Olfactory SystemAvery Klein & Taylor Willits

Anatomy ● Olfactory Nerves

○ each of the first pair of cranial nerves, transmitting impulses to the brain from the smell receptors in the mucous membrane of the nose.

● Olfactory Bulbs○ Bulb shaped in forebrain○ Contains mitral cells that receive info

from the olfactory cells. ○ The olfactory cells are found within the

nasal epithelium and pass their information through the cribriform plate of the ethmoid bone.

Anatomy Continued● Olfactory Tract

○ a bundle of afferent nerve fibers from the mitral and tufted cells of the olfactory bulb that connects to several target regions in the brain

● Olfactory Cortex○ Area of cerebral cortex that processes

odors and receives nerve signals

CellsThe olfactory receptor neurons are incorporated into a limited region of the nasal epithelium in the superior nasal cavity.

● Olfactory sensory neurons: ○ The olfactory sensory neurons of the olfactory epithelium

are bipolar neurons.○ Express odorant receptors on the cilia

● Supporting cells: ○ Non neural cells in olfactory epithelium located in apical

layer of the pseudostratified ciliated columnar epithelium. ● Basal cells:

○ Resting on basal lamina of olfactory epithelium● Brush cells:

○ microvilli-bearing columnar cell with its basal surface

Physiology ● Smell starts when you sniff molecules from the

air into your nostrils. At the very back of your

nose, there is a region called the Olfactory

Epithelium, a little patch of skin that is key to

everything you smell. The Olfactory Epithelium

has a layer of Olfactory receptor cells.

○ Special neurons that sense smells (like the

taste buds of your nose).

● Olfactory receptors that bind to odor molecules, causing an electrical response that spreads through the Sensory neuron to the olfactory nerve fibers at the back of the nasal cavity.

Physiology Pt.2 ● When odor molecules hit the back of your nose they get

stuck in a layer of mucus covering the Olfactory Epithelium. They then get fired and send signals through the Olfactory tract up to your brain. Your brain has

● Smell information passes from the receptor cells neurons to the bulbs (the olfactory bulbs has sensory receptors that are actually part of the brain) and tracts of the first cranial nerve which passes into the frontal lobes of the brain. ○ Tract divides into medial and lateral striae which pass

info to the olfactory cortex, where smell is perceived.

-Your brain has 40 million different Olfactory receptor neurons. Your olfactory neurons are the only neuron in the body that gets replaced regularly.

Olfactory Epithelium ● The olfactory receptor neurons are

located in a small region within the superior nasal cavity called the olfactory epithelium.

○ Contains bipolar sensory neurons, which each have dendrites that extend from the apical surface of the epithelium into the mucus lining the cavity.

- As airborne molecules are inhaled through the nose, they pass over the olfactory epithelial region and dissolve into the mucus. These odorant molecules bind to proteins that keep them dissolved in the mucus and help transport them to the olfactory dendrites.

Detection of Odor● Smell is mainly detected by chemoreceptors

(responsive to chemical stimuli)

● Olfactory Epithelium consists of of millions of

Olfactory Receptors

● Receptors detect the odors and send signals

to the olfactory bulbs across the Cribriform

Plate

● In the Olfactory Bulbs they are sent across

Olfactory Tracts to the Olfactory Cortex of the

Brain

Olfactory Cortex● Olfactory Cortex is located in the Temporal

Lobe● Also involved in organizing sensory input● part of the cerebral cortex that processes

olfactory information

Limbic System● Contains

○ Olfactory Cortex○ Hypothalamus○ HippoCampus○ Amygdala

Homeostatic Imbalances : Some of the causes of olfaction problems are allergies, nasal polyps, viral infections and head trauma.

-Without your sense of smell, food tastes different

● Hyposmia○ Reduced ability to detect odors

● Anosmia○ Inability to detect odors at all○ Some may be born without a sense of

smell, which is called congenital anosmia.

● Causes○ Recent Injury or Illness○ Frontal Head Injuries○ Hormonal Disturbances

● Very Serious Condition○ All sense are hand in hand

Anosmia: ● Inability to detect orders at all. ● Causes:

○ Injury to nose and smell nerves or head trauma○ Cocaine abuse ○ Exposure to toxic chemicals○ Certain medical conditions such as Alzheimer's diseases & Parkinson's disease

hormonal disturbances○ some may be born without a sense of smell, which is called congenital

anosmia.

Treatments: steroid nasal spray, steroid tablets, & surgeries

Hyposmia● Reduced ability to detect odors ● Causes:

○ Allergies ○ Head or nose injuries○ Infections such as the flu ○ Deviated nasal septum

Treatments: medication & surgeries

Citeshttp://library.open.oregonstate.edu/aandp/chapter/15-2-smell/

https://www.sciencedirect.com/topics/neuroscience/olfactory-tract

https://courses.lumenlearning.com/austincc-ap1/chapter/special-senses-smell-olfaction/

https://www.utmb.edu/otoref/grnds/smell-2012-01/smell-pic-2012-0130.pdf

https://www.webmd.com/brain/anosmia-loss-of-smell

https://emedicine.medscape.com/article/861242-overview

https://www.nidcd.nih.gov/health/smell-disorders