LECTURE 18: OLFACTION AND TASTE REQUIRED READING: Kandel text, Chapter 32 Smell and Taste are the chemical senses Smell (olfaction) is the discriminating sensation of volatile chemical odorants by the olfactory system Taste is discriminating sensation of soluble chemicals by the gustatory system Olfaction is far more discriminating than taste, and much of our subtle perceptual tinctions in flavors require integrating gustatory, olfactory & somatosensory informati
LECTURE 18: OLFACTION AND TASTE. REQUIRED READING: Kandel text, Chapter 32. Smell and Taste are the chemical senses Smell (olfaction) is the discriminating sensation of volatile chemical odorants by the olfactory system - PowerPoint PPT Presentation
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LECTURE 18: OLFACTION AND TASTEREQUIRED READING: Kandel text, Chapter 32
Smell and Taste are the chemical senses
Smell (olfaction) is the discriminating sensation of volatile chemical odorants by theolfactory system
Taste is discriminating sensation of soluble chemicals by the gustatory system
Olfaction is far more discriminating than taste, and much of our subtle perceptualdistinctions in flavors require integrating gustatory, olfactory & somatosensory information
ODORS ARE DETECTED BY NASAL OLFACTORY SENSORY NEURONS
Apical dendrite of sensory neuron projects through support cells to nasal cavity, andis capped by dendritic cilia projecting into specialized mucus in the cavity
Olfactory sensory neurons are fairly short-lived (1-2 months), and regenerate from basal stem cells
Each sensory neuron responds to a single odorant or a specific repertoire of chemically related odorants
An odor is ENCODED by the specific combination of neurons which respond to it
Sensory neurons respond to odorant by inward current flow, which depolarizes neuron.
There is a relationship between odorant concentration and size/duration of inward current;sufficient depolarization triggers action potential.
DIFFERENT TASTE STIMULI USE DIFFERENT SIGNAL TRANSDUCTION METHODS
SWEET-sensing taste cells use 7-TMreceptor coupled to Gs.
Sugars act through Gs to producecAMP, and PKA phosphorylates
and closes potassium leak channels,causing depolarization
Alternatively, some substances(artificial sweeteners) bind receptors
coupled to Gq which activatesPLC to increase Ca+2 through IP3
BITTER-sensing taste cells use 7-TM receptors coupled to various G proteins. Bitter sensation is method for
recognizing TOXIC compounds.
There is a family of related bitter receptors.
Some receptors couple to Gq which activatesPLC to increase Ca+2 through IP3
Other receptors couple to gustducin, whichactivates cyclic nucleotide phosphodiesterases
A few bitter compounds act by directly blockingleak potassium channels
TRANSMISSION OF TASTE INFORMATION TO THE BRAINAND PERCEPTION OF TASTE
Integration of taste stimuli first occurs in afferant gustatory fibers, since each fiber receives inputfrom multiple taste cells of different types. Each gustatory afferent fiber has a response profile to 5 tastes
Taste stimuli project to the gustatory cortex, where it is consciously perceived.
Taste stimuli are integrated with somatosensory inputs to generate perception of where tasty substance is.Taste perception is also shaped by parallel olfactory input;
the somatosensory stimulus “fools” us to perceive the olfaction as part of the taste.