chemical sense Flashcards
What type of receptors are smell and taste?
Chemoreceptors (respond to dissolved chemicals)
Where is the olfactory epithelium located?
- Roof of nasal cavity
- Covers superior nasal concha and septum
What are the 3 cell types in olfactory epithelium and functions?
- Olfactory sensory neurons (bipolar neurons with radiating olfactory cilia )
- Supporting cells (produce pigment + surround and
cushion olfactory receptor cells ) - olfactory stem cells ( lie at
base of epithelium)
Why are olfactory neurons classified as bipolar?
- Have apical dendrites terminate in knob
- Long, largely nonmotile cilia,
olfactory cilia, radiate from
knob. Covered by mucus
(solvent for odorants)
How do olfactory sensory neurons form the olfactory nerve (CN I) and reach the brain?
Nonmyelinated axons gather into fascicles → form CN I (olfactory nerve)
Pass through cribriform plate (ethmoid bone)
Synapse in olfactory bulbs (overlying the nasal cavity)
How many smell receptor genes do humans have, and how do they detect thousands of odors?
- 400 receptor types (1 gene → 1 protein per neuron)
1 receptor binds multiple odorants
1 odorant activates multiple receptors
1 olfactory neuron – 1 receptor
List the 5 steps of olfactory transduction:
- Odorant binds to receptor
- Receptor Activates G protein (Gₒₗᶠ)
- Triggers adenylate cyclase → makes cAMP
- cAMP opens cation channels (Na⁺/Ca²⁺ enter)
- Na⁺ causes depolarization → APs to brain
What 2 properties must a chemical have to be smelled?
Volatile (gaseous state)
Soluble in olfactory mucus
How do odorants trigger action potentials?
- Dissolve in mucus → bind cilia receptors
- Open cation channels → receptor potential
- At threshold → AP to olfactory bulb
How are olfactory signals organized in glomeruli?
- Axons with same receptor type converge on 2 glomeruli
- 1 odorant → multiple glomeruli (combinatorial coding)
Each glomerulus receives input from only one receptor type
Each glomerulus receives input from only one receptor type
What happens at the olfactory bulb?
Filaments of olfactory nerves synapse with mitral cells located in overlying olfactory bulb. Synapse occurs in structures called glomeruli.
What is the role of mitral cells and glomerulus?
- Mitral cells are Second-order neurons that: Mitral cells amplify, refine, and relay signals
-Axons from neurons with same
receptor type converge on given type of glomerulus
Trace the olfactory pathway beyond the bulb:
Mitral cells → olfactory tract → Piriform cortex (primary olfactory cortex)
- Some info sent to Limbic system (amygdala/hypothalamus) → emotional responses
What are common causes of anosmia?
- Head injuries that tear olfactory nerves
- Aftereffects of nasal cavity inflammation
- Neurodegeneration: Parkinson’s/Alzheimer’s
What causes olfactory hallucinations (phantosmia)?
- Temporal lobe epilepsy (olfactory cortex involvement)
- olfactory aura due to epileptic seizures
Where are most of the 10,000 taste buds located? What are the primary location on the tongue?
Papillae (peglike projections) on tongue:
- Fungiform papillae: Mushroom-shaped (scattered)
- Vallate papillae: 8-12 in “V” at back
- Foliate papillae: Side walls
List the 5 basic tastes and their triggers:
Sweet: Sugars, alcohol (energy source)
Sour: H⁺ ions (spoilage warning)
Salty: mental ions (inorganic salts)/ Na+
Bitter: Alkaloids (caffeine, nicotine, quinine)
Umami: amino acids Glutamate and aspartate (protein-rich foods)
What are the 3 cell types in taste buds?
Gustatory epithelial cells:
- Have gustatory hairs (microvilli) that project into taste pores
- Sensory dendrites: Coil around gustatory cells → signal to brain
- Basal epithelial cells: Stem cells that divide (replace others every 7-10 days)
What 3 conditions must be met for taste perception?
Dissolved in saliva
Diffuses into taste pore
Contacts gustatory hairs
How does tastant binding trigger signals?
binding of food chemical
–> Depolarizes gustatory cell → releases neurotransmitter (ATP) —> Binds sensory dendrites → generator potential → APs
How are salty/sour tastes detected?
- Salty: Na⁺ influx → direct depolarization
- Sour: mediated by H+, which enters through a specific H+ channel and causes both direct depolarization and release of Ca2+ from intracellular stores
What links sweet/bitter/umami detection?
All use G protein (gustducin) → Ca²⁺ release → depolarization
Why does food taste bland with a blocked nose?
80% of flavor comes from smell (olfaction)
