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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