Anatomical language provides a standardized system for describing the body and the actions its parts perform. Terms like superior and inferior describe relative positioning, while others describe specific movements that occur at the joints. Retraction is one of these movement terms used to communicate precisely how a body part moves in relation to the rest of the body. This terminology ensures clear and consistent communication about the body’s mechanics for anyone studying human anatomy.
Retraction Defined
Retraction refers to the movement of a body part backward in the horizontal or transverse plane. This action pulls the structure toward the posterior of the body, or toward the midline in the case of the shoulder blades. The movement is defined by its direction, pulling a body segment back from an extended position.
To understand retraction, it is paired with its opposite action, protraction. Protraction is the movement of a body part forward along the same plane, pushing it anteriorly or away from the midline. For example, protraction of the jaw pushes the lower jaw forward, while retraction pulls it back to its resting position.
This antagonistic relationship is present in the joints that allow this type of movement. Protraction and retraction work together, allowing a body part like the shoulder or jaw to travel both forward and backward. The ability to move a structure along this horizontal axis is important for many daily activities and contributes to the body’s overall range of motion.
Key Anatomical Locations
Retraction is most commonly referenced in the anatomy of the upper torso and head, involving the scapulae and the mandible. These two locations allow for the most recognizable retraction movements. Understanding the movement at these sites is important for analyzing posture and joint function.
Scapular retraction involves the movement of the shoulder blades (scapulae) on the back of the rib cage. Pulling the shoulder blades toward the spinal column performs a retraction. This action moves the shoulder girdle posteriorly and medially, bringing the shoulder joints into a more aligned position.
The other primary site is the mandible, the lower jawbone. Mandibular retraction is the backward movement of the jaw, pulling the chin toward the neck. This movement is part of the complex chewing cycle and helps position the jaw during mastication.
The Muscles That Facilitate Retraction
Retraction is executed by specific muscle groups that contract to pull the bone structure backward. For the scapulae, the primary muscles responsible for pulling the shoulder blades together are the rhomboid major and minor muscles. These muscles run diagonally from the spine to the medial border of the scapula.
The middle fibers of the trapezius muscle also play a role, running horizontally across the upper back to pull the scapulae toward the midline. These muscles must shorten their length to draw the scapulae closer to the center of the back. The latissimus dorsi muscle can also assist with scapular retraction.
For mandibular retraction, the temporalis muscle is the primary retractor of the jaw. This large, fan-shaped muscle is located on the side of the head. The posterior fibers of the temporalis are horizontally oriented and contract to pull the lower jaw backward. Other muscles, such as the digastric muscle and the deep fibers of the masseter, also contribute to this movement.