Sense of Smell and Taste Overview

Overview

This lecture covers the anatomy and physiology of smell (olfaction) and taste (gustation), including how sensory cells translate chemical stimuli into signals our brain understands and the impacts of losing these senses.

Case Study: Olivia and Anosmia

• Olivia, a healthy 35-year-old, lost her sense of smell after head trauma, a condition called anosmia.
• Anosmia can be caused by head trauma, infections, or aging and impacts both smell and much of taste.
• Loss of smell affects safety (e.g., detecting smoke), enjoyment of food, and emotional well-being.

The Science of Smell (Olfaction)

• Smell detects volatile (gaseous) molecules, which enter the nose and reach the olfactory epithelium.
• The olfactory epithelium contains millions of olfactory sensory neurons with unique odorant receptors.
• Odorant molecules dissolve in nasal mucus and bind to neuron receptors, triggering action potentials.
• Neuronal signals converge in glomeruli, where axons synapse with mitral cells.
• Mitral cells relay smell signals to the brain’s olfactory cortex and limbic system, linking scent with memory and emotion.
• Humans have about 40 million olfactory neurons capable of detecting at least 10,000 different smells.

The Science of Taste (Gustation)

• Taste is detected by taste receptor epithelial cells in taste buds located between fungiform papillae on the tongue.
• Taste buds contain 50–100 cells each; gustatory cells do the tasting, basal cells replace them weekly.
• Gustatory hairs project through taste pores where tastants (food molecules) bind after dissolving in saliva.
• Different tastes (sweet, salty, sour, bitter, umami) are detected throughout the tongue, not in isolated regions.
• Salty tastes trigger sodium channels; sour tastes use hydrogen ion channels; all tastants ultimately create action potentials.
• Taste signals travel via the 7th, 9th, and 10th cranial nerves to the cerebral cortex.

Interaction Between Taste and Smell

• Smell and taste work together; about 80% of taste is due to smell.
• Airborne compounds from food reach olfactory receptors while chewing, enhancing flavor perception.
• Blocking the nose reduces the ability to distinguish subtle flavors.

Key Terms & Definitions

• Anosmia — loss of the sense of smell, often also diminishing taste.
• Olfactory epithelium — tissue in the nasal cavity containing olfactory sensory neurons.
• Glomerulus — structure in the olfactory bulb where neuron signals converge.
• Mitral cell — neuron in the olfactory bulb relaying signals to the brain.
• Taste bud — cluster of receptor cells sensing chemicals in food.
• Gustatory cell — taste receptor cell in a taste bud.
• Basal cell — stem cell that regenerates gustatory cells.
• Tastant — chemical compound that triggers taste.

Action Items / Next Steps

• Review anatomy of olfactory and gustatory pathways.
• Test taste regions by sampling different flavors across the tongue.
• Read further about sensory disorders like anosmia.