What is the nervous system?

The nervous system is divided into two major divisions: the peripheral nervous system and the central nervous system. The peripheral nervous system is a network of nerves throughout the body, handling everything from regulating the heart rate to flexing the hand or foot. It also receives information (pain and temperature, for example), much of which is sent to the brain. This information is analyzed and coordinated by the central nervous system. The central nervous system is made up of the spinal cord and brain.

What is the spinal cord?

The spinal cord runs from the base of the brain down the middle of the back and ends just above the waist. It is made up of nerve cells (neurons) and long nerve fibers (axons). These relay all incoming information from the rest of the body to the brain and all outgoing information from the brain to the rest of the body. Unlike the nerves of the peripheral nervous system, those in the central nervous system do not regenerate once they have been injured. Therefore, when the spinal cord is injured, a patient will have varying degrees of paralysis if these axons become destroyed.

Thirty-three ring-shaped bones called vertebrae form the spinal column (spine) and protect the spinal cord from injury. If these bones are broken or damaged, paralysis is not necessarily the result once the bones are stabilized. For this reason, a person may break his or her back or neck without suffering paralysis. It is when the damage reaches the spinal cord that serious, long-term or permanent effects often result. The extent and region of the body affected by this damage depends upon the region of the spinal cord involved.

What are the regions of the spinal cord?

The spinal column and spinal cord consist of four regions, with each region controlling a particular part of the body. These regions can be categorized even further into 31 pairs of peripheral spinal nerves. These nerve pairs extend from the spinal cord through spaces in the vertebrae, connecting the spinal cord with other nerves throughout the peripheral nervous system. In general, the higher the spinal cord is injured, the more severe the injury. The regions of the spine are numbered in descending order from the brain.

  • Cervical region (C1 to C8): Located in the neck, this region controls the back of the head, the neck, shoulders, arms, hands, and diaphragm
  • Thoracic region (T1 to T12): This region is located in the upper back and controls the torso and parts of the arms
  • Upper lumbar (L1 to L5): Located in the middle of the back just below the ribs. The upper lumbar region controls the hips and legs
  • Sacral segments (S1 to S5): Just below the upper lumbar region in the middle of the back. This region controls movement in the groin, toes, and some parts of the legs

Partial and complete spinal cord injuries

There are two types of spinal cord injuries: complete and partial. If a spinal cord injury is complete, there is no function below the point of injury. This means the patient will experience no sensation or voluntary movement and that both sides of the body, for example have both arms, will usually be equally affected. A complete injury can result in the paralysis of all four limbs (quadriplegia) or the lower half of the body (paraplegia).

For partial injuries, a patient may be able to move one limb more than the other or be able to feel more with one side than the other. The level of incomplete injuries may vary from patient to patient, and can affect the body in different ways. For example, a C-6 injury may result in having no hand control but having wrist control. A C-5 injury may deprive a patient of wrist and hand control, but not arm and shoulder control.

Aside from having a loss of sensation and movement, patients with a spinal cord injury may also experience bladder and bowel complications. Spinal cord injuries often affect fertility in males. If the spinal cord injury is high (example, C-1 or C-2), the patient may need a respirator or diaphragmatic pacemaker to breathe properly.

Other complications that may result from a spinal cord injury are an inability to regulate blood pressure, low blood pressure, reduced control of body temperature, an inability to sweat that occurs below the level of injury, and chronic pain. Patients with spinal injuries also have an increased susceptibility to respiratory disease and autonomic dysreflexia. Autonomic dysreflexia is primarily the result of the body being unable to control the blood pressure. This is especially a concern for patients who have a spinal cord injury at T-6 or above. The signal responsible for "telling" the blood vessels to relax cannot be processed because of the injury. With autonomic dysreflexia, these blood vessels intermittently remain constricted, thus elevating the blood pressure and possibly leading to life-threatening complications such as stroke. External methods of lowering the blood pressure to a safe level are often necessary.

How common is spinal cord injury?

Spinal cord injury occurs in various countries throughout the world with an annual incidence of 15 to 40 cases per million. For some of these people, the injury is the result of a disease, such as polio or spina bifida. However, for most, the spinal cord injury is the result of trauma. The leading traumatic cause of spinal cord injuries is automobile accidents, causing 44 percent of all injuries. Other causes of spinal cord injuries, in descending order of frequency, include violence (gunshot wounds, for example), falls, and sports. While sports only account for 8 percent of all spinal cord injuries, 60 percent of those sports-related injuries are a result of diving accidents. For spinal cord injuries occurring over age 45, falls overtake automobile accidents as the number one cause.

Males account for over 80 percent of patients with spinal cord injuries. The average patient age is 33, but the most frequent age of injury is 19.

Treatment and management

When the spinal cord is damaged, significant swelling of the spinal cord and the surrounding areas occurs. During this time, nerve cells continue to deteriorate. A variety of treatment strategies to limit or slow the process are under investigation.

Neural prostheses

One approach for treating patients with spinal cord injuries is to compensate for lost function by using neural prostheses to bypass the areas of damage. This is done by connecting electrical and mechanical devices with the nervous system to compensate for lost motor and sensory functions. For example, neural prostheses for deafness, known as cochlear implants, are now in widespread use and have been very effective in improving hearing. The first neural prostheses for patients with spinal cord injuries are now being tested.

The United States Food and Drug Administration (FDA) approved one of these devices, a prosthesis that allows basic hand control. Patients use their shoulder muscles to control the device, and with training, can perform activities of daily life that they would otherwise be unable to perform, such as using silverware, pouring a drink, answering a telephone, and writing a note.

Neural prostheses are complex and contain many intricate components, such as implantable stimulators, electrodes, leads and connectors, sensors, and programming systems. There are many technical considerations in selecting each component. The electronic components must be as small as possible. Biocompatibility between electrodes and body tissue is also necessary to prevent injury to the patient and damage to the device. Neural prostheses also must be evaluated for usefulness and long-term safety.

Further research and an improved and increased understanding of brain circuits may eventually lead to prostheses that can provide sensory information to the brain. This would improve both the safety of the devices and the patient's ability to perform certain tasks. Devices now being developed may eventually enable people with spinal cord injuries to stand unassisted and perform other actions using signals from the brain--instead of muscles--to control movement. Ultimately, researchers may be able to harness reflexes or the innate pattern-generating abilities of the spinal cord's central pattern generators to help people with spinal cord injuries walk.

With the current wave of new technology, it is easy to forget just how far medical science has come in treating spinal cord injuries. As recently as 50 years ago, most patients died within a few weeks from a spinal cord injury due to complications related to infections or bodily dysfunctions. Nowadays, not only do spinal cord injury patients survive, many thrive. Once the injury has been stabilized, physical therapy and advances in assistive devices allow patients to work, travel, compete in sports, and raise families. Nevertheless, while the years ahead offer promise for people with spinal cord injuries, today's patients face many challenges in their everyday lives.

Education about one's injury and local support groups are some of the best tools for managing the injury and preventing further complications. The following organizations can provide additional information about spinal cord injuries:

Christopher Reeve Paralysis Foundation

500 Morris Avenue

Springfield, NJ 07081 (800) 225.0292


National Spinal Cord Injury Association

6701 Democracy Blvd., Suite 300-9

Bethesda, MD 20817 (800) 962.9629


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