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: Taste Taste Bud 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(Gustatory Nucleus) 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 tongue. 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. thalamus (VPMpc) project on reticular C. Brodmann area 43 nuclei (especially D. parainsular cortex the parabrachial E. parabrachial nucleus in the pons) 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 nucleus ambiguus and salivatory VII. facial nerve nuclei for reflex IX. glossopharyngeal activity nerve X. vagus nerve 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 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 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