The Wales star appeared to take a blow to the head in an accidental collision.
Scarlets lament failings
For Ulster it was a heartening response after losing their unbeaten Pro12 record last time out away to Munster.
However, the Scarlets have now fallen to their fifth defeat in six games - and that run looks likely to worsen as the bottom side in Pool Five fulfil their European pool fixtures over the next fortnight.
The visitors struck first with a Thomas penalty after nine minutes but he scuffed a chance to put the visitors 6-0 up.
Instead Ulster, who lost full-back Adam D'Arcy to injury, hit back when Scarlets were penalised at a scrum and Ruan Pienaar - making his 50th appearance for Ulster - made no mistake to level the scores.
The South African number nine added two more penalties to leave it 9-3 at half-time.
Ulster came out of the traps quickly with a 43rd-minute try under the posts which came after number eight Williams off-loaded to Rob Herring, who provided Diack with the score which was easily converted by Pienaar.
Another Pienaar penalty five minutes later took it to 19-3 and then Williams got over after a scrum fro try number two with Pienaar adding the extras to take it to 26-3.
The Scarlets, though, now having seen North stretchered off, hit back with Turnbull getting over with just over 10 minutes remaining and Thomas converted to make it 26-10.
With the game now breaking up, Trimble took a good angle and scythed through to score with Cave adding the drop-kicked conversion with only seven minutes left on the clock.
Ulster then grabbed their bonus when a penalty try was awarded and Aled Thomas was binned after he had interfered with Paddy Jackson's scoring pass from an offside position.
Jackson then added the conversion and Ulster finished the rout when Neil McComb was driven over with Jackson again doing the needful.
Scott Williams's injury-time try and conversion were mere consolation.
Andrew for D'Arcy (14), Wallace for L Marshall (41), Heaney for Pienaar (69), Black for Court (72), Annett for Herring (72), Afoa for Macklin (41), McComb for Tuohy (36), Wilson for Williams (58).
Newton, North, Maule, J Davies, K Phillips, A Thomas, Knoyle, John, E Phillips, Adriaanse, Timani, Kelly, Turnbull, J Edwards, McCusker.
S Williams for North (64), G Davies for Knoyle (61), R Jones for John (64), Myhill for E Phillips (69), Manu for Adriaanse (54), Vallejos for Timani (54), Price for J Edwards (27).
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