Taste Chapter 15 1 What is the purpose of each of the 4 primary tastes ie what important info do they give us that is necessary for our survival a Four basic tastes Pg 475 generally agreed to describe human taste experience in sodium chloride b Salty Pg 475 taste quality produced by the cations of salts sodium any of the four taste qualities that are i Sodium must be available in the body in relatively large quantities to maintain nerve and muscle function c Sour Pg 475 taste quality produced by the hydrogen ion in acids i Taste signals bacteria spoiled foods d Bitter Pg 475 substances like quinine and caffeine generally considered unpleasant produced by i Usually signals poison toxic chemicals e Sweet Pg 475 quality produced by some sugars such as glucose fructose and sucrose three particularly biologically useful to us and our sweet receptors are tuned to them i Sweet tastes sugars provide carbohydrates our bodies fuel 2 Understand the anatomy of the taste system know the names of the different types of papillae what where are the taste buds and taste cells what is the taste pore where do fibers of the taste cranial nerves synapse w taste cells a Papillae Pg 471 any of the multiple structures that give the tongue its bumpy appearance from the smallest to largest the papillae types that contain taste buds are fungiform foliate circumvallate and filiform most of the bumpy appearance have no taste function small structures on the tongue that provide i Filiform Pg 471 1 Located on the anterior portion of the tongue different species have different shapes ii Fungiform Pg 471 distributed most densely on the edges of the tongue especially the tip Mushroom shaped structures that are 1 Taste buds are buried in the surface iii Circumvallate Pg 472 inverted V on the rear of the tongue mound like structures each surrounded by a trench like a moat circular structures that form an 1 Much larger than fungiform taste buds are buried inside the moat 2 Also on the roof of your mouth in the spot where the bone ends the space between the hard and soft pallets on the roof of your mouth b iv Foliate Pg 472 located on the rear of the tongue lateral to the circumvallate papillae where the tongue attaches to the mouth folds of tissue containing taste buds Inside the papillae are taste buds Pg 470 globular clusters of cells that has the function of creating neural signals conveyed to the brain by the taste nerves some of the cells in a taste bud have specialized sites on their apical projections that interact with taste stimuli some of the cells form synapses with taste nerve fibers i Taste buds contain multiple taste receptor cells each of which responds to a limited number of molecule types Pg 471 a cell within a taste bud that contains sites on its apical projection that can interact with taste stimuli 1 These sites fall into two major categories those interacting with charged particles sodium and hydrogen and those interacting with specific chemical structures ii Taste buds are pseudounipolar a single process exits the cell body and then splits in peripheral and central limbs 1 Peripheral axons make up the nerves that project into the tongue Chorda tympani and glossopharyngeal central axons project to the brain iii Each taste bud is a cluster of elongated cells organized like the segments of an orange 1 The tips of some of the cells end in slender microvilli Pg 472 extensions of the cell membrane on the tips of some taste bud cells that extend into the taste pore contains sites that bond to taste substances a Microvilli contain receptors ionotropic or metabotropic receptor proteins and are stimulated by tastants Pg 473 any stimulus that can be tasted b Each taste receptor cell has one type of receptor so it responds to a limited number of molecules c Receptor cells synapse with axons of 3 cranial nerves i Vagus facial and glossopharyngeal ii But not all receptor cells synapse on nerve fibers some fibers beanch off so an individual cell can be innervated by more than one taste fiber like fungiform 1 This is important because taste receptors die and renew after ten days and this allows a fiber to convey the same message to the brain even when the other cells in its branch die and renew 3 Understand the physiology of the taste receptors how do salty sweet sour and bitter substances each lead to action potentials in the taste nerves a Chewing breaks down food substances into molecules which are dissolved in saliva the saliva born food molecules flow in the taste pore that leads to the taste buds b Salt and sour both are small charged molecules and use ionotropic receptors i Salt sodium enter through channels on the microvilli and depolarization allows more sodium and calcium to come in the neurotransmitter releases and then there s an action potential in the taste nerve 1 Serotonin is documented as a main neurotransmitter used by taste receptor cells ii Sour acids in water have a free proton hydrogen hydrogen enters the cell through the ion channel blocking the potassium channel which means depolarization then sodium and calcium come into the cell through voltage gated channels the neurotransmitter releases causing an AP on the taste nerve c Bitter and sweet tastants stimulate metabotropic receptors i Bitter sweet and umami molecule binds to the metabotropic receptor on the microvilli activating G protein receptors making the second messenger calcium comes into the cell through the membrane and from internal stores sodium channels open and potassium channels are blocked the neurotransmitters released and an AP 4 What cranial nerves innervate the tongue What brain regions in order get info about taste What are the roles of the insular cortex and the orbitofrontal cortex a Cranial nerves Vagus Glossopharyngeal Chorda Tympani branch of the facial nerve Chorda Tympani Pg 468 branch of the cranial nerve that carries taste information from the anterior mobile tongue and exits the tongue with the lingual branch of the trigeminal nerve b Cranial nerves medulla and pons nucleus of the solitary tract thalamus dorsomedial nucleus and ventroposterior nucleus insular cortex orbitofrontal cortex secondary taste cortex association cortex i The cranial nerves first stop is at the NST which gets taste information from all of the different nerves ii From the NST it goes to the thalamus where two different parts of the thalamus receive information 1 Ventroposterior nucleus same thalamic nucleus that deals with touch
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