This article describes the anatomy of the head and neck of the human body, including the brain, bones, muscles, blood vessels, nerves, glands, nose, mouth, teeth, tongue, and throat.
Structure Bones The head rests on the top part of the vertebral column, with the skull joining at C1 (the first cervical vertebra known as the atlas). The skeletal section of the head and neck forms the top part of the axial skeleton and is made up of the skull, hyoid bone, auditory ossicles, and cervical spine.
The skull can be further subdivided into: the cranium (8 bones: frontal, 2-parietal, occipital, 2-temporal, sphenoid, ethmoid), and the facial bones (14 bones: 2-zygomatic, 2-maxillary, 2-palatine, 2-nasal, 2-lacrimal, vomer, 2-inferior conchae, mandible).
The occipital bone joins with the atlas near the foramen magnum, a large hole () at the base of the skull. The atlas joins with the occipital condyle above and the axis below. The spinal cord passes through the foramen magnum.
Muscles Group Name Nerve Function facial expression Epicranius: Frontalis and Occipitalis facial nerve eyebrows and scalp facial expression Orbicularis oris facial nerve closes lips facial expression Zygomaticus major facial nerve smiling facial expression Zygomaticus minor facial nerve smiling facial expression Levator labii superioris facial nerve upper lip facial expression Levator labii superioris alaeque nasi facial nerve upper lip facial expression Depressor labii inferioris facial nerve lower lip facial expression Depressor anguli oris facial nerve frowning facial expression Platysma facial nerve frowning (during fear or shock) facial expression Buccinator facial nerve cheeks facial expression Mentalis facial nerve chin facial expression Platysma facial nerve frowning facial expression Risorius facial nerve mouth angle facial expression Orbicularis oculi facial nerve closes eye facial expression Nasalis facial nerve flare nostrils facial expression Corrugator supercilli facial nerve eyebrow facial expression Levator palpebrae superioris oculomotor nerve upper eyelid chewing – lower mandible Masseter Trigeminal nerve closing and protruding mandible, chewing – lower mandible Temporalis Trigeminal nerve elevates and controls side to side movement of mandible chewing – lower mandible Medial pterygoid Trigeminal nerve elevates mandible, chewing – lower mandible Lateral pterygoid Trigeminal nerve protracts mandible, opens mouth. tongue – extrinsic Genioglossus hypoglossal nerve protraction, tongue – extrinsic Styloglossus hypoglossal nerve elevation and retraction, tongue – extrinsic Hyoglossus hypoglossal nerve depresses tongue tongue – extrinsic Palatoglossus Pharyngeal plexus, pharyngeal branch of vagus nerve elevates tongue while swallowing oral cavity floor Digastric Trigeminal nerve and Facial nerve hyoid and mandible movement oral cavity floor Stylohyoid Facial nerve elevates hyoid oral cavity floor Mylohyoid Trigeminal nerve hyoid and mandible movement oral cavity floor Geniohyoid Cervical nerve C-1 hyoid, tongue, and mandible movement move head Sternocleidomastoid Accessory nerve nodding and turning move head Semispinalis dorsal rami of cervical nerves extends head, supports turning move head Splenius capitis dorsal rami of middle and lower cervical nerves extend head, supports turning move head Longissimus capitis dorsal rami of middle and lower cervical nerves extends head, supports turning move head Rectus capitis posterior major Suboccipital nerve C-1 extends head move head Rectus capitis posterior minor Suboccipital nerve C-1 extends head
Skin The head and neck is covered in skin and its appendages, termed the integumentary system. These include hair, sweat glands, sebaceous glands, and sensory nerves. The skin is made up of three microscopic layers: epidermis, dermis, and hypodermis. The epidermis is composed of stratified squamous epithelium and is divided into the following five sublayers or strata, listed in order from outer to inner: Stratum corneum, Stratum lucidum, Stratum granulosum, Stratum spinosum, Stratum germinativum, also called stratum basale. The deepest layer is the miotic layer, stratum basale producing daughter cells by mitosis.
Mouth
The mouth, also called the oral cavity, is the entranceway into the digestive system containing both primary and accessory organs of digestion.
Teeth
Two rows of teeth are supported by facial bones of the skull, the maxilla above and the mandible below. Adults have 32 permanent teeth, and children have 20 deciduous teeth. There are various tooth shapes for different jobs. For example, when chewing, the upper teeth work together with the lower teeth of the same shape to bite, chew, and tear food. The names of these teeth are: (1) Incisors, there are eight incisors located in the front of the mouth (four on the top and four on the bottom). They have sharp, chisel-shaped crowns that cut food. (2) Cuspids (or canine tooth), the four cuspids are next to each incisor. Cuspids have a pointed edge to tear food. (3) Premolars (or bicuspids), the four pairs of molars are located next to the cuspids. They crush and tear food. (4) Molars, there are twelve molars, in sets of three, at the back of the mouth. They have wide surfaces that help to grind food.
The white visible part of a tooth is called the crown. The rounded upper projections of the back teeth are cusps. The hard white exterior covering of the tooth is the enamel. As the tooth tapers below the gumline, the neck is formed. Below the neck, holding the tooth into the bone, is the root of the tooth. The inner portions of the tooth consist of the dentin, a bonelike tissue, and the pulp. The pulp is a soft tissue area containing the nerve and blood vessels to nourish and protect the tooth, located within the pulp cavity.
A tooth sits in a specialized socket called the alveolus. The tooth is held in location by a periodontal ligament, with the assistance of cementum. Teeth are surrounded by gingiva, or gums, part of the periodontium, support tissue of oral cavity protection. The periodontium includes all of the support membranes of the dental structures surround and support the teeth such as the gums and the attachment surfaces and membranes. These include epithelial tissues (epithelium), connective tissues, (ligaments and bone), muscle tissue and nervous tissue.
Salivary glands
There are three sets of salivary glands: the parotid, the submandibular and the sublingual glands. The (exocrine) glands secrete saliva for proper mixing of food and provides enzymes to start chemical digestion. Saliva helps to hold together the formed bolus which is swallowed after chewing. Saliva is composed primarily of water, ions, salivary amylase, lysozymes, and trace amounts of urea.
Tongue The tongue is a specialized skeletal muscle that is specially adapted for the activities of speech, chewing, developing gustatory sense (taste) and swallowing. The tongue contains two sets of muscles, the intrinsic- involved with shape of tongue, and the extrinsic- involved with tongue movement. It is attached to the hyoid bone. Terms meaning tongue include "glosso" () and "lingual" ().
Nose
Microanatomy The outer surfaces of the head and neck are lined by epithelium. The protective tissues of the oral cavity are continuous with the digestive tract are called mucosa or mucous membranes. The cells of the inner oral cavity are called the buccal mucosa.
The oral cavity is lined by a stratified squamous epithelium containing about three layers of cells. They line the oral, nasal, and external auditory meatus, (ear), providing lubrication and protection against pathogens.
The lips are also protected by specialized sensory cells called Meissner's corpuscles.
Blood, lymph and nerve supply Blood supply Blood circulates from the upper systemic loop originating at the aortic arch, and includes: the brachiocephalic artery, left common carotid artery and left subclavian artery. The head and neck are emptied of blood by the subclavian vein and jugular vein.
The brachiocephalic artery or trunk is the first and largest artery that branches to form the right common carotid artery and the right subclavian artery. This artery provides blood to the right upper chest, right arm, neck, and head, through a branch called right vertebral artery. The right and left vertebral artery feed into the basilar artery and upward to the posterior cerebral artery, which provides most of the brain with oxygenated blood. The posterior cerebral artery and the posterior communicating artery are within the circle of Willis.
The left common carotid artery divides to form the: internal carotid artery (ICA) and an external carotid artery (ECA). The ICA supplies the brain. The ECA supplies the neck and face.
The left subclavian artery and the right subclavian artery, one on each side of the body form the internal thoracic artery, the vertebral artery, the thyrocervical trunk, and the costocervical trunk. The subclavian becomes the axillary artery at the lateral border of the first rib. The left subclavian artery also provides blood to the left upper chest and left arm.
Blood–brain barrier
The blood–brain barrier (BBB) is semi-permeable membrane that controls the capillary leak potential of the circulatory system. In most parts of the body, the smallest blood vessels, called capillaries, are lined with endothelial cells, which have small spaces between each individual cell so substances can move readily between the inside and the outside of the capillary. The endothelial cells of capillaries in the brain lack these spaces. Instead, the endothelial cells fit tightly together to create a tight junction which prevents substances from passing out of the bloodstream.
Specialized glial cells called astrocytes form a tight junction or protective barrier around brain blood vessels and may be important in the development of the BBB. Astrocytes may also be responsible for transporting ions (electrolytes) from the brain to the blood.
Venous drainage
Blood from the brain and neck flows from: (1) within the cranium via the internal jugular veins, a continuation of the sigmoid sinuses. The right and left external jugular veins drain from the parotid glands, facial muscles, scalp into the subclavian veins. The right and left vertebral veins drain the vertebrae and muscles into the right subclavian vein and into the superior vena cava, into the right atrium of the heart.
Lymphatic system
The lymphatic system drains the head and neck of excess interstitial fluid via lymph vessels or capillaries, equally into the right lymphatic duct and the thoracic duct.
Lymph nodes line the cervical spine and neck regions as well as along the face and jaw.
The tonsils also are lymphatic tissue and help mediate the ingestion of pathogens.
Tonsils in humans include, from superior to inferior: nasopharyngeal tonsils (also known as adenoids), palatine tonsils, and lingual tonsils.
Together this set of lymphatic tissue is called the tonsillar ring or Waldeyer's ring.
Nerve supply The spinal nerves arise from the spinal column. The top section of the spine is the cervical section, which contains nerves that innervate muscles of the head, neck and thoracic cavity, as well as transmit sensory information to the CNS.
The cervical spine section contains seven vertebrae, C-1 through C-7, and eight nerve pairs, C-1 through C-8.
There is the formation of an extensive network of nerve groups or tracts attaching to the spinal cord in arrangements called rami or plexus.
The sensory branches of spinal nerves include: lesser occipital, C-2, great auricular, (C-2 and C-3); transverse cervical, C-2 and C-3; and supraclavicular, C-3 and C-4. These nerve groups transmit afferent (sensory) information from the scalp, neck, and shoulders to the brain.