Head and neck anatomy
Head and neck anatomy focuses on the structures of the head and neck of 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.
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 abscessed 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
- (a) 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, vomer, 2-inferior conchae, mandible).
As the fetus develops, 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 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.
The
| Group | Name | Nerve | Function |
| facial expression | Epicranius: Frontalis and |
facial nerve | eyebrows and scalp |
| facial expression | Orbicularis oris | facial nerve | lips |
| facial expression | Zygomaticus | facial nerve | smiling |
| facial expression | Levator labii superioris | facial nerve | upper lip |
| facial expression | facial nerve | lower lip | |
| facial expression | facial nerve | cheeks | |
| facial expression | Mentalis | facial nerve | chin |
| facial expression | Platysma | facial nerve | frowning |
| facial expression | facial nerve | mouth angle | |
| facial expression | Orbicularis oculi | facial nerve | closes eye |
| facial expression | Corrugator supercilli | facial nerve | eyebrow |
| facial expression | Levator palpebrae superioris | oculomotor nerve | upper eyelid |
| chewing - lower mandible | Masseter | mandibular nerve | closing and protruding mandible, |
| chewing - lower mandible | Temporalis | mandibular nerve | elevates and controls side to side movement of mandible |
| chewing - lower mandible | mandibular nerve | elevates mandible, | |
| chewing - lower mandible | mandibular nerve | protracts mandible, opens mouth. | |
| tongue - extrinsic | Genioglossus | hypoglossal nerve | protraction, |
| tongue - extrinsic | Styloglossus | hypoglossal nerve | elevation and retraction, |
| tongue - extrinsic | Hyoglossis | hypoglossal nerve | depresses tongue |
| tongue - extrinsic | Palatoglossus | 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 | dorsal rami of middle and lower cervical nerves | extends head, supports turning |
Circulatory system
Blood circulates from the upper systemic loop
originating at the aortic arch, and includes: the brachiocephalic artery, left common carotid and
left
Blood supply
The brachiocephalic artery or trunk is the first and largest artery that branches to
form the right common carotid artery and the
The left common carotid artery divides to form the:
The left subclavian artery and the right subclavian artery, one on each side of the body form the
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. Endothelial tissue 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 junction and substances cannot pass out of the bloodstream. Some molecules, such as
Specialized glial cells called
Blood return
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
Lymphatic system
The lymphatic system drains the head and neck of excess interstitial fluid via
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.
Oral cavity
The mouth, also called the (
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 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, tongue, hard palate, soft palate, and floor of the mouth.
Teeth
Humans normally will produce two sets of teeth called primary dentition, or
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 dentin formation, (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
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.
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.
Adults have 32 permanent teeth, and children have 20 deciduous teeth.
Salivary glands
There are three sets of
Saliva also 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.
Periodontium
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.
This includes epithelial tissues (epithelium), connective tissues, (ligaments and
Tongue
The tongue is a specialized skeletal muscle that is specially adapted for the activities of speech, chewing, developing gustatory sense (taste) and swallowing.
It is attached to the
Terms meaning tongue include "glosso" and "lingual."
Mucosa
The protective tissues of the oral cavity are continuous with the digestive tract are called mucosa or mucous membranes.
They line the oral, nasal, and external auditory meatus, (ear), providing lubrication and protection against pathogens.
This is a stratified squamous epithelium containing about three layers of cells.
The lips are also protected by specialized sensory cells called Meissner's corpuscles.
The cells of the inner oral cavity are called the buccal mucosa.
Nervous system
The nervous system is composed of a central nervous system (CNS),
brain and
The CNS receives sensory (afferent) input from the PNS and directs the flow of information to association neurons (interneurons), located in the grey matter of the spinal cord and brain to create chemical synapse responses which in turn cause the formation of motor (efferent nerve) responses to stimulus.
The CNS is protected by the cranium,
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.- the 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.
Cranial nerves
Cranial nerves directly impact the sensing and processing of smell,
The control of the face and mouth also involves extensive coordination of cranial nerves. The face is controlled primarily by two nerves, trigeminal nerve which provides sensations to the face, and the facial nerve which controls facial expression and taste to two-thirds of the tongue, it also controls secretion of saliva and tears. Injury of the trigeminal nerve may result in loss of muscles of mastication. Injury to the facial nerve may result in paralysis of the facial muscles, Bell's palsy, loss of taste, and closure of the eyes.
The oral cavity control is also coordinated by three nerves; the glossopharyngeal
nerve which also controls various sensations including taste and proprioception, salivary gland secretion, and muscles of the mouth and neck; accessory nerve that mediates swallowing movements and head positioning; and the hypoglossal nerve that controls the tongue muscles for speech and swallowing actions. Injury of the
glossopharyngeal nerve may result in swallowing difficulty, reduction in saliva production, loss of sensation in the
throat, and loss of taste. Injury of the accessory nerve may result in paralysis of the sternocleidomastoid muscle and the
Hearing and balance are another control function the cranial nerves, the vestibulocochlear nerve, which transmits sound and balance sensory information from the
The vagus nerve can also impact the head and neck. If the nerve pair is injured in the upper body, it may lead to difficulty in swallowing, possibly paralyzing the vocal cords, and interruption of sensations from many organs.
Spinal nerves
The spinal nerves arise from the spinal column. The top section of the spine is the
cervical section, which contains nerves that
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 plexus.
The sensory branches of spinal nerves include: lesser occipital, C-2,
greater articular, (C-2 and C-3); transverse
cervical, C-2 and C-3; and
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 nerve branches, 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 (
Note: Damage to the spinal cord above C-5 may result in respiratory arrest and death if not medically treated.
Endocrine system
The endocrine system is under the direct supervision of the nervous system,
using the negative feedback principal of homeostasis, to create hormones which act as chemical instant messengers. The hypothalamus connects directly to the
The pituitary gland is 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
In the neck are the thyroid and parathyroid glands, that secrete hormones that control metabolism and blood calcium levels. The four parathyroid glands are situated upon the dorsal (back) surface of the thyroid gland.
Respiratory system
The respiratory System involves:
- (1) the nasal cavity for filtering, moistening, and warming the air
- (2) the pharynx or throat which is the combining point for respiratory and digestive system
- (3) larynx or voice box containing the epiglottis
- (4) trachea, or windpipe
- (5) bronchus breathing tubes of the lungs
- (6) lungs primary organs of respiration
- (7) the respiratory membranes consisting of the alveoli and surrounding capillary network of the pulmonary loop of the circulatory system
The critical pathway between the respiratory and digestive systems is the cartilage flap epiglottis which shuts during
swallowing to prevent
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 breathing may 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.
Integumentary system
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 (skin), 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
surface (
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.
Sensory neurons
Specialized sensory nerves are scattered throughout the epidermis and dermis allowing for a wide range of sensations to be
detected by the sensation of
Located within stratum basale are the most
Located just below the epidermis are Meissner's corpuscles which are very important in detecting subtle differences in texture, and Merkel cells monitor skin pressure.
The hair follicle endings detect hair movements, Krause corpuscles respond to pressure and cold, and are located on lips, tongue, and genitals.
The Pacinian corpuscles lay deep within the hypodermis, as do Ruffini ending, which detect heat. (See references below)
Inflammatory response
Within the deeper layers of the dermis and hypodermis, is a specialized type of connective tissue areolar connective tissue, which mediates the
The macrophages when disturbed by tissue trauma will devour as many invading pathogens as possible and perform cleaning of damaged tissue. The mast cells release histamine and heparin which 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).
Anaphylactic shock
Anaphylactic shock requires advanced medical care immediately; but other first aid measures include rescue breathing (part of CPR) and administration of epinephrine using an EpiPen for immediate administration of epinephrine (adrenaline) to reverse swelling and to keep the respiratory airway (trachea) open.
Disease awareness
Health care workers must exercise caution when performing care procedures on patients. The Universal precautions for health care workers are recommended by the
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.
Oral cancer may have a viral link.
- (3) Minor viral infections include:
Mumps is a viral infection of the parotid salivary glands. Chicken pox is a viral infection that can spread to the mouth.
- (4) Other diseases include:
Gingivitis gum disease, periodontal disease, oral forms of syphilis and gonorrhea. Dental caries or dental cavities. Thrush (Candidiasis) fungal infection. Tonsillitis is an inflammation of the tonsils and may cause a sore throat and fever. In chronic cases tonsillectomy may be required.
- (5) Temporomandibular joint diseases and disorders, commonly called TMJ.
- (6) Autoimmune diseases such as: Crohn's disease of 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,
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 dystrophy ) - (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.
References
- http://www.med-ed.virginia.edu/courses/rad/cspine/anatomy1.html
- http://www.pediatric-orthopedics.com/Topics/Bones/Skull/Skullduggery/Foramen_Magnum/foramen_magnum.html
- Skull bones
- ADHA Dental Hygene
- Medline, Crohn disease
- Brain-blood barrier, University of Washington
- Skin nerve receptors
- Cells Alive, Anatomy of a splinter
See also
External links
- Core Curriculum Syllabus: Review of Anatomy
- Core Curriculum Syllabus: Review of Anatomy - Temporal Bone and Ear
- Dental anatomy, CSU
- Head and Neck Anatomy
- Neuroscience for Kids
- American Dental Hygienists Association, Website
- Histology of peridontium
- The TMJ Association
- Inflammatory response
- The Anatomy Wiz: Soft Tissue Neck.
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|
|
|---|---|
| Cranial sutures | Coronal -
Lambdoid - Occipitomastoid -
Sphenofrontal - Sphenoparietal -
Sphenosquamosal - Sphenozygomatic
-Squamosal - Zygomaticotemporal -
|
| Fontanelles | Anterior fontanelle - |
| Foramina of multiple bones | Inferior orbital fissure - Foramen lacerum - Jugular foramen - Nasolacrimal canal |
| Fossae | Anterior cranial fossa - Middle cranial fossa -
|
| Other compound structures | Asterion - Nasion - Pterion - Dacryon - Zygomatic arch - Calvaria - Temporal fossa - Infratemporal fossa - Stephanion - Pterygomaxillary fissure - Pterygopalatine fossa |
| List of muscles of head and neck: the head | |
|---|---|
| scalp/eyelid | occipitofrontalis ( |
| extraocular | |