What is the term used for wooden planks laid across railway tracks, to hold the tracks in position?

Sleepers (also called railroad ties) are the rectangular wooden supports laid perpendicular to railway tracks. They hold the rails to the correct gauge and transfer loads to the ballast and subgrade beneath. The other options are unrelated: syringe is a medical instrument, sleep-inns is not a real term, and symposium refers to a conference or academic gathering.