Physiology of Taste and Smell Flashcards
What are the receptors for taste and smell?
Chemoreceptors (stimulated by binding of particular chemicals)
Purpose of ability to taste and smell?
Pleasurable/objectionable sensation
Provides a checkpoint for quality control, e.g: expired food has a bad smell
Influence flow of digestive juices
How is taste perception influenced?
By info from smell receptors
What is taste also known as?
Gustation
Location of the sensory receptor cells of taste?
Mainly packaged in taste buds (sense of organs of taste)
Constituents of taste buds?
Sensory receptor cells and support cells
These are both arranged alternately (like slices of an orange)
Additionally, there are also basal cells
Life span of taste receptor cells?
10 days
How are taste receptor cells replaced?
By basal cells that are also within the taste buds
Locations of taste buds?
Mainly on the: • Tongue • Palate • Epiglottis • Pharynx
How are taste buds arranged on the tongue?
In the papillae on the tongue
What are papillae?
Finger-like, raised bumps on the dorsum of the tongue that produce the rough appearance
4 types of papillae on the tongue?
- Filiform (most common but are the only ones that do not contain taste buds)
- Fingiform
- Vallate
- Foliate
How do taste buds communicate with the NS?
Taste receptor cells, within the buds, synapse with afferent nerve fibres
Steps in the transmission of info from the taste buds to the brain?
- Binding of taste-provoking chemical (AKA tastant) to the receptor cells stimulates a depolarisaion
- Receptor potential initiates an action potential in the afferent nerve fibres, which synapse with receptor cells
- Signals are conveyed by the CNs, via the brainstem and the thalamus, to the cortical gustatory areas
How do afferent taste fibres reach the brainstem?
Facial nerve (chorda tympani branch) - anterior 2/3rd region of the tongue
Glossopharyngeal nerve - posterior 1/3rd of the tongue
vagus nerve - areas other than the tongue, e.g: pharynx and epiglottis
5 primary tastes?
Salty - stimulated by chemical salts, esp. NaCl
Sour - stimulated by acids which contain free H+ ions
Sweet - stimulated by configuration of glucose
Bitter - stimulated by a diverse group of tastants, inc. e.g: alkaloids, poisonous substances and toxic plant derivatives
Umami (meaty/savory): triggered by amino acids, esp. glutamate
What is ageusia and potential causes?
Loss of taste function that may be caused by:
• Nerve damage
• Local inflammation, e.g: glossitis, radiation, tobacco
• Endocrine disorders
What is hypogeusia?
Reduced taste function:
• Chemotherapy
• Drugs
What is dysgeusia?
Distortion of taste function: • Glossitis • Gun infections • Tooth decay • Reflux • URT infections • Drugs and chemotherapy • Neoplasms • Zinc deficiency
What is the olfactory mucosa and where is it located?
Patch of mucosa in the dorsal roof of the nasal cavity
3 constituent cell types in the olfactory mucosa?
- Olfactory receptor cells - specialised ending of renewable afferent neurons
- Supporting cells -
- Basal cells - secrete mucous
Structure of the olfactory receptor cells?
Each neuron has a thick, short dendrite and an expanded end, called an OLFACTORY ROD; from here, cilia project from the surface of the olfactory mucosa
How many cilia project from each olfactory receptor neuron?
10-12
What are odorants?
Molecules that can be smelled; they bind to the cilia
Lifespan of olfactory receptors and how are they replaced?
2 months
Basal cells act as precursors for new olfactory receptor cells
How is the olfactory nerve formed?
Axons of olfactory receptors collectively form the afferent fibres of the olfactory nerve
Describe the olfactory pathway
Olfactory nerve pierces the cribriform plate of the thmoid bone and enters the olfactory bulbs (in the inferior surface of the brain)
From here, neurones pass along the olfactory tract to reach the temporal love and olfactory areas
Function of the olfactory bulbs?
Transmit smell info to the brain
How do odorants reach the smell receptors?
During quiet breathing, by diffusion; sniffing enhances smelling by drawing air currents upwards within the nasal cavity
2 necessities for a substance to be smelled?
- Sufficiency volatile - some of its molecules can dissolve in the mucous coating of the olfactory mucosa
- Sufficiency water soluble - dissolve in the mucous coating of the olfactory mucosa
Sensitivity of olfactory receptors?
Different sensitivity to different substances
What is anosmia and porential causes?
Inability to smell: • Viral infection • Allergy • Nasal polyps • Head injury
What is hyposmia?
Reduced ability to smell:
• As for anosmia
May be an EARLY SIGN of Parkinson’s disease
What is dysosmia?
Altered sense of smell:
• Differently interpreting some odours
• Hallucinations of smell
