The spinal cord is a long bundle of nerves and cells that extends from the lower portion of the brain to the lower back. It carries signals between the brain and the rest of the body.
This article covers the key anatomy of the spinal cord and its functions.
It also provides some information about spinal cord injuries.
The length of the spinal cord varies from person to person. According to some estimates, females have a spinal cord of about 43 centimeters (cm), while males have a spinal cord of about 45 cm.
The spinal cord comprises three parts: the cervical (neck), thoracic (chest), and lumbar (lower back) regions.
Three layers of tissue protect the spinal cord: the dura mater, arachnoid mater, and pia mater. Doctors call these layers “meninges.” The layers are as follows:
- Dura mater: This is the outermost layer of the spinal cord’s meninges. It is a tough, protective coating.
- Epidural space: Between the dura and arachnoid space is the epidural space. This is where doctors may insert local anesthetic to reduce pain during childbirth and some surgical procedures, such as those to operate on a lung or abdominal aneurysm.
- Arachnoid mater: The arachnoid mater is the middle layer of spinal cord covering.
- Subarachnoid space: This is located between the arachnoid mater and pia mater. Cerebrospinal fluid (CSF) is located in this space. Sometimes, a doctor has to sample CSF to test for the presence of infection, such as meningitis. They can also inject local anesthetic into this space for some surgical procedures, such as a cesarean delivery or a knee replacement.
- Pia mater: The pia mater is the layer that directly covers the spinal cord.
Covering the spinal cord and its protective layers is the vertebral column, or the spinal bones. These bones start at the base of the skull and extend down to the sacrum, a bone that fits into the pelvis.
The cervical, thoracic, and lumbar regions have different numbers of bones. Most people have seven spinal bones in the cervical column, 12 in the thoracic column, and five in the lumbar column.
If a person were to take a “slice” of the spinal cord horizontally, they would see a circular area in the middle covered in protective layers (the meninges). Extending from this circular area are nerve projections. These extend from the spinal cord to provide sensation to different areas in the body.
Key areas of a cross-section of the spinal cord include:
- Gray matter: The gray matter is the dark, butterfly shaped region of the spinal cord made up of nerve cell bodies.
- White matter: The white matter surrounds the gray matter in the spinal cord and contains cells coated in myelin, which makes nerve transmission occur more quickly. Nerve cells in the gray matter are not as heavily coated with myelin.
- Posterior root: The posterior root is the part of the nerve that branches off the back of the spinal column. Looking at the spinal cord cross-section, the top wings of the gray matter “butterfly” reach toward the spinal bones. The bottom wings are toward the front of the body and its internal organs.
- Anterior root: The anterior root is the part of the nerve that branches off the front of the spinal column.
- Spinal ganglion: The spinal ganglion is a cluster of nerve bodies that contain sensory neurons.
- Spinal nerve: The posterior and anterior roots come together to create a spinal nerve. There are 31 pairs of spinal nerves. These control sensation in the body, as well as movement.
The spinal cord does not extend for the entire length of the spine. It usually stops in the top parts of the lumbar spine.
For adults, this is usually the first or second lumbar vertebrae. Children’s spinal cords may stop slightly lower, at the second or third lumbar vertebrae.
The spinal cord plays a vital role in various aspects of the body’s functioning. Examples of these key functions include:
- Carrying signals from the brain: The spinal cord receives signals from the brain that control movement and autonomic functions.
- Carrying information to the brain: The spinal cord nerves also transmit messages to the brain from the body, such as sensations of touch, pressure, and pain.
- Reflex responses: The spinal cord may also act independently of the brain in conducting motor reflexes. One example is the patellar reflex, which causes a person’s knee to involuntarily jerk when tapped in a certain spot.
These functions of the spinal cord transmit the nerve impulses for movement, sensation, pressure, temperature, pain, and more.
The spinal cord is a delicate part of the body. It is therefore susceptible to injury. Vehicle accidents, gunshot wounds, and damage while playing sports are all potential causes of spinal cord injury.
Due to the part it plays in providing movement and sensation, sustaining damage to any part of the spinal cord could cause permanent changes to a person’s functioning.
Healthcare providers may not always know right away how much function a person will lose after injury.
There are two main types of spinal cord injury: complete and incomplete.
A complete spinal cord injury causes a complete loss of sensation and motor function below the level of the injury.
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According to the American Academy of Neurological Surgeons (AANS), almost half of all spinal cord injuries are complete. The spinal cord does not necessarily need to be physically cut for a complete injury to occur, but the damage might be so significant that blood cannot flow to the nerve tissue, causing it to die.
An incomplete spinal cord injury occurs when the person still has some function at or below the point of the injury. They may still be able to move one side of the body or have some function or sensation.
According to the AANS, around 250,000–450,000 people in the United States are living with a spinal injury.
Sometimes, surgical procedures and the passing of time can reduce some of the effects of a spinal cord injury. Doctors will often use repeated imaging scans and nerve function studies to determine how significant a person’s spinal cord damage may be.
The spinal cord is a complex organization of nerve cells responsible for movement and sensation. It carries signals between the brain and the rest of the body.
Having knowledge of the location and structure of the protective spinal cord coverings can help healthcare professionals provide pain relief for certain procedures.
Spinal cord injuries can range from sensory loss to incomplete or complete paralysis. A person should always wear protective equipment when playing sports or during other activities to reduce their risk of injury.
However, it will not always be possible to prevent such an injury.