Page 931 - Fundamentals of anatomy physiology
P. 931
918 Unit 5 Environmental Exchange
Any object in your mouth can trigger a salivary reflex. It stim- Figure 24–8a is a sectional view through an adult tooth.
ulates receptors monitored by the trigeminal nerve (N V) or The bulk of each tooth consists of a mineralized matrix similar
taste buds innervated by cranial nerve VII, IX, or X. Parasym- to that of bone. This material, called dentin, differs from bone
pathetic stimulation speeds up secretion by all the salivary in that it does not contain cells. Instead, cytoplasmic processes
glands. As a result, you produce large amounts of saliva. The extend into the dentin from cells in the central pulp cavity, an
role of sympathetic innervation is unclear. Evidence suggests interior chamber. The pulp cavity receives blood vessels and
that it provokes the secretion of small amounts of very thick nerves through the root canal, a narrow tunnel located at the
saliva. root, or base, of the tooth. Blood vessels and nerves enter the
root canal through an opening called the apical foramen to
The salivatory nuclei are also influenced by other brain supply the pulp cavity.
stem nuclei, as well as by the activities of higher centers. For
example, chewing with an empty mouth, smelling food, or The root of each tooth sits in a bony cavity or socket called
even thinking about food begins an increase in salivary secre- the tooth socket or an alveolus. Collagen fibers of the periodon-
tion rates. That is why chewing gum keeps your mouth moist. tal ligament extend from the dentin of the root to the alveolar
Irritating stimuli in the esophagus, stomach, or intestines also bone, creating a strong articulation known as a gomphosis.
speed up production of saliva, as does nausea. Increased saliva
production in response to unpleasant stimuli helps reduce the p. 291 A layer of cementum (se-MEN-tum) covers the dentin
stimulus by dilution, by rinsing, or by buffering strong acids of the root. Cementum protects and firmly anchors the peri-
or bases. odontal ligament. Cementum is histologically similar to bone
and is less resistant to erosion than is dentin.
The Teeth
The neck of the tooth marks the boundary between the
Tongue movements are important in passing food across the root and the crown, the exposed portion of the tooth that
opposing surfaces, or occlusal surfaces, of the teeth. These sur- projects beyond the soft tissue of the gingiva. A shallow groove
faces carry out chewing, or mastication (mas-ti-KA. -shun), of called the gingival sulcus surrounds the neck of each tooth.
food. Mastication breaks down tough connective tissues in The mucosa of the gingival sulcus is very thin and is not
meat and the plant fibers in vegetables. It also helps saturate tightly bound to the periosteum. The epithelium is bound to
the food with salivary secretions and enzymes. the tooth at the base of the sulcus. This epithelial attachment
prevents bacterial access to the lamina propria of the gingiva
Figure 24–8 Teeth. and the relatively soft cementum of the root. When you brush
and massage your gums, you stimulate the epithelial cells and
Crown Enamel strengthen the attachment. A condition called gingivitis, an in-
flammation of the gingivae caused by bacterial infection, can
24 Neck Dentin occur if the attachment breaks down.
Pulp cavity
Gingiva A layer of enamel covers the dentin of the crown. Enamel,
Gingival which contains calcium phosphate in a crystalline form, is
sulcus the hardest biologically manufactured substance. Adequate
amounts of calcium, phosphates, and vitamin D3 during
Cementum Incisors Cuspids Bicuspids Molars
(canines) (premolars)
Root Periodontal ligament
Upper
jaw
Root canal
Alveolar process Lower
Apical foramen jaw
a A diagrammatic section through a typical Branches of alveolar b The adult teeth from the right side of the upper and
adult tooth. vessels and nerve lower jaws. Figure 24–9a,b provides a view of the
occlusal surfaces.
