PERCEPTION - lecture 5

What do the chemical senses respond to?

chemical stimulation from the environment

How many distinct chemoreceptor sensory systems are there? What are they?

3 Distinct Chemoreceptor Sensory Systems (4 in Many Species)

1. olfaction

2. gustation

3. trigeminal

4. vameronasal* (*ANIMALS ONLY)

What is the olfaction system?

smell

What is the gustation system?

taste

What is the trigeminal sense?

chemical irritation (burning/spice)

What is the vomeronasal system?

smell (animals only?)

What perceptual system results from the Sensory Interactions Across Multiple Sensory Systems?

FLAVOR

What is flavor? What chemical senses contribute to it?

the resulting perceptual experience from food/drink

• OLFACTION (most important), Trigeminal, gustation (minor contributor)

What is the most critical chemical sense in taste? Why?

olfaction (smell)

• the most critical determinant

What (5) sensory elements affect flavor?

• Sound–auditory effects (food sounds)

• Vision–visual effects (color, presentation,

• Touch/texture/temperature (mouthfeel)

  • freezing sugary food to minimize sweetness

• Taste & trigeminal–flavor/spice

• Smell

What other factors affect flavor?

• Cultural factors–flavor preferences established by early dietary choices

  • Willingness to try new foods

  • Flavor preferences/aversions—starts with breast milk

• Genetics–differences in olfactory receptors and taste bud populations

What chemical senses contribute to flavor?

1. OLFACTION (most important)

2. trigeminal

3. gustation (minor contributor)

olfaction - Why is smell important? (what functions does it serve?)

• FLAVOR - the most important sensory determinant

• Early warning system

• attractiveness

• QoL

• Memory trigger

  • imporving mood?

What gives off energy (an odor) in the olfactory system?

any volatile substance (gives off vapors)

• Released from source and travels through air

What are the characteristics of odors?

• Must be water and lipid (fat) soluble

• Over 10,000 different odors

What happens in the olfactory nasal cycle? Characteristics of nasal activity?

The shape of the nasal cavity directs air into the upper cavity

• Side-to-side fluctuation in nasal airflow

• Changes periodically (45 min - 1 hr)

• Parallels ultradian rhythms of hemispheric activity

Why does nasal airflow fluctuate?

to help prevent adaptation

What is anosmia?

the complete loss of smell

What is the key characteristic of the olfactory system? What causes it (3)?

FRAGILE–losses are permanent

1. nasal sinus disease

2. respiratory infections

3. head trauma

What does scent loss indicate?

early sign of many disorders–alzheimer’s (90%); parkinson’s (90%); schizophrenia (reduced olfactory bulbs and olfactory abilities)

• Toxins entering the brain

What receptor is in charge of olfactory transduction?

Olfactory Epithelium (Olfactory Mucosa)

What is the Olfactory Epithelium (Olfactory Mucosa)?

postage size stamp region at top of nasal cavity

* Surrounded by respiratory epithelium

* contains olfactory receptors

What are olfactory receptors? How many are there?

~10 million receptors embedded in layers of supporting CNS cells

Where do olfactory receptors terminate?

olfactory cilia (hairlike structures on cells)–actual receptor sites

Olfaction - What are CNS cells?

Central Nervous System cells

• Only brain neurons that regenerate on a consistent basis (6 to 8 weeks)

• Where olfactory receptors are

How does olfactory transduction and reception occur? (5 steps)

1. Odor molecules bind to specific proteins on surface of cilia

   1. lock and key analogy (energy fits right into the receptor sites and activates it)

2. Activates Second Messenger System which Generates Action Potentials

3. Axons of olfactory receptors form olfactory nerve

4. Axons synapse onto glomeruli of olfactory bulb (1000:1 reduction)

5. Projections from olfactory bulb forms LATERAL OLFACTORY TRACT

What are the (5) olfactory pathways in the brain?

• Primary Olfactory Cortex

  • piriform cortex

  • entorhinal

• Secondary olfactory cortex

• Thalamus - Medial Dorsal Nucleus (minor connection)

• The Limbic System

• Hippocampus

What is the relationship between the olfactory system and the primary olfactory cortex?

smell perception

What is the relationship between the olfactory system and secondary olfactory cortex?

integrates smell with taste

What is the relationship between the olfactory system and the limbic system?

emotion integration

What is the relationship between the olfactory system and the hippocampus?

memory integration

Olfaction - What kind of information is coded (DILT)? How?

• Duration = limited–adaptation, periodic nature of odors

• Intensity = number of neurons firing & firing rate

• Location = poorly idenitifed–no internasal comparison

• Type = 10,000+ odors

What is the Stereochemical Theory of Olfaction? What’s its problem?

• the odor of a molecule is determined by its molecular shape and size

  • structure-activity relaitonship (lock and key)

• PROBLEM = Enantiomers–molecules that are mirror images of each other but produce entirely different odors

What are specific anosmias?

• Inability to smell a particular odor with an otherwise normal sense of smell.

  • Most are odors with biological relevance

What (5) factors influence inter-individual differences in olfactory sensitivity?

• Age = sensitivity decreases with age

• Gender = women have better sensitivity

• Time of day = in line with circadian rhythms

• Odorant = we have greater sensitivity to certain odorants

• Genetic = differences in receptors

How do odors function as communication in animals?

• Pheromones–chemical signals within a species

• Marking territory, attraction, mating behaviors

Do human pheromones exist?

• Body odor

• Menstrual synchrony

• Some females show preference for androstenone-related odors

What is the vomeronasal system? What is its accessory structure?

the Second (Accessory) Olfactory System in Many Species

• VNO (vomernasal organ)

What is the vomeronasal organ (VNO) energy stimulant? How does transduction occur?

• Energy = nonvolatile chemical stimuli

• Transduction = base of nasal cavity and connects to accessory olfactory bulb

What are the characteristics of the vomeronasal organ (VNO) in animals? What does it trigger?

• Found in many mammalian and reptilian species for pheromonal effects

• Often triggers Flehmen response (specialized behavior in many mammals where the animal curls back its upper lip & exposes front teeth and gums)

What is the human vomeronasal organ (VNO)?

the Jacobson’s Organ.

Gustation & Trigeminal - What are the 5 primary tastes? What are their molecular/ionic properties?

• Umami = “delicious taste”

• Sweet = organic (CARBon-based molecules = ENERGY)

• Salty = compounds that break into 2 ions–CRITICAL!

• Sour = acids that break into ions

• Bitter = closely related to sweet

What is gustation’s stimulus (chemical energy)? What is its receptor?

any soluble substance (dissolves in water);

Gustatory receptor cells with specialized taste buds

What are the characteristics of gustatory receptors? Where are they located and where do they terminate?

• Gustatory receptor cells with specialized taste buds on papillae (bumps on tongue)

  • 9000-10,000 buds—varies with age (reverse U-function)

    • Lifespan = ~10 days

• terminate in microvilli (cilia of gustatory receptor cells)—chemical contact

• Found throughout oral cavity (tongue, soft palate, upper esophagus, cheek, epiglottis)

What (4) types of papillae are involved in gustation?

• Circum papillae (large circular structures)

• Foliate papillae (sides of tongue)

• Fungiform papillae (anterior part of tongue)

• Filiform papillae (anterior portion of tongue–NO TASTE FUNCTION)

What are gustation’s (7) pathways to the brain?

• 3 major cranial nerves (Chorda tympani; Glossopharyngeal; Vagus)

• Orbitofrontal cortex

• Frontal lobe - Gustatory cortex

• thalamus - Ventral posterior medial nucleus

• Medulla - Nucleus of the solitary tract

Which 3 cranial nerves does gustation interact with? Where are they located?

• Chorda tympani = front ⅔ of tongue

• Glossopharyngeal = back ⅓ of tongue

• Vagus = back of throat & epiglottis

gustation - what types of information gets coded? How? (DILT)

• Duration = limited–tastes can linger until mouth is cleaned

• Intensity = firing of neurons and firing rate

• Location = around the mouth

• Type = 5 different tastes through cross-fiber patterning

What is gustation’s relationship with the orbitofrontal cortex?

integrates smell with taste

What is gustation’s relationship with the solitary tract (Medulla)?

• regulates homeostatic mechanisms–breathing, HR, etc.

• hunger/satiety

• Gag reflex

What (4) factors influence inter-individual differences in gustatory sensitivity?

• Age = sensitivity decreases with age

• Gender = women have better sensitivity

• Illness = disorders (hypergeusia or dysgeusia)

• Genetics = NUMBER of taste buds (nontasters/tasters/supertasters)

What interactive variables affect taste/taste preferences? (5)

• Interactions/Suppression = reduction of one taste by another

• Hunger = increases sensitivity to sweet and salty

• Genetics = innate preferences for SWEET (energy) and SALTY (critical for neural functioning/water homeostasis)

• Modifiers = substances that affect taste perception

• Nutritional deficiencies = can trigger specific hungers

What is the trigeminal system?

common chemical sense–mechanism of action (stimulation by chemical irritants)

What is the trigeminal system stimulus?

• stimulus = any chemical irritant or pungent stimulus

  • produces a wide range of reflexive responses designed to remove irritation

What are the (5) trigeminal system pathways to the brain?

• Parietal lobe - Somatosensory cortex

• Insula

• limbic system - Cingulate cortex

• Thalamus - Medial dorsal nucleus

• Trigeminal nerve–enters at Pons