The general ability to taste as well as the ability to sense specific tastes is genetically determined. Studies in large populations demonstrate that taste variation is common. About 25% of the population, referred to as “super-tasters,” have more than the normal number of lingual papillae and a high density of taste buds. Rare individuals in this group, such as wine, brandy, coffee, or tea tasters, have prodigious taste discrimination and taste memory. These individuals are characterized by their extreme sensi-tivity to the chemical phenylthiocarbamide (PTC) and its derivative 6-N-propylthiouracil (PROP); they typically re-port an intensely bitter taste after a drop of PTC/PROP solution is placed on the tip of their tongue. On the other side of the spectrum (about 25% of the population) are in-dividuals known as “nontasters,” with a smaller than normal number of lingual papillae and a lower density of taste buds. When tested with PTC/PROP solution, these individuals are unaware of its bitter taste. Many clinical conditions can affect taste perception. They include lesions in the nerves that transmit the taste sensa-tion to the central nervous system; inflammations of the oral cavity; mucosal disorders including radiation-induced in-flammation of the lingual mucosa; nutritional deficiencies; endocrine disorders such as diabetes mellitus, hypogo-nadism, and pseudohypoparathyroidism; and hormonal fluctuations during menstruation and pregnancy. Some rare genetic disorders also affect taste sensation. Type I familial dysautonomia (Riley-Day syndrome) causes se-vere hypogeusia (decreased ability to detect taste) be-cause of the developmental absence of taste buds and fungiform papillae. This sensory and autonomic neuropathy is an autosomal recessive disorder caused by a mutation in the DYS gene (also referred to as the IKBKAP gene) lo-cated on chromosome 9. In addition to hypogeusia, these individuals experience other symptoms related to develop-mental defects in the peripheral and autonomic nervous systems, including diminished lacrimation, defective ther-moregulation, orthostatic hypotension, excessive sweating, loss of pain and temperature sensation, and absent re-flexes. A test that detects the causative mutation in the DYS gene has recently been developed to confirm the di-agnosis of familial dysautonomia.
nerve (cranial nerve IX) and vagus nerve (cranial nerve X) posterior to the sulcus.
 Motor innervation for the musculature of the tongue is supplied by the hypoglossal nerve (cranial nerve XII).
 Vascular and glandular innervation is provided by the sympathetic and parasympathetic nerves. They supply blood vessels and small salivary glands of the tongue. Ganglion cells are often seen within the tongue. These cells belong to postsynaptic parasympathetic neurons and are destined for the minor salivary glands within the tongue. The cell bodies of sympathetic postsynaptic neurons are located in the superior cervical ganglion.
Teeth are a major component of the oral cavity and are essential for the beginning of the digestive process. Teeth are embedded in and attached to the alveolar processes of the maxilla and mandible. Children have 10 deciduous (primary, milk) teeth in each jaw, on each side:  A medial (central) incisor, the first tooth to erupt (usually in the mandible) at approximately 6 months of age (in some infants, the first teeth may not erupt until 12 to 13 months of age)  A lateral incisor, which erupts at approximately 8 months  A canine tooth, which erupts at approximately 15 months  Two molar teeth, the first of which erupts at 10 to 19 months and the second of which erupts at 20 to 31 months