Smell and Taste DSA (Dr. Karius) TEST 2 Flashcards
Relevance of Taste and Smell
- Smell and Taste interact with other stimuli to produce the Flavor of the FOOD we Ingest, stimulating appetite and the enjoyment of Food
- Due to the HIGH TURNOVER RATE of the Odorant and Taste Receptors, the ability to Smell and Taste CHANGES with AGE and a result of Certain Pharmacological Treatments (Chemotherapy)
a) MERCAPTAN or related Chemicals are added to Natural Gas to alert us to the presence of Natural Gas, there is an Age-specific DECLINE in the ability to DETECT those Odorants
b) Changed perceptions about what Smells or Tastes good can profoundly affect Appetite and Food preferences
Receptors and Their Transduction Mechanisms
- The Odorant Receptors (OR) are located on the CILIA that Protrude into the Mucus Layer
a) Human express about 350 different Odorant Receptors
b) MULTIPLE Chemicals (Odorants) are capable of activating EACH RECEPTOR
- Odorant Receptors are G- Protein COUPLED Receptors that create cAMP to OPEN a Cyclic- Nucleotide GATED ION Channel. G Protein is a Gs Protein, but specific to OLFACTORY RECEPTORS!!!!!!
- If an Odorant PERSISTS for more than a Few Mins, the SENSITIVITY of the Channel to the Cyclic AMP is REDUCED, DECREASING Na+ and Ca++ Entry. A Smaller generator POTENTIAL results, reducing the probability of an Action Potential in the AXON!
Receptors and their Transduction Mechanisms Cont
- Each Olfactory Neuron EXPRESSES the SAME ODORANT Receptor on ALL of its CILIA!!!!
- Although the ENTIRE Olfactory Epithelium excesses Odorant Receptors, DIFFERENT Odorant Receptors are Localized to DIFFERENT Parts of the Olfactory Epithelium, but NOT EQUALLY between these areas!
- Another Detail: EACH ZONE (Area) in the Olfactory Epithelium has a DIFFERENT RECEPTORS Type that Predominates, even though many different Receptor Types are PRESENT in EACH ZONE!
- Different odorant Receptors are LOCALIZED to DIFFERENT parts of the Olfactory Epithelium, but NOT Equally between these areas!!!
- **The ADVANTAGE of the Distributed Localization seen here is that we are abel to smell things even when we have a cold because of the Receptors being on Different areas of the Epithelium!!!
- Each Odorant ACTIVATES DIFFERENT Combinations of Odorant Receptors to produce its Characteristic Odor
- Odorant CONCENTRATIONS CHANGES the Perceived Smell, at Higher Concentrations, the Odorant starts to Bind to Receptors with a LOWER AFFINITY for the Odorant in Addition to the Receptors with a HIGHER AFFINITY!!!
Trace Amine-Associated Receptors
- There is a Second, but Smaller, set of Odorant Receptors known as the TRACE AMINE-ASSOCIATED RECEPTORS (TAARs) in Humans as well as other Vertebrates
- Activation of these DOES NOT necessarily lead to CONSCIOUS AWARENESS of an Odor and seem, instead, to produce Physiologic/ Endocrine Responses to PHEROMONES!!!!!!!!!!!!!!!!!
(Many of the Chemicals that activates the TAARs are found in Greatest Concentration in Urine from the male of the species being studied)
Transmission to the Brain
- Axons of the Olfactory Neurons pass through the CRIBRIFORM PALTE and SYNAPSE on the Neurons of the OLFACTORY BULB
- The OLFACTORY BULB consists of FIVE LAYERS. The Cell Bodies of MITRAL, PERIGLOMERULAR, and TUFTED Cells are found in these layers, along with an Additional Layer for GRANULE CELL BODIES (The Granule Cells are NOT Activated Directly by the Olfactory Cells)
- Within the Olfactory Bulb, we find GLOMERULI, where the Axon Terminals from Olfactory Neurons Synapse (EAA) on the Dendritic Trees of the Post-Synaptic Neurons
- **There are THREE Kind of Post-Synaptic Neurons:
1) Mitral Cells (Axons go to the Olfactory Cortex)
2) Tufted Cells (Axons go to the Olfactory Cortex)
3) PERIGLOMERULAR CELLS (Axons REMAIN in the OLFACTORY BULB)
Transmission to the Brain Cont 1
- All the Axons from the Olfactory neurons expressing the SAME Odorant Receptors CONVERGE on Two Glomeruli (One Medial, One Lateral) located in the IPSILATERAL OLFACTORY BULB!!!!
- There is Tremendous CONVERGENCE of the Olfactory Neurons onto the Mitral/ Tufted Cells!!!!!!!
- It also appears that Neighboring Olfactory GLOMERULI are associated with CHEMICALLY SIMILAR ODORANTS!!!!
Transmission to the Brain Cont 2
- As noted, MITRAL and TIFTED Cell Axons will join the OLFACTORY TRACT and RELAY INFORMATION to the Brain!
- The PERIGLOMERULAR CELLS release GABA at their Synaptic Contacts with Other Glomeruli and INHIBIT the activity from those Glomeruli!!!!!!!!
- Since these Glomeruli are likely RELATED Odorants, this means that the Odorant producing the STRONGEST Stimulation will SUPPRESS the Input from other Glomeruli that weren’t as STRONGLY ACTIVATED and IMPROVE the SIGNAL SPECIFICITY to the BRAIN!!!
- The GRANULAR CELLS also release GABA at their Synaptic Contacts but they Synapse with the MITRAL and TUFTED Cells. It is believed that they also work to INCREASE the SPECIFICITY of the message going to the Olfactory Cortex
Olfactory Cortex
- First Possible Synapse is in the ANTERIOR OLFACTORY NUCLEUS!!! These Synapses RELAY the Information to the CONTRALATERAL SIDE. Axons also continue on to the IPSILATERAL SIDE!!!
- Olfactory Cortex is actually composed of Several Different parts, including :
1) The Anterior Olfactory Nucleus
2) The PIRIFORM CORTEX!!!!!!!!
3) The Anterior Cortical Amygdaloid Nucleus
4) The Periamygdaloid Cortex
5) The LATERAL ENTORHINAL CORTEX!!!!!!!!!!! - As you would expect, the Olfactory Cortex as a whole is responsible for Identifying the Odorant and arriving at an experience of “SMELL”. However, that is NOT the ONLY processing that must occur!!
Entorhinal Cortex Additional Processing
- The ENTORHINAL CORTEX projects to the HIPPOCAMPUS, which is IMPORTANT in MEMORY FORMATION!!!!!!!
- Olfactory Input facilitates BOTH Memory FORMATION and RECALL!!!!!
Piriform Cortex Additional Processing
- The PIRIFORM CORTEX Projects to the LATERAL HYPOTHALAMUS, which is IMPORTANT in CONTROL of APPETITE. Olfactory Inputs, shockingly, can INFLUENCE APPETITE!!!!!
- The PIRIFORM CORTEX also projects to the MEDIAL ORBITOFRONTAL CORTEX (Via THALAMUS) to provide Information that will be used to IDENTIFY the FLAVOR of Foods, among other things!!!!
Olfactory Cortex Sending Input BACK
- The Olfactory Cortex also sends Input BACK TO the Olfactory Bulb/ Olfactory Epithelium to MODIFY the RECEPTORS RESPONSES to Odorants!!!!!
Taste
- Taste (Gustation) is a Chemical Sense that interacts closely with OLFACTION
- The receptors for Taste (The Taste Buds) are primarily located on the TONGUE, associated with he DIFFERENT PAPILLAE. There are as many as 10,000 Taste Buds in the Human
Taste Buds and their Transduction Mechanisms
There are FIVE Taste Buds/ Receptors distributed on the Tongue/ Mouth:
1) SOUR:
- Produced when the HYDROGEN ION Enters the Taste bud via a HYDROGEN- ION CHANNEL
2) SALT:
- Salty tastes a produced when the SODIUM or CALCIUM ION enter the Taste Bud via a SODIUM or CALCIUM CHANNEL
3) BITTER (Citrus Peels):
- Use SECOND MESSENGER SYSTEMS to Depolarize the Cell, but it DOES NOT DIRECTLY relate to the Metabotropic Receptors that detect the Umami Sensation
4) SWEET:
- Use SECOND MESSENGER SYSTEMS to Depolarize the Cell, but it DOES NOT DIRECTLY relate to the Metabotropic Receptors that detect the Umami Sensation
5) UMAMI (Savory):
- The Umami Taste Receptor is a Metabotropic GLUTAMATE Receptor activated by the Amino Acid GLUTAMATE!!!
Transmission of Taste to the Brain/ Processing
- GUSTATORY INPUTS travel a Straight-Forward path to the Brain
There are Synapses in the:
- NTS!!!
- THALAMUS
- GUSTATORY CORTEX (Includes Anterior INSULAR Cortex)
- From the THALAMUS, the Axons go to the CORTEX and to the LATERAL HYPOTHALAMUS. Once again, this Input has a SIGNIFICANT IMPACT on APPETITE!!!!!
- The Gustatory Cortex seems to be STRONGLY Involved in Identifying the Basic Taste and Innate Responses such as ATTRACTION to SWEET Tastes or AVERSION to BITTER Tastes
Perception of Flavor
- Perception of Flavor Requires:
1) GUSTATORY INPUT from the GUSTATORY CORTEX
2) OLFACTORY INPUT form the OLFACTORY CORTEX (Especially Piriform Cortex!!!!!!)
3) SOMATOSENSORY Information from the MOUTH!!!!!!
- Neurons from ALL THREE AREAS of Cortex SEND Axons to the LATERAL POSTERIOR ORBITOFRONTAL Cortex to produce the Sensation of FLVAOR and APPRECIATION of Food!!!
- Odorants arising from Food in the Mouth, although they ACTIVATE Olfactory neurons in the Olfactory Epithelium, will be PERCEIVED as being part of the TASTE SENSATION (Localized to the Mouth). Since this is a COMMON OCCURRENCE, a Large Part of what we “Taste” was really decide in OUR NOSES! Anything that INTERFERES with the Sensation of Smell WILL ALTER the Tastes/ Flavor we PERCEIVE!!!!!!!
