Chapter 6 The Muscular System 185 Copyright Goodheart-Willcox Co., Inc. into a single large muscle that inserts on the mastoid process of the temporal bone. Contracting together, the sternocleidomastoid muscles produce flexion of the head and neck. When one muscle contracts alone, the result is rotation of the head toward the opposite side. The platysma is a single, thin, flat, superficial muscle that blankets the entire anterior and lateral portions of the neck. It originates in the connective tissue covering the chest muscles and inserts in the tissues around the mouth. Contraction of the platysma pulls the corners of the mouth downward. It is also activated when opening the mouth wide. SELF CHECK 1. In what way are facial muscles different from most other muscles? 2. Which muscles assist with chewing? 3. What movements result from contraction of the sternocleidomastoid muscles? Muscles of the Trunk The trunk muscles provide stability for the vertebral column. They are also responsible for maintaining upright posture. American football players train to The buccinator and zygomaticus muscles form part of the sides of the face. The buccinator extends from the maxilla and mandible to the orbicularis oris. When it contracts, this muscle compresses the cheek. Zygomaticus is named after its origin on the zygomatic bone. It attaches to the skin and muscle around the corners of the mouth contraction of the zygomaticus produces smiling. Chewing Muscles The major muscle used for chewing is the masseter, which connects the zygomatic process of the temporal bone to the mandible, or jaw bone. Contraction of the masseter elevates the mandible, bringing the teeth together. An assistive muscle for chewing is the temporalis, which covers a large portion of the temporal bone and connects the temporal bone to the mandible. The buccinators also assist with chewing when they contract to hold the cheeks firm. Neck Muscles The paired sternocleidomastoid muscles are primary supporters and movers of the head. Each muscle has two heads—one that originates on the sternum, and one that originates on the clavicle. The heads fuse Muscles of the Head and Neck Facial Muscles Muscle Origin Insertion Primary Functions Frontalis epicranial aponeurosis skin above eyebrows raises eyebrows, wrinkles forehead Occipitalis temporal bone epicranial aponeurosis pulls scalp posteriorly Orbicularis oculi frontal bone and maxilla tissue encircling eyes closes eyes, enables squinting Nasalis maxilla lateral to nose bridge and cartilage of nose modifies size of nostrils Orbicularis oris mandible and maxilla skin and muscle around mouth closes lips, produces kissing motion Buccinator maxilla and mandible orbicularis orbis compresses cheek Zygomaticus zygomatic bone skin and muscle at corners of mouth the “smiling” muscle Platysma connective tissue over chest muscles tissue around mouth pulls corners of mouth down, opens mouth wide Chewing Muscles Muscle Origin Insertion Primary Functions Masseter zygomatic arch of temporal bone mandible closes the jaw Temporalis temporal bone mandible assists masseter with closing jaw Neck Muscles Muscle Origin Insertion Primary Functions Sternocleidomastoid two heads arise from the sternum and clavicle mastoid process of temporal bone flexion of head, rotation of head toward opposite side of contraction Figure 6.14 Goodheart-Willcox Publisher