A surgical instrument, comprising: a surgical end effector; and an elongated shaft assembly defining a longitudinal tool axis and being operably coupled to the surgical end effector, the elongated shaft assembly including a flexible segment comprising: a longitudinally extending, elongated articulation spine including two lateral sides; and a plurality of ribs (510, 520) extending laterally from each lateral side of said articulation spine along a length thereof; wherein: the two lateral sides of the articulation spine comprise: a right lateral side; and a left lateral side and wherein the plurality of ribs (510, 520) comprises: at least three right ribs protruding from the right lateral side of the articulation spine such that first spaces are provided between the right ribs, each of the first spaces having a first space width; and at least three left ribs protruding from the left lateral side of the articulation spine such that second spaces are provided between the left ribs, each of the second spaces having a second space width; characterised in that: the spine includes a length and a width that tapers along said length, wherein a distal portion of the flexible segment articulates at an articulation rate that is faster than another articulation rate of another portion of the flexible segment that is proximal to the distal portion upon application of articulation motions to the surgical end effector; and the first space widths sequentially decline in magnitude proceeding from a proximal end of the flexible segment to a distal end of the flexible segment and wherein the second space widths sequentially decline in magnitude proceeding form the proximal end of the flexible segment to the distal end of the flexible segment. a surgical end effector; and an elongated shaft assembly defining a longitudinal tool axis and being operably coupled to the surgical end effector, the elongated shaft assembly including a flexible segment comprising: a longitudinally extending, elongated articulation spine including two lateral sides; and a plurality of ribs (510, 520) extending laterally from each lateral side of said articulation spine along a length thereof; wherein: a longitudinally extending, elongated articulation spine including two lateral sides; and a plurality of ribs (510, 520) extending laterally from each lateral side of said articulation spine along a length thereof; wherein: the two lateral sides of the articulation spine comprise: a right lateral side; and a left lateral side and wherein the plurality of ribs (510, 520) comprises: at least three right ribs protruding from the right lateral side of the articulation spine such that first spaces are provided between the right ribs, each of the first spaces having a first space width; and at least three left ribs protruding from the left lateral side of the articulation spine such that second spaces are provided between the left ribs, each of the second spaces having a second space width; characterised in that: a right lateral side; and a left lateral side and wherein the plurality of ribs (510, 520) comprises: at least three right ribs protruding from the right lateral side of the articulation spine such that first spaces are provided between the right ribs, each of the first spaces having a first space width; and at least three left ribs protruding from the left lateral side of the articulation spine such that second spaces are provided between the left ribs, each of the second spaces having a second space width; characterised in that: at least three right ribs protruding from the right lateral side of the articulation spine such that first spaces are provided between the right ribs, each of the first spaces having a first space width; and at least three left ribs protruding from the left lateral side of the articulation spine such that second spaces are provided between the left ribs, each of the second spaces having a second space width; characterised in that: the spine includes a length and a width that tapers along said length, wherein a distal portion of the flexible segment articulates at an articulation rate that is faster than another articulation rate of another portion of the flexible segment that is proximal to the distal portion upon application of articulation motions to the surgical end effector; and the first space widths sequentially decline in magnitude proceeding from a proximal end of the flexible segment to a distal end of the flexible segment and wherein the second space widths sequentially decline in magnitude proceeding form the proximal end of the flexible segment to the distal end of the flexible segment.