Taste innervation

Fig. 1.—Diagrammatic Representation of the Three Steps in the Taste-cell Transduction. Step 1, interaction of stimulus (S) with membrane-bound receptor (R) to form stimulus-receptor complex (SR) step 2, conformational change (SR) to (SR), brought about by interaction of S with R (this change initiates a change in plasma-membrane conformation of taste cells, probably below the level of the tight junction) and step 3, conformational changes of the membrane result in lowered membrane resistance, and the consequential influx on intracellular ionic species, probably Na. This influx generates the receptor potential which induces synaptic vesicular release to the innervating, sensory nerve, leading to the generator potential.

Taste receptor cells are organized into taste buds 825 Sensory afferents within three cranial nerves innervate the taste buds 826 Information coding of taste is not strictly according to a labeled line 826 Taste cells have multiple types of ion channels 826 Salts and acids are transduced by direct interaction with ion channels 826 Taste cells contain receptors, G proteins and second-messenger-effector enzymes 827... 

Figure 5. flower,) Diagram of the peripheral and central connections of a sensory ganglion cell innervating the taste buds of the tongue, (upper) Illustration of the connections of sensory ganglion cells and the pulse signals used to encode sensory... 

Studies on human taste sensations confirm and extend our understanding of the types of chemical signals measured by these oral chemoreceptor systems. There are, for instance, several distinct sensations elicited by chemical stimulation of fungiform papillae innervated by the geniculate ganglion, indicating that a neural functional complexity similar to that described above for... 

Four cranial nerves subserve the sense of taste, three of these (facial, glossopharyngeal and vagus) innervate taste bud systems (Fig. 1) and one (trigeminal) supplies free nerve ending receptors. Both of these types of receptors respond to chemical stimuli. Only the taste bud systems of the facial and glossopharyngeal nerves have been studied in sufficient detail with many food compounds. 

Figure 1. Diagram of the three cranial nerves and associated sensory ganglia that innervate taste buds. As illustrated, electrical recordings were taken from single neurons in the ganglia. Geniculate ganglion in facial nerve petrosal in glossopharyngeal nodose in vagus.

The main criteria used to classify the units in Table I were stimulus response measures i.e., the units discharged or were inhibited by different chemical compounds. In addition, other criteria were used to supplement the chemical stimulus response differentiation. Thus, the two main groups in the cat (acid units and amino acid units) can also be differentiated by spontaneous activity measures, latency to electrical stimulation, area of tongue innervated, and differential response to solution temperature (3-5). This comparative work has led to a modular view of peripheral taste systems in which the different neural groups are seen to have distinct receptors responding to distinct types of chemical signals (e.g., Br nsted acids and Br nsted bases), with either excitation or inhibition. The stimulus chemistry of these groups will be briefly described. 

Schematic diagram of the gustatory pathway in rodents. Taste receptor cells are innervated by one of three cranial nerves (VII, IX, or X), which project topographically into the rostral portion of nucleus of the solitary tract (NST). Cells within the NST send projections into the reticular formation (RF), through which connections are made to oral motor nuclei V, VII, and XII and the nucleus ambiguous (NA). Ascending fibers connect to the parabrachial nuclei (PbN) of the pons, from which two parallel pathways emerge. One pathway carries taste information to the insular cortex (IC) via the ventral posterior medial nucleus, parvicellularis (VPMpc), of the thalamus. The other pathway projects into areas of the limbic forebrain involved in food and water regulation, reinforcement, reward, and stress, including the lateral hypothalamus (LH), the central nucleus ofthe amygdala (CeA), and the bed nucleus of the stria terminalis (BST). These areas and the IC are interconnected and send descending projections back to both the PbN and NST...

Khaisman EB. 1976. Particular features of the innervation of taste buds of the epiglottis in monkeys. Acta Anat 95 101-115. 

Kinnamon JC. 1987. Organization and innervation of taste buds. Neurobiology of taste and smell. Finger TE, Silver WL, editors. New York Wiley pp. 277-297. 

Miller IJ Jr, Spangler KM. 1982. Taste bud distribution and innervation on the palate of the rat. Chem Senses 7 99-108. 

Smith DV, Akeson RA, Shipley MT. 1993. NCAM expression by subsets of taste cells is dependent upon innervation. J Comp Neurol 336 493-506. 

Some erections are mediated by a sacral nerve reflex arc (e.g., erections can occur while the patient is sleeping). However, in the conscious patient, sensory sexual stimulation mediates erections via the central nervous system. That is, when a patient sees an attractive partner, hears sweet words, smells a particular scent, or tastes or touches a pleasant object, this can result in an erection. In this case, the patient s brain processes this information and the nervous impulse is carried down the spinal cord to peripheral cholinergic nerves that innervate the vascular supply to the corpora, resulting in an erection. 

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