3.4 Chemoreception, olfactory, esthesiology, and neuroscience

What are the two components of the olfactory system?

The main olfactory system and the accessory olfactory system

Main/primary olfaction system

Olfactory bulb directly accesses limbic system

Main/primary olfaction system uses what brain parts

Piriform cortex and other areas, Amygdala, neocortical and subcortical pathways

Accessory or secondary olfactory system

Vomeronasal organ > accessory olfactory bulb (behind OB) > limbic system

- flehmen

What is the function of the Vomeronasal organ (VNO)?

It processes pheromones and is connected to the accessory olfactory bulb.

accessory/secondary olfaction system uses what brain parts

Amygdala and subcortical pathways

detection

activated when something meaningful is detected

- true or false, yes or no

Discrimination

more cognitive

- comparing different smells

- multiple choice

Identification

matching to sample

- go find

Scaling

measure/quantify/analyze subjective experience of olfaction

What types of receptors do fish use for detecting pheromones?

Crypt cell receptors, microvillus receptors, and ciliary receptors.

What is Schreckstoff?

An alarm substance produced by club cells in fish when their skin is injured.

Two types of epidermal secretory cells in fish

Mucus and club cells

- able to produce shreckstoff

Which cell produces the alarm substance

club cell if skin is injured

What is Shrekreaktion

fear/fright reaction

How can fear shrekreaktion in fish be assessed?

Using a scale from 0 (no reaction) to 6 (most intense reaction).

do humans have a functioning vomeronasal

No!

What is the role of the limbic system in olfactory processing?

It is directly accessed by the olfactory system, bypassing the thalamus.

Direct access to the limbic system, by passing the thalamus - smelling or sniffing

Smelling

cortical access via the thalamus: higher order processing - smelling or sniffing

sniffing

What is the significance of sniffing in mammals?

It is the main olfactomotor behavior used to process scents.

What is the first point of contact with the olfactory system

the olfactory epithelium

- contains sensory cells

Which vertebrates have relatively poor olfactory capabilities?

Cetaceans and most birds.

Are pheromones always species-specific?

not necessarily

- truffles and pigs

is the VNO necessary to process pheromones?

no!

- but it may be able to process non-biologically relevant odours

when is mating behaviour disrupted in hamsters

both olfactory systems are damaged

- VNO

- olfactory epithelium

What disrupts sexual behaviour in hamsters

lesions of the medial amygdala

What does the involvement of the olfactory epithelium demonstrate

direct effects of pheromones on sexual behaviour and involvement of the main olfactory system

Brain regions involved in pheromones - regulation of sexual behaviour

Preoptic area

Hypothalamus

Amygdala

What happens to many species when the VNO is removed

disrupted sexual behaviour

VNO specializes in processing what kind of chemicals

large non-volatile chemicals and small water/mucus soluble chemicals.

What behaviors do amphibians use for olfactory detection?

Nose-tapping or trickling of water.

Reptiles and VNO behaviour

Tongue - flicking

Mammals and VNO behaviours

nose rubbing, lip smacking, nasopalatine duct, vascular pumping action

Finding the source of odours

Directionality

Intensity gradients

Finding source methods - orientation in a smooth gradient (diffusion)

Kinesis

Taxis

What is kinesis in the context of olfactory navigation?

A random walk based on movement to find odor sources.

What is taxis in olfactory navigation?

A non-random guiding behavior towards an odor source.

Types of taxis

Tropotaxis and klinotaxis

What is tropotaxis?

Simultaneous sampling or stereo-olfaction

- different spatial gradient between two sets of receptors

Examples of tropotaxis

nostrils and forked tongues

What is klinotaxis

sequential sampling

- using the axis/grid

Examples of klinotaxis

Horizontal: back-and-forth movements of the head

Vertical: up and down movement of head

Orientation in a turbulent flow - two processes

Detection of direction of the source

Detection of the direction of the flow (wind/current)

Two types of detection of flow

Anemotaxis and Rheotaxis

What is anemotaxis?

Orientation in relation to wind direction.

What is rheotaxis?

Orientation in relation to water current direction.

What is casting?

Zig-zagging across the flow

- loops around the source

What is the role of mechanosensors in detecting directionality?

They help identify the direction of wind or water currents.

- whiskers