Chapter 15 Anatomy

Chapter 15 – Special Senses

The Chemical Senses

Chemical senses – gustation (taste) and olfaction (smell)

▪Their chemoreceptors respond to chemicals in aqueous solution

▪Taste – to substances dissolved in saliva

▪Smell – to substances dissolved in fluids of the nasal membranes

The Sense of Taste

▪Most of the 4,000 or so taste buds are found on the tongue

▪Taste buds are found in papillae of the tongue mucosa

▪Papillae come in four types: filiform, foliate, fungiform, and

circumvallate

▪Fungiform and circumvallate papillae contain taste buds

Anatomy of a Taste Bud

▪Each gourd-shaped taste bud consists of three major cell types

▪Supporting cells – insulate the receptor

▪Basal cells – dynamic stem cells

▪Gustatory cells – taste cells

Taste Sensations

▪There are five basic taste sensations

▪Sweet – sugars, saccharin, alcohol, and some amino acids

▪Salt – metal ions

▪Sour – hydrogen ions – citrus fruits

▪Bitter – alkaloids such as quinine and nicotine

▪Umami – elicited by the amino acid glutamate (MSG)

Physiology of Taste

▪In order to be tasted, a chemical:

▪Must be dissolved in saliva

▪Must contact gustatory hairs

▪Binding of the food chemical:

▪Depolarizes the taste cell membrane, releasing neurotransmitter

▪Initiates a generator potential that elicits an action potential

Gustatory Pathway

▪Cranial Nerves VII, IX, and X carry impulses from taste buds to the

solitary nucleus of the medulla

▪These impulses then travel to the thalamus, and from there fibers

branch to the:

!1

▪Gustatory cortex (taste)

▪Hypothalamus and limbic system (appreciation of taste)

Influence of Other Sensations on Taste

▪Taste is 80% smell

▪Thermoreceptors, mechanoreceptors, nociceptors also influence tastes

▪Temperature and texture enhance or detract from taste

Sense of Smell

▪The organ of smell is the olfactory epithelium, which covers the

superior nasal concha

▪Olfactory receptor cells are bipolar neurons (replaced every 60 days or

so)...