The Anatomy of the Spinal Cord

The spinal cord is part of the central nervous system. This long structure runs down the center of your back, and it mediates messages between the brain and the peripheral nerves. The spinal cord is primarily composed of nerves, which are organized in systematic pathways, also described as tracts. 

The spine (backbone) encloses and protects the spinal cord. Damage to the spinal cord can occur as a result of problems such as traumatic injuries, infections, and disease. Treatment for conditions that affect the spinal cord often includes rehabilitation and may also involve medication and/or surgery. 

Anatomy

The spinal cord is adjacent to and below the medulla, which is the lowest part of the brain. The top region of the spinal cord extends down from the medulla all the way to the lower back.

Cerebrospinal fluid (CSF), with nutrients and immune cells, flows around the spinal cord. Meninges, which are layers of protective connective tissue, surround the spinal cord and CSF.

Meninges are composed of three thin layers—the innermost pia mater, the middle arachnoid mater, and the outermost dura mater. All of these structures—the spinal cord, CSF, and meninges—are enclosed in the backbone, which is also referred to as the spine and the vertebral column. 

Structure and Location

From top to bottom, the regions of the spinal cord include the cervical, thoracic, lumbar, and sacral levels. Each of these levels corresponds to spinal nerves that emerge from the spinal cord toward structures of the body, such as the arms, legs, and trunk. 

A coating called myelin (a type of fat) insulates all nerves. The white matter tends to have more myelination than the grey matter, giving it a whiter appearance when viewed with a microscope. 

The grey matter of the spinal cord is shaped somewhat like an open-winged butterfly lying across the center of the spinal cord. This butterfly-shaped gray matter contains nerve roots. The white matter is composed of several tracts (pathways) that travel up and down the spinal cord. 

Regions of the spinal cord include the following.

Anterior Horn

This region is the frontal portion of the gray matter of the spinal cord, and it is composed of nerves that send motor signals to the spinal nerves. 

Lateral and Anterior Tracts

These white matter pathways carry motor signals down the spinal cord in the corticospinal tract. This tract travels all the way down the spinal cord at the front and sides of the white matter regions.

Motor control of the voluntary muscles (muscles you choose to move) travels through the spinal cord in the corticospinal tract. Motor signals are initiated in the motor strip, a region of the cerebral cortex of the brain.

These motor signals travel down the internal capsule, and then cross over to the other side of the body in the brain stem. From there, these messages are sent to the anterior horn and the lateral and anterior tracts of the spinal cord. The motor message exits the spinal cord through the ventral root (the front portion) of the spinal nerves. 

Dorsal Horn

This area is the posterior region of the grey matter. The spinal nerves deliver sensory messages such as light touch, position sense, and vibration to the dorsal horns. 

Posterior Tracts

Also described as the spinothalamic tract, this is a long, white matter pathway that extends all the way up the spine to the brain. The spinal cord mediates sensation coming from the skin, bones, and internal organs.

Your skin detects these sensations and sends messages from peripheral sensory nerves (embedded in the skin) to the spinal nerves, then to the dorsal horn and up through the spinothalamic tracts, crossing over to the other side of the spinal cord before reaching the brain.

Eventually, these messages reach the brain stem, then the thalamus, and then the sensory strip, which is directly behind the motor strip in the cerebral cortex of the brain.

Lateral Horn

The lateral horns of the spinal cord are located at the two sides of the gray matter. This area is composed of nerves that mediate autonomic functions of the body. The autonomic nervous system regulates involuntary functions (actions you don't purposely control), such as digestion and breathing. 

Function

The primary role of the spinal cord is to relay sensory, motor, and autonomic messages between the brain and the rest of the body. Myelinated nerves along the pathways of the spinal cord send electrical signals to each other to facilitate these actions. 

Motor 

The motor messages sent through the corticospinal tract eventually reach the corresponding muscle as the spinal nerve branches into smaller peripheral motor nerves that extend to the target muscle. As a result of this nerve stimulation, you can voluntarily move your arms, legs, neck, back, and abdominal muscles. 

Sensory 

Your spinal cord sends messages from your peripheral sensory nerves to your brain, allowing you to detect sensations that include light touch, vibration, pain, temperature, and the position of your body.

Autonomic 

The spinal cord sends messages to regulate the internal organs of the body. This includes control of smooth muscles, such as the muscles that move your lungs, stomach, intestines, bladder, and uterus. 

Associated Conditions

There are a number of medical problems that can affect the spinal cord. Disease of the spinal cord is often described as myelopathy. These conditions cause impairment of motor, sensory, and/or autonomic function.

Myelopathy also often causes spasticity, which is stiffness of the affected arm and/or leg. The symptoms of any spinal cord problem typically correspond to the section of the spinal cord that is impaired. Sometimes, spinal cord injuries also affect functions that are controlled by areas below the level of spinal cord damage due to disruption of the spinal cord tracts.

Conditions that affect the spine include:

Multiple sclerosis (MS)

This is a demyelinating condition that may affect the brain and/or spine. Multiple sclerosis lesions in the spine can cause weakness, sensory loss, tingling, and pain, and they may affect bowel and bladder function. 

Spinal Cord Compression

When the spinal cord is placed under physical pressure, weakness, sensory loss, and autonomic deficits can occur. Severe degenerative disease of the bone or cartilage of the spine can cause these structures to fall out of place—potentially resulting in physical impingement on the spinal cord. Metastatic (spreading throughout the body) cancer can cause spinal cord compression as well.

Trauma

An injury can cause the spine to move out of place and can even cause a spine fracture (break), which can injure the spinal cord. Injuries may also cause spinal cord compression due to bleeding, and an injury can directly damage the spinal cord.

Amyotrophic Lateral Sclerosis (ALS)

Sometimes called Lou Gehrig's disease, this is a rare condition characterized by the gradual degeneration of the motor neurons located in the spinal cord. ALS causes progressive weakness and, eventually, a complete loss of muscle control. As a result, most individuals affected by ALS need a high level of supportive care.

Currently, there is no cure for ALS. However, medications such as Radicava (edaravone), Rilutek (riluzole), and Relyvrio (sodium phenylbutyrate/ taurursodiol) can help relieve the symptoms and improve the quality of life for people with this condition.

Meningitis

An infection or inflammation of the meninges, often described as spinal meningitis, can cause symptoms such as a headache, stiff neck, fever, nausea, and vomiting. Episodes of bacterial meningitis require antibiotics. Other types of meningitis may require anti-inflammatory therapy or other treatments that target the cause. 

Vitamin B12 Deficiency

A deficit in this vitamin can cause many medical issues, including anemia, nerve damage, and subacute combined degeneration of the spinal cord, which is a very rare demyelinating condition that can cause weakness, sensory loss, and stiffness. 

Cancer

Spinal cord cancer is not common, but tumors can develop in any region of the spinal cord. Late-stage cancer often metastasizes to the spine and/or spinal cord, causing spinal cord compression. Meningeal carcinomatosis is the spread of cancer cells throughout the meninges and CSF.

Spinal Cord Infarct

If the blood supply to the spinal cord is interrupted, an area of the spine might not receive an adequate supply of blood. This can lead to severe damage, with resulting loss of spinal cord function. 

Spinal Muscular Atrophy (SMA)

A hereditary condition that can cause substantial muscle weakness, SMA is characterized by degeneration of the motor neurons in the spinal cord. There are a few treatments used for SMA, including Spinraza (nusinersen) and Zolgensma (onasemnogene abeparvovec).

Polio

This contagious viral infection is usually preventable with a vaccine. In some instances, the infection involves one or more regions of the spinal cord, causing muscle paralysis of the areas that are controlled by the affected spinal cord regions.

Rehabilitation

Spinal cord diseases and injuries typically require medical and/or surgical interventions. Treatment may include steroids to reduce inflammation or antibiotics to target bacterial infections. Certain neurological conditions, such as MS, ALS, and SMA, also can improve with prescription medications indicated for the specific conditions. 

If you have spinal cord compression, you may need surgery to reduce pressure on your spinal cord due to cancer or a bone impingement. Cancer may require treatment with chemotherapy and radiation therapy. 

Therapies also usually include physical therapy and rehabilitation exercises. Some people may need to use a cane, walker, or wheelchair while recovering from a condition involving the spinal cord.