The anatomy of nocturia pelvic muscles (large arrows) is relaxed. As the bladder (broken outline) fills, it is distended downwards by gravity “G.” If the uterosacral ligaments (USLs) are weak, they continue to descend until the stretch receptors “N” are stimulated, activating the micturition reflex “O” once the cortical closure reflex “C” has been overcome. PCM, pubococcygeus muscle; LP, levator plate; LMA, conjoint longitudinal muscle of the anus.