Ch. 17 An Introduction

to Special Senses

Olfaction- SMELL

Gustation- TASTE

*Interactive: pgs. 453-457

Olfaction

Olfactory Organs

Location: Nasal Cavity (on either side of septum)

Two Layers

Olfactory Epithelium

Olfactory Receptor Cells

Basal Cells (regenerative stem cells)

Lamina Propria (underneath)

Areolar tissue, blood vessels, & nerves

Olfactory Glands (Bowman’s Glands): form mucus

Olfactory Receptors

Specialized neurons

Knob projects to epithelium

Up to 20 cilia on each knob

Provide surface area for interaction with water and

lipid soluble compound interaction

Olfactory reception occurs when these chemicals

interact with odorant-binding proteins

Olfactory Pathways

Axons from olfactory epithelium group into 20 or more bundles

Move through the cribriform plate of ethmoid bone

Reach Olfactory bulbs of cerebrum, then efferent fibers travel to hypothalamus and limbic system

*Olfactory receptors do not adapt well to continued stimulus, which is why you eventually lose your sensitivity to persistent smells

*Only sense to directly reach cerebral cortex

Gustation

Taste Receptors (Gustatory Receptors)

Superior tongue, and adjacent pharynx and larynx

Receptors and epithelium for specialized structures

called taste buds (about 3000 in adults)

Lingual Papillae (3 types on the Tongue)

Filiform: provide friction, but have no taste buds

Fungiform: about 5 taste buds each

Cirumvallate: as many as 100 taste buds each

Taste Receptors

Each taste bud contains about 40 slender

spindle shaped cells Basal cells: stem cells

Gustatory cells: taste receptors

have microvilli surrounded by openings filled with fluid

called taste pores

Replaced every 10 days

Gustatory Pathway

Taste buds innervate the facial,

glossopharyngeal, and vagus nerves

Sensory information then carried to medulla,

thalamus, and sensory cortex

Sense of texture and heat is carried by

trigeminal nerve

*sense of taste increased by olfactory receptors

Vagus

Nerve

Gustatory Discrimination

Primary Taste Sensation

Sweet, salty, sour, and bitter

Less know taste sensations

Umami: pleasant taste receptive to presence of

amino acids, small peptides, and nucleuotides

(cirumvallate papillae)

Water: receptors in pharynx processed in

hypothalamus and affect water balance & blood

volume