In the acute phase, primary damage occurs as a direct result of trauma when structural thresholds are surpassed, leading to immediate physical and biochemical cellular alterations. It begins within seconds of the injury, is marked by systemic as well as local events (Tator et al. 1998, Hulsebosch 2002). These include systemic hypotension, spinal shock, vasospasm, ischemia, plasma membrane compromise, derangements in ionic homeostasis, and accumulation of neurotransmitters. Diverse groups of cells and molecules from the nervous, immune, and vascular systems are involved in each phase. Most participating cells reside in the spinal cord, but others are summoned to the site of injury from the circulatory system (Liverman et al. 2005). Some acute phase events continue into the sub-acute phase, and also some subacute phase events continue into the chronic phase