Unit 9-2: Smell

We smell with our nose.

false. we smell with our olfactory epithelium

The taste receptors uses many different systems while the olfactory receptors use ____

1 system

What are some ways olfactory response can terminate?

1. odorants diffuse away 2. scavenger enzymes in mucus layer breaks them down 3. cAMP may activate other pathways to end transduction

Describe the major components and functions of the olfactory epithelium

3 types of cells Olfactory nerve - axons from olfactory receptor cells (efferent odor information) Cribriform plate - supports the olfactory bulb Cilia - contains odorant receptors that bind chemical odors Mucus layer - mucopolysaccharides, antibodies, enzymes, odorant binding proteins (concentrate odors)

Which of the following are true? Select all that apply.

B. Olfactory receptors only use one type of molecular signaling system. D. Transduction molecules are found in cilia.

How are olfactory maps organized?

Neurons responsive to certain odors are grouped together in spatial maps on olfactory bulbs

Diagram signal transduction in an olfactory receptor neuron.

Odorants bind to membrane odorant receptor proteins --> stimulate G-protein (Golf) --> activate adenylyl cyclase --> form cAMP --> bind cAMP to a cyclic nucleotide-gated cation channel --> open cation channels and allow influx of Na+ and Ca2+ --> open Ca2+ activated Cl- channels --> cause current flow and membrane depolarization (receptor potential)

What mechanism(s) does the brain use to distinguish between smells?

Olfactory map, temporal code, and population code

Describe the 3 major cells that make up the olfactory epithelium

Olfactory receptor cells- sites of transduction; genuine neurons Supporting cells- similar to glia; help produce mucus Basal cells- source of new receptor cells

Draw the pathway that olfactory information takes, from receptor to primary olfactory cortex. Identify other regions of the brain that receive olfactory information.Compare and contrast similarities and differences between gustatory and olfactory transduction

Olfactory receptors -> olfactory bulb -> 3 connections; 1. hypothalamus -> involved in survival. 2. amygdala-> fear and emotions. 3. primary olfactory cortex. Amygdala and primary -> hypothalamus and Medial dorsal thalamus -> orbitofrontal cortex (secondary olfactory cortex) Hypothalamus -> lateral posterior orbitofrontal cortex. Goes directly to primary cortex. Very fast. That's when you have information consciously.

Design an experiment to define the chemotopic map for odorants in the brain

Receptive fields. Maps in brain where information is organized. Maps are located in primary sensory cortices (primary olfactory cortex). Record from neurons in brain and then present odorant and see if there are increased firing rate. Then do throughout the olfactory cortex to create the map. Chemotopic maps are not location based. Not mapping out where on the tongue. Stimuli are diffusely presented to all of the cells. Organized for chemical type.

Discuss the genetics of odor receptors

Six hundred thirty OR genes were localized to 51 different chromosomal loci distributed over 21 human chromosomes. -each receptor gene has unique structure --> receptor protein binds to different odorants

how are smells represented using population coding and temporal coding?

Temporal coding- depends on timing of spikes to encode quality of odors -Also time code dealing with breathing (temporal). More AP than inhale than an exhale. Coding smell as stronger then. Neurons spontaneously fire. 2nd order neurons are detecting smell in first place .Third order integrates the information. Increased firing rates gets concentrated in the middle of the inhalation cycle. 3rd order neurons look at where there is the most alignment from the sums of the 2nd order. -Odor information is encoded by the detailed timing of spikes within cells and between groups of cells as well as by the number, temporal pattern, rhythmicity, and cell-to-cell synchrony of spikes. Help to discriminate between similar odors but not broad categories in bees. Population coding- back to idea that different neurons have different information about cells. Preference. Not that each have completely different odorants. Citrus contains multiple odorants.

Transduction is

a process that converts stimuli in the environment into electrical responses in sensory receptor cells.

What is the consequence of knocking out critical proteins of the olfactory cAMP pathway in mice or cutting olfactory axons?

anosmia occurs.

The olfactory epithelium contains all of the following types of cells except _______ cells.

glomerular

What is the function of odorant-binding proteins in the mucus?

may concentrate odorants

how is info organized in the olfactory bulb?

neurons are in a specific place in the bulb and each cell detects different odorants. Clustering together. This is when it starts to get organized.

receptors proteins in the vomeronasal system have a set of receptor proteins that can detect _____

pheromones

Outputs from the olfactory bulb make synaptic connections to all of the following except the

thalamus