ANATOMY OF TASTE ORGANS
Small organ located on the tongue in terrestrial vertebrates that functions in the perception of taste. In fish, taste buds occur on the lips, the flanks, and the caudal (tail) fins of some species and on the barbels of catfish. Taste receptor cells, with which incoming chemicals from food and other sources interact, occur on the tongue in groups of 50~150. Each of these groups forms a taste bud, which is grouped together with other taste buds into taste papillae. The taste buds are embedded in the epithelium of the tongue and make contact with the outside environment through a taste pore. Slender processes (microvilli) extend from the outer ends of the receptor cells through the taste pore, where the processes are covered by the mucus that lines the oral cavity. At their inner ends the taste receptor cells synapse, or connect, with afferent sensory neurons, nerve cells that conduct information to the brain. Each receptor cell synapses with several afferent sensory neurons, and each afferent neuron branches to several taste papillae, where each branch makes contact with many receptor cells. The afferent sensory neurons occur in three different nerves running to the brainthe facial nerve, the glossopharyngeal nerve, ... (200 of 808 words) The human tongue Tongue The tongue is a muscle on the floor of the mouth that manipulates food for chewing and swallowing (deglutition). It is the primary organ of taste, as much of the upper surface of the tongue is covered in papillae and taste buds. A secondary function of the tongue is speech, in which the organ assists. It is sensitive and kept moist by saliva, and is richly supplied with nerves and blood vessels to help it move.
Drawing of an anterior view of the tongue and oral cavity, with cheeks removed for clarity. Lateral view of the tongue, with extrinsic muscles highlighted. The tongue is made mainly of skeletal muscle. The tongue extends much further than is commonly perceived, past the posterior border of the mouth and into the oropharynx. The dorsum (upper surface) of the tongue can be divided into two parts:
- an oral part (anterior two-thirds of the tongue) that lies mostly in the mouth
- a pharyngeal part (posterior third of the tongue), which faces backward to the oropharynx
The two parts are separated by a V-shaped groove, which marks the terminal sulcus Other divisions of the tongue are based on the area of the tongue:
Muscles of tongue 3/4 view of a 6.5 cm human tongue. The intrinsic muscles lie entirely within the tongue, while the extrinsic muscles attach the tongue to other structures. The extrinsic muscles reposition the tongue, while the intrinsic muscles alter the shape of the tongue for talking and swallowing. Papillae and taste buds Taste bud The oral part of the tongue is covered with small bumpy projections called papillae. There are four types of papillae:
- Filiform (thread-shape)
- Fungiform (mushroom-shape)
- Circumvallate (ringed-circle)
- Foliate (leaf-shape)
All papillae except the filiform have taste buds on their surface. The circumvallate are the largest of the papillae. There are 8 to 14 circumvallate papillae arranged in a V-shape in front of the sulcus terminalis, creating a border between the oral and pharyngeal parts of the tongue. There are no lingual papillae on the underside of the tongue. It is covered with a smooth mucous membrane, with a fold (the lingual frenulum) in the center. If the lingual frenulum is too taut or too far forward, it can impede motion of the tongue, a condition called ankyloglossia. The upper side of the posterior tongue (pharyngeal part) has no visible taste buds, but it is bumpy because of the lymphatic nodules lying underneath. These follicles are known as the lingual tonsil. The human tongue can detect five basic taste components: sweet, sour, salty, bitter and umami. The sense of taste is referred to as a gustatory sense. Contrary to the popular myth and generations of schoolbooks, there are no distinct regions for tasting different tastes. This myth arose because Edwin G. Boring replotted data from one of Wundt!!!s students (Hanig) without labeling the axes, leading some to misinterpret the graph as all or nothing response.The common conception of taste has a significant contribution from olfaction.
Motor innervation of the tongue is complex and involves several cranial nerves. All the muscles of the tongue are innervated by the hypoglossal nerve (cranial nerve XII) with one exception: the palatoglossal muscle is innervated by the X cranial nerve, the Vagus nerve via the pharyngeal plexus. Sensory innervation of the tongue is different for taste sensation and general sensation.
- For the anterior two-thirds of the tongue, general sensations and taste sensations are carried via different nerves.
- Somatic sensations travel from the tongue via the lingual nerve, a major branch of the mandibular nerve (itself a branch of the trigeminal nerve). This nerve also carries general sensation from areas of the oral mucosa and gingiva of the lower teeth.
- Taste sensation is carried to the facial nerve via the chorda tympani. The chorda tympani also carries parasympathetic fibers from the facial nerve to the submandibular ganglion.
- The posterior one-third of the tongue has a simpler innervation, as both taste and general sensations are carried by the glossopharyngeal nerve.
The underside of a human tongue The tongue receives its blood supply primarily from the lingual artery, a branch of the external carotid artery. The floor of the mouth also receives its blood supply from the lingual artery. The triangle formed by the intermediate tendon of the digastric muscle, the posterior border of the mylohyoid muscle, and the hypoglossal nerve is sometimes called Pirogov!!!s, Pirogoff!!!s, or Pirogov-Belclard!!!s triangle. In area is the lingual artery, a good place to stop uncontrolled bleeding in the tongue. There is also secondary blood supply to the tongue from the tonsillar branch of the facial artery and the ascending pharyngeal artery. Length The average length of the tongue from the oropharynx to the tip is 10 cm (4 in). Stephen Taylor holds the world record for the world!!!s longest tongue. It measures 9.5 cm (3.7 in) from the tip to the center of his closed top lip. Annika Irmler holds the record for longest female tongue, at 7 cm (2.75 in