The Republic of Ireland U21 international has agreed to join the Pilgrims until January.
Sheridan, 20, scored two Scottish Premier League goals in 14 games while on loan at Motherwell during the second half of last season. He could make his debut against Queens Park Rangers on Saturday.
Coventry City have signed the England U21 international Martin Cranie from Portsmouth for an undisclosed fee.
Cranie has penned a three-year contract with the Sky Blues.
"Martin's a player we've liked for some time, he's young and he's got it all ahead of him," manager Chris Coleman told the club's official website.
"He's proven himself at England U21 level so he has the kind of quality we want to bring here and I'm very much looking forward to working with him."
Newcastle United have signed defender Danny Simpson on loan from Manchester United.
The right-back, 22, has joined the Magpies until January. He has made just eight first-team appearances for United after progressing through the youth ranks.
He has spent time on loan at Royal Antwerp, Sunderland, Ipswich Town and Blackburn Rovers during recent seasons.
The Hull City manager Phil Brown has abandoned his pursuit of Cardiff City striker Ross McCormack.
The Tigers have been tracking the 22-year-old Scotland international throughout the summer but Brown has now revealed he has called off his interest.
The Middlesbrough manager Gareth Southgate has dismissed rumours suggesting that Premier League side Everton have lodged an offer for midfielder Gary O'Neil.
O'Neil, 26, who has also been linked with Fulham, is currently playing on despite a hernia problem, with Southgate unaware of any possible transfer moves.
"Whether it's come from an agent we don't know, but we have very good links with Everton at boardroom and every other level. It would appear to be a rumour rather than substance," he said.