4: Head and Neck Anatomy and Physiology

Head and Neck Anatomy and Physiology

For the dental hygienist, knowledge of the skeletal, muscular, nervous, and circulatory systems of the head and neck region is essential for client assessment and evaluation; radiography and reading radiographs; and client referral for abnormal conditions. An understanding of the circulatory and lymphatic systems enables the dental hygienist to locate sources of oral infection, trace the spread of disease in the head and neck, and identify nerves and anatomic landmarks for safe and effective delivery of local anesthetic agents.

Anatomic Nomenclature

Location of an anatomic structure is based on the body in the anatomic position; the term anatomic position denotes a body standing erect, head facing directly forward, with arms at the sides and palms facing forward (Figure 4-1)

Planes—the sections of the body are divided into imaginary flat surfaces called planes; a plane is a flat surface determined by the location of these three points in space:

Relative positions

1. Anterior or ventral—structures nearest the front side of the body or head

2. Posterior or dorsal—structures nearest the back side of the body or head

3. Tongue surfaces—an exception to the previous anatomic positions is the surfaces of the human tongue, which still has the anatomic orientation of a four-footed animal; the dorsal surface of the tongue is the top surface, and the ventral surface of the tongue is the bottom surface

4. Medial—structures closest to the median plane of the body and head

5. Lateral—structures farthest from the median plane of the body and head (for example, ears are lateral to the nose or eyes)

6. Superficial—structures located toward the surface of the body

7. Deep—structures located internally the surface of the body

8. Proximal—near the source of attachment

9. Apex—the tip or pointed end of a structure

10. Contralateral—structures on the opposite side of the body

11. Cranial or superior—toward the head

12. Caudal or inferior—toward the tail

Osteology

Definition—the study of bones

Classification—bone and cartilage are classified as rigid and firm connective tissues; they contain large amounts and various types of intercellular material (or matrix; plural, matrices) and few cells; with the exception of cartilage, connective tissue is highly vascular

Function—bone supports organs and structures; provides attachments for muscles and ligaments; is involved in movement, body defense, and repair mechanism; protects the soft tissues and organs of the body

Histology of bone (see the section on “Connective Tissue” in Chapter 2)

1. Intramembranous ossification—osteoblasts are formed from a network of mesenchymal cells; osteoblasts secrete collagen and a matrix of mucoproteins that form osteoids; this matrix initially forms bone

2. Endochondral ossification—hyaline cartilage “template” becomes mineralized and is replaced by bone; osteoids are formed within cartilage

3. Cartilage—noncalcified, avascular, pliable connective tissue; three types of cartilage:

Descriptive terminology

1. Bony prominences—a process is a general term used to describe any prominence on a bony surface

2. Bony depressions

3. Bony openings

4. Skeletal articulations—areas where bones are joined; articulations can be movable or immovable

Axial Skeleton

Bones of the head are grouped into two categories:

Neurocranium, or cranial bones (eight bones)—bones that surround the brain

1. Frontal bone (single bone) (Figure 4-2)

2. Parietal bones (paired bones) (see Figure 4-2)

3. Temporal bones (paired bones)

a. Form the lateral walls of the skull

b. Articulate on each side of the skull with the zygomatic and parietal bones, and sphenoid and occipital bones

c. Divided into three portions:

4. Occipital bone (single bone) (see Figure 4-2)

5. Sphenoid bone (single bone)

a. Articulates with the ethmoid and frontal bones anteriorly and the temporal and occipital bones posteriorly

b. Body of the sphenoid bone contains the sphenoid sinuses and the sella turcica, the seat of the pituitary gland, which supplies numerous hormones to the body

c. Pterygoid processes project down from the body of the sphenoid bone in an inferior, backward direction; its landmarks include:

d. Greater sphenoid wings—lateral projections in the temporal area

e. Lesser sphenoid wings—anterior process

6. Ethmoid bone (single bone) (see Figure 4-2)

Viscerocranium, or facial bones (14 bones)—surround the face (Figure 4-3)

1. Inferior nasal conchae (paired bones)

2. Nasal bones (paired bones) (see Figure 4-3)

3. Vomer (single bone)

4. Lacrimal bones (paired bones) (see Figure 4-3)

5. Zygomatic bones (paired bones)—(see Figure 4-3)

6. Maxillae (paired bones)—have a body and four processes (see Figure 4-3)

a. The body contains the maxillary sinus and forms the lower and medial rims of the orbits and the borders of the nasal cavity (piriform aperture); other landmarks are:

b. The frontal process articulates with the frontal bone, forming the medial orbital rim; it articulates with the lacrimal bone within the orbit

c. The alveolar process (see the section on “Supporting Tissues” in Chapter 2)

d. Zygomatic process

e. Palatine processes

7. Palatine bones (paired bones)

8. Mandible (single bone) (see Figure 4-3)

a. Largest, strongest, and only movable facial bone; articulates with the temporal bones on both sides

b. Body—horizontal portion runs from the anterior to the lateral aspects; landmarks include:

c. Ramus—projects vertically and backward from the body of the mandible

Neck bones

Paranasal Sinuses

The Muscular System

Descriptive terminology

Muscles of facial expression—most facial muscles are superficial, paired muscles originating in bone and inserting into skin; they are innervated by the seventh cranial or facial nerve and are responsible for functions related to speech, emotional expression, and mastication

1. Epicranial or occipitofrontalis muscle—scalp region; composed of two bellies (the fleshy, contractile part of a muscle), the frontal and occipital, which are connected by the epicranial aponeurosis; raise the eyebrows and scalp

2. Orbicularis oculi muscle—surrounds the eye; closes the eyelid

3. Corrugator supercilii muscle—superior to the orbicularis; wrinkles the forehead

4. Orbicularis oris muscle—encircles the mouth; closes lips

5. Buccinator muscle—anterior part of the cheek; originates on the maxilla, mandible, and pterygomandibular raphe and inserts into the angle of the mouth; functions to pull the mouth laterally, thereby shortening the cheek, and as an aid in keeping food on the chewing surfaces of the teeth

6. Risorius muscle—mouth region; acts in smiling and widening the mouth

7. Levator labii superioris muscle—upper lip; raises the upper lip

8. Levator labii superioris alaeque nasi muscle—upper lip; raises the upper lip and dilates the nose, as in sneering

9. Zygomaticus minor muscle—upper lip; raises the upper lip

10. Zygomaticus major muscle—angle of the mouth; pulls the angle of the mouth laterally, causing the appearance of a smile

11. Levator anguli oris muscle—angle of the mouth; elevates the corner of the mouth, as in smiling

12. Depressor labii inferioris muscle—lower lip; lowers the lower lip to expose lower teeth

13. Mentalis muscle—chin area; raises the chin, narrows the vestibule near mandibular incisors

14. Platysma muscle—neck region; originates in the clavicle fascia and inserts in the region of the mandible and facial muscles of the mouth; pulls down the corners of the mouth, raising the skin of the neck

Muscles of mastication—four paired muscles, all inserting on the mandible, innervated by the fifth cranial or trigeminal nerve; they are responsible for movement of the jaw

1. Masseter muscle—most superficial, largest, and strongest of the four muscles

2. Temporalis muscle

3. Medial (internal) pterygoid muscle (Figure 4-4)

4. Lateral pterygoid muscle; lies within the infra-temporal fossa (see Figure 4-4)

Cervical muscles—paired superficial, large, easily palpated muscles, both innervated by cranial nerve XI (accessory nerve)

Hyoid muscles—all are attached to the hyoid bone; usually grouped as suprahyoid or infrahyoid muscles, depending on their relationship to the hyoid; they aid in mastication and swallowing

1. Suprahyoid muscle group—located superior to the hyoid; acts to raise the hyoid and the larynx

a. Digastric muscle

b. Mylohyoid muscle—forms the floor of the mouth

c. Stylohyoid muscle

d. Geniohyoid muscle—located on the floor of the mouth

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Jan 1, 2015 | Posted by in Dental Hygiene | Comments Off on 4: Head and Neck Anatomy and Physiology
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