Muscle Positions and Actions

Muscle Position & Action

Facial Muscles

Buccinator

• Position: Forms most of the cheek, giving it shape.
• Action: Compresses the cheek to keep food in the mouth during chewing (mastication).

Risorius

• Position: In the lower cheek, joins to the corner of the mouth.
• Action: Pulls back the angles of the mouth, as in smiling and grimacing.

Mentalis

• Position: Forms the chin.
• Action: Lifts the chin and pulls the bottom lip outwards.

Triangularis

• Position: Corner of the lower lip, extends over the chin.
• Action: Pulls the corner of the mouth downwards.

Zygomaticus

• Position: Runs down the cheek towards the corner of the mouth.
• Action: Pulls the corner of the mouth upwards and sideways, as in smiling and laughing.

Masseter

• Position: Runs down and back from the cheek to the angle of the jaw.
• Action: Raises the lower jaw during mastication.

Neck and Upper Body Muscles

Sternocleidomastoid

• Position: Runs either side of the neck.
• Action: Pulls the head down towards the shoulders, rotates the head to the side, and pulls the head forward to the chest (flexion of the neck).

Platysma

• Position: Front of the throat, covers the neck.
• Action: Pulls down the lower lip and the angles of the mouth, forms horizontal wrinkles on the neck.

Trapezius

• Position: Kite-shaped muscle in the upper back and sides of the neck.
• Action: Rotates the shoulders, pulls back the scapula, pulls the shoulders back, and assists in rotating the arms.

Pectoralis

• Position: Front of the chest, under the breast.
• Action: Pulls the arm forward and assists in the rotation of the arm.