Chemical Senses: Taste & Smell Lecture PDF

THE CHEMICAL SENSES: TA S T E & S M E L L SMELL THE NOSE Olfactory epithelium: Supporting cells Basal cells (differentiation) Olfactory receptor neurons Olfactory receptor cells Dendritic knob Cilia B U D DY T H E B E A G L E Yo...

THE CHEMICAL SENSES: TA S T E & S M E L L SMELL THE NOSE Olfactory epithelium: Supporting cells Basal cells (differentiation) Olfactory receptor neurons Olfactory receptor cells Dendritic knob Cilia B U D DY T H E B E A G L E You: 6 million olfactory neurons Buddy: 200-300 million olfactory neurons SIGNAL TRANSDUCTION 1. Odorant molecule binds 2. GOLF activated 3. Second messenger (cAMP) activated 4. Na+, K+, and Cl- channels open O L FA C T O R Y ENCODING 400 kinds of olfactory receptors BUT humans can distinguish between far more than 400 smells Implication: not a labeled lines system NOSE TO CORTEX 1. Receptor cells to Mitral cells Glomeruli Olfactory bulb 2. Olfactory tract 3. Cortex W H AT A B O U T T H E T H A L A M U S ? The olfactory system is the only sensory system that does not involve sensory processing at the level of the thalamus G U S TAT O RY S E N S AT I O N A N D TA S T E P E R C E P T I O N F I V E B A S I C TA S T E S salty sour sweet bitt umami er W H Y D O W E TA S T E ? Sweet: maintain energy stores Bitter: avoid poisons/toxins Sour: detect ripeness, spoiling Salty: regulate hydration Umami: ensure protein intake RANGE OF RESPONSIVENESS All 5 tastes can be perceived anywhere on the tongue where taste receptors are found Each taste cell responds selectively to one taste Genetic variation in taste receptivity Related to structural differences in papillae SIGNAL TRANSDUCTION Sweet: T1R2 + T1R3 (GPCR) Bitter: T2R family of receptors Sour: H+ ion channel (OTOP1) Salty: Na+ ion channel and TRPV1 variant Umami: mGluR (GPCR) and T1R1 + T1R3 Cranial nerves Facial (VII): anterior 2/3 of tongue Glossopharyngeal (IX): posterior 1/3 Vagus (X): root of tongue G U S TAT O RY PAT H W AY 1. Taste receptors to solitary nucleus (via cranial nerves VII, IX, X) 2. Solitary nucleus to ventral posterior medial nucleus of the thalamus 3. Thalamus to gustatory cortex Anterior insula and frontal operculum TA S T E E N C O D I N G Labeled lines: specific pathways respond selectively to specific tastes Pattern coding: relative activity across ensembles