The critical change that initiates the neuronal excitation involves the conversion of metarhodopsin I to metarhodopsin II, which is associated with deprotonation of the Schiff's base and change in color from red to yellow.
O cambio crítico que inicia a excitación neuronal implica a conversión da metarrodopsina I a metarrodopsina II, que está asociada coa desprotonación da base de Schiff e o cambio de cor de vermello a amarelo.