Final answer:
Flexion is the movement that decreases the angle between two bones at a joint, while extension increases the angle, generally straightening a joint. They are types of angular movements that occur in the sagittal plane and are essential for the wide range of motion in synovial joints. Excessive flexion or extension beyond the normal range of motion is termed hyperflexion or hyperextension.
Step-by-step explanation:
Flexion and extension are types of angular movements at the synovial joints. Flexion is a movement that decreases the angle between two bones at a joint, such as bending the elbow or the knee. Conversely, extension is an increase in the angle between two bones, generally straightening a joint, like straightening the arm at the elbow or the leg at the knee. Flexion and extension occur in the sagittal plane.
In the upper limb, moving the arm forward and up is considered flexion at the shoulder, while moving it back to the anatomical position is extension. The movement when bending the fingers towards the palm is flexion at the metacarpophalangeal and interphalangeal joints, and straightening them is extension. For the lower limb, bringing the thigh forward and upward constitutes flexion at the hip joint, and moving it backward represents extension. In the case of the knee, bending it to bring the foot towards the posterior thigh is knee flexion, while straightening the knee is extension.
Hyperflexion and hyperextension refer to excessive flexion or extension of a joint beyond its normal range of motion, which can lead to injury as seen in some whiplash cases, affecting the cervical region of the neck.