The damage from the spinal cord injury affects the sending and receiving of messages from the brain to the body's systems that control sensory, motor, and autonomic function below the level of injury Messages from the body below the level of injury can no longer get to the brain. The brain cannot send messages to the body below the level of injury.

It is important to distinguish between injuries that occur in the spinal cord proper from those that occur to the conus medullaris or to the cauda equina.

A spinal cord injury with preservation of segments of spinal cord below the level of injury usually produces an upper moter neuron (UMN) type of injury or spastic paralysis. The intrinsic reflexes are now uninhibited and become hyperreflexic and lead to increased muscle tone, spasms, and spasticity.

A conus medullaris injury, without preservation of spinal cord segments below the lesion, or a cauda equina injury produces a lower motor neuron (LMN) type of injury or flaccid paralysis. With this type of injury, the stimuli cannot reach the spinal cord; therefore, the reflexes and muscle tone remain decreased or absent (flaccid).

The neurologic level of injury is defined as "the most caudal (lowest) segment of the spinal cord with normal sensory and/or motor function on both sides of the body".

The physician examines the 28 dermatomes [the nerve roots that receive sensory information from the skin areas] for sensitivity to pin prick and light touch. The motor levels are tested in the 10 paired myotomes [groups of muscles].

The sensory and motor level need to be evaluated for both the right and left sides of the body. It is not unusual to have a discrepancy between the lowest normal motor level and the lowest normal sensory level. The physician uses this evaluation to classify the injury as complete or incomplete and assign a level of injury.

Another way that the level of spinal cord injury can be categorized is tetraplegia and paraplegia. Tetraplegia, previously called quadriplegia, refers to injuries of the cervical region of the spinal cord. Paraplegia refers to injuries which occur in the thoracic, lumbar, or sacral segments.

When a spinal cord injury is graded as incomplete, it means the cord has been partially damaged. An incomplete injury has partial preservation of sensation and/or motor function below the neurologic level of injury and includes the lowest sacral segment. A complete injury indicates a complete blockage of nerve messages. With a complete injury there is no sensation or motor function in the lowest sacral segment.

The nerve rootlets leave the spinal cord continually and then aggregate into nerve roots. In a spinal cord injury, only fractions of the rootlets going to a nerve root level may be damaged. Therefore, the nerve root, which is equivalent to a spinal segment, may be only partially damaged.

Also included in the neurological assessment is the classification of Clinical Syndromes. The syndromes include Central Cord Syndrome, Brown-Sequard Syndrome, Anterior Cord Syndrome, Conus Medullaris Syndrome, and Cauda Equina Syndrome. A mixed or unclassified syndrome is sometimes present.

A recently added classification used in the evaluation process is the Functional Independence Measure(FIM). The FIM is a method for monitoring and evaluating progress associated with treatment. It measures daily life activities in the areas of self care, sphincter control, mobility, locomotion, communication an social cognition. Activities such as eating, toileting, and dressing are rated on a scale which measures dependence/independence.