Head and Neck Anatomy: Part II – Musculature
Glossary of Directional Terms

Movement Terms

abduction – Movement away from the midline in the frontal place.

adduction – Movement towards the midline in the frontal place.

depression – Movement inferiorly.

elevation – Movement superiorly.

extension – Increasing the angle of a joint (straightening the joint).

flexion – Decreasing the angle of a joint.

hyperextension – Increasing the angle of a joint past straight.

lateral rotation – Rotation around an axis in the lateral direction.

medial rotation – Rotation around an axis in the medial direction.

protract – Movement anteriorly in a horizontal plane.

retract – Movement posteriorly in a horizontal plane.

Other Terms

action – The movement created when a muscle moves (see movement terms above).

agonist – The muscle that is performing the action.

antagonist – The muscle that opposes the movement crated by the agonist.

insertion – The moving end of the muscle.

origin – The stationary end of the muscle.

synergist – A muscle with an action not being performed but involved in making the movement more efficient. These muscles are usually a pair of muscles that are antagonists that when contracted stabilize the origin of the prime mover.