Flexibility of the neck is important for humans’ ability to observe their environment, but this ability also makes it a vulnerable structure. Within the neck are major blood vessels and nerves that connect the brain to all structures below the head, including the heart and lungs. Unlike the chest, which has the ribcage to protect the heart and lungs, the neck lacks a complete bony shield, which would limit its flexibility.
The neck joint allows pivot (side to side) movement. The upper portion of the spine is the cervical spine (annotated with a “C” and numbered from top down). The neck joint consists of vertebrae C1 and C2, also known as the atlas and axis. The cranium, which houses the brain, sits on top of C1. The C1 and C2 vertebrae differ from other vertebrae in that they possess transverse foramina (singular, foramen), holes through which blood vessels can pass, in addition to the neural foramina, the pathways taken by nerves along the spine. The Internet Society of Orthopaedic Surgery & Trauma outlines other important structures of the cervical spine.
The head is able to turn on the spine because of how the atlas and axis are joined together. A bony protrusion on the axis, called the dens, points up through a hole in the atlas. Facet joints with articular cartilage between the bones are also present between the cervical vertebrae (C1-C7), allowing additional movement of the neck. As with any other joint, connective tissues span the connections to control movement. The joints also make the neck vulnerable to conditions like whiplash.
The movement of the neck joint is made possible by the actions of muscles. The neck contains many muscles that are involved in facial movement, swallowing, and upper arm and shoulder movement. The muscles involved directly in neck flexibility are the sternohyroid, longus capitis (offers flexibility along the spine, including the cervical spine), rectis capitis, semispinalis capitis, splenius capitis, and sternocleidomastoid. Due to the interconnection of the neck muscles with the trapezius muscle and other back and shoulder muscles, damage to neck muscles and neck pain can affect the entire upper body.
Vulnerable Structures in the Neck
The spinal cord passes from the base of the brain through the spinal (vertebrae) column. Trauma to the back of the neck or breakage of the vertebrae can damage the cord, resulting in paralysis or cervical spinal fluid accumulation, which can back up into the brain ventricles causing herniation (often leading to death) or brain damage. The Institute of Neurological Disorders and Stroke offers a more comprehensive look at spinal cord damage.
The presence of the jugular and carotid, the major vein and artery of the upper body, respectively, outside of the spine make the body vulnerable when the neck is damaged. The external blood vessels serving the face run alongside the neck, protected only by the skin and thin muscles. The neck is also the location of the throat. The throat begins as the internal anatomical structure known as the pharynx. The pharynx leads into both the esophagus and the windpipe (known as the trachea, via a ring of cartilage known as the larynx or voicebox). For decades, injuries to the throat have been known to potentially crush the larynx and block the trachea, causing asphyxiation.