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This article describes theanatomy of thehead andneck of the human body, including the brain, bones, muscles, blood vessels, nerves, glands, nose, mouth, teeth, tongue, and throat.
The head rests on the top part of thevertebral column, with the skull joining at C1 (the firstcervical vertebra known as theatlas). The skeletal section of the head and neck forms the top part of theaxial skeleton and is made up of theskull,hyoid bone,auditory ossicles, andcervical spine.
The skull can be further subdivided into:
Theoccipital bone joins with the atlas near theforamen magnum, a large hole (foramen) 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.
| Group | Name | Nerve | Function |
|---|---|---|---|
| facial expression | Epicranius:Frontalis andOccipitalis | 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 ofvagus nerve | elevates tongue while swallowing |
| oral cavity floor | Digastric | Trigeminal nerve andFacial 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 ofcervical 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 |
The head and neck is covered inskin and its appendages, termed theintegumentary system. These includehair,sweat glands,sebaceous glands, and sensory nerves. The skin is made up of three microscopic layers:epidermis,dermis, andhypodermis. Theepidermis is composed of stratifiedsquamous epithelium and is divided into the following five sublayers or strata, listed in order from outer to inner:
The mouth, also called the oral cavity, is the entranceway into thedigestive system containing both primary and accessory organs of digestion.
Two rows of teeth are supported by facial bones of the skull, themaxilla above and themandible 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:
The white visible part of a tooth is called thecrown. The rounded upper projections of the back teeth arecusps. The hard white exterior covering of the tooth is theenamel. As the tooth tapers below the gumline, theneck is formed. Below the neck, holding the tooth into the bone, is theroot of the tooth. The inner portions of the tooth consist of the dentin, a bonelike tissue, and thepulp. The pulp is a soft tissue area containing the nerve and blood vessels to nourish and protect the tooth, located within thepulp cavity.
A tooth sits in a specialized socket called the alveolus. The tooth is held in location by aperiodontal ligament, with the assistance ofcementum. Teeth are surrounded bygingiva, or gums, part of theperiodontium, support tissue of oral cavity protection. Theperiodontium 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 andbone),muscle tissue andnervous tissue.
There are three sets ofsalivary 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 formedbolus which is swallowed after chewing. Saliva is composed primarily of water, ions,salivary amylase,lysozymes, and trace amounts ofurea.
The tongue is a specializedskeletal muscle that is specially adapted for the activities of speech, chewing, developinggustatory 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 thehyoid bone. Terms meaning tongue include "glosso" (from Greek) and "lingual" (from Latin).
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The outer surfaces of the head and neck are lined byepithelium. The protective tissues of the oral cavity are continuous with the digestive tract are calledmucosa or mucous membranes. The cells of the inner oral cavity are called thebuccal mucosa.
The oral cavity is lined by a stratifiedsquamous epithelium containing about three layers of cells.[citation needed] They line the oral, nasal, andexternal auditory meatus, (ear), providing lubrication and protection againstpathogens.
Thelips are also protected by specialized sensory cells calledMeissner's corpuscles.
Blood circulates from the uppersystemic loop originating at theaortic arch, and includes: thebrachiocephalic artery, leftcommon carotid artery and leftsubclavian artery. The head and neck are emptied of blood by thesubclavian vein andjugular vein.
Thebrachiocephalic artery or trunk is the first and largestartery that branches to form theright common carotid artery and theright subclavian artery. This artery provides blood to the right upper chest, right arm, neck, and head, through a branch called rightvertebral artery. The right and left vertebral artery feed into thebasilar artery and upward to theposterior cerebral artery, which provides most of the brain with oxygenated blood.Theposterior cerebral artery and theposterior communicating artery are within thecircle of Willis.
Theleft common carotid artery divides to form the:internal carotid artery (ICA) and anexternal carotid artery (ECA). The ICA supplies the brain. The ECA supplies the neck and face.
Theleft subclavian artery and theright subclavian artery, one on each side of the body form theinternal thoracic artery, the vertebral artery, thethyrocervical trunk, and thecostocervical trunk. The subclavian becomes the axillary artery at the lateral border of the first rib. Theleft subclavian artery also provides blood to the left upper chest and left arm.
Theblood–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, calledcapillaries, are lined withendothelial 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 atight junction which prevents substances from passing out of the bloodstream.
Specializedglial cells calledastrocytes 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.
Blood from the brain and neck flows from: (1) within thecranium via theinternal jugular veins, a continuation of thesigmoid sinuses. The right and leftexternal jugular veins drain from theparotid 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 thesuperior vena cava, into theright atrium of theheart.
The lymphatic system drains the head and neck of excessinterstitial fluid vialymph vessels orcapillaries, equally into theright lymphatic duct and thethoracic duct.
Lymph nodes line the cervical spine and neck regions as well as along the face and jaw.
Thetonsils also are lymphatic tissue and help mediate the ingestion of pathogens.
Tonsils in humans include, from superior to inferior:nasopharyngeal tonsils (also known asadenoids),palatine tonsils, andlingual tonsils.
Together this set of lymphatic tissue is called the tonsillar ring orWaldeyer's ring.
Thespinal nerves arise from thespinal column. The top section of the spine is the cervical section, which contains nerves thatinnervate muscles of the head, neck andthoracic 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 orplexus.
Thesensory branches of spinal nerves include:lesser occipital, C-2,great auricular, (C-2 and C-3);transverse cervical, C-2 and C-3; andsupraclavicular, C-3 and C-4. These nerve groups transmit afferent (sensory) information from the scalp, neck, and shoulders to the brain.
Themotor branches of spinal nerves include:ansa cervicalis, dividing into a superior root, C-1, and an inferior root, C-2 and C-3, and thephrenic nerve, C-3 to C-5, thesegmental nerve branches, C-1 to C-5. These nerve groups transmitefferent nerve (motor) information from the brain to muscle groups of the scalp, neck,diaphragm (anatomy), and shoulders.
Additionally there are: (C5-C8, and T1)Brachial plexus, providing the entire nerve supply of the shoulder and upper limb; and includessupraclavicular branches (dorsal scapular,suprascapular,long thoracic) lateral cord (musculocutaneous,lateral antibrachial cutaneous, lateral head ofmedian nerve), medial cord (ulnar, medial head of median nerve,medial antibrachial cutaneous,medial brachial cutaneous), posterior cord (axillary, radial), controlling the arm.
Damage to a person's spinal cord above C-5 may result inrespiratory arrest and death if medicinal aid does not intervene.
Twelve pairs ofcranial nerves emerge from the brain; these affect movements and sensation, and some special organs such ashearing of parts of the head and neck.
Movements of the neck includes:flexion,extension, (nodding yes), androtation (shaking head no).
The mouth has evolved to support chewing, (mastication) and swallowing (deglutition), and speech (phonation).
In addition to the teeth, other structures that aid chewing are the lips,cheeks,tongue,hard palate,soft palate, and floor of the mouth.
Several glands of theendocrine system are found within the head and neck.Endocrine means that the secretion is used within the body.Endocrine glands are termed as ductless and release their secretions directly into the blood. Theendocrine system is under the direct supervision of the nervous system, using thenegative feedback principal ofhomeostasis, to create hormones which act as chemical instant messengers.
Thehypothalamus connects directly to thepituitary gland, both through thecirculatory system and by direct connection of neurons. Also, within thecranium, thepineal gland, which attaches to thethalamus, controls the body's 24-hour rhythmscircadian rhythm through the release ofmelatonin.
Thepituitary gland secreteshormones that directly impact the body as well as hormones that indirectly control body functions because they activate other endocrine glands, such as theadrenal cortex (ACTH) and thethyroid gland (TSH). These two glands when stimulated by pituitary hormones then release their own hormones.The pituitary gland has two lobes, the anterior lobe and the posterior lobe. The anterior lobe secretes:growth hormone (GH),Luteinizing hormone (LH),Follicle stimulating hormone (FSH),Adrenocorticotropic hormone (ACTH),Thyroid-stimulating hormone (TSH),Prolactin (PRL), and the posterior lobe secretes: Antidieuretic hormone (ADH), andOxytocin. There is an intermediate lobe, in adult humans it is just a thin layer of cells between the anterior and posterior pituitary, nearly indistinguishable from the anterior lobe. The intermediate lobe producesmelanocyte-stimulating hormone (MSH).
In the neck are thethyroid andparathyroid glands, that secrete hormones that controlmetabolism and bloodcalcium levels. The four parathyroid glands are situated upon the back surface of the thyroid gland.
The respiratory system begins in the head and neck, withair entering and leaving the body through the mouth and nose. The respiratory system involving the head and neck includes:
These lead down into thelower respiratory tract. A critical junction between the respiratory and digestive systems is theepiglottis, a cartilage flap which shuts during swallowing to preventaspiration. The epiglottis is normally open to support respiration and shuts during swallowing to prevent food and fluids from entering the trachea, activating the gag reflex or initiates the choking mechanism.
Thenervous system is composed of acentral nervous system (CNS),brain andspinal cord, and theperipheral nervous system (PNS),cranial nerves andspinal nerves. The CNS is located within thedorsal cavity, and the PNS extends through theventral cavity. The central nervous system provides control and coordination of alleleven body systems and utilizes theendocrine system to formhormone chemical messengers that transport through the blood to influence the activity of individual cells of the body and their associated tissues, organs and systems.
The CNS receives sensory (afferent) input from the PNS and directs the flow of information toassociation neurons (interneurons) to createchemical synapse responses which in turn cause the formation of motor (efferent nerve) responses tostimulus. Association neurons are located in thegrey matter of the spinal cord and the brain.
The CNS is protected by thecranium,vertebral column,meninges,cerebrospinal fluid. The spinal cord is an extension of the brain. The spinal cord and thebrain stem are joined at the base of the cranium at theforamen magnum. Most of the functions of the head and neck are directly influenced by the brain and transmitted to the PNS via the cranial nerves and spinal nerves of the cervical portion of the spine.
The PNS has two subdivisions
The facial bones usually form into pairs and then fuse together. As the cranium fuses,sutures are formed that resemble stitching between bone plates. In a newborn, the junction of the parietal bones with the frontal and occipital bones, form the anterior (front) and posterior (back)fontanelle, or soft spots. The separation of the cranial bone plates at time of birth facilitate passage of the head of the fetus through the mother'sbirth canal, orpelvic girdle. The parietal bones, and occipital bone can overlap each other in the birth canal, and form the unusual looking "cone head" appearance in a newborn when delivered in a natural, or vaginal, delivery.
Humans normally will produce two sets of teeth called primary dentition, ordeciduous teeth, and secondary dentition, orpermanent teeth.
Atooth is the toughest known substance in the body exceeding bones in density and strength.Tooth enamel lends great strength to the tooth structure. The formation of a developing tooth includes the process ofdentin formation, (see:dentinogenesis) and enamel formation, (see:amelogenesis). The tooth breaks through the gum into the mouth in a process called eruption. The formation of teeth begins in early fetal development and goes through six stages:
Severe viral infections that affect the mouth, lips, or the oral cavity include:Oral cancer may have a viral link.
Infected teeth can on rare occasions cause infection to spread leading tocavernous sinus thrombosis,mediastinitis, orLudwig's angina causing airway blockage.
Diseases may be transmitted by contact of the head, mouth, or body fluids, such asHerpes Simplex Virus Type I (HSV-1), Herpes Simplex Virus Type II (HSV-2)genital herpes, which may present as a lesion on the lips, and contactable via skin to skin contact
Careful observation of the oral cavity, teeth and gums may reveal indicators of other medical conditions. For example, a person suffering from the eating disorder,bulimia nervosa may show signs of excessive tooth and gum erosion.
The airway in the head and neck may be obstructed with swelling associated with an enlarged tongue (macroglossia), tonsils, with swelling associated withanaphylactic shock,angiooedema, or aforeign body.
Anaphylactic shock requires advanced medical care immediately; but other first aid measures includerescue breathing (part ofCPR) and administration ofepinephrine using an EpiPen for immediate administration of epinephrine (adrenaline) to reverse swelling and to keep the respiratory airway (trachea) open.