Physiology of Taste and Smell Flashcards
What kind of receptors are for taste and smell
Chemoreceptors
What does stimulation of taste and smell receptors induce
A pleasurable or objectionable sensation
What does taste and smell provide
A checkpoint for quality control
e.g. off food, poison etc.
What does taste and smell also affect when in association with food intake
Flow of digestive juices
What is taste perception influenced by
Information from smell receptors
Where are the sensory receptor cells of taste located
Packaged in the taste buds
What are the taste buds
Organs of taste
What do taste buds consist of
sensory receptor cells and support cells arranged like slices of orange
What is the life span of a taste receptor cell
10 days
What are the taste receptor cells replaced form
Basal cells within the taste buds
What do taste receptor cells within taste buds synapse with
Afferent nerve fibres
Where are taste buds located
tongue
palate
epiglottis
pharynx
Where are the majority of taste buds
In the papillae of the tongue
Describe the appearance of papillae
Finger like structures which give rise to the rough appearance of the dorm of the tongue
Seen as little red dots or raised bumps
How many types of papillae do we have?
Name these
4 Filiform fungiform vallate foliate
What type of papillae do not contain taste buds
Filiform
What alters cell ionic channels to produce depolarising receptor potential
Binding of taste provoking chemical (tastant)
The receptor potential initiates what
Aciton potentials in afferent nerve fibres which synapse with receptor cells
How do afferent taste fibres reach the brainstem
Via 3 cranial nerves:
VII (chorda tympani branch of facial nerve) - anterior 2/3rds of the tongue
IXth - posterior third of the tongue
X - caranial (vagus) nerve - areas other than the tongue e.g. epiglottis and pharynx
What are the 5 primary tastes
salty sour sweet bitter umani (meaty or savory)
What stimulates salty taste
Sodium chloride (chemical salts)
What stimulates sour taste
Acids which contain free hydrogen ions (H+)
What stimulates sweet taste
configuration of glucose
What stimulates unami taste
amino acids especially glutamate
What is ageusia
loss of taste function
What can cause aguesia
Nerve damage, local inflammation e.g. glossitis, radiation, tobacco, some endocrine disorders
What is Hypogeusia
Reduced taste function
What can cause Hypogeusia
Chemotherapy or medications
What is Dysgeusia
Distortion of taste function
What can cause Dysgeusia
Glossitis Gum infections tooth decay reflux URI medications neoplasms chemo zinc deficiency
Where is olfactory mucosa found
In the ceiling of the nasal cavity
What types of cells are found in olfactory mucosa
Olfactory receptor cells
supporting cells
basal cells
What are olfactory receptors
Specialised endings of renewable afferent neurones
Describe the appearance of each neuron
It has a thick short dendrite and an expanded end called an olfactory rod
Where are cilia in relation to the olfactory rods
They project to the surface of the olfactory mucosa (10-12 cilia per olfactory receptor neuron)
What bind to cilia
Odorants (molecules that can be smelled)
What is the life span of olfactory receptors
About 2 months
What do basal cells act as
precursors for new olfactory receptor cells
What do axons of olfactory receptors collectively form
Afferent fibres of olfactory nerve
Where do the olfactory receptors lie?
They pierce the cribriform plate of the ethmoid bone and enter the olfactory bulbs in the inferior surface of the brain
What is the function of the olfactory bulbs
They transmit smell information to the brain
What happens to odorants during quiet breathing
They only reach smell receptors by diffusion
What does the act of sniffing do
enhances smelling by drawing air currents upwards within the nasal cavity
In order to be smelled, what 2 things must a substance be
Sufficiently volatile (some of its molecules can enter the nose with inspired air) Sufficiently water soluble (can dissolve in the mucus coating of olfactory mucosa)
How many odours can humans discriminate between and how
Thousands - olfactory receptors have different sensitivity to different substances
What is anosmia
Inability to smell
What can cause anosmia
Viral infections, allergy, nasal polyps, head injury
What is hyposmia
reduced ability to smell
What might hyposmia be an earl sign of
Parkinson’s disease
What is dysosmia
Altered sense of smell
What are some examples of dysosmia
Differently interpreting some odours and hallucinations of smell
