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Chapter 7 Location Size Direction of fibers Number of origins Location of origins and insertion Action flexor Extensor Levator and depressor Muscles of the head and neck control human facial expressions Muscles of mastication control the mandible (lower jaw) frontalis o Expression: Surprise o Location: Either side of forehead o Function: Raises eyebrow and wrinkles forehead Depressor anguli oris o Expression: doubt, disdain, contempt o Location: along side of chin o Function: depresses corner of mouth Orbicularis oris o Expression: doubt, disdain, contempt o Location: ring-shaped muscle found around mouth o Function: compresses and closes the lips Platysma o Expression: horror o Location: broad, thin muscular sheet covering the side of neck and lower jaw o Function: draws corners of mouth downward and backward Zygomaticus major o Expression: laughing or smiling o Location: extends diagonally upward from corner of mouth o Function: raises corner of mouth Nasalis o Expression: flaring nostrils o Location: over nasal bones o Function: closes and opens nasal openings Orbicularis oculi o Expression: sadness o Location: Surrounds eye orbit underlying the eyebrows o Function: Closes the eyelid and tightens the skin on the forehead Masseter o Location: Covers the lateral surface of mandible o Function: Closes the jaw Temporalis o Location: Located on the temporal fossa of the skull o Function: Raises the jaw, closes the mouth, and draws back the jaw Sternocleidomastoid o Location: large muscles extending diagonally down sides of neck o Function: flexes head; rotates head toward opposite side from muscle