Merck Manual

Please confirm that you are not located inside the Russian Federation

honeypot link

Spinal Cord

By

Kenneth Maiese

, MD, National Heart, Lung, and Blood Institute

Last full review/revision Mar 2021| Content last modified Mar 2021
Click here for the Professional Version
GET THE QUICK FACTS
Topic Resources

The spinal cord is a long, fragile tubelike structure that begins at the end of the brain stem and continues down almost to the bottom of the spine. The spinal cord consists of bundles of nerve axons forming pathways that carry incoming and outgoing messages between the brain Brain The brain’s functions are both mysterious and remarkable, relying on billions of nerve cells and the internal communication between them. All thoughts, beliefs, memories, behaviors, and moods... read more Brain and the rest of the body. The spinal cord contains nerve cell circuits within itself that control coordinated movements such as walking and swimming, as well as urinating. It is also the center for reflexes, such as the knee jerk reflex (see figure Reflex Arc: A No-Brainer Reflex Arc: A No-Brainer When a neurologic disorder is suspected, doctors usually evaluate all of the body systems during the physical examination, but they focus on the nervous system. Examination of the nervous system—the... read more ).

Like the brain, the spinal cord is covered by three layers of tissue (meninges). The spinal cord and meninges are contained in the spinal canal, which runs through the center of the spine. In most adults, the spine is composed of 33 individual back bones (vertebrae). Just as the skull protects the brain, vertebrae protect the spinal cord. The vertebrae are separated by disks made of cartilage, which act as cushions, reducing the forces on the spine generated by movements such as walking and jumping. The vertebrae and disks of cartilage extend the length of the spine and together form the vertebral column, also called the spinal column.

How the Spine Is Organized

A column of bones called vertebrae make up the spine (spinal column). The vertebrae protect the spinal cord, a long, fragile structure contained in the spinal canal, which runs through the center of the spine. Between the vertebrae are disks composed of cartilage, which help cushion the spine and give it some flexibility.

Like the brain, the spinal cord is covered by three layers of tissue (meninges).

How the Spine Is Organized
How the Spine Is Organized

Spinal nerves: Emerging from the spinal cord between the vertebrae are 31 pairs of spinal nerves. Each nerve emerges in two short branches (roots):

  • One at the front (motor or anterior root) of the spinal cord

  • One at the back (sensory or posterior root) of the spinal cord

The motor roots carry commands from the brain and spinal cord primarily to skeletal muscles to control movement.

The sensory roots carry sensory information (pain, temperature, vibration, limb position) to the brain from other parts of the body.

Cauda equina: The spinal cord ends about three fourths of the way down the spine, but a bundle of nerves extends beyond the cord. This bundle is called the cauda equina because it resembles a horse’s tail. The cauda equina carries nerve impulses, both motor and sensory, to and from the legs.

Like the brain, the spinal cord consists of gray and white matter. The butterfly-shaped center of the cord consists of gray matter. The front wings (usually called anterior or ventral horns) contain motor nerve cells (neurons), which transmit information from the brain or spinal cord to muscles, stimulating movement. The back part of the butterfly wing (usually called the posterior or dorsal horns) contains sensory nerve cells, which transmit sensory information from other parts of the body through the spinal cord to the brain. The surrounding white matter contains columns of nerve fibers (axon bundles) that carry sensory information to the brain from the rest of the body (ascending tracts) and columns that carry motor impulses from the brain to the muscles (descending tracts).

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version
Others also read

Test your knowledge

Overview of the Autonomic Nervous System
The sympathetic nervous system is responsible for each of the following functions EXCEPT:
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID

Also of Interest

Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
TOP