Your neck packs airway, gullet, glands and the brain's blood supply into four compartments
The neck holds up the head, lets it swivel in every direction, and shields the nerves linking brain and body. Crammed inside a surprisingly small column are the windpipe, the throat, the thyroid and the main arteries feeding the brain, all sorted into four tidy anatomical compartments.
Anatomists split the human neck into a vertebral compartment, a visceral one and a pair of vascular ones. The first holds the cervical vertebrae, cushioned by cartilage discs, whose alignment sets the neck's shape, together with the stretch of spinal cord running through them. The visceral compartment carries the trachea, larynx and pharynx along with the thyroid and parathyroid glands. Each vascular compartment is a carotid sheath beside the windpipe, bundling the vagus nerve, the common carotid artery and the internal jugular vein. Lymph nodes cluster around the vessels. One naming quirk trips people up: the Latin word for neck is cervix, so cervical can mean either the neck or the neck of the uterus.
The muscles sit outside those compartments and mark out two triangles. The front triangle, bounded by the sternocleidomastoid, the lower jaw and the midline, contains small muscles above and below the hyoid bone. The upper set lifts the hyoid and the lower set pulls it down, and working together they make speech and swallowing possible. The rear triangle, between the sternocleidomastoid, the trapezius and the collarbone, houses muscles such as the levator scapulae and the three scalenes. Skin sensation at the front comes from spinal nerve roots C2 to C4 and at the back from C4 and C5.
Above all, the neck is the brain's supply line. The common carotid artery forks at about the level of the thyroid cartilage. Its external branch sends eight vessels to the neck, face and scalp, while the internal branch climbs without giving off any branches in the neck, enters the skull through a canal in the temporal bone and bends into an S-shaped loop known as the carotid siphon. It ends by feeding the front of the brain and the eye and joins the ring of vessels called the Circle of Willis.
A second route runs through the bones themselves. The vertebral arteries, which spring from the subclavian arteries, thread upward through holes in the sides of the vertebrae from C6 to C2 and then unite with the basilar artery to supply the brainstem, cerebellum and back of the brain.
Source: Neck
