Chapter 17: The Special Senses Muse Bio 2440 Lecture #4 5/21/13

Comparison of General and Special Senses General Senses Special Senses Include somatic sensations (tactile, thermal, pain, and proprioceptive) and visceral sensations. Scattered throughout the body. Simple structures. Include smell, taste, vision, hearing and equilibrium. Concentrated in specific locations in the head. Anatomically distinct structures. Complex neural pathway.

Olfaction: Sense of Smell Olfactory epithelium contains 10-100 million receptors. Olfactory receptor- a bipolar neuron with cilia called olfactory hairs. - Respond to chemical stimulation of an odorant molecule. Supporting cells- provide support and nourishment. Basal cells- replace olfactory receptors.

Olfactory Epithelium and Olfactory Receptors

Olfactory Epithelium and Olfactory Receptors continued…

Smell (Olfaction) Olfactory Pathways Arriving information reaches information centers without first synapsing in thalamus

Olfactory epithelium Olfactory tract Olfactory bulb Nasal conchae Route of inhaled air (a) Figure 15.21a

Mitral cell (output cell) Olfactory tract Mitral cell (output cell) Glomeruli Olfactory bulb Cribriform plate of ethmoid bone Filaments of olfactory nerve Lamina propria connective tissue Olfactory gland Axon Basal cell Olfactory receptor cell Olfactory epithelium Supporting cell Dendrite Olfactory cilia Mucus Route of inhaled air containing odor molecules (b) Figure 15.21a

Physiology of Olfaction Can detect about 10,000 different odors. Odorant binds to the receptor of an olfactory hair→ G-protein activation→ activation of adenylate cyclase→ production of cAMP→ opening of Na+ channels→ inflow of Na+ →generator potential→ nerve impulse through olfactory nerves→ olfactory bulbs→ olfactory tract→ primary olfactory area of the cerebral cortex.

Olfactory transduction

Figure 17-2 Olfactory and Gustatory Receptors Olfaction and gustation are special senses that provide us with vital information about our environment. Although the sensory information provided is diverse and complex, each special sense originates at receptor cells that may be neurons or specialized receptor cells that communicate with sensory neurons. Stimulus Dendrites Specialized olfactory neuron Stimulus removed Action potentials Stimulus Threshold Generator potential to CNS 11

Summary of sense of smell Odorant molecule binds one of 10-100 million receptors. Conformational change in receptor interacts with G protein G protein activates adenylate cyclase to generate cAMP cAMP opens Na+ channels to initiate depolarization. Information on number of action potentials decoded by olfactory bulbs. Animals have greater numbers of receptors thus better sense of smell Usually 10,000 times greater.

Sense of Taste Receptor organs are taste buds Found on the tongue On the tops of fungiform papillae On the side walls of foliate papillae and circumvallate (vallate) papillae

Circumvallate papilla Taste bud (b) Enlarged section of a circumvallate papilla. Figure 15.23b

(a) Taste buds are associated with fungiform, Epiglottis Palatine tonsil Lingual tonsil Foliate papillae Fungiform papillae (a) Taste buds are associated with fungiform, foliate, and circumvallate (vallate) papillae. Figure 15.23a

Gustation: Sense of Taste Taste bud

Structure of a Taste Bud Flask shaped 50–100 epithelial cells: Basal cells—dynamic stem cells Gustatory cells—taste cells Microvilli (gustatory hairs) project through a taste pore to the surface of the epithelium

Figure 17-3b Gustatory Receptors Taste buds Circumvallate papilla Fungiform papilla Filiform papillae The structure and representative locations of the three types of lingual papillae. Taste receptors are located in taste buds, which form pockets in the epithelium of fungiform or circumvillate papillae. 18

(c) Enlarged view of a taste bud. Connective tissue Gustatory hair Taste fibers of cranial nerve Stratified squamous epithelium of tongue Basal cells Gustatory (taste) cells Taste pore (c) Enlarged view of a taste bud. Figure 15.23c

Taste (Gustation) Gustatory Discrimination Primary taste sensations Sweet (sugars) Salty Sour (acids) Bitter (alkali) umami - savory (fat)

Taste Sensations - chemical triggers There are five basic taste sensations Sweet—sugars, saccharin, alcohol, and some amino acids Sour—hydrogen ions Salt—metal ions Bitter—alkaloids such as quinine and nicotine Umami—amino acids glutamate and aspartate

Taste (Gustation) Gustatory Discrimination Dissolved chemicals contact taste hairs Bind to receptor proteins of gustatory cell Salt and sour receptors Chemically gated ion channels Stimulation produces depolarization of cell Sweet, bitter, and umami stimuli G proteins: (proteins that bind GTP- secondary messengers) gustducins

Figure 17-2 Olfactory and Gustatory Receptors Receptor cell Stimulus Stimulus removed Stimulus Receptor cell Threshold Receptor depolarization Synapse Axon of sensory neuron Axon Action potentials Stimulus Synaptic delay to CNS Generator potential 23

Figure 17-2 Olfactory and Gustatory Receptors Salt and Sour Receptors Sweet, Bitter, and Umami Receptors Salt receptors and sour receptors are chemically gated ion channels whose stimulation produces depolarization of the cell. Receptors responding to stimuli that produce sweet, bitter, and umami sensations are linked to G proteins called gustducins (GUST-doos- inz)protein complexes that use second messengers to produce their effects. Sweet, bitter, or umami Sour, salt Gated ion channel Membrane receptor Resting plasma membrane Inactive G protein Active G protein Channel opens Depolarized membrane Active G protein Active 2nd messenger Inactive 2nd messenger Depolarization of membrane stimulates release of chemical neurotransmitters. Activation of second messengers stimulates release of chemical neurotransmitters. 24

Anatomy of Taste Buds and Papillae Taste bud- made of three types of epithelial cells: supporting cells, gustatory receptor cells and basal cells. About 50 gustatory cells per taste bud. Each one has a gustatory hair that projects through the taste pore. Taste buds are found in the papillae. Three types of papillae: vallate (circumvallate), fungiform and foliate.

Physiology of Gustation Five types of taste: sour, sweet, bitter, salty and umami. Tastant dissolves in saliva → plasma membrane of gustatory hair→ receptor potential→ nerve impulse via cranial nerves VII, IX and X→ medulla→ thalamus→ primary gustatory area of the cerebral cortex.

Influence of Other Sensations on Taste Taste is 80% smell Thermoreceptors, mechanoreceptors, nociceptors in the mouth also influence tastes Temperature and texture enhance or detract from taste

Gustatory Pathway

Specialist taste buds map to certain regions of tongue Maps differ somewhat , but generally

Actions of the Major Tastants 15-30 30