Head and neck anatomy
Head and neck anatomy is a specialized study of the human body quite frequently studied in depth by surgeons, dentist, and dental technicians. This branch of study focuses on the bones, muscles, circulatory system, nerves, glands, and nose, mouth, teeth, tongue, and throat structures.
Dental perspective
Dental students focus their studies on teeth and the support structures of teeth. However, there are no independent structures or systems of the body. An abcessed tooth may quickly spread pathogens to other body organs and systems. For example an infected tooth may lead to heart disease (Endocarditis) and kidney disease (Glomerulonephritis) if the pathogen is either a staphylococcus aureus (staph) or streptococcal (strep) bacterium.
Musculoskeletal System
The head is positioned upon the superior portion of the vertebral column, attaching the skull upon the atlas (anatomy). The skeletal section of the head and neck forms the superior segment of the axial skeleton and is comprised of skull, hyoid bone, auditory ossicles, and cervical spine. The skull can be further subdivided into (1) cranium, (eight bones), and (2) facial bones, (fourteen bones). The occipital bone 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).
Muscles of facial expression include: (1) Epicranius (includes the (1.a)Frontalis (eyebrows) and (1.b) Occipitalis (scalp)), (2) Orbicularis oris (lips), (3) Zygomaticus (smiling), (4) Levator labii superioris (upper lip), (5) Depressor labii inferioris (lower lip), (6) Buccinator (cheeks), (7) Mentalis (chin), (8) Platysma (frowning), (9) Risorius (mouth angle), (10) orbicularis oculi (closes eye), (11) Corrugator supercilli (eyebrow), (All innervated by Cranial nerve VII, Facial nerve) and (12) Levator palpebrae superioris (upper eyelid) Note: Innverated by cranial nerve III Oculomotor nerve.
Muscles of chewing, lower mandible include: (1) Masseter (closing and protruding mandible), (2) Temporalis (elevates and controls side to side movement of mandible), (3) Medial pterygoid (elevates mandible), (4) Lateral pterygoid (protracts mandible, opens mouth). Note: All innervated by the mandibular division of cranial nerve V, Trigeminal nerve.
Muscles that move the toungue - extrinsic include: (1) Genioglossus (protraction), (2) Styloglossus (elevation and retraction), (3) Hyoglossis (depresses tongue), All innervated by cranial nerve XII Hypoglossal nerve) and (4) Palatoglossus (elevates tongue while swallowing) Innervated by Pharyngeal plexus, pharyngeal branch of cranial nerve X Vagus nerve.
Muscles of the oral cavity floor include: (1) Digastric (hyoid and manbible movement), Innervation: Cranial nerves V and VII, Trigeminal nerve and Facial nerve (2) Stylohyoid, (elevates hyoid), cranial nerve VII Facial nerve (3) Mylohyoid, (hyoid and manbible movement) Innervation: Cranial nerve V, Trigeminal nerve, (4) Geniohyoid, (hyoid, tongue, and manbible movement) Innervation: Cervicle nerve C-1.
Muscles that move the head include: (1) Sternocleidomastoid (nodding and turning) Innervation: cranial nerve XI Accessory nerve, (2) Semispinalis (extends head, supports turning) Innervation: dorsal rami of cervical nerves, (3) Splenius capitis, (extend head, supports turning) Innervation: dorsal rami of middle and lower cervical nerves, (4) Longissimus capitus, (extends head, supports turning) Innervation: dorsal rami of middle and lower cervical nerves.
Oral Cavity
The mouth, (oral cavity) is the entranceway into the digestive system containing both primary and accessory organs of digestion. The mouth is designed to support chewing, (mastication) and swallowing, (deglutition), and speech. Two rows of teeth are supported by facial bones of the skull, the maxilla above and the mandible below. 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, tougue, hard palate, soft palate, and floor of the mouth.
Teeth
Humans normally will produce two sets of teeth called primary dentition, (or deciduous teeth) and secondary dentition or permanent teeth .
A tooth 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 of inserting enamel on the dentin, (see: Dentinogenesis) layer as the tooth breaks through the gum line is called amelogenesis. The formation of teeth begins in early fetal development and goes through four stages: (1) bud stage, (2) cap stage, (3) bell stage, and (4) crown, or calcification, 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 visable 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.
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. And, (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. Adults have 32 permanent teeth, and children have 24 deciduous teeth.
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 also helps to hold together the formed bolus which is swallowed after chewing.
Disease Awareness
Health care workers must exercise caution when performing care procedures on patients. The Universal Safety Precautions for 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:
(1) 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 B Virus (HBV), Hepatitis C Virus (HCV), Herpes Simplex Virus Type 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.
Mumps is a viral infection of the paratoid salivary glands. Chicken pox is a viral infection that can spread to the mouth. Oral cancer may have a viral link.
Other diseases include: Gingivitis gum disease, periodontal disease, oral forms of syphilis and gonorrhea.
Dental caries or dental cavities. Thrush (Candidiasis) fungal infection.
Crohn disease of the oral cavity, see reference
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 excessing tooth and gum erosion.
Patient Screening
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, (2) hypertension, (3) heart defects, (4) heart disease, (5) kidney disease, (6) other allergens, such as latex allergy. (7) history of stroke or transient ischemic attack (TIA), (certain oral sedation methods may trigger a TIA), (8) neuromuscular disorders, (such as muscular distrophy), (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 osteoporosis.