Olfaction: Sense of Smell

By: Olivia Deering, Erica Czosnyka, Taylor Craig, Lara

Anatomy of the Olfactory System:

-Big components are:

● Olfactory receptors

● Olfactory bulbs

Olfactory Receptors:

● Located in:- Olfactory mucosa- Region: olfactory epithelium

● Olfactory receptor cells- neurons with hair like projections (cilia)- These extend into a thick layer of mucosa of the olfactory epithelium

Olfactory Receptors:● Each olfactory neuron has:- One odor receptor- They are bipolar- Transmit olfactory info centrally

● Olfactory nerve:- Capable of regeneration- ^product new neurons - Rebuild function in CNS- Unmyelinated- Covered by schwann cells

Olfactory Bulbs:

● Part of the brain connected by nerves to the olfactory epithelium - Right above olfactory epithelium - Separated by bone called cribriform plates

Structures that make up the Olfactory System:

● Basal cells: - New stem cells where new olfactory cells develop- Capable of division...olfactory epithelium replaced every 2-4 weeks

Structures that make up the Olfactory System:

● Vestibules:- Forward section within and above each nostril- Nose has 2 cavities separated by a septum

Structures that make up the Olfactory System:

● Dendrites:- Project from nerve cells into nasal cavity-covered by thin layer of moisture- When moisture dissolves, it stimulates olfactory nerve cells

Structures that make up the Olfactory System:● Mitral Cells- Neurons that are apart of this system- Located in the olfactory bulb- Receive info from axons of olfactory receptor neurons, forming synapses

Structures that make up the Olfactory System:

● Neural Glial Cells (Sustentacular Cells)- Supporting cells- Metabolic and physical support- Have microvilli and webs- Nuclei of these cells are located in other- olfactory epithelial cells

Structures that make up the Olfactory System:● Bowman’s Glands- Secrete mucus- Immunoglobulins are secreted

here providing defense and enzymes that break down organic chemicals

● Nasal mucosa:- Allows olfactory receptor

neurons to have direct access to odorant molecules

Extra Important Info:

● Sinus cavities- Located: bony skull on both sides of nose

● Olfaction is a form of chemoreception- Chemicals activate olfactory system-odorants

Overview:

Physiology of smell:

-Begins nasal cavity (specific odor receptors found upper roof with cilia)

-Receptor sensibility (mechanics of airflow) is involved

-Odor dissolves on the mucous membrane on the cilia, this activates a G-Protein that releases calcium, AP is generated

-After sti, odor is destroyed

Interpretation:

- Brain interprets patterns in electric activity as odors- The only other chemical system that can identify, make sense of and memorize

is the immune system

- Associative learning

Pathway of Olfactory:1st pathway: Olfactory mucosa (nasal cavity)

- Lines upper and posterior parts of nasal cavity and olfactory nerve

- Fibers collect to form up to 20 bundles

Cells:

- Mitral Cells: neurons located in olfactory bulbs/ receive info from the axons of receptors forming synapses called glomeruli

- Granule/periglomerular: are formed off of mitral cells

Pathway of Olfactory:

2nd pathway: Olfactory bulb

- Oval structure that lies about cribriform plate

- Olfactory tract: nerve that synapses with the second order neurons and continues as another structure

- Olfactory receptor fibers synapse with neurons in the olfactory bulb (cranial nerve I)

- Impulses are interpreted in olfactory cortex- Glomerulus: cluster of nerve endings

The Olfactory Receptors:

Olfactory Receptors:

- Transduction occurs in receptors located on cilia at the ends of neurons

- Passive pathway: molecules reach olfactory mucosa from inhaled air

- Assisted pathway: molecules attach to an olfactory binding protein that transports them directly to receptors

Olfactory Receptors Extra Info:

- 10 - 100 million olfactory receptors contained within the olfactory epithelium- Olfactory epithelium lies in the superior part of each nostril- Olfactory membrane has a surface area of 2.4 square centimeters

Olfactory epithelium:

- Olfactory receptors- Sustentacular cells: structural support cell- Basal cells: stem cells capable of division of olfactory cells

How common are smell disorders?

❏ One to two percent of North Americans report problems with their sense of smell.

❏ In one study, nearly one-quarter of men ages 60–69 had a smell disorder, while about 11 percent of women in that age range reported a problem.

❏ Interactions with other senses:Many people who have smell disorders also notice problems with their sense of taste.

Smell Disorders : Hyposmia

❏ Reduced ability to detect odors.❏ Most common of nasal disorders❏ Causes: allergies, nasal polyps, viral infections and head

trauma❏ Treatment: treating the underlying cause of your

hyposmia is enough to treat the hyposmia.

Smell Disorders: Anosmia

● Anosmia is the complete inability to detect odors. In rare cases, someone may be born without a sense of smell.

● Up to 4 million people in the United States have hyposmia or anosmia.● Causes: Nasal congestion, nasal polyps, injury to the nose and smell

nerves, exposure to toxic chemicals, or old age.● Treatment: Decongestants may help to open up your nasal passages if it is just

congestion; however, if nasal polyps are the cause surgery may be needed.● Nasal polyps are small noncancerous growths in the nose and sinuses that

block the nasal passage.

Smell Disorders: Parosmia

● Parosmia is a change in the normal perception of odors a. Ex) when the smell of something familiar is distortedb. Ex) when something that normally smells pleasant now smells foul

● Causes: most as a result of upper respiratory tract infections and exposure to harmful solvents causing the damage to olfactory receptor neurons

● Treatment: symptoms decrease over time, people will not be affected for their lifetime

● Diagnosing: techniques are used to help deduce whether a specific case is attributed to just one stimulating odor or to a group of odors

Smell Disorders: Phantosmia

● The sensation of an odor that isn’t there● Can occur in one nostril or both● Causes: head injury or upper respiratory infection● Treatment:usually goes away on its own or when

illness associated with it resolves● Nasal saline drops or antidepressant medications may

be recommended

Works Cited

● https://www.utmb.edu/otoref/Grnds/smell-2012-01/smell-pic-2012-0130.pdf● https://www.nidcd.nih.gov/health/smell-disorders ● https://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0025088/● https://www.kenhub.com/en/library/anatomy/the-olfactory-pathway● http://neuroscience.uth.tmc.edu/s2/chapter09.html ● http://ucalgary.ca/pip369/mod8/smell/pathways ● http://teachmeanatomy.info/head/cranial-nerves/olfactory-cni/ ● http://www.ablongman.com/html/psychplace_acts/olfaction/anatomy.html● https://www.britannica.com/science/nose#ref145153● http://teachmeanatomy.info/head/cranial-nerves/olfactory-cni/● http://flipper.diff.org/app/items/3370