What is the composition and location of the olfactory epithelium?
The olfactory epithelium is located in the upper nose and contains the dendrites of olfactory neurons , which are chemoreceptors.
How are odorants perceived?
Olfactory receptors are chemoreceptors that transduce chemical signals into sensations the brain interprets as smell. Specific odorants bind to specific receptors that activate specific brain regions.
How do odorants activate olfactory receptors?
The binding of chemicals to the olfactory neuron dendrites activates receptors , leading to activation of the second messenger cAMP. This causes sodium entry through membrane channels , resulting in depolarization and action potential formation.
Why is it difficult to smell when you have a cold?
Increased mucous production during a cold virus infection overlays the nasal membrane and prevents odorant chemicals from reaching the olfactory neurons.
How does the brain differentiate between different smells (e.g., popcorn vs. steak)?
Specific odorants activate different receptors that synapse with different regions of the cerebral cortex. The greater the frequency of action potentials generated by a specific receptor, the more intense the smell will be perceived.
What is unique about olfactory neurons in terms of regeneration?
Olfactory neurons can be replaced as basal cells differentiate to form new neurons within the olfactory epithelium. This is one of the few places where adult human neurons can be replaced.
How quickly does adaptation to smell occur?
Adaptation to most smells occurs very quickly, usually within a minute, unless the smell is particularly strong
What is the path of olfaction from the receptors to the brain?
The olfactory neurons project through the cribriform plate of the ethmoid bone and synapse within the olfactory bulb on the inferior surface of the cerebrum. The olfactory bulb connects to the brain as the Olfactory tract (CN I).
Which brain structures are involved in the conscious perception, memory, and emotion related to smell?
- Olfactory Cortex of Temporal Lobe: Conscious perception of smell.
- Hippocampus: Olfactory memory.
- Amygdala: Emotional responses to smell.
- Reticular Formation: Visceral responses to smell
Why are smells strongly correlated with emotion and memory?
The olfactory cortex links tightly with the limbic system
What are papillae and where are taste buds located?
Papillae are bumps on the tongue that provide friction. Taste buds are contained within the papillae and respond to chemicals dissolved in the saliva.
How often are taste buds replaced?
Taste buds last from 3 to 10 days before basal cells grow to replace them.
What is the general process by which tastants activate gustatory receptors?
The perception of taste involves a brain response to sensations transduced by chemoreceptors in the mouth and on the tongue. Perception depends on which receptors are activated and where those receptor neurons synapse within the gustatory cortex.
What is the pathway of taste sensations to the cerebral cortex?
Like most sensory stimuli, taste sensations are transmitted first to the thalamus before being directed to the gustatory region of the cerebral cortex
What causes the sensation of Sweet?
Dissolved carbohydrates.
What causes the sensation of Sour?
Increased hydrogen ion concentrations (acids).
What causes the sensation of Salty?
Dissolved sodium ions.
What causes the sensation of Bitter?
Alkaloids.
What is Umami?
Amino acids in proteins.Umami is the savory taste (e.g., beef or chicken broth).
Which CN transmits taste from the anterior 2/3 of the tongue?
CN VII (Facial nerve)
Which CN transmits taste from the posterior 1/3 of the tongue?
CN IX (Glossopharyngeal nerve)
Which CN transmits taste from the epiglottis and pharynx walls?
CN X (Vagus nerve)
Which CN is responsible for texture and pain associated with taste?
-CN V (Trigeminal nerve)
-Transmits texture and pain sensations associated with peppery, spicy, and temperature stimuli.
Why is smell an important component of taste?
Much of taste is actually smell. If olfactory receptors are blocked, taste sensations will be dulled and food will taste bland.
