Emery was sacked in November after leading the Gunners to their worst run since 1992, ending his reign with a 2-1 Europa League defeat to Eintracht Frankfurt.
His fellow Spaniard Arteta was appointed in December and despite not turning the club’s form around, the 37-year-old has instilled a fresh mentality and desire into his players.
Arsenal, who have only won six out of 25 Premier League games this term, are unbeaten in five in the league, a run extended to seven outings in all competitions.
Speaking to reporters about the club’s form, Leno highlighted Arteta’s instant impact as well as providing insight into how disjointed the team was under Emery.
Leno said: “[Arteta] has, in this short time, a big impact because you can see the intensity we play with. Also the structure in the team and the mentality out of the pitch.
“Before it was, I don’t want to say a mess, it was a little bit confusing, everybody was doing different things and we were not a team – not in the dressing room, not on the pitch, and you could see this.
“I think with Mikel it changed completely. The first day he came he was not talking too much about tactics, he was talking about how we behave in the dressing room, when we go to the games we have to be more professional, more like a team.
“I think it is not only what he has learned from Pep Guardiola, when you talk with all of the people that worked with him, they say he’s a very clever guy with tactics and how to improve players.”