Vernon Philander, who made a handful of appearances for the west country side in 2012, enjoyed himself against his former team-mates, picking up three wickets for 10 in the session.
Marcus Trescothick was bowled by the South African for nought in the first over and Tom Abell soon followed, caught behind for 10.
A stand of 78 for the third wicket appeared to be steering Somerset’s ship back on course but three wickets in ten deliveries confirmed Nottinghamshire’s dominance.
Johannes Myburgh had battled his way to 49 from 77 balls before having his off stump knocked flat by Steven Mullaney.
James Hildreth made 32 but then elected not to play at a ball from the returning Philander, with devastating consequences.
Mullaney picked up his second wicket as Tom Cooper played a leading edge to James Taylor at point to leave the Somerset innings in disarray.