physiology of taste and smell Flashcards
where does the tongue develop embryology
develops in the back of the neck in occipital somites
mesoderm = muscle
ectoderm = surface, branchial arch
what develops from the first brachial arch
tuberculum midline and lateral lingual swellings
from the mucosal surface of the anterior 2/3 of the tongue
trigeminal nerve (CN V) for touch and pain; facial nerve (CN VII) for taste
what develops from the third brachial arch
cupula (hypobranchial eminence)
forms the posterior 1/3 of the tongue (pharyngeal tongue)
glossopharyngeal nerve (CN IX)
what develops from the mesoderm in the upper neck (occipital somites)
intrinsic and extrinsic muscles
hypoglossal nerve (CN XII)
what are the extrinsic muscle of the tongue
genioglossus, hyoglossus and styloglossus
- with palatoglossus, moves tongue back forwards up and down
what are the intrinsic muscles of the tongue
vertical, horizontal and longitudinal
what are the 5 primary taste
sour
salty
sweet
bitter
savoury/ umami
what chemicals create sour
acid, H+
what chemicals create salty
Na+
what chemicals create sweet
glucose
what chemicals create bitter
coffee, beer, quinine, blue cheese, olives
what chemicals create savoury/ umami
glutamate
what is the purpose of bitter taste
bitterness is the most sensitive and has a protective function
- protects against poison ingestion
- children will not eat bitter things, but you can train yourself to like them
what innervates the anterior 2/3 of the tongue
lingual nerve (trigeminal, CN V)
chorda tympani (facial, CN VII)
what innervates the posterior 1/3 of the tongue
glossopharyngeal (CN IX)
what innervates the solitary nucleus of the medulla
gustatory cortex (anterior insula + inferior frontal gyrus)
thalamus
what are the other sensory inputs involved in flavour
pungency - pain/ temperature receptors
coolness (menthol) - temperature receptors
fattiness - controversial
temperature - enhances release of odorants to the nose
texture - crunchy/ creamy
how can ear surgery affect taste
ear surgery can cause damage to the chorda tympani
- unilateral - minimal symptoms
- bilateral - unpleasant metallic taste in mouth
what surgery can damage the lingual nerve
surgery to sublingual and submandibular salivary glands
- unilateral loss of taste and loss of common sensation in the floor of the mouth and tongue
how does dry mouth arise
autoimmune diseases
radiotherapy to head and neck
drugs
nothing to dissolve chemicals in
describe the structure of the nose
horizontal structure 7cm long
warms and humidifies incoming air
what creates quiet breathing
laminar airflow over the inferior turbinate (projections with thick vascular mucosa)
what happens to air in sniffing
turbulence to mix the air and send odorants to the roof of the nose
- olfactory mucosa sits just below cribriform plate, olfactory bulbs just above
- cribriform plate is very thin + fragile DONT POKE THINGS DIRECTLY UPWARDS IN THE NOSE
how are odorant molecules detected
dissolve in nasal mucus
detected by rhodopsin-like detectors on dendrites of olfactory
each receptor responds to more than one odorant (based on molecular shape, size, polarity, charged groups
each odorant stimulates more than one receptor
where does the olfactory nerve (CN I) project to
amygdala
hippocampus -> memory, why is smell so evocative and plays a large role in attraction
- attempts to find people with different genetic makeup (different immune system)
parahippocampal gyrus
how is congenital anosmia acquired
Kallmann syndrome (hypogonadotropic hypogonadism)
rhinosinusitis
neurological disorders (Alzheimer’s, Parkinson’s, MS)
base of skull fracture
brain tumour
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