Primum Non Nocere

March 3, 2012

Anatomy 101: Muscles - Upper Neck and Face
As humans, a huge amount of our communication is non-verbal, and subconscious queues given by facial movements can say as much as any exclamation.
Almost all muscle on the head and neck is considered skeletal (voluntary) muscle, and the muscles that control the finest expressions originate from the facial bones, and insert on the skin. Aside from the chewing muscles, there are few that both insert and originate on bone.
Like skeletal muscles in the rest of the body, the muscles of the face sometimes have an antagonistic partner - that is, a muscle that performs the opposite action. Since muscles cannot perform a pushing action, the antagonist is needed to pull its partner back into place. One of the more obvious examples of this is the biceps brachii and the triceps brachii - if you had one without the other, the arm would only be able to move in one direction! Unlike the rest of the body, however, the muscles of the head and neck do not control limbs or need to push body parts, and don’t always need one or more antagonists.
Some of the significant facial muscles include:
Frontalis and corrugator: Control the forehead and eyebrows, respectively. When they’re used repeatedly, furrows in the brow develop. The corrugator muscle is generally where people getting Botox of the eyebrow have injections.
Obicularis oculi and obicularis oris: Circular muscles that work to “purse” the eyelids and lips, respectively.
Temporalis; masseter; and medial and lateral pterygoid: Muscles that are primary in chewing. The temporalis comes from the temple and elevates and retracts the jaw. The masseter and medial pterygoid also work to elevate and retract the jaw, and the lateral pterygoid depresses, opens, and protrudes the mandible, as well as moving it laterally.
Buccinator: Draws the lips wide and tight, and keeps food in contact with the teeth.
Levator labii: Raises the upper lip.
Depressor labii: Lowers the lower lips.
Risoris: Draws the lips into a smile (by the way, the whole “13 muscles required to smile/56 required to frown” is nonsense).
[Images: Anatomie generale des viscères en situation…avec l’angeologie, et la nevrologie de chaque partie du corps humain. Jacques Gautier d’Agoty, 1746]