PSYC 212 Lecture Notes - Lecture 22: Olfactory Receptor Neuron, Olfactory Mucosa, Olfactory Bulb
16 May 2018
School
Department
Course
Professor
PSYC 212 – Lecture 22 – April 10th
Olfaction (Dr. Frasnelli)
Introduction
• We perceive our environment via physical and chemical interactions. Physical senses: (1)
audition – pressure waves hit the eardrum and later hair cells in the inner ear. (2) Vision
– photons hit rods and cones of the retina. (3) Touch – pressure and vibration act on
sensory cells of the skin. With chemical senses, we have direct contact between the
source of stimulation, and these molecules get direct contact with the sensory cells.
Chemical senses: (1) taste, gustation, (2) smell, olfaction, (3) trigeminal system.
Taste
• We perceive taste stimuli via the interaction between soluble substances with gustatory
receptors located in the taste buds of the tongue (and elsewhere in the oral cavity). We
can distinguish: sweet, sour, salty, bitter, umami, and that’s it.
Smell
• We perceive smells via olfactory receptors located in the olfactory mucosa in the upper
portion of the nasal cavity. We can distinguish between millions of different odors.
Olfactory stimuli are volatile substances.
Trigeminal System
• The trigeminal system (chemesthesis) is a third chemosensory system next to smell and
taste. Its receptors are located on fibres of the trigeminal nerve of the nasal and oral
mucosa. Trigeminal stimuli evoke sensation such as: irritation, burning, freshness,
tingling, etc.
Olfaction
• To understand olfaction, we must first look at the organ which is responsible for the
perception of the sense of smell. Nose and cathedral comparison: once you get into the
nose (or a cathedral), there’s a lot of space. The septum separates the two nasal
categories. The septum typically deviates to one side or the either.
Olfactory Receptor Neurons (ORN)
• ORN are situated in the roof of the nasal category. The receptors are in their cilia. ORN
are surrounded by supporting cells and can regenerate from stem cells.
The Olfactory Code
• Humans have approximately 400 different types of olfactory receptors. Each olfactory
receptor neuron (ORN) carries only one type of receptor. Each ORN can be activated by
different substances – one odorant can activate different receptors. Each substance can
activate different types of ORN. Nearly infinite combinations are possible, and this is
why we can distinguish millions of odors.
Olfaction Macroscopic Structures
• Axons of the ORN pass through the cribriform plate of the ethmoid bone and reach the
olfactory bulb.
Organization
• Axons of all olfactory neurons carrying one type of receptor converge to two glomeruli
within the olfactory bulb. Within these glomeruli, you have the first synapse in the
Document Summary
Psyc 212 lecture 22 april 10th. Introduction: we perceive our environment via physical and chemical interactions. Physical senses: (1) audition pressure waves hit the eardrum and later hair cells in the inner ear. (2) vision. Photons hit rods and cones of the retina. (3) touch pressure and vibration act on sensory cells of the skin. With chemical senses, we have direct contact between the source of stimulation, and these molecules get direct contact with the sensory cells. Chemical senses: (1) taste, gustation, (2) smell, olfaction, (3) trigeminal system. Taste: we perceive taste stimuli via the interaction between soluble substances with gustatory receptors located in the taste buds of the tongue (and elsewhere in the oral cavity). We (cid:272)a(cid:374) disti(cid:374)guish: s(cid:449)eet, sou(cid:396), salty, (cid:271)itte(cid:396), u(cid:373)a(cid:373)i, a(cid:374)d that"s it. Smell: we perceive smells via olfactory receptors located in the olfactory mucosa in the upper portion of the nasal cavity. We can distinguish between millions of different odors.
