cord is the main pathway of communication between the brain and the rest of the body. It is a long, thick, fragile structure that extends downward from the base of the brain. The cord is protected by the back bones (vertebrae) of the spine (spinal column). The vertebrae are separated and cushioned by disks made of cartilage. The spine is divided into four sections, and each section is referred to by a letter. Cervical (C): Neck Thoracic (T): Chest Lumbar (L): Lower back Sacral (S): Pelvis and tailbone Within each section of the spine, the vertebrae are numbered beginning at the top. These labels (letter plus a number) are used to indicate locations (levels) in the spinal cord. Doctors can sometimes determine where the spinal cord is damaged—the level—based on the symptoms a person has. For examples, if a person's legs, trunk, and hands are paralyzed but the person can move shoulders and elbows normally, the cervical spinal cord between levels 7 and 8 (C7 to C8) is damaged. Along the length of the spinal cord, 31 pairs of spinal nerves emerge through spaces between the vertebrae. Each spinal nerve runs from a specific vertebra in the spinal cord to a specific area of the body. Based on this fact, the skin’s surface has been divided into areas called dermatomes. A dermatome is an area of skin whose sensory nerves all come from a single spinal nerve root. Loss of sensation in a particular dermatome enables doctors to locate where the spinal cord is damaged. The surface of the skin is divided into specific areas, called dermatomes. A dermatome is an area of skin whose sensory nerves all come from a single spinal nerve root. Sensory nerves carry information about such things as touch, pain, temperature, and vibration from the skin to the spinal cord. Spinal roots come in pairs—one of each pair on each side of the body. There are 31 pairs: There are 8 pairs of sensory nerve roots for the 7 cervical vertebrae. Each of the 12 thoracic, 5 lumbar, and 5 sacral vertebrae has one pair of spinal nerve roots. In addition, at the end of the spinal cord, there is a pair of coccygeal nerve roots, which supply a small area of the skin around the tailbone (coccyx). There are dermatomes for each of these nerve roots. Sensory information from a specific dermatome is carried by sensory nerve fibers to the spinal nerve root of a specific vertebra. For example, sensory information from a strip of skin along the back of the thigh, is carried by sensory nerve fibers to the 2nd sacral vertebra (S2) nerve root. A spinal nerve has two nerve roots (a motor root and a sensory root). The only exception is the first spinal nerve, which has no sensory root. Motor root:The root in the front (the motor or anterior root) contains nerve fibers that carry impulses (signals) from the spinal cord to muscles to stimulate muscle movement (contraction). Sensory root:The root in the back (the sensory or posterior root) contains nerve fibers that carry sensory information about touch, position, pain, and temperature from the body to the spinal cord. Doctors can often tell where the spinal cord is damaged based on symptoms and results of a physical examination. Nerves from the lowest parts of the spinal cord go to the anus, not to the feet. The spinal cord ends in the lower back (around L1 or L2), but the lower spinal nerve roots continue, forming a bundle that resembles a horse’s tail (called the Cauda Equina Syndrome ). The spinal cord is highly organized. The center of the cord consists of gray matter shaped like a butterfly. Its "wings" are called horns: The front (anterior or motor) horns contain nerve cells that carry signals from the brain or spinal cord through the motor root to muscles. The back (posterior or sensory) 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. The outer part of the spinal cord consists of white matter that contains pathways of nerve fibers (called tracts or columns). Each tract carries a specific type of nerve signal either going to the brain (ascending tracts) or from the brain (descending tracts). 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. 