fer ent ▁n erve ▁to ▁the ▁central ▁nerv ous ▁system ▁( C NS ). ▁The ▁C NS ▁receives ▁this ▁message ▁and ▁sends ▁an ▁appropriate ▁response ▁via ▁an ▁e f fer ent ▁n erve ▁( also ▁known ▁as ▁a ▁motor ▁neur on ) ▁to ▁effect or ▁cells ▁located ▁in ▁the ▁same ▁initial ▁area ▁that ▁can ▁then ▁carry ▁out ▁the ▁appropriate ▁response . ▁ ▁In ▁the ▁case ▁of ▁the ▁ph ary n ge al ▁ref lex : ▁ ▁the ▁sens ory ▁lim b ▁is ▁medi ated ▁pre domin antly ▁by ▁C N ▁IX ▁( gl oss oph ary n ge al ▁n erve ) ▁the ▁motor ▁lim b ▁by ▁C N ▁X ▁( v ag us ▁n erve ). ▁ ▁The ▁g ag ▁ref lex ▁involves ▁a ▁br isk ▁and ▁brief ▁elev ation ▁of ▁the ▁soft ▁pal ate ▁and ▁bil ater al ▁contra ction ▁of ▁ph ary n ge al ▁mus cles ▁ev oked ▁by ▁touch ing ▁the ▁posterior ▁ph ary n ge al ▁wall . ▁Touch ing ▁the ▁soft ▁pal ate ▁can ▁lead ▁to ▁a ▁similar ▁ref lex ▁response . ▁However , ▁in ▁that ▁case , ▁the ▁sens ory ▁lim b ▁of ▁the ▁ref lex ▁is ▁the ▁C N ▁V ▁( tr ig em inal ▁n erve ). ▁In ▁very ▁sensitive ▁individuals , ▁much ▁more ▁of ▁the ▁brain ▁stem ▁may ▁be ▁involved ; ▁a ▁simple ▁g ag ▁may ▁en large ▁to ▁ret ch ing ▁and ▁vom iting ▁in ▁some . ▁ ▁Supp ression ▁and ▁activation ▁Sw allow ing ▁unus ually ▁large ▁objects ▁or ▁placing