Primary damage is defined as the immediate effects of an injury to the spinal cord. The broad effects of damage to the spinal cord depend on three main factors; the severity of the injury, the region of the spinal cord to which the injury occurred, and the type of nerve that is damaged.
Primary spinal cord damage is most commonly the result of two types of injury: contusion—bruising of the spinal cord as a result of a blow or a fall—and compression—damage as a result of increased pressure, either from an external or an internal force. Internal causes of injury include the growth of a tumor, internal bleeding as a result of injury (known formally as spinal hematoma), illnesses causing inflammation such polio or transverse myelitis, and illnesses such as osteoporosis and cervical spondylosis, which may cause damage to the vertebrae. Two rather less common types of spinal cord injury are laceration (cuts to the spinal cord from a knife, bullet, or other object) and transection (complete severing of the spinal cord).
Generally, a person will experience loss of sensation or movement to all parts of the body below the injury—for instance, if the injury occurs to the lumbar (lower-middle back) region of the spinal cord, the person will probably lose sensation and/or movement from the waist down. The higher the location of the damaged area, the greater the impairment is. As you may remember from the section of this website on basic anatomy, the specific regions of the spinal cord and the areas they innervate are identified by a combination of a letter (C, T, L, or S, standing for cervical, thoracic, lumbar, and sacral) and a number. The diagram below shows both the letter/number tags and the anatomical regions with which communication will be damaged if that region of the spinal cord is injured.
The more specific effects of spinal cord injury are determined by the type of nerve that has been damaged. Damage to motor nerves results in paralysis, or loss of control of movement. Damage to somatosensory nerves results in loss of sensation and perception; one can no longer feel touch, pain, temperature, or be able to tell without looking where in space the nerve-damaged body part is positioned.
Another important area of nerve control is of the autonomic nervous system; the circuits of the nervous system that regulate involuntary aspects of body function, such as the heart, the digestive system, and the respiratory system. Damage to region T6 or above disconnects the sympathetic nerves (which control the constriction of blood vessels) of this region from nerves above. The sympathetic nerves will continue to operate automatically; any stimulation can produce a bout of overreaction called autonomic dysreflexia. Symptoms of this commonly seen effect of spinal cord injury include sweating and a highly elevated heart rate.
Spinal cord damage can be categorized according to whether it is complete or incomplete. A person with complete damage retains no sensation or control of movement in the areas innervated by the injured region. Those with incomplete damage retain some sensation or movement control. Since 1988, about 45% of all spinal cord damage has been complete, 55% incomplete.
Individuals with complete spinal cord damage are often broadly divided according to which limbs are no longer useable. Paraplegics have lost the use of their legs, usually as a result of an injury below region T1. Quadriplegics have lost the use of all limbs as a result of an injury to T1 or above. Those with injuries to C3 and above are less likely to survive; if they do, they require an artificial respirator in order to breathe because of the loss of motor control in the diaphragm, a muscle that controls the expansion of the lungs.
The deficits of those with incomplete damage usually can be described by one of the following syndromes. Those with anterior cord syndrome retain some sensation coming from the uninjured pathways at the back of the spinal cord, but have lost movement control and most detailed sensory abilities. Central cord syndrome causes weakness or paralysis of the arms (and sometimes a decrease in leg strength) as a result of injury to pathways at the center of the cervical spinal cord. Brown-Sequard syndrome occurs as a result of damage to only one side of the spinal cord; individuals with this type of damage will experience loss of motor control below the injury on whatever side the injury occurred, and will experience loss of sensation on the opposite side of the body because the sensory nerves cross over to the opposite side once they reach the spinal cord (i.e., damage to the right T3 regions of the spinal cord would cause paralysis of the right leg and loss of sensation in the left).
Spinal concussions can cause either complete or incomplete damage, but the effects are usually temporary, lasting one or two days.
For the longer term effects of spinal cord injury, see the section on Secondary Damage.