Gustation, Olfaction, and Hearing Essentials

Gustation (Taste)

  • Taste is a chemical sense: chemoreceptors detect tastants.

  • Olfaction is the other chemical sense (smell); chemicals stimulate receptors.

  • Papillae shapes (4): fungiform, filiform, foliate, circumvallate (44 shapes).

  • Taste buds contain taste receptor cells; receptor cells are replaced by surrounding epithelial cells when damaged.

  • Taste pore: opening through which tastants contact receptors.

  • Cranial nerves for taste (3): Facial, Glossopharyngeal, Vagus (VII, IX, X).

  • 5 tastes: Salty, Sweet, Umami, Sour, Bitter (55 tastes).

  • Taste pathway leads to brain for perception of quality and intensity.

Receptors and Sensory Types

  • Exteroceptors: external stimuli.

  • Interoceptors: internal stimuli.

  • Proprioceptors: body position/balance.

  • Thermoreceptors: temperature.

  • Nociceptors: pain.

  • Osmoreceptors: osmotic pressure in bloodstream.

  • Mechanoreceptors: pressure/Touch.

Gustatory Pathway and Protective Reflexes

  • Stimuli can increase saliva and gastric juice (stomach activity).

  • Tastants can activate protective reactions: gagging, reflexive vomiting.

  • Taste involves thermoreceptors and nociceptors (pain) in some contexts.

Olfactory System and Smell

  • Olfactory system relies on neurons; olfactory epithelium surrounds olfactory nerves.

  • Olfactory neuron(s) connect to the olfactory bulb and form the olfactory nerve and tract.

  • Processing occurs in the frontal and temporal lobes.

  • Anosmia: complete loss of smell.

  • Adaptation: diminished response to ongoing odor exposure.

  • Smell is closely linked to emotion and flavor perception.

Physiology of Smell and Hearing

  • Olfactory sensory neuron → olfactory bulb → mitral cells.

  • Olfactory tracts + olfactory nerve transmit signals to brain; processed in frontal/temporal lobes.

  • Hearing and balance structures:

    • External ear: auricle/pinna, helix, external acoustic meatus (ear canal).

    • Middle ear: tympanic membrane; ossicles: malleus, incus, stapes (33 bones) that transmit vibrations to the inner ear.

    • Oval window is where stapes transmits to the inner ear.

    • Inner ear: cochlea (hearing) and semicircular canals (balance/equilibrium).

    • Otoliths: crystals involved in sensing gravity and linear acceleration.

  • Ossicles names and order: malleus, incus, stapes.