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Taste and Smell

Rodolfo T. Rafael,M.D.

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SMELL or Olfaction

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Chemical Senses

· smell, taste, and the general chemical sense · nature of the stimulus is the same but the degree of sensitivity is different

­ 0.000125M ethyl alcohol- smell ­ 5M- taste ­ 10M- stinging effect on the inside of the cheek.

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Olfactory (Nasal) Mucosa

· RECEPTORS

­ within the olfactory mucosa

· presence of tubular Bowman's gland · absence of the rhythmic ciliary beating · yellow brown pigment

­ mucous layer covers the entire epithelium

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Olfactory (Nasal) Mucosa

· Innervation

­ olfactory nerve ­ some branches of trigeminal nerve

· irritative character of some odorants

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Olfactory (Nasal) Mucosa

· Histologic Structure

­ Three Cell Type

· Receptor cell (Bipolar neurons)

­ dendrites- terminate in a knob cilia project from the knob mucous layer axons- form the olfactory nerve columnar shape microvilli new receptor cell replacement of receptor cell by mitosis

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Supporting Cell

­ ­

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Basal cell (stem cells)

­ ­

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Olfactory (Nasal) Mucosa

· Location

­ superior nasal concha ­ superior position not directly exposed to the flow of inspired air ­ Odorant molecules sniffing-(short, forceful inspirations) produce turbulence transport molecules to the receptor cell www.clinicacayanga.dailyhealthup

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Stimuli

· Odorant molecules

­ dissolve in the mucous layer lining the nose the olfactory receptors

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Stimuli

· An odorant molecule must be:

­ Volatile

· olfactory receptors transported by air chemicals

­ Water- Soluble (to some degree)

· penetrate the watery mucous layer

­ Lipid- Soluble (to some degree)

· penetrate the cell membranes

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Receptors

· Sensitivity

­ Number of Odorants

· can discriminate dextro- and levorotatory, cis- and transconformation of molecule

­ Concentration

· limited ability to discriminate differences in odorant conc. in ambient air

­ Adaptation

· very rapidly

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Receptors

· Receptor Potential

­ adsorption generates a depolarizing receptor potential in the receptor cell · odorant molecule receptor G protein adenylate cyclase catalyzes formation cyclic adenosine 3' 5' ­monophosphate (cAMP) opens Ca2+ channels activates Cl- channels Cl- flows out of the cell MEMBRANE DEPOLARIZE · Sensory perception is based on the pattern of receptors activated by the stimulus · electro-olfactogram (EOG) www.clinicacayanga.dailyhealthup 14

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Smell Phenomena

· Masking

­ strong odors tend to mask weaker ones

· Antagonism

­ when two odors in appropriate relative concentrations are sniffed together both are diminished

· eg. iodoform is antagonized by balsam of Peru

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Anomalies of Olfaction

· Anosmia

­ loss of the sense of smell ­ Temporary

· · · inflammation of the nasal mucosa application of cocaine olfactory bulb or nerve are absent

­ Permanent

· Hyperosmia

­ increase sensitivity of the sense of smell ­ Common

· · hysteria increase intracranial pressure

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GUSTATORY

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a substance to be tasted must be in solution or dissolved by the saliva

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Gustatory Sensation

· taste stimuli are detected by taste receptors

­ tonque ­ mouth ­ pharynx

· taste must be distinguished from flavor, which includes the olfactory, tactile, and thermal attributes of food in addition to taste.

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Gustatory Sensation

· · · · Stimuli Receptors Transduction Encoding

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Stimuli

· · substances must be dissolve in the saliva before they can stimulate taste receptors Four Basic Types of Taste Sensation

­ Sweet Sensation · organics (sugar, glycols, aldehyde) · tip of the tonque Bitter Sensation · alkaloids (quinine, caffeine)

­ harmful

­

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back of the tonque

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Stimuli

· Salty Sensation ­ anions of ionizable salts ­ front half of each side of the tonque · Sour Sensation ­ acids ­ posterior half of each side of the tonque

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Receptors

· Taste cell are located within tastebuds papillae Taste Buds

­ Distribution

· tonque papillae, hard and soft palate, epiglottis, and pharynx cluster of 40-60 taste cell Taste Pore Taste Cells

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Structure

· · ·

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Receptors

· Taste Pore

­ allow substances to reach interior of the taste bud ­ taste receptormicrovilli

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Receptors

· Taste Cells- communicate with gustatory nerve endings by synaptic transmission

­ Innervation

· facial · glossopharyngeal · vagus nerve

­ tactile and temperature receptor

· trigeminal nerve

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Receptors

· Innervation

­ facial, glossopharyngeal, and vagus nerve

· taste buds in the anterior two third of the tonque

­ ­ lingual branches of the facial nerve lingual nerve » cell bodies- geniculate ganglion » nerve terminals- nucleus solitarius of the medulla glossopharyngeal nerve » cell bodies- superior and inferior ganglia » nerve terminals- nucleus solitarius

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taste buds in the posterior third of the tonque

­

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Taste receptors in the Pharyngeal aspect of the tonque, hard palate, soft palate, and epiglottis

­ vagus nerves » cell bodies- superior and inferior ganglia » nerve terminals- nucleus solitarius.

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Receptors

­ Regeneration

· each taste cell has a life cycle of only a few days · degenerating cell replace by a cell that arises from the basal epithelial cell · contact with the afferent neuron maintain taste cell cycle

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Taste Pathway

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Papillae

· Gustatory

­ ­ Fungiform · anterior two-thirds of the tonque · 8-10 taste buds Circumvallate · V shaped, row of 7-12 · posterior part · 200 taste buds Foliate · lateral border of the tonque anterior to the circumvallate papillae · numerous taste buds Filiform · not gustatory structure · play a role in breaking up food particles

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· Mechanical

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Transduction

· Sweet-tasting substances

­ Opening Na+ selective channels

· blocked by amiloride

­ Activating adenylate cyclase

· cAMP produced by adenylate cyclase leads to the closing of K+ selective channels

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Transduction

· Bitter-tasting substances

­ inositol triphosphate (IP3)

· increases intracellular Ca2+ levels release of synaptic transmitter activation of the gustatory nerve fiber

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Transduction

· Salty-tasting substances

­ activate amiloridesensitive Na+ channel ­ No specific Na+ receptor has been identified

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Transduction

· Sour-tasting substances

­ citric acid ­ raising the intracellular H+ which blocks K+ channels

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Transduction

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Encoding

· Each nerve fiber responds to more than one taste stimulus responds best to one of the four primary taste qualities coding of a gustatory sensation is not a simple, labeled-line, chemical sensory system Depends on the pattern of nerve fibers

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Taste Phenomena

· Contrasts and Masking

­ simultaneous contrast are well developed in taste.

· · · sweet and acid reciprocally raise their threshold sweet and bitter lower neutral distilled water tastes like dilute alkali, but after an acid solution it tastes sweet.

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After-taste

­ ­ it is a familiar experience that the tastes of certain substances cling to the tonque (quinine) inability to perceive any taste

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Taste Blindness or Ageusia

­

Thank You!

For Not Listening

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