Why are the words "mano" & "manasa" used in the opening Dhammapada verses?

The well-known yet often differently translated opening verses of the Dhamma use the Pali words "mano" and "manasa", as follows: > **Mano**pubbaṅgamā dhammā, > > **mano**seṭṭhā **mano**mayā; > > **Manasā** ce paduṭṭhena, > > bhāsati vā karoti vā; > > Tato naṃ dukkhamanveti, > > cakkaṃva vahato padaṃ. > > **Mano**pubbaṅgamā dhammā, > > **mano**seṭṭhā **mano**mayā; > > **Manasā** ce pasannena, > > bhāsati vā karoti vā; > > Tato naṃ sukhamanveti, > > chāyāva anapāyinī What do the Pali words "mano" and "manasa" specify refer to & why are they used in Dhammapada verses 1 & 2?