Spinal cord injury causes myelopathy or damage to white matter or myelinated fiber tracts that carry sensation and motor signals to and from the brain. It also damages gray matter in the central part of the spinal, causing segmental losses of interneurons and motoneurons. Spinal cord injury can occur from many causes, including: ...

Spinal cord injury causes myelopathy or damage to white matter or myelinated fiber tracts that carry sensation and motor signals to and from the brain. It also damages gray matter in the central part of the spinal, causing segmental losses of interneurons and motoneurons. Spinal cord injury can occur from many causes, including:

Trauma
Tumor
Ischemia
Developmental disorders
Neurodegenerative diseases
Demyelinative diseases

Cervical (neck) injuries usually result in full or partial tetraplegia. Depending on the exact location of the injury, one with a spinal cord injury at the cervical may retain some amount of function as detailed below, but are otherwise completely paralyzed.

C3: vertebrae and above: Typically lose diaphragm function and require a ventilator to breathe.
C4: May have some use of biceps and shoulders, but weaker
C5: May retain the use of shoulders and biceps, but not of the wrists or hands.
C6: Generally retain some wrist control, but no hand function.
C7 and T1: Can usually straighten their arms but still may have dexterity problems with the hand and fingers. C7 is generally the level for functional independence.

Thoracic injuries

Injuries at the thoracic level and below result in paraplegia. The hands, arms, head, and breathing are usually not affected.

T1 to T8: Most often have control of the hands, but lack control of the abdominal muscles so control of the trunk is difficult or impossible. Effects are less severe the lower the injury.
T9 to T12: Allows good trunk and abdominal muscle control, and sitting balance is very good.