Spinal cord

The spinal cord is a long, thin structure made of special tissues called nervous tissue. It runs from the lower part of the brainstem, called the medulla oblongata, down through the backbone, known as the vertebral column, in animals with backbones, or vertebrate animals. In the middle of the spinal cord is a small, hollow space called the central canal, which holds a fluid called cerebrospinal fluid. The spinal cord is protected by layers of tissue called the meninges and is surrounded by bony parts of the spine known as the neural arches. Together with the brain, the spinal cord forms the central nervous system.

In humans, the spinal cord starts at the back of the head, near the occipital bone, and passes through an opening in the skull called the foramen magnum. From there, it enters a bony tunnel in the spine, called the spinal canal, beginning at the first cervical vertebrae. It goes down to a point between the first and second lumbar vertebrae, where it ends and becomes a group of nerves called the cauda equina. In adults, the spinal cord is about 45 centimeters long in men and 43 centimeters long in women. Its width changes along its length, being widest in the neck and lower back areas and narrower in the chest.

The spinal cord has many important jobs. It helps send messages from the brain to the rest of the body and brings back information from the body to the brain. It also helps control quick, automatic actions called reflexes, like pulling your hand away from something hot. The spinal cord contains special groups of cells called spinal interneurons that form patterns to control movements, such as walking, by creating rhythms in the muscles.

Structure

The spinal cord is the main pathway for information connecting the brain and the body. It is much shorter than the backbone that protects it. In humans, the spinal cord starts in the brainstem and goes down to a point near the second lumbar vertebra, ending in a thin extension called the filum terminale.

On average, the human spinal cord is about 45 centimetres long in males and 43 centimetres in females. It has special enlargements in the neck and lower back areas to control the arms and legs. The spinal cord is made of segments, each sending out pairs of nerves that connect to the body. These nerves carry sensory information to the brain and motor commands from the brain to the body.

The spinal cord is protected by three layers of tissue called meninges. These layers help keep the spinal cord safe and healthy. Inside the spinal cord, there is a central canal filled with cerebrospinal fluid, which helps protect and nourish the nerves. The spinal cord has grey matter in the center, where nerve cell bodies are located, and white matter on the outside, which carries nerve signals up and down the cord.

Development

The spinal cord forms from part of the neural tube as it develops. It goes through four main stages: the neural plate, neural fold, neural tube, and finally the spinal cord. Special signals help different parts of the spinal cord grow, creating cells that control movement and senses. As the spinal cord forms, it creates a small hollow space inside that later fills with fluid.

Studies have shown that some cells naturally stop growing to help the nervous system develop properly. This process is important for building the right connections in the spinal cord.

Spinal cord tracts

The spinal cord helps carry information to and from the brain using special pathways called tracts.

Ascending tracts

There are two main pathways in the spinal cord that carry information up to the brain. These are the dorsal column–medial lemniscus pathway and the anterolateral system.

The dorsal column–medial lemniscus pathway carries information about touch and position. Signals travel up the spinal cord and connect to special areas in the brain.

The anterolateral system carries information about pain and temperature. Signals also travel up the spinal cord and connect to areas in the brain that process these feelings.

Descending tracts

Descending tracts carry motor commands from the brain to the body. These pathways help control movements by connecting the brain to muscles through special nerve cells in the spinal cord.

The corticospinal tract is important for coordinated movements of the limbs. Signals travel from the brain down through the spinal cord to connect with nerve cells that control muscles.

Other functions

The spinal cord helps control many quick reactions in the body, called reflexes, without needing help from the brain. It also has special groups of nerve cells that create patterns for movements like walking.

In animals, there are connections that help detect light touches. In humans, knowing what to expect can change how the spinal cord reacts very quickly.

Clinical significance

A congenital disorder called diastematomyelia happens when part of the spinal cord is split, usually around the upper lumbar vertebrae.

Injury

Injuries to the spinal cord can happen when there is a strong force on the spine, like a fall or an accident. This can break the bones or the soft parts of the spine, and sometimes the spinal cord itself can be hurt. When this happens, a person might lose feeling or movement in parts of their body. In mild cases, they might only lose some hand or foot movement. In more serious cases, they might lose movement in their legs or all of their body below the injury.

Injuries to the upper parts of the spinal cord are common, as are injuries to the lower back part of the spine. Spinal injuries can also happen because of diseases, not just accidents.

Stenosis

Main article: Spinal stenosis

Spinal stenoses in the lower back are often caused by problems with the disks between the bones, changes in the joints, extra growth of bone, or the slipping of bones. Rarely, too much fat around the spine can press on the nerves and spinal cord.

Tumors

Main article: Spinal tumor

Spinal tumors can grow inside or outside the protective covering of the spinal cord.

Procedures

The spinal cord ends around the first and second lower back bones, but the space that holds special fluid in the spine goes further down. Doctors can take samples of this fluid from between the third and fifth lower back bones to check for problems, without hurting the spinal cord. In babies, the spinal cord grows longer as they develop.

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