How SCI occurs
A spinal cord injury (SCI) usually begins with a sudden, traumatic blow to the spine that fractures or dislocates vertebrae. SCI can occur in other ways, such as a sudden viral attack.
This photo is from an MRI of the neck of a client who fell during work due to the fault of a general contractor. It shows a severe dislocation of the C6-7 vertebrae.
The most common causes of SCI are car crashes, falls and violence.
In the case of trauma, damage is instant when displaced bone fragments, disc material, or ligaments bruise or tear into spinal cord tissue. Axons are severed or destroyed, and neural cell membranes are broken. Blood vessels may rupture and cause heavy bleeding in the central grey matter (this can spread to other areas of the spinal cord in a few hours).
Within minutes, the spinal cord swells and fills the entire cavity of the spinal canal at the injury level. This cuts off blood flow, which also cuts off oxygen to spinal cord tissue. Blood pressure drops, sometimes dramatically, as the body loses its ability to self-regulate. As blood pressure lowers even further, it interferes with the electrical activity of neurons and axons. All these changes can cause a condition known as spinal shock that can last from several hours to several days.
There is some controversy among neurologists about the extent and impact of spinal shock, and even its definition in terms of physiological characteristics. It appears to occur in approximately half the cases of spinal cord injury. It is usually directly related to the size and severity of the injury. During spinal shock, even undamaged portions of the spinal cord become temporarily disabled and can’t communicate normally with the brain. Complete paralysis may develop, with loss of reflexes and sensation in the limbs.
The crushing and tearing of axons is just the beginning of the devastation that occurs in the injured spinal cord and continues for days. The initial physical trauma sets off a cascade of biochemical and cellular events that kills neurons, strips axons of their myelin insulation, and triggers an inflammatory immune system response. Days or sometimes even weeks later, after this second wave of damage has passed, the area of destruction has increased – sometimes to several segments above and below the original injury – and so has the extent of disability.
These facts are provided by the National institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/sci/detail_sci.htm#144133233