Extension
If you are speaking about an arm, for instance, its called extension or extending.
Orthodontist
Extension in medical term means the action of stretching part of your body.
Aplasia is the medical term meaning absence of development.
Depression is the medical term meaning the act of lowering a body part. So opening your mouth is also depressing your mandible.
Elevation is the medical and common term meaning lifting.
Amputation?
The superiormost parts of the body are farthest from the ground.
Medulla
Extremity is the medical term meaning distant part.
Ischemia is the medical term meaning restricting blood flow to a body part.
Atrophy is the wasting away of a body part.
Dorsal or posterior mean back of the body.
Inferior is the medical term meaning toward the lower parts of the body.