Final answer:
The correct motions occurring in the sagittal plane around a medial-lateral axis are flexion and extension. These are different from abduction and adduction, which happen in the coronal plane, and rotation, which does not occur in the sagittal plane.
Step-by-step explanation:
Motion in the Sagittal Plane
Motions in the sagittal plane, such as flexion and extension, occur around a medial-lateral axis. To clarify, (a)-(b) specifically state that flexion and extension motions happen in the sagittal plane, which is described as an anterior-posterior plane of motion. These types of movements can be observed at various joints including the shoulder, hip, elbow, knee, and several joints within the hand and foot. In contrast, motions like abduction and adduction take place in the coronal plane, and as such, they are not the movements occurring in the sagittal plane.
Abduction and adduction involve moving the limbs, hands, or feet away from or toward the midline of the body, respectively. These motions are typical in condyloid, saddle, and ball-and-socket joints. On the other hand, circumduction is a circular movement combining flexion, adduction, extension, and abduction, and it occurs in both the biaxial and multiaxial joints.
Rotation pertains to the pivoting movement around the longitudinal axis of a bone, which is not a sagittal plane motion either. Therefore, the correct answer to the student's question is b) Flexion and Extension.