▁neur ons . ▁G row th ▁factors ▁are ▁not ▁expressed ▁or ▁re - ex pressed ; ▁for ▁instance , ▁the ▁ext rac ell ular ▁matrix ▁is ▁lack ing ▁l amin ins . ▁Gli al ▁sc ars ▁rapidly ▁form , ▁and ▁the ▁gl ia ▁actually ▁produce ▁factors ▁that ▁in hib it ▁rem y el ination ▁and ▁ax on ▁repair ; ▁for ▁instance , ▁NO GO ▁and ▁N I - 3 5 . ▁The ▁ax ons ▁themselves ▁also ▁lose ▁the ▁potential ▁for ▁growth ▁with ▁age , ▁due ▁to ▁a ▁decrease ▁in ▁G AP 4 3 ▁expression , ▁among ▁others . ▁ ▁S lower ▁deg ener ation ▁of ▁the ▁dist al ▁segment ▁than ▁that ▁which ▁occurs ▁in ▁the ▁peri pher al ▁nerv ous ▁system ▁also ▁cont ributes ▁to ▁the ▁in hib itory ▁environment ▁because ▁in hib itory ▁my elin ▁and ▁ax onal ▁de br is ▁are ▁not ▁cleared ▁away ▁as ▁quickly . ▁All ▁these ▁factors ▁contribute ▁to ▁the ▁formation ▁of ▁what ▁is ▁known ▁as ▁a ▁gli al ▁scar , ▁which ▁ax ons ▁cannot ▁grow ▁across . ▁The ▁proxim al ▁segment ▁attempts ▁to ▁reg ener ate ▁after ▁injury , ▁but ▁its ▁growth ▁is ▁h inder ed ▁by ▁the ▁environment . ▁It ▁is ▁important ▁to ▁note ▁that ▁central ▁nerv ous ▁system ▁ax ons ▁have ▁been ▁proven ▁to ▁reg row ▁in ▁perm iss ive ▁environments ; ▁therefore , ▁the ▁primary ▁problem ▁to ▁central ▁nerv ous ▁system ▁ax onal ▁reg ener ation ▁is ▁crossing ▁or ▁elimin ating ▁the ▁in hib itory ▁les ion ▁site . ▁Another ▁problem ▁is ▁that ▁the