Gustatory & Olfactory System Histology Flashcards
Describe gross anatomy of posterior 1/3 of tongue
Displays aggregations of lymphatic tissue, the lingual tonsils
Describe histology of dorsal surface of tongue
Nonkeratinized stratified squamous epithelium supported by lamina propria associated with muscle core of tongue
What are the intrinsic muscles of the tongue?
Superior longitudinal
Inferior longitudinal
Transversus linguae
Verticalis linguae
Serous and mucous glands extend across the lamina propria and the muscle. Where do their ducts open into?
Crypts and furros of lingual tonsils and circumvallate papillae
Describe lingual papillae
Mucosal projections on dorsal surface of tongue
Formed by a highly vascular connective tissue core an a covering of stratified squamous epithelium
What are the four types of lingual papillae?
Filiform papillae: narrow conical and most abundant
Fungiform papillae: mushroom-shaped, has taste buds
Circumvallate papillae: has taste buds
Foliate papillae: leaf-shaped and rudimentary in humans
Describe geographic tongue
Thought to be oral manifestation of psoriasis (dermatological condition which causes patches of dry, flakey, itchy skin)
Manifests as area of erythema, with atrophy of filiform papillae of tongue, surrounded by serpiginous, white, hyperkeratotic border
Serous (Ebner’s) glands in the connective tissue are in contact with underlying muscle and are associated with foliate and circumvallate papilla. What do they secrete?
Lingual lipase and Von Ebner’s gland protein (VEGP)
What does Von Ebner’s gland protein (VEGP) do?
Undertakes selective binding of sapid (flavorful) chemicals and their transport to taste receptors
Describe location of circumvallate papillae
In posterior part of tongue, aligned in front of sulcus terminalis
Occupies a recess in mucosa and is surrounded by ciruclar furrow or trench
What are the three components of a taste bud?
Taste receptor cells Supporting cells (immature taste cells) Precursor cells (basal cells)
Describe cycle of taste bud
Taste receptor cells have a life span of 10-14 days
Precursor cells give rise to supporting (immature taste) cells, which in turn, become mature taste receptor cells
What does the basal portion of a taste receptor cell make contact with?
Afferent nerve terminal derived from neurons in sensory ganglia of facial, glossopharyngeal, and vagus nerves
Describe the biochemistry of taste
Taste is initiated when soluble chemicals (tastants) diffuse through taste pore and interact with G-protein gustducin linked to receptors TR1 and TR2 in apical microvilli of taste receptor cells
GTP binds to Galpha and activates ion channels in taste receptor cells
Ionic changes cause either depolarization or hyperpolarization of cells
An increase in intracellular Ca2+ triggers release of neurotransmitters at afferent synapse with afferent nerve terminal
Nerve fibers innervate types I-III taste buds, and all three function in discrimination of taste. About __ fibers innervate a single taste bud
50
Facial nerve carries the five taste sensations (sweet, sour, bitter, salty, umami), while glossopharyngeal nerve may carry ____
Sweet and bitter
Where are the sweet, salty, and sour taste receptors on the tongue?
Sweet (sugars): tip of tongue
Salty (sodium): posterior and lateral to tip of tongue
Sour (acidic, H+): on anterior 2/3 of dorsum and along lateral margin
Describe individuals with sensitive form of hTAS2R38 taste receptor gene
They rate kohlrabi (which contains glucosinolates that inhibit iodine uptake by thyroid) as more bitter than do people with less sensitive form of gene
Depending on version of gene, there are different sensitivities
Describe umami
Taste of monosodium glutamate
Linked to specialized receptor for L-glutamate and other amino acids
Distribution of receptors is unknown
Glutamate signals presence of proteins and causes intake of proteinious foods
Glutamate Is found in meats, cheeses, several vegetables, and is often added to processed food as a flavor enhancer
Can promote food consumption (could help elderly and ill at risk for malnutrition)
Describe taste perception of taste buds
Each taste bud can discern all five tastes but appear to concentrate on two
Taste buds on palate register primarily bitter and sour, while posterio pharynx & epiglottis register all five
Receptor cells are tuned to respond to single taste modalities and are innervated by individually tuned nerve fibers
Each taste quality is specified by activity of non-overlapping cells and fibers
Describe fat and receptor CD36
CD36 recognizes texture of fat
Also functions to facilitate uptake of fatty acids
May possibly increase preference for fatty foods
Altered C36 decreases desire for fatty foods
Describe origin, sensory innervation, and innervation of taste buds for anterior 2/3 of tongue
Origin: median tongue bud, lateral lingual swellings
Sensory: lingual nerve (branch of CNV)
Taste: facial nerve (CNVII)
Describe origin, sensory innervation, and innervation of taste buds of posterior 1/3 of tongue
Origin: hypopharyngeal eminence
Sensory: glossopharyngeal nerve (IX)
Taste: glossopharyngeal nerve. Vagus (X) near base of tongue
Describe origin and innervation of muscles of tongue
Develop from mesoderm of occipital myotomes that migrate into developing tongue Hypoglossal nerve (XII)
