Physiology of Taste and Smell Flashcards
What kind of receptor are those for taste and smell?
Chemoreceptors = stimulated by binding of particular chemicals
What does stimulation of taste and smell receptors induce?
Pleasurable or objectionable sensation
What do taste and smell provide a checkpoint for?
Quality control (ie has food gone off etc)
What do taste and smell influence in association with food intake?
Flow of digestive juices
What influences taste perception?
Information from smell receptors
What is gustation?
Term for sense of taste
Where are the sensory receptor cells of taste mainly packaged?
In taste buds
What are the sense organs of taste?
Taste buds
What do taste buds consist of?
Sensory receptor cells and support cells arranged like slices of orange
What is the life span of taste receptor cells?
About 10 days = replaced by basal cells within taste buds
What do taste receptor cells synapse with inside taste buds?
Afferent nerve fibres
Where are taste buds present?
Tongue, palate, epiglottis, pharynx
Where are the majority of taste buds found?
Sit in papillae in the tongue
What are the papillae of the tongue?
Finger-like structures which give rise to rough appearance of dorsum of tongue = seen in tongue as little red dots/raised bumps
How many types of papillae are in the human tongue?
4 types = filiform (most common, no taste buds), fungiform, vallate, foliate
What does the binding of taste-provoking chemicals (tastant) to receptors cells cause?
Alters cell ionic channels and produces depolarising receptor potential
What does the receptor potential created by the binding of taste-provoking chemicals cause?
Initiates action potentials in afferent nerve fibres which synapse with receptor cells
What conveys the signals from the tongue to the brain?
Cranial nerves = via brainstem and thalamus to cortical gustatory areas
What are some cranial nerves that carry afferent taste fibres to the brainstem?
7th = chorda tympani branch of facial nerve 9th = glossopharyngeal 10th = vagus
Where does the chorda tympani branch of the facial nerve innervate in relation to taste?
Anterior 2/3 of the tongue
Where does the glossopharyngeal nerve innervate in relation to taste?
Posterior 1/3 of tongue
Where does the vagus nerve innervate in relation to taste?
Areas in mouth other than tongue
What are the five primary tastes?
Salty, sour, sweet, bitter, umami
What causes a salty taste?
Stimulated by chemical salts, especially sodium chloride
How does a sour taste arise?
Stimulated by acids which contain free hydrogen ions
What causes someone to taste sweetness?
Receptors stimulated by configuration of glucose
What causes a bitter taste?
Stimulated by diverse group of tastants = alkaloids, toxic plant derivatives
How does a umami taste arise?
Triggered by amino acids, especially glutamate
Are abnormalities of taste permanent?
Not always = may be temporal or permanent
What is agensia?
Loss of taste function = may be caused by nerve damage, local inflammation or some endocrine disorders
What is hypogensia?
Reduced taste function = caused by chemotherapy or some medication
What is dysgensia?
Distortion of taste function
What are some causes of dysgensia?
Glossitis, gum infections, tooth decay, URTI, medication, neoplasm, chemotherapy, zinc deficiency
Where is the olfactory mucosa?
Patch of mucosa in ceiling (dorsal roof) of nasal cavity
What are the cell types contained in the olfactory mucosa?
Olfactory receptor cells, supporting cells, basal cells
What is the term for the sense of smell?
Olfaction
Which cells in the olfactory mucosa secrete mucus?
Basal cells
What are olfactory receptors?
Specialised endings of renewable afferent neurons
What is present in each olfactory receptor?
Each neuron has a thick short dendrite and an expanded end (called an olfactory rod)
What projects from olfactory rods?
Cilia = project to surface of olfactory mucosa
How many cilia project from each olfactory receptor neuron?
About 10-12 cilia per neuron
What are odorants?
Molecules that can be smelled = bind to cilia
What is the life span of olfactory receptors?
About 2 months
What act as precursors for new olfactory receptors?
Basal cells
What do the axons of olfactory receptors form?
Collectively form afferent fibres of olfactory nerve
Where do the afferent fibres of the olfactory nerve pierce?
The cribriform plate of the ethmoid bone = enter olfactory bulb in inferior surface of brain
Where do the olfactory bulbs transmit smell information to?
The brain
Where do neurons pass to once they leave the olfactory bulb?
Pass along the olfactory tract to reach the temporal lobe and olfactory areas
Why do odorants only reach smell receptors by diffusion during quiet breathing?
Olfactory mucosa is above the normal path or airflow
Why does sniffing enhance smelling?
Draws air currents upwards within the nasal cavity
What is needed for a substance to be smelled?
Sufficient volatility = can enter with inspired air
Sufficient water solubility = can dissolve in mucus coating olfactory mucosa
Are olfactory receptors equally sensitive to all substances?
No = different sensitivity for different substances
What is anosmia?
Inability to smell = may be temporal or permanent, due to viral infection, allergy, nasal polyps or head injury
What is hyposmia?
Reduced ability to smell = similar causes to anosmia, may be early sign of Parkinson’s disease
What is dysosmia?
Altered sense of smell = differently interpreting some smells or hallucinations of smell
