Neuro: 1:00 - 2:00
Monday, February 9, 2009
Scribe: Strud Tutwiler
Proof: Ryan O’Neill
Dr. Lester Taste & Smell Page 1 of 3
The audio for this lecture did not record correctly. Audio from student’s recording was unclear at some points and did not start until [S2]. It is too big to place in dropbox.
I. Introduction [S1]: from my notes a. Vision, photoreceptor. CN II, LGN, VI visual cortex b. Auditory, Hair cell, CN VIII, MGN, Heschel’s gyrus c. Taste d. Smell makes it directly to cortex w/o having to go through the thalamus . e. Pain is a little bit different from touch sensation. f. Modified epithelial cells on neurons and generally receptor cells (photoreceptor, hair cells, and mechanoreceptors).
g. We will talk about the CNs involved and go through most all of them, except CN XI.
h. CNs will most likely be on the exam! Some sort of sensory mechanism involves … excitatory with glutamate as transmitter usually. Could be Na channel, G-coupled protein receptor (mechanoreceptor). i. There is a big class of receptor called TRP channels, involved in taste (spicy, hot, menthol). Trip channels can detect changes in temperature (hot & spicy, cold & menthol).
II. Learning Objectives [S2] a. Know anatomy and function
III. Gustatory & Olfactory Systems [S3] a. In humans, sense of taste and smell go together. Gustatory = the sense of taste. Photons for photon receptors, vibrations make sound frequencies. Smell and taste are chemicals. Your body perceives it as a chemical interaction from food or odorants in atmosphere.
b. Axel won the Nobel Prize recently for cloning family of G-protein receptor involved in olfaction. There are thousands of these receptors; a large portion of our genome is attributed to olfaction. Olfaction goes to limbic associated structure. It was important in primary man to detect noxious chemicals. c. Both cells can turnover. Foreign research: Nasal epithelial can be used to create stem cells. Taste buds as well have turnover of one month. d. Concept of Labeled Line (modality of vision, auditory, taste, etc). Submodalities are within modalities.
Submodalities are sorted out in cortex. In olfaction, similar receptors come together and send similar smells up to cortex.
IV. Significance [S4] a. Taste and smell have a high significance. One can often associate smells with experiences (childhood or emotional memories). b. Wide spread into limbic system.
V. Perception of Flavor [S5] a. Clinically relevant to treat together. b. Taste and smells is perceived as flavor. Flavor is composed of smell, taste, and texture. Changing texture can cause people to perceive things as different.
c. Multiple sensations are ultimately integrated together in the frontal lobe and limbic system.
VI. Taste [S6]
VII. Blue Tongue Disease [S7] a. Unsure if Blue Tongue Disease really exists. b. Picture is not really Blue Tongue Disease. Can paint blue dye on tongue to show the taste buds. Only a fraction of the papillae contains the taste buds.
VIII. Taste Buds [S8] a. Do not memorize the difference types of papillae. Within bumps are buds themselves. Individual taste buds are within papillae. Each taste bud contains 50-150 taste cells.
IX. Papillae, Buds, & Cells [S9] a. Top left is taste bud. b. Bottom right is individual taste cell. Hole is where chemicals can diffuse in and react with certain receptors on taste cell.
X. Learning Objective #1 [S10] a. There are different views as to where sensations are on tongue. View them as a myth.
b. Do not worry about learning where taste sensations are on tongue. Ex. Salty on side.
XI. Innervation [S11] a. Need to know that there are 3 cranial nerves involved in taste (VII, IX, and X). All go to separate places in the brainstem. Some are on palate, epiglottis, and tongue. b. Taste buds on the palate and epiglottis are important for swallowing and vomiting (sensing of food - motor behavior).

Neuro: 1:00 - 2:00
Monday, February 9, 2009
Scribe: Strud Tutwiler
Proof: Ryan O’Neill
Page 2 of 3 Dr. Lester
XII. Rostral Medulla [S12]
Taste & Smell a. Cut through the olive and pyramid in rostral medulla. Nucleus contract of solitary is the two white circles in top of figure on right. Staining myelin in slide. b. Really long tract (dark – resembles pupil in figure) in center of nucleus with multiple sensory innervations
(visceral sensations)
XIII. CNs and Solitary Nucleus/tract [S13] a. This tract picks up information from gut, heart. It detects pressure changes. Many chemoreceptors are present. b. Taste is found in the rostral portion of the solitary nucleus. Brain stem of the basilar nerve. Chorda tympani is a branch of the facial nerve that goes through the middle ear (see in gross lab), passed eardrum, and on down to tongue.
c. Know CNs 7, 9, and 10 innervate taste sensation.
XIV. Learning Objective #2 [S14]
XV. Taste Transduction [S15] a. Have cillary on ion channels that are pulled opened, leading to ion influx, and depolarization. b. Microvillae (inside taste bud; also seen on olfactory epithelial cells) increase surface area/volume. More surface area to detect chemicals. c. These cells are small epithelial cells stretched out; they are not neurons. Do not need action potential.
If they get a small amount of depolarization, it will spread to end and open Ca channels. Vesicles fuse and transmitter is released.
d. Common mechanism: Photoreceptors are the same. Get depolarized, Ca channels open, vesicles fuse, and transmitter is released. Not Neurons = Not Action Potentials. Get passive spread of the signal. e. Has to be large enough to open Ca channels. Get activation of this part of the CN. The bigger the depolarization, the stronger the smell, stronger the taste, or louder the sound. f. The bigger the depolarization in the CN, the more action potentials produced.
XVI. G-protein & Ion Channels [S16] a. Same thing, but not asked specifically to remember all of this. This is being modified by ongoing research.
b. TRP (transient receptor potential) channels are important in sense of taste. The Na controls the taste of salt and the H control sour. c. We have channels for hydrogen ions. There are a mixed of detector receptor mechanisms. The four main ones are sweet, salty, sour, and bitter. d. This slide is important (reinforces last slide) because it shows flow of depolarization, Ca influx, transmitter release, and increase firing of afferent nerve. e. Mechanoreceptors (Dr Wells) – afarin release with the same mechanism. Some of the G-proteins might release
Ca from intracellular store. Ca can go on to act as a transmitter.
XVII. Anatomical Path [S17] a. In rostral medulla, there are local interactions involved in reflexes (swallowing and vomiting). Auditory sends up frequency and loudness to cortex (sound localization in brainstem).
b. Sensation of taste ultimately has to get to the cortex. Generally, they go through the thalamus.
c. Synapses on DMN X (dorsal motor nucleus of vagus nerve). d. Do not worry about remembering stuff on rostral pons (synapses in parabrachial nucleus). This is not used in humans; the limbic system is used in people.
e. Interested in taste, epithelial cell, cranial nerve, interaction with medulla, thalamus (VPM).
f. VPM (ventral posterior medial ) of thalamus. This is part of the somatotopic map (Dr Well’s lecture). Need to know that we end in insula (primary cortex for taste). g. Drawing of sylvan fissure and insula (teeth). Opercula cortex (lips around teeth).
XVIII. Cortical Processing [S18] a. INS (insula) and OP (opercula; lips covering insula) looking at coronal section. Look down Sylvain Fissure. b. Shows Parabrachial to VPM in thalamus (follows sensory modality). Other projections are part of the limbic system. c. Taste and smell both ends in orbitofrontal. Olfactory bulb sits under the orbitofrontal cortex. Has integrative processing of taste, touch, and smell in frontal cortex.
XIX. Learning Objectives #3 & 4 [S19]
XX. Broad Tuning of Taste Pathway [S20] a. Talking about submodalities, do not confuse this with label line. Within taste, there are different submodalities. b. In a single neuron, we do not think there is one signal for sweet. When we record cells in nucleus in solitary tract, we find multiple sensations. c. By the time, the signals reach the orbital cortex, the cells respond to a single taste. Maybe some processing takes place in the thalamus (weed out some of the signals).
XXI. Neural Coding of Taste [S21]

Neuro: 1:00 - 2:00
Monday, February 9, 2009
Scribe: Strud Tutwiler
Proof: Ryan O’Neill
Dr. Lester Taste & Smell Page 3 of 3 a. This is a Labeled line for submodality of taste. Multiple sensations come off. They are finely tuned by the time they reach the cortex.
XXII. Olfaction [S22] a. joke
XXIII. Teaching Objective #5 [S23]
XXIV. Anatomical Points [S24] a. From gross anatomy, the frontal lobe sits in the cribiform plate. Main points: It is one part of the special senses, where the receptor cell is a neuron. b. All olfactory nerves pass through cribiform plate and olfactory epithelial. This is really the olfactory tract or bulb
(correct terminology). CN I synapse at olfactory bulb. CN I is the only CN to leave brain and go to periphery. c. This area is where we end up for olfaction. No thalamic relay, they go straight to the cortex (frontal and temporal lobe).
XXV. Olfactory Receptor Neurons [S25] a. CN I is for olfaction.
XXVI. Epithelia – surface area [S26] a. Olfactory nerve end with sensory epithelial ends sticking out. b. This is looking up at our endothelial. Huge surface area / volume ratio to detect odorants and chemicals.
XXVII. Olfactory Transduction [S27] a. Receptors on end of sensory epithelials detect mechanical change and cause depolarization. Depolarization is spread to the soma. This is a real neuron though, so it generates an action potential. This is the only difference.
b. These cells are lost and then turned over.
c. All of these are G-protein coupled. There are thousands of genes encoding for olfactory receptors. Each is capable of detecting different motor neurons. Some people who work in the perfume industry can finely discriminate between odorants. d. Therefore, ion channels open up, action potentials travel down neurons, and transmitters are released to stimulate olfactory tract.
XXVIII. Learning Objective #5 [S28]
XXIX. Glomeruli – olfactory bulb [S29] a. Understand how CNS convergence. The bottoms colored things are sensory epithelial receptors detecting odors. b. In the olfactory bulb, similar odorants are detected together. The red ones will find their way to a single mitral cell in the Glomeruli. c. This leads to processing because the receptor can only detect one type of odorant.
d. What goes on in olfactory bulb is lateral inhibition (surround inhibition). It will inhibit the ones next to it to enhance/tune receptor cells and mechanisms.
XXX. CNS pathways [S30] a. Looking at bulb from ventral surface of brain. Shows frontal cortex. Part of the temporal cortex is sliced away, horizontal slide. b. The olfactory cortex is sometimes called the Piriform cortex. Probably in uncus or parahippocampal gyrus. c. Close to amygdala and thalamus. The olfactory system feeds directly into a circuit at the site of the hippocampus. d. Piriform temporal lobe goes to the orbitofrontal.
XXXI. Learning Objective #6 [S31]
XXXII. Thalamic Relay [S32] a. Do not remember diagram. Helps you remember that you end at frontal cortex and may go through thalamus
(uncertain). It does not need to go through the thalamus to get to primary cortex. b. Have smell and taste integration going on.
Limbic system also feeds this.
XXXIII. Damage [S33] a. Clinically important: if you lose sense of smell, most people perceive a lack of taste. Everything tastes bland.
b. Dopamine connection with olfaction . May hear about with Parkinson’s in early detection signs. c. Need to catch disease before it progresses. Some people argue that loss of smell is early detection of
Parkinson’s disease. d. People can have seizures, near hippocampus and cortex, where people perceive horrible smells or taste.
[End 39 min]