Physiology Of Smell Flashcards
What nerve mediates common odours
Olfactory nerve (CN I)
What nerve mediates the less common odours (odours associated with irritation/burning)
Trigeminal nerve (somatosensory) (CN V)
What is a key component of the trigeminal somatosensory system
It has a protective mechanism that prevent inhalation of harmful substances
Where is the olfactory neuroepithelium located in the nasal cavity
The olfactory cleft - mostly in the cribriform plate but also some very small parts of superior & middle turbinate & septum
Describe the structure of the olfactory neuroepithelium
pseudostratified columnar epithelium
What are the four main cell types in the olfactory neuroepithelium
Basal cells, supporting cells, bi-polar sensory neurones, duct cell of bowmans gland
What is the role of the basal cells in the olfactory neuroepithelium
Form new olfactory cells
What is the role of the supporting cells in the olfactory neuroepithelium
Insulates & protects
What is the role of the duct cells of bowman’s gland in the olfactory neuroepithelium
Secretes mucus
What is the role of the bi-polar sensory neurons in the olfactory neuroepithelium
They extend down into the inner layer of the nose with odourant receptor- containing cilia.
They join with other neurons to form olfactor nerves filaments (collectively known as the olfactory nerve)
Process of smell. STEP 1 - Smell detected by ____________ within the olfactory neuroepithelium
Smell detected by olfactory receptors within the olfactory neuroepithelium
Process of smell. STEP 2 - The binding of odor molecules to olfactory receptors initiates a ____________________
The binding of odour molecules to olfactory receptors initiates a signal transduction
Process of smell. STEP 3 - The signal transduction cascade in the olfactory receptors converts ____________ into ____________
The signal transduction cascade in the olfactory receptors converts olfactory stimuli into neural signals
Process of smell. STEP 4 - Axons of the olfactory receptors assemble into bundles of ____________
Axons of the olfactory receptors assemble into bundles of olfactory nerves
Process of smell. STEP 5 - The olfactory nerves penetrate the _______________________ of the ethmoid bone and enter the cranial cavity
The olfactory nerves penetrate the small foramina in the cribriform plate of the ethmoid bone and enter the cranial cavity
Process of smell. STEP 6 - Once in the cranial cavity, the fibres enter the _____________, which lies in the olfactory groove within the ______________
Once in the cranial cavity, the fibres enter the olfactory bulb, which lies in the olfactory groove within the anterior cranial fossa
Process of smell. STEP 7 - From the olfactory bulb neurons pass along the _______ to reach each ________ lobe and olfactory areas
From the olfactory bulb neurons pass along the olfactory tract to reach each temporal lobe and olfactory areas
Why does smell play an important role in taste
A significant amout of retrograde airflow from the nasopharynx occurs during swallowing
Why does sniffing enhance smell
It draws air currents upwards within the nasal cavity
What are the two requirements for a substance to be smelled
It must be volatile & water soluble
What is the role of mucous in smell
It aids in odourant dispersion & allows odourant diffusion/ protein-bound transport to the olfactory receptors
Ansomia definition
Inability to smell
Hyposmia definition
reduced smell
Dysosmia definition
Altered smell
Phantosmia definition
Smell perceived in the absence of stimulus
What are the two types of causes of abnormality in smell
Conductive & sensorineural
What are 3 conductive causes of abnormality in smell
- Nasal polyps
- Rhinitis
- Nasal mass
What are 5 sensorineural causes of abnormality in smell
- Viral (common cold, COVID)
- Head trauma
- Neurological conditions - Parkinsons, Alzheimers
- Brain tumours
- Medications
How can you assess olfaction
UPSIT - smell identification test (‘scratch and sniff’)
