The structure felt when running a hand down the middle of the back is the spine, specifically the vertebral column or spinal column. It consists of individual vertebrae stacked on top of each other, forming the backbone. The primary function of the vertebral column is to provide structural support and protection for the spinal cord, a crucial part of the central nervous system. Additionally, the spine facilitates movement, flexibility, and posture. The bony processes and surrounding ligaments contribute to the overall stability and functioning of the back, ensuring the body’s structural integrity and protecting the delicate spinal cord.