Physiology of Taste and Smell Flashcards
What are branchial arches?
The branchial arches are embryologic structures that develop into anatomic structures in the adult human.
What structures of the tongue arise from the first branchial arch of the endoderm?
- Tuberculum impar (midline) and lateral lingual swellings.
- Form the mucosal surface of the anterior 2/3rds of the tongue
- Trigeminal nerve for touch and pain
- Facial nerve for taste
What structures of tongue arise from 3rd branchial arch of endoderm?
- Cupula
- Posterior 1/3rd of tongue
- Glossopharyngeal nerve
What structures of tongue arise from mesoderm in upper neck?
- Intrinsic and extrinsic muscles
- Hypoglossal nerve
What is the role of the fingiform papillae?
Carry taste buds
What is the role of the filiform papillae?
Rough surface for manipulation of food.
How many taste buds do we have?
2000-8000 to detect substances dissolved in saliva.
What are the 5 primary tastes?
- Sour (acid, H+)
- Salty (Na+)
- Sweet (glucose)
- Bitter (cofee, beer)
- Savoury/umami (glutamate)
Why is biterness so sensitive?
It is a protective function towards poisons
What structures and cranial nerves are present in the anteroir 2/3rds of the tounge?
- Lingual nerve (Trigeminal, CN V)
- Chorda tympani (facial nerve CN VII)
What cranial nerve is found in the posterior 1/3rd of the tounge?
-Glossopharyngeal nerve (CN IX)
Where do taste fibres synapse and then what happens to them?
In solitary muscles of medulla.
They then run up to gustatory cortex and the thalamus also plays a role.
What are other sensory inputs that contribute to taste and some examples and also where these inputs are mediated?
- Pungency (chilli)- pain and temp. receptors
- Coolness (menthol)- temp. receptors
- Fattiness - specific fat taste or respnose to creamy texture?
- Temperature - enhances release of odorants to nose, imporves texture
- Texture (crunchy crisps, creamy foods)
What are some clinical defects that can affect taste?
-Ear surgery can cause damage to the chorda tympani
Unilateral has minimal symptoms
Bilateral gives unpleasant metallic taste in mouth
-Dry mouth affects taste
-Surgery to submandibular and sublingual salivary glands could damage lingual nerve:
-unilateral; loss of taste and loss of common sensation in floor of mouth and tounge
What contributes to flavour?
Mostly due to smell
Sight, memory, mood, expectation and context can also affect this
What is the structure of the nose?
- Horizontal structure (7cm long)
- Olfactory mucosa sits just belowcribriform plate, olfactory bulbs just above
- Consists of septum, middle turbinate, inferior turbinate
What is one of the basic functions of the nose?
Warms and humidifies incoming air.
Compare quiet breathing and sniffing?
- Quiet = laminar airflow over the inferior turbinate
- Sniff = turbulence to mix the air and send odorants to the roof of the nose
Describe the action of olfactory receptors?
- Odorant molecules in the air dissolve in nasal mucus
- Detected by rhodopsin like detectors on dendrites of olfactory cells
- Each receptor responds to more than one odorant
- Each odorant stimulates more than one receptor
- The combination of this provides the response
- Detection threshold varies
What does the detection threshold of olfactory receptors depend on?
-On solubility, pH and no. of receptors
Where does the olfactory nerve project to?
- Amygdala
- Hippocampus
- Parahippocampal gyrus
- The only sensory modality that doesnt relay primarily to the thalamus
What is a clinical defect that can result from nose dysfunction and what can cause it?
-Congenital anosmia; can have seroius causes such as base of skull fracture, neuro disorders, brain tumour, kallmans syndrome, COVID.
What problems does anosmia lead to?
- Cant appreciate food
- Risks to health (smoke alarm, gas appliances, sell by dates)
- Impact on quality of life (physocological, many become suicidal).
