The invention relates to a seat that comprises: a base; a sitting portion and a back support mounted on the base; a back including a shell and a padding attached to the shell; at least one attachment point provided with attachment means for attaching the back holder to the back; a headrest; and a headrest holder. The seat further includes: a bearing profile section adapted for attachment to the top of the shell of the back; and an arm with a planar aspect extending between the padding and the shell of the back, wherein said arm extends down to the attachment point(s) and is held rigidly by the attachment means of the back to the back holder.