<P> Ditunno et al. proposed a four - phase model for spinal shock in 2004 as follows: </P> <P> Phase 1 is characterized by a complete loss--or weakening--of all reflexes below the SCI . This phase lasts for a day . The neurons involved in various reflex arcs normally receive a basal level of excitatory stimulation from the brain . After an SCI, these cells lose this input, and the neurons involved become hyperpolarized and therefore less responsive to stimuli . </P> <P> Phase 2 occurs over the next two days, and is characterized by the return of some, but not all, reflexes below the SCI . The first reflexes to reappear are polysynaptic in nature, such as the bulbocavernosus reflex . Monosynaptic reflexes, such as the deep tendon reflexes, are not restored until Phase 3 . Restoration of reflexes is not rostral to caudal as previously (and commonly) believed, but instead proceeds from polysynaptic to monosynaptic . The reason reflexes return is the hypersensitivity of reflex muscles following denervation--more receptors for neurotransmitters are expressed and are therefore easier to stimulate . </P> <P> Phases 3 and 4 are characterized by hyperreflexia, or abnormally strong reflexes usually produced with minimal stimulation . Interneurons and lower motor neurons below the SCI begin sprouting, attempting to re-establish synapses . The first synapses to form are from shorter axons, usually from interneurons--this categorizes Phase 3 . Phase 4 on the other hand, is soma - mediated, and will take longer for the soma to transport various growth factors, including proteins, to the end of the axon . </P>

A sign of initial resolution of spinal shock is