Head and neck
The head and neck are two highly complex regions of the body. Their structures are closely interrelated due to them being compacted into a small area. A study of the cross-sectional anatomy of these areas allows a visual medium that facilitates the understanding of their structural organization. This will permit a unique representation of the positions, sizes, shapes, and relationships of the head and neck structures.
The head’s bony framework mainly consists of the cranium and mandible. The cranium houses the brain and is formed of several fused bony components. The mandible forms the lower mobile jaw and holds the lower teeth in place. The two major groups of muscles in the head include the muscles of mastication: the masseter, temporalis, medial pterygoid and lateral pterygoid; and the muscles of facial expression that are grouped according to region.
The ocular group of muscles consists of the orbicularis oculi, the depressor supercilii and the corrugator supercilii. The nasal group of muscles consists of the nasalis, procerus, levator labii superioris alaeque nasi and depressor septi nasi muscles. And the oral group consists of the orbicularis oris, buccinators, as well as other upper and lower group of muscles that act on the lips and mouth. The tongue is also one of the major muscles in the oral region. It is formed of both intrinsic and extrinsic group of muscles.
The major organs of the head are the cerebrum, brainstem, cerebellum and sensory organs. The cerebrum is formed of two cerebral hemispheres. The brainstem is comprised of the medulla oblongata, pons, and midbrain. The cerebellum is a structure present posterior to the brain. The meninges are membranous structures covering both the brain and spinal cord. They are formed of three distinguishable layers, the dura, arachnoid, and pia mater. In the head region, the dura mater separates into dural partitions and dural venous sinuses. The sensory organs are the eyes, nose, ears, and mouth, together with their associated structures.
The neck is comprised of skin, fascia, bones, muscles, organs, vessels and nerves. The bony framework of the neck is made up of the seven cervical vertebrae (C1-C7), the hyoid bone, the manubrium of the sternum, and the right and left clavicles. The muscles of the neck include the superficial platysma, the deep sternocleidomastoid, and the suprahyoid and infrahyoid group of muscles. It also consists of prevertebral and paravertebral muscles. The prevertebral muscles include the rectus capitis anterior, rectus capitis lateralis, longus capitis, and longus coli. The paravertebral muscles, on the other hand, include the scalenus anterior, scalenus medius, and scalenus posterior muscles. The levator scapula and trapezius muscles can also be considered as parts of the neck.
In the neck region, other major structures include the pharynx, larynx, trachea, thyroid and parathyroid glands, and the spinal cord. The pharynx can be divided into three portions - the nasopharynx, oropharynx, and laryngopharynx. The larynx is situated just below the pharynx, while the trachea lies posterior to it. The trachea connects the larynx and pharynx to the lungs. The thyroid gland is situated anteriorly in the neck and the four tiny parathyroid glands are located on its back. The spinal cord extends from the medulla oblongata and runs posteriorly throughout the neck.
The arteries of the head and neck regions are mainly the carotid and vertebral arteries together with their branches. Other arteries include the inferior thyroid, cervical, and suprascapular arteries. The veins, on the other hand, are the external, internal and anterior jugular veins together with their tributaries, and the dural venous sinuses as well. The nerves present in the head and neck regions mainly involve the twelve pairs of cranial nerves (CNI- CN XII) and the cervical plexus. This includes their various branches and divisions.
Computed tomography (CT) and magnetic resonance imaging (MRI) are indispensable tools for evaluating conditions involving the head and neck. These conditions include but are not limited to trauma, swelling, bleeding, and tumors. Both of the aforementioned scans depend on the cross-sectional analysis of the complex anatomic structures in these regions, and play a vital role in clinical practice.