Axial musculature

The muscular system, like the skeletal system, is divided into axial and appendicular divisions. The axial musculature arises from and inserts on the axial skeleton. It positions the head and spinal column and helps move the rib cage, which makes breathing possible.
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The muscles of facial expression originate on the surface of the skull. The largest group is associated with the mouth; it includes the orbicularis oris and buccinator. The frontal and occipital bellies of the occipitofrontalis control movements of the eyebrows, forehead, and scalp. The platysma tenses skin of the neck and depresses the mandible.
The muscles of the back are arranged into three distinct layers: superficial, intermediate, and deep.Only the deepest of these layers is composed of the intrinsic (or true) back muscles. These intrinsic back muscles are innervated by the posterior rami of the spinal nerves, and they interconnect the vertebrae.The superficial layer contains the splenius of the neck and upper thorax.The intermediate group is composed of the erector spinae of the trunk.The deep layer is composed of the transversospinales, which consists of the semispinalis group and the multifidus, rotatores, interspinales, and intertransversarii muscles. These muscles interconnect and stabilize the vertebrae.Other muscles of the vertebral column are the longus capitis and longus colli, which rotate and flex the neck, and the quadratus lumborum muscles in the lumbar region, which flex the spine and depress the ribsThe oblique and rectus muscles lie between the vertebral column and the anterior midline. The abdominal oblique muscles (external oblique and internal oblique) compress underlying structures or rotate the vertebral column; the rectus abdominis is a flexor of the vertebral column.The oblique muscles of the neck and thorax include the scalenes, the intercostals, and the transversus muscles. The external intercostals and internal intercostals are important for breathing because they move the ribs.The diaphragm is important in breathing. It separates the abdominopelvic and thoracic cavities.Muscles of the perineal region and pelvic diaphragm extend from the sacrum and coccyx to the ischium and pubis. These muscles (1) support the organs of the pelvic cavity, (2) flex the joints of the sacrum and coccyx, and (3) control the movement of materials through the urethra and anus.The perineal region (the pelvic floor and associated structures) is divided into an anterior urogenital triangle and a posterior anal triangle. The pelvic floor consists of the consists of the pelvic diaphragm and surrounding muscles.