Olfaction and Gustation Flashcards
Olfactory epithelium and olfactory bulb
-the olfactory cells synapse with secondary sensory neurons in the olfactory bulb. Axons of the olfactory cells form the olfactory nerve (first cranial nerve)
Olfactory epithelium
-Olfactory receptor cells are sensory neurons.
-Basal cells are stem cells that can regenerate sensory cells
-supporting cells provide structure and release chemicals to block toxins
-Bowmans gland produces mucus layer surrounding cilia
-odor detecting GPCRs are located in the cilia
Olfactory Ensheathing Cells Aid Axon Guidance in Olfactory Neurons
-The axons of olfactory receptor neurons are myelinated to speed conduction
-The axons are also surrounded by olfactory ensheathing cells that assist in forming a path for the axons going to the olfactory bulb
-Transplants of olfactory ensheathing cells have been used experimentally to repair severed axons in the spinal cord
Glomeruli Receptor and odor specificity
-each odorant receptor type (GPCR) is expressed in ~2000 olfactory cells and innervate two discrete glomeruli. Therefore, a glomerulus codes for a specific GPCR
How many olfactory receptors are there? Glomeruli? olfactory cells? why?
-400 distinct olfactory receptor GPCRs
-800 glomeruli on each side of the brain
-2 glomeruli for each type of GPCR
-5-10 million olfactory cells
-1000 olfactory cell axons per glomerulus
Using these 400 pair of glomeruli, humans can detect ~trillion scents. Each GPCR can respond to a spectrum of odorants. One odorant can stimulate several GPCRs. Result us a huge combinatorial coding.
Combinatorial coding of odorants
-400 receptors can detect a trillion scents
Anosmia
loss of smell
Parosmia
distorted sense of smell.
what innervates the taste buds
-taste buds are innervated by 3 cranial nerves
-Chorda tympani–> branch of the facial nerve (CNVII) innervates anterior 2/3 of tongue
-Glossopharyngeal nerve–> CN IX innervates the taste buds on posterior 1/3 of the tongue
-Vagus nerve (CN X) innervates a few taste buds in the larynx and upper esophagus
Taste Bud
Taste bud contains multiple taste receptor cells, all sensitive to the same tastant, plus supporting cells and basal cells
-taste buds are found in the tongue, palate, esophagus and epiglottis
-lifespan of a taste receptor cell is ~1 week
Taste Receptors subtypes
-Sour: Acid detector, spoiled food
-Salt: Sodium channel
-Sweet: Carbohydrate detector
-Bitter: most natural poisons are bitter
-Umami: Modified glutamate receptor GPCR, protein detector
Sour and salt receptors are channels (channel mediated transduction) and the others are GPCRs
T1R1 and T1R2
-GPCRs for Umami and sweet taste transduction
-both receptors are dimers with T1R3
T2R
-A large family of bitter taste GPCRs
-bitter taste receptors are also found in gut and lung, mediating responses to toxins and bacteria
Gustatory Central Pathways
-the pathway for conscious taste detection includes 3 cranial nerves that go to the solitary nucleus in the medulla, then to the thalamus, and then to the gustatory cortex (MTC–> medulla, thalamus, gustatory cortex )
-There are additional gustatory pathways going from thalamus to limbic system (hippocampus and amygdala)
Gustatory agnosia
Loss of taste sensitivity
Hypergeusia
Increase in taste sensitivity
Dysguesia
Distortion in taste detection
Taste with age
there is a loss of taste buds, fungiform papillae, and a decrease in taste sensitivity with age
