SCI
Info
How
the spinal cord works
Spinal cord injury
What happens to the cord
Effects of spinal cord injury
Cure, return and recovery
The spinal cord and the brain together make up the central nervous system. Nerve cells in the brain send signals to the spinal cord directing function and movement throughout the body. Nerve cells in the body send signals to the brain, via the spinal cord, regarding all forms of sensation. Paralysis occurs when communication between the brain and the body fails. The failure can be located in the brain, as in the case of stroke, or in the spinal cord, as in the case of traumatic spinal cord injury.
The brain is partially shielded from injury by the skull and the spinal cord, by the bones of the spine. The spine is divided into five sections: the cervical or neck region (C1 – C8), the upper back or thoracic region (T1 – T12), the lumbar or mid-to-low back region (L1 – L5), the sacral or low back region (S1 – S5), and the coccygeal region. Nerves from each section of the spine carry signals to and from specific parts of the body. The cervical region controls signals to and from the neck, arms, and hands. The thoracic region controls the torso and some parts of the arms. The lumbar section controls signals to and from the hips and legs. The sacral section is responsible for the groin, toes, and some parts of the legs.
Nerve cells, which are also called neurons, have several parts, each with a role to play in transmitting signals between the brain and the body. A basic understanding of spinal cord injury requires introduction of two of these parts: the cell body and the axon.
A signal originates in a cell body, then travels via a thin fiber (the axon) to another cell body. In some cases, one axon delivers a signal all the way to its final destination (an axon can be several feet long). In others, cell bodies act as relay stations, receiving a signal then passing it on to the next cell body, via axons. This neural circuitry is responsible for all communication between the brain and body.
There are approximately 100 billion neurons in the brain and spinal cord combined. As many as 10,000 different subtypes of neurons have been identified, each specialized to send and receive only certain types of information.
Spinal cord injury (SCI) occurs when a traumatic event damages the cells in the spinal cord, interrupting the relay of signals between the brain and the body. The vast majority of spinal cord injuries involve bruising or crushing of the spinal cord. A few involve severing or tearing of the cord.
Approximately 450,000 people in the United States are currently living with spinal cord injuries. More than 10,000 new spinal injuries occur in the U.S. every year. Women account for only 18 percent of those injured. The most common cause of spinal cord injury is motor vehicle accident. Falls and acts of violence are the next most common causes.
A complex series of events takes place when an injury to the spinal cord occurs. Some nerve cells in the cord are instantly destroyed and/or damaged by the trauma. The number of cells affected depends on the severity of the trauma. But even those cells that survive the initial trauma may be destroyed.
In response to an injury, the soft tissue of the spinal cord swells. Because the cord is confined within the bones of the spinal column, the swelling results in reduced blood flow to the nerve cells in the cord. Nerve cells have a very high rate of metabolism, which means they require plenty of oxygen for healthy functioning. This makes them particularly vulnerable to any reduction in blood flow. Therefore, normal swelling makes the injury worse until the swelling can be relieved. In addition, dying nerve cells release chemicals that kill neighboring nerve cells. The total effect is a cascade of damage crippling the body’s ability to communicate with itself.
In addition to nerve cell death, several other factors impede communication. Some cell bodies that manage to survive no longer have intact axons. Though the cell body is capable of transmitting a signal, the attached axon has been cut, effectively severing communication between the cell body and other cell bodies. Furthermore, many axons that remain intact have been stripped of their myelin. Myelin is a coating that improves the speed and reliability of nerve signal transmission. Circuitry formed by demyelinated axons, though complete, is often impaired or useless. Finally, a fluid-filled cavity and scar develop in place of the tissue damaged initially. This creates a physical and chemical barrier for axons trying to regrow.
Spinal cord injury usually causes paralysis, loss of sensation and loss of reflex function below the point of injury. This can include autonomic activity such as breathing and other activities such as bowel and bladder control. Symptoms such as pain, muscle spasms, and sexual dysfunction may also be present. SCI patients are susceptible to secondary medical problems as well. Bladder infections, lung infections, and bed sores are all common occurrences. However, despite these similarities, no two spinal cord injuries are alike.
The way a spinal cord injury manifests in a particular person depends on two factors: the placement of the injury and the degree of injury. The placement of the injury dictates the location of potential losses while the degree of injury dictates the extent and type of losses.
The placement of the injury refers to the vertebral level at which the cord was damaged, i.e. C6 or T10 or L1. Loss of movement and/or sensation can be expected in those body areas that communicate through nerves at and below the level of injury. For instance, a person injured at C6 would likely maintain use and sensation in the shoulders and biceps (controlled at C5) but lose movement/sensation in the triceps (C7), hands (C8/T1), abdominal muscles (T8 – T12), legs (L1 – L5), bowel and bladder (S1/S2) and sexual areas (S4/S5). An injury at L1 would manifest losses in the legs, bowel, bladder and sexual areas (L1 – S5), while sparing the arms, torso and everything else communicating above L1. Two people injured at the same level will experience losses in the same areas of the body but the type and extent of loss may be very different. That is because the degree of each injury dictates the type and degree of loss.
The degree of injury refers to the extent to which nerves cells were destroyed or damaged at the point of injury. A relatively minor bruising of the spinal cord might disrupt voluntary movement but spare most sensation. More significant bruising might affect movement and many types of sensation while sparing sensitivity to temperature, for instance. Some people experience the ability to move some part of the body but only on one side, for instance the left foot but not the right. Though both feet are controlled at the same level of the spine, the cells involved may not have been uniformly damaged. Typically, the results of nerve cell damage are anything but uniform: sensitivity to deep pressure but not light touch and only on the right bicep; voluntary flexing of the left ankle but inability to straighten it or feel it moving; control of abdominal muscles and the ability to sense an itch but inability to feel the scratch. The possibilities are endless. It all depends on the number and type of nerve cells affected.
Some injuries involve such extensive damage to the nerve cells that no sensation or movement is spared. Such injuries are referred to as “complete.” When any sensation or movement below the point of injury remains, the injury is classified as “incomplete.”
Currently, there is no cure for spinal cord injury. Treatment for acute SCI includes techniques to relieve cord compression, drug therapy to minimize swelling immediately after injury, and stabilization of the vertebrae to prevent further damage. However, methods for reducing the extent of injury and for restoring function and sensation remain elusive.
The human body has many organs and tissues that can heal after an injury without intervention. Time and the absence of anything aggravating the injury are, sometimes, all that is needed. But many cells of the central nervous system are so specialized that they cannot divide and create new cells. As a result, recovery from spinal cord injury is much more complicated. The task is made even more difficult by those chemicals and processes, normally occurring in the body’s response to SCI, that inhibit the survival or growth of nerve cells.
Despite the complexity, many people with SCIs do improve. Statistically speaking, people with incomplete injuries are more likely to experience return of some function or feeling. However, the degree of return varies dramatically from person to person and does not occur in every injury. Complete injuries are considered significantly less likely to improve, yet there are many documented cases of complete classifications being downgraded to incomplete. The complexity and individuality of each spinal cord injury makes it very difficult to predict the course of one injury based on that of another, even when the injuries occur at the same level or to the same degree.
Though almost any improvement is heartily welcomed by those living with SCI, return typically falls considerably short of normal functioning. However, advancements in current research may soon change that. Numerous teams of scientists around the world are exploring ways to help the spinal cord heal. Many surgical and drug therapies are being investigated and several are currently in clinical trials. In addition, new rehabilitation techniques, cyber technology, and a host of alternative medical approaches are all being explored. There are still no proven methods, nor any results that have approached full recovery, but the body of knowledge is steadily growing.
Sources:
National
Institute of Neurological Disorders and Stroke
Christopher and Dana Reeve Paralysis
Resource Center
Spinal
Cord Injury Resource Center