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Spinal Cord
The spinal cord is a long, fragile tubelike structure that begins at the end of the brain stem and continues down almost to the bottom of the spine. The spinal cord consists of nerves that carry incoming and outgoing messages between the brain and the rest of the body. It is also the center for reflexes, such as the knee jerk reflex (see Figure: Reflex Arc: A No-Brainer).
Like the brain, the spinal cord is covered by three layers of tissue (meninges). The spinal cord and meninges are contained in the spinal canal, which runs through the center of the spine. In most adults, the spine is composed of 33 individual back bones (vertebrae). Just as the skull protects the brain, vertebrae protect the spinal cord. The vertebrae are separated by disks made of cartilage, which act as cushions, reducing the forces generated by movements such as walking and jumping. The vertebrae and disks of cartilage extend the length of the spine and together form the vertebral column, also called the spinal column.


What is a spinal cord injury?
A spinal cord injury (SCI) is damage to the spinal cord that results in a loss of function, such as mobility and/or feeling. Frequent causes of spinal cord injuries are trauma (car accident, gunshot, falls, etc.) or disease (polio, spina bifida, Friedreich’s ataxia, etc.).
The spinal cord does not have to be severed for a loss of function to occur. In fact, in most people with spinal cord injury, the cord is intact, but the damage to it results in loss of function. Spinal cord injury is very different from back injuries, such as ruptured disks, spinal stenosis or pinched nerves.
A person can "break their back or neck" yet not sustain a spinal cord injury, if only the bones around the spinal cord (the vertebrae) are damaged and the spinal cord is not affected. In these situations, the individual may not experience paralysis after the bones are stabilized.


What are the spinal cord and the vertebra?
The spinal cord is the major bundle of nerves that carries nerve impulses to and from the brain to the rest of the body. The brain and the spinal cord constitute the central nervous system. Motor and sensory nerves outside the central nervous system constitute the peripheral nervous system. Another diffuse system of nerves that controls involuntary functions, such as blood pressure and temperature regulation, are called the sympathetic and parasympathetic nervous systems.
The spinal cord is about 18 inches long and extends from the base of the brain, down the middle of the back, to about the waist. The nerves that lie within the spinal cord are upper motor neurons (UMNs), and their function is to carry the messages back and forth from the brain to the spinal nerves along the spinal tract. The spinal nerves that branch out from the spinal cord to the other parts of the body are called lower motor neurons (LMNs).
These spinal nerves exit and enter at each vertebral level and communicate with specific areas of the body. The sensory portions of the LMN carry messages about sensation from the skin and other body parts and organs to the brain. The motor portions of the LMN send messages from the brain to the various body parts to initiate actions such as muscle movement.
The spinal cord is surrounded by rings of bone called vertebra. These bones constitute the spinal column (back bones). In general, the higher in the spinal column the injury occurs, the more dysfunction a person will experience. The vertebra are named according to their location. The eight vertebra in the neck are called the cervical vertebra. The top vertebra is called C-1, the next is C-2, etc. Cervical spinal cord injuries usually cause loss of function in the arms and legs, resulting in quadriplegia. The 12 vertebra in the chest are called the thoracic vertebra. The first thoracic vertebra, T-1, is the vertebra where the top rib attaches. Injuries in the thoracic region usually affect the chest and the legs, resulting in paraplegia. The vertebra in the lower back between the thoracic vertebra, where the ribs attach, and the pelvis (hip bone), are the lumbar vertebra. The sacral vertebra run from the pelvis to the end of the spinal column. Injuries to the five lumbar vertebra (L-1 thru L-5) and similarly to the five sacral vertebra (S-1 thru S-5) generally result in some loss of function in the hips and legs.


What are the effects of a spinal cord injury?
The level of injury to the spinal cord is helpful in predicting what parts of the body might be affected by paralysis and loss of function. Remember that in incomplete injuries, there will be some variation in these prognoses.
Cervical (neck) injuries usually result in quadriplegia. Injuries above the C-4 level may require a ventilator for the person to breathe. C-5 injuries often result in shoulder and biceps control, but no control at the wrist or hand. C-6 injuries generally yield wrist control, but no hand function.
Individuals with C-7 and T-1 injuries can straighten their arms, but still may have dexterity problems with the hand and fingers. Injuries at the thoracic level and below result in paraplegia, with the hands not affected. At T-1 to T-8, there is most often control of the hands, but poor trunk control resulting from a lack of abdominal muscle control. Lower thoracic injuries (T-9 to T-12) allow good trunk control and good abdominal muscle control. Sitting balance is very good. Lumbar and sacral spinal cord injuries yield decreasing control of the hip flexors and legs.




International Journal of Neurology


International Journal of Neurology


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