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.
When all the erector spinae muscles contract together, they extend or hyperextend the vertebral column. When only one side contracts, the trunk, neck or head move laterally toward the contracting side. The movement is accomplished because the articular facets of the vertebrae glide on each other.hen all the erector spinae muscles contract together, they extend or hyperextend the vertebral column. When only one side contracts, the trunk, neck or head move laterally toward the contracting side. The movement is accomplished because the articular facets of the vertebrae glide on each other.