Â© 2000 John Wiley & Sons, Inc. An inverse relationship between household income and violence exposure in youth hasbeen reported in numerous studies (e.g., Garbarino & Crouter, 1978; Gelles, 1992; Gelles& Straus, 1979; Steinberg, Catalano, & Dooley, 1981).
The head, attached to the top of the vertebral column, is balanced, moved, and rotated by the neck muscles (). When these muscles act unilaterally, the head rotates. When they contract bilaterally, the head flexes or extends. The major muscle that laterally flexes and rotates the head is the sternocleidomastoid.
Rotation describes the action of moving the head from side to side, lateral motion brings the ear to the shoulder, flexion moves the chin to the chest (as in looking down), and hyperextension moves the neck so that the head tilts upward.he muscles of the neck run from the base of the skull to the upper back and work together to bend the head and assist in breathing.