THE NOSE KNOWS: Mammal Olfaction Mammal Olfaction

What Is The Olfactory System? What Is The Olfactory System?  The olfactory system is a sensory system used for olfaction, or the sense of smell and chemoreception.  Chemoreception is detection of certain chemical stimuli (odorants ) in the environment.  Most mammals have two distinct parts to their olfactory system: Main Olfactory Bulb and an Accessory Olfactory Bulb.

The Main Olfactory System (bulb) detects volatile, airborne substances (chemicals), while the Accessory Olfactory Bulb is receptive to fluid-phase stimuli. receptive to fluid-phase stimuli.

 There is a subsystem from the MOS, which is the VNO or vermeronasal organ. AkA Jacobson’s Organ.  This arose in tetrapods.  Used for pheromone detection  Separate from the MOS but works with in conjunction with it to establish necessary behavior  There is a tissue layer on the roof of the nasal cavity behind the nostrils called the olfactory epithelium. It is an epithelial layer of the olfactory system directly responsible for detecting odors.

Jacobson’s Organ  Or the VNO, vermeronasal organ is a chemosensory organ in the nasal septum of roof of the mouth in vertebrates used for pheromone detection  A cat will open its mouth like it’s smiling to allow air into the mouth for maximum chemoreception. This activity is called Flehmen Response.  The information received through this organ goes directly to the thalamus which controls homeostasis, apetite and sexual desire  Many mammals do this

How well can you smell?  Anosmia: no sense of smell  Hyposmia: decreased sense of smell  Hyperosmia: increased sense of smell  Dysosmia: confused sense of smell

FUNCTION  The mechanism of the olfactory system can be divided into a peripheral one, sensing an external stimulus and encoding it as an electric signal in neurons, and a central one, where all signals are integrated and processed in the central nervous system, causing the brain to send appropriate signals to the rest of the body to respond accordingly to the stimulus it just received.

 To accomplish all of these functions, the olfactory system uses many areas of the brain. Representations of the odor may be encoded by space (a pattern of activated neurons across a given olfactory region corresponds to the odor), time (a pattern of action potentials by multiple neurons corresponds to the odor) or a combination of the two. Neurons (also called nerve cells) are the primary cells of the nervous system

The olfactory system does several things:  Create a representation of the odor  Determine the concentration of the odor  Distinguish a new odor from the background environmental odors  Identify the odor across different concentrations  Pair the odor with a memory of what the odor represents

Can Fish Smell?  They do have an olfactory system and the ability of chemoreception  They also share with mammals, a sensory epithelium and olfactory bulb. Water enters the olfactory system through an opening in the face called a nare.

WHY SMELL? WHY SMELL?  Most mammals experience their world through their noses. Their life depends on it.

A Few Reasons To Smell Olfactory messages  Species recognition  Individual recognition  Group recognition  Mother/Infant recognition  Marking territory  Signal Social Dominance  Influence the Physiology of others  Sexual Signals

Sources of Olfactory Signals  Urine  Feces  Gland secretions

Individual Recognition The Indian Mongoose has anal glands that produce 6 different Acids.

Species Recognition

Group Recognition The Gliding Opossum marks all group members with his male dominant scent

Mother/Infant Recognition A blind newborn kitten will smell the way to its mother and latch on to a teat. At this point smell ensures the kitten’s survival. The safe environment will also allow for normal, healthy development

Lemur marks his territory

Man marks his territory

Signaling Social Dominance

Physiological Influence Odor in the urine of male mice stimulates female mice to come into estrus

Sexual Signals Elephants have temporal lobe secretions (musth)

A Variety of Noses

More Noses

This is my nose

It’s All About The Snout