- Head and neck anatomy
Head and neck anatomy focuses on the structures of the
headand neckof the human body, including the brain, bones, muscles, blood vessels, nerves, glands, nose, mouth, teeth, tongue, and throat. It is an area frequently studied in depth by surgeons, dentists, dental technicians, and speech language pathologists.
Knowledge of head and neck anatomy is of paramount importance for dental surgeons and students. Knowledge of anatomy of nerves and other vital structures in the head and neck allows the dentist to perform diagnosis and surgery. For example an infected tooth can on rare occasions cause infection to spread leading to
cavernous sinus thrombosis, mediastinitis, or Ludwig's anginacausing airway blockage. Which of these potentially fatal outcomes occurs depends largely on the anatomy of the head and neck.
The head is positioned upon the superior portion of the
vertebral column, attaching the skull upon C-1, (the atlas). The skeletal section of the head and neck forms the superior segment of the axial skeletonand comprises skull, hyoidbone, auditory ossicles, and cervical spine. The skull can be further subdivided into:
cranium, (8 bones: frontal, 2-parietal, occipital, 2-temporal, sphenoid, ethmoid)), and
* (b) facial bones, (14 bones: 2-zygomatic, 2-maxillary, 2-palentine, 2-nasal, 2-lacrimal, volmer, 2-inferior conchae, mandible).
As the fetus develops, the facial bones usually form into pairs, and then fuse together. As the cranium fuses,
suturesare formed that resemble stitching between bone plates.
In a newborn, the junction of the paritial 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's birth canal, or pelvic girdle. The parietial 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.
occipitalbone articulates with the atlas near the foramen magnum. The atlas articulates with the occipital condyle superiorly and the axis inferiorly. The spinal cord passes through the foramen magnum providing continuity for the central nervous system(CNS). Articulation (anatomy)of the neck includes: flexion, extension, hyperextension(nodding yes), and rotation(shaking head no).
Bloodcirculates from the upper systemic looporiginating at the aortic arch, and includes: the brachiocephalic artery, left common carotidand left subclavian artery. The head and neck are emptied of blood by the subclavian veinand jugular vein.
The brachiocephalic artery or trunk is the first and largest
arterythat branches to form the right common carotidartery 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 arteryand upward to the Posterior cerebral artery, which provides most of the brain with oxygenated blood.The posterior cerebral arteryand the posterior communicating arteryare 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 axiliary 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(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. Endothelialtissue has small spaces between each individual cell so substances can move readily between the inside and the outside of the vessel. However, in the brain, the endothelial cells fit tightly together to create a tight junctionand substances cannot pass out of the bloodstream. Some molecules, such as glucose, are transported out of the blood by active transport.
glialcells called astrocytesform a tight junction or protective barrier around brain blood vessels and may be important in the development of the BBB. Astrocytes may be also be responsible for transporting ions ( electrolytes) from the brain to the blood.
Blood from the brain and neck flows from: (1) within the
craniumvia the internal jugular veins, a continuation of the sigmoid sinuses. The right and left external jugular veinsdrain 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 atriumof the heart.
The lymphatic system drains the head and neck of excess
interstitial fluidvia lymph vesselsor capillaries, equally into the right lymphatic ductand the thoracic duct. Lymph nodesline the cervical spine and neck regions as well as along the face and jaw.
tonsilsalso 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
mouth, also called the ( oral cavity) or buccal cavityis the entranceway into the digestive systemcontaining both primary and accessory organs of digestion.
The mouth is designed to support chewing, (mastication) and swallowing, (deglutition), and speech (phonation).
Two rows of teeth are supported by facial bones of the skull, the
maxillaabove and the mandiblebelow.
Teeth are surrounded by
gingiva, or gums, part of the periodontium, support tissue of oral cavity protection.
In addition to the teeth, other structures that aid chewing are the
lips, cheeks, tongue, hard palate, soft palate, and floor of the mouth.
Humans normally will produce two sets of teeth called primary dentition, or
deciduous teeth, and secondary dentition, or permanent teeth.
toothis the toughest known substance in the body exceeding bones in density and strength. Tooth enamellends great strength to the tooth structure. The formation of a developing tooth includes the process of dentinformation, (see: Dentinogenesis) and enamel formation, (see: amelogenesis. As the tooth breaks through the gum into the mouth, the process is called eruption. The formation of teeth begins in early fetal development and goes through six stages:
* (1) initiation stage, 6th - 7th week
* (2) bud stage, 8th wk
* (3) cap stage, 9th-10 wk
* (4) bell stage, 11th-12th wk
* (5) apposition
* (6) maturation stage
Tooth enamel is white initially but is susceptible to stains from coffee and cigarette usage. A tooth sits in a specialized socket called
gomphosis. The tooth is held in location by a periodontal ligament, with the assistance of cementum.
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
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:
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.
Premolarsor (bicuspids), the four pairs of molars are located next to the cuspids. They crush and tear food.
Molars, there are twelve molars, in sets of three, at the back of the mouth. They have wide surfaces that help to grind food.
Adults have 32 permanent teeth, and children have 20 deciduous teeth.
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. Salivaalso helps to hold together the formed bolus which is swallowed after chewing.
Saliva is composed of primarily of water, ions,
salivary amylase, lysozymes, and trace amounts of urea.
periodontiumincludes all of the support membranes of the dental structures surround and support the teeth such as the gums and the attachment surfaces and membranes.
This includes epithelial tissues (
epithelium), connective tissues, ( ligamentsand bone), muscletissue and nervous tissue.
tongueis a specialized skeletal musclethat is specially adapted for the activities of speech, chewing, developing gustatorysense (taste) and swallowing.
It is attached to the
Terms meaning tongue include "glosso" and "lingual."
The protective tissues of the oral cavity are continuous with the digestive tract are called
mucosaor mucous membranes.
They line the oral, nasal, and
external auditory meatus, (ear), providing lubrication and protection against pathogens.
This is a stratified
squamous epitheliumcontaining about three layers of cells.
lips are also protected by specialized sensory cells called Meissner's corpuscles.
The cells of the inner oral cavity are called the
The nervous system is composed of a
central nervous system(CNS), brainand spinal cord, and the peripheral nervous system(PNS), cranial nervesand spinal nerves. The CNS is located within the dorsal cavity, and the PNS extends through the ventral cavity. The central nervous system provides control and coordination of all eleven body systems and utilizes the endocrine systemto form hormonechemical 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 to association neurons( interneurons), located in the grey matterof the spinal cord and brain to create chemical synapseresponses which in turn cause the formation of motor ( efferent nerve) responses to stimulus.
The CNS is protected by the
cranium, vertebral column, meninges, cerebrospinal fluid. The spinal cord, which is an extension of the brain, and brain stemare joined at the base of the cranium at the foramen 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
somatic nervous system(SNS). The SNS is associated with the voluntary control of body movements through the action of skeletal muscles, and also reception of external stimuli.
autonomic nervous system(ANS). The ANS is divided into subsystems: the sympathetic nervous system(SNS) and the parasympathetic(PNS) nervous systems. The SNS and PNS often have opposing effects in the same organs or physiological systems, and the ANS is a major factor in maintaining homeostasis.
The spinal nerves arise from the
spinal column. The top section of the spine is the cervical section, which contains nerves that innervatemuscles of the head, neck and thoracic cavity, as well as transmit sensory information to the CNS.
The cervical spine section contains seven vertabrae, 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
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.
The motor branches of spinal nerves include:
ansa cervicalis, dividing into a superior root, C-1, and an inferior root, C-2 and C-3, and the phrenic nerve, C-3 to C-5, the segmental nervebranches, C-1 to C-5. These nerve groups transmit efferent 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 includes supraclavicular branches( dorsal scapular, suprascapular, long thoracic) lateral cord ( musculocutaneous, lateral antibrachial cutaneous, lateral head of median nerve), medial cord (ulnar, medial head of median nerve, medial antibrachial cutaneous, medial brachial cutaneous), posterior cord (axillary, radial), controlling the arm.
Note: Damage to the spinal cord above C-5 may result in
respiratory arrestand death if not medically treated.
endocrine systemis under the direct supervision of the nervous system, using the negative feedbackprincipal of homeostasis, to create hormones which act as chemical instant messengers. The hypothalamusconnects directly to the pituitary gland, both through the circulatory systemand by direct connection of neurons. Also, within the cranium, the pineal gland, which attaches to the thalamus, controls the body's 24 hour rhythms circadian rhythmthrough the release of melatonin. Endocrineindicates that the secretion is used within the body. Endocrine glands are termed as ductless and release their secretions directly into the blood.
pituitary glandis also called hypophysis, or "master gland". It secretes hormones that directly impact the body as well as hormones that indirectly control body functions because they activate other endocrine glands, such as the adrenal cortex(ACTH) and the thyroid 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), and Oxytocin(OT). 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 produces melanocyte-stimulating hormone(MSH).
In the neck are the
thyroidand parathyroid glands, that secrete hormones that control metabolismand blood calciumlevels. The four parathyroid glands are situated upon the dorsal (back) surface of the thyroid gland.
The respiratory System involves:
* (1) the
nasal cavityfor filtering, moistening, and warming the air
* (2) the
pharynxor throat which is the combining point for respiratory and digestive system
larynxor voice box containing the epiglottis
* (4) trachea, or windpipe
bronchusbreathing tubes of the lungs
lungsprimary organs of respiration
* (7) the respiratory membranes consisting of the
alveoliand surrounding capillary network of the pulmonary loopof the circulatory system
The critical pathway between the respiratory and digestive systems is the cartilage flap epiglottis which shuts during swallowing to prevent aspiration. The epiglottis is normally open to support respiration and shuts during swallowing to prevent food and fluids from enterng the trachea, activating the gag reflex or initiates the choking mechanism. The respiratory system is involved in
ventilation (physiology)and cellular respiration. Its functioning during oral procedures and surgery is essential to good patient care. If the patient stops breathing, heart failure will result within four to six minutes. The use of cardiopulmonary resuscitation(CPR) and rescue breathingmay be required to revive the patient.
Other illnesses that may present a concern to the health care professional include:
influenza, pulmonary embolism, cystic fibrosis, and respiratory distress syndrome, ARDS.
The integumentary system comprises
skin, and the appendages of skin, such as hair, nails, sweat glands, sebaceous glands, and sensory nerves.
Skin comprises three layers: epidermis,
dermis, and hypodermis.
The epidermis is composed of stratified
squamous epitheliumand is divided into the following five sublayers or strata, listed in order from surface ( superficial) to deep are:
Stratum germinativumalso called stratum basale. The deepest layer is the miotic layer, stratum basale producing daughter cells by mitosis.
Within the deeper layers of the dermis and hypodermis, is a specialized type of connective tissue
areolar connective tissue, which mediates the inflammatory response, or self-healing capacity of the body. The areolar tissue comprises collagenfibers and elastic fiberswhich contain several cells which are trapped within the tissue matrix. These cells, when disturbed by tissue damage, will release chemical and mechanical factors that signal the body's immune system to initiate clean-up, destruction of invading pathogens, and tissue repair. The cells involved are macrophages, mast cells, fibroblasts, and plasma cells.
The macrophages when disturbed by tissue trauma will devour as many invading
pathogensas possible and perform cleaning of damaged tissue. The mast cells release histamineand heparinwhich help initiate the inflammatory response. The fibroblast help repair or replace damaged sections of matrix, and the plasma cells are capable of producing antibodies for pathogen destruction.
The inflammatory response system produces four distinct signs of activation: redness, swelling, heat, and pain (or itching). When these symptoms are confined to a specific site, it is termed as localized inflammation. In severe reactions involving a widespread inflammation response, or systemic inflammation (
Anaphylactic shock requires advanced medical care immediately; but other first aid measures include
rescue breathing(part of CPR) and administration of epinephrineusing an EpiPen for immediate administration of epinephrine (adrenaline) to reverse swelling and to keep the respiratory airway (trachea) open.
Health care workers must exercise caution when performing care procedures on patients. The
Universal precautionsfor health care workers are recommended by the Centers for Disease Control and Prevention(CDC) are the standard precaution for self protection.
Severe viral infections that affect the mouth, lips, or the oral cavity include:
Human Immunodeficiency Virus(HIV) and the Acquired Immunodeficiency Syndrome(AIDS). Mouth lesions may not be visible, but body fluids are the source of infection.
* (2) Other viral infections may be just as easy to contact and as difficult to cure such as:
Hepatitis BVirus (HBV), Hepatitis C Virus(HCV), Herpes Simplex VirusType I (HSV-1), Herpes Simplex Virus Type II (HSV-2) genital herpes. Either form of the viral infection may present as a lesion on the lips. Direct skin to skin contact may cause infection. Oral cancermay have a viral link.
* (3) Minor viral infections include:
Mumpsis a viral infection of the parotid salivary glands. Chicken poxis a viral infection that can spread to the mouth.
* (4) Other diseases include:
Gingivitisgum disease, periodontal disease, oral forms of syphilisand gonorrhea. Dental cariesor dental cavities. Thrush ( Candidiasis) fungal infection. Tonsillitisis an inflammation of the tonsils and may cause a sore throat and fever. In chronic cases tonsillectomymay be required.
Temporomandibular jointdiseases and disorders, commonly called TMJ.
* (6) Autoimmune diseases such as:
Crohn's diseaseof the oral cavity, see reference below.
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 nervosamay show signs of excessive tooth and gum erosion.
Prior to any oral sedation methods being used on a patient, screening must be done to identify possible health concerns. Prevention is the best cure.
Identify any of the following that may apply:
* (1) known drug allergies, and sensativities,
* (6) other
allergens, such as latex allergy
* (7) history of
strokeor transient ischemic attack(TIA), (certain oral sedation methods may trigger a TIA)
* (8) neuromuscular disorders, (such as
* (9) a current list of medications and herbal supplements taken by the patient
A patient with any of these conditions must be evaluated for special procedures to minimize the risk of patient injury due to the sedation method.
In addition to the above mentioned precautions, patients should be interviewed to determine if they have any other condition that may lead to complications while undergoing treatment. Any head, neck, or spinal cord injuries should be noted as well as any diagnosis of
* [http://clem.mscd.edu/~raoa/axialskel/sld010.htm Skull bones]
* [http://www.adha.org/kidstuff/index.html ADHA Dental Hygene]
* [http://www.medscape.com/medline/abstract/11875926 Medline, Crohn disease]
* [http://faculty.washington.edu/chudler/bbb.html Brain-blood barrier, University of Washington]
* [http://faculty.washington.edu/chudler/receptor.html Skin nerve receptors]
* [http://www.cellsalive.com/ouch.htm Cells Alive, Anatomy of a splinter]
* [http://www.bcm.edu/oto/studs/anat.html Core Curriculum Syllabus: Review of Anatomy] at
Baylor College of Medicine
* [http://www.bcm.edu/oto/studs/anat/tbone.html Core Curriculum Syllabus: Review of Anatomy - Temporal Bone and Ear] at
Baylor College of Medicine
* [http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/pregastric/dentalanat.html Dental anatomy] at
Colorado State University
* [http://faculty.washington.edu/chudler/skull.html Neuroscience for Kids] at
University of Washington
* [http://www.dental.pitt.edu/informatics/periohistology/en Histology of peridontium] at
University of Pittsburgh
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