Journal #1: List the 5 special senses Fun fact: Humans have five to six million odor detecting cells, but that is nothing compared to the animal kingdom. Rabbits have 100 million and a dog 220 million Objective #1: Describe the sensory organs of smell (olfaction) and taste (gustation) and trace their sensory pathways to the brain.

Ch. 17 An Introduction to Special Senses Olfaction- SMELL Gustation- TASTE *Interactive: pgs. 550-554

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