A device (10; 410; 610) including: a steerable shaft with a proximal end and distal end, wherein the proximal end can be manipulated by an operator to control the distal end; an articulation section (50; 450; 650) at or near the distal end of the shaft, wherein the articulation section (50; 450; 650) comprises several articulation links and is configured to move the distal end relative to the proximal end; at least one elongate member (100; 500; 700) configured to control movement of the articulation section (50; 450; 650) in one or more directions and to lock and unlock the articulation section (50; 450; 650), wherein: the at least one elongate member (100; 500; 700) extends through an internal passage of the articulation section (50; 450; 650), a distal end of the at least one elongate member (100; 500; 700) is attached to the distal end of the shaft, the at least one elongate member (100; 500; 700) is configured to move longitudinally to curve the articulation section (50; 450; 650), and the at least one elongate member (100; 500; 700) includes at least one protrusion (505; 705); and a cinching element (550; 750) fixedly or movably coupled to the device and comprising at least one detent configured to engage with the at least one protrusion (505; 705) to limit movement of the at least one elongate member (100; 500; 700) within the internal passage and thereby lock the articulation section (50; 450; 650). a steerable shaft with a proximal end and distal end, wherein the proximal end can be manipulated by an operator to control the distal end; an articulation section (50; 450; 650) at or near the distal end of the shaft, wherein the articulation section (50; 450; 650) comprises several articulation links and is configured to move the distal end relative to the proximal end; at least one elongate member (100; 500; 700) configured to control movement of the articulation section (50; 450; 650) in one or more directions and to lock and unlock the articulation section (50; 450; 650), wherein: the at least one elongate member (100; 500; 700) extends through an internal passage of the articulation section (50; 450; 650), a distal end of the at least one elongate member (100; 500; 700) is attached to the distal end of the shaft, the at least one elongate member (100; 500; 700) is configured to move longitudinally to curve the articulation section (50; 450; 650), and the at least one elongate member (100; 500; 700) includes at least one protrusion (505; 705); and the at least one elongate member (100; 500; 700) extends through an internal passage of the articulation section (50; 450; 650), a distal end of the at least one elongate member (100; 500; 700) is attached to the distal end of the shaft, the at least one elongate member (100; 500; 700) is configured to move longitudinally to curve the articulation section (50; 450; 650), and the at least one elongate member (100; 500; 700) includes at least one protrusion (505; 705); and a cinching element (550; 750) fixedly or movably coupled to the device and comprising at least one detent configured to engage with the at least one protrusion (505; 705) to limit movement of the at least one elongate member (100; 500; 700) within the internal passage and thereby lock the articulation section (50; 450; 650).