SensorySensory systemssystems

Taste/gustatoryTaste/gustatory SensorySensory systemssystems –– basicbasic conceptsconcepts

 ModalityModality ofof SensationSensation  ReceptorReceptor  SensorySensory TractTract  primaryprimary neuronneuron  secondarysecondary neuronneuron  tertiarytertiary neuronneuron  terminationtermination ReceptorsReceptors ofof sensorysensory systemssystems -- primaryprimary sensorysensory neuronsneurons

The distal ending of the primary afferents is the receptor

A special receptor cell conveys to primary afferents ReceptorsReceptors ofof sensorysensory systemssystems -- primaryprimary sensorysensory neuronsneurons

pseudounipolar

part of PNS (except jaw proprioception)

bipolar

part of CNS Sensory (afferent) systems

 GGeneraleneral (somatic)(somatic) sensationssensations –– somatosensorysomatosensory systemssystems  superficial (exteroceptive) – skin :  pain and temperature  vibration, touch and pressure  stereognosia  deep (proprioceptive) - joints and tendons  interoceptive (visceroceptive) - organs and blood vessels  SSpecialpecial sensationssensations  visual system  vestibulocochlear system  gustatory system  olfactory system TasteTaste (gustatory)(gustatory) pathwaypathway

Modality:Modality: TasteTaste Sensation Sensation Receptor:Receptor: Bud CranialCranial Nerve: Nerve: VII, VII, IX, IX, X X

11stst Neuron:Neuron: GeniculateGeniculate GanglionGanglion (VII)(VII) InferiorInferior GanglionGanglion (IX,(IX, X)X) 22ndnd Neuron:Neuron: NucleusNucleus TractusTractus SolitariusSolitarius (Gustatory() Nucleus) solitariothalamicsolitariothalamic fiber fiber (central (central tegmental tegmental tract) tract) 33rdrd Neuron:Neuron: ThalamusThalamus (VPMpc)(VPMpc) InternalInternal capsule capsule ------Corona Corona radiata radiata Termination:Termination: GustatoryGustatory AreaArea BrodmannBrodmann area area 43 43 & & parainsular parainsular cortex cortex TastesTastes areare differentiallydifferentially distributeddistributed onon thethe tonguetongue TongueTongue andand linguallingual papillaepapillae

50% of the taste buds

25% of the taste buds 25% of the taste buds

Other locations of taste buds - soft palate, oropharynx, and epiglottis CircumvallateCircumvallate papillaepapillae TasteTaste budsbuds

There are about 2000 taste buds in the human . This number decreases progressively with age. Taste buds are lost at a rate of 1% per year with increased rate after 40 years of age. Sensory transduction in taste cells GustatoryGustatory pathwayspathways

Anterior 2/3 of tongue – CN VII Posterior 2/3 of tongue – CN IX Oropharynx – CN X GustatoryGustatory partpart ofof solitarysolitary nucleusnucleus integratesintegrates tastetaste pathwayspathways andand visceralvisceral sensorysensory informationinformation

salivatory solitarius

There is a close relationship of gustatory ambiguus and visceral information → we should quickly recognize if we are eating something CN IX that is likely to make us sick and respond

GustatoryGustatory informationinformation relaysrelays viavia VPMVPM

VPL Thalamic neurons serving taste are grouped separately from neurons concerned with other sensory modalities of the tongue

VPM GustatoryGustatory pathwayspathways

A. nucleus tractus solitarius Axons of solitar y (gustatory nucleus) nucleus neurons B. (VPMpc) project on reticular C. Brodmann area 43 nuclei (especially D. parainsular cortex the parabrachial E. parabrachial nucleus in the ) nucleus before reach ing VPM, giving on 1. solitariothalamic their way collateral fiber (central branches to such tegmental tract) nuclei as the 2. corona radiata and salivatory VII. nuclei for reflex IX. glossopharyngeal activity nerve X. TasteTaste pathwayspathways ProcessingProcessing ofof gustatorygustatory informationinformation SensorySensory systemssystems

Smell/olfactorySmell/olfactory OlfactoryOlfactory pathwaypathway

Modality:Modality: OlfactionOlfaction Receptor:Receptor: Olfactory Olfactory receptor receptor cell cell of of olfactory olfactory epithelium CranialCranial Nerve: Nerve: I I(Olfactory (Olfactory Nerve) Nerve)

1st1st Neuron:Neuron: OlfactoryOlfactory Bulb Bulb ------Mitral Mitral & & Tufted Tufted Cell Cell olfactoryolfactory tract tract oolfactorylfactory striae striae Termination:Termination: PrimaryPrimary Olfactory Olfactory Area Area (Rhinencephalon) (Rhinencephalon) piriformpiriform lobe lobe( (prepiriformprepiriform cortex, cortex, entorhinal entorhinal cortex) cortex) corticomedialcorticomedial amygdala anterioranterior perforated perforated substance substance(olfactory (olfactory tubercle) tubercle) OlfactoryOlfactory nervenerve (CN(CN I)I)

CN I StructureStructure ofof thethe olfactoryolfactory epitheliumepithelium

 OlfactoryOlfactory receptorreceptor cellscells -- bipolarbipolar sensorysensory neuronsneurons  knoblike expansion extending beyond the epithelial surface (receptors)  100 million receptor cells in the olfactory mucosa  Bowman'sBowman's glandsglands moistenmoisten secretionssecretions →→ dissolvedissolve thethe gaseousgaseous substancessubstances  SupportingSupporting (( ssustentacular)ustentacular) ccellsells →→ microvillimicrovilli  BasalBasal cellscells -- progenitorsprogenitors OdorantOdorant receptorsreceptors && odorantodorant signalsignal transductiontransduction

Odorant receptors are G-protein coupled receptors (GPCRs)

DNA encodes for ~1000 –2000 different olfactory GPCRs

Each olfactory receptor neuron expresses 1 –3 of these GPCRs

OOlfactorylfactory bulbbulb receivesreceives signalssignals fromfrom olfactoryolfactory sensorysensory neuronsneurons

Inhibitory interneurons (granule & periglomerular cells) modulate sensory neuron input OlfactoryOlfactory bulbbulb && tracttract CentralCentral olfactoryolfactory projectionsprojections The olfactory system is thus unique among the sensory systems in that it does not include a thalamic relay from primary receptors en route to a cortical region

Olfactory nerve & bulb

Piriform cortex (paleocortex)

Thalamus

Neocortex OlfactoryOlfactory informationinformation processingprocessing

emotive aspects of olfaction

pheromones

conscious discrimination of odors