Chapter 17: The Special Senses

Muse Bio 2440Lecture #4 5/21/13

Comparison of General and Special Senses

General Senses Include somatic

sensations (tactile, thermal, pain, and proprioceptive) and visceral sensations.

Scattered throughout the body.

Simple structures.

Special Senses 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

Figure 15.21a

Olfactory tract

Olfactory bulb

(a)

Nasalconchae

Route ofinhaled air

Olfactoryepithelium

Figure 15.21a

Mitral cell (output cell)

Olfactorygland

Olfactorytract

Olfactoryepithelium

Filaments of olfactory nerve

Cribriform plate of ethmoid bone

Lamina propria connective tissue

Basal cell

Supporting cell

Dendrite

Olfactory cilia

Olfactory bulb

Glomeruli

Axon

Olfactory receptor cell

Mucus

Route of inhaled aircontaining odor molecules(b)

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 specialsenses that provide us with vitalinformation 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

Specializedolfactoryneuron

to CNS

Stimulusremoved

Actionpotentials

Stimulus

Threshold

Generator potential

Summary of sense of smellOdorant molecule binds one of 10-100 million receptors.Conformational change in receptor interacts with G proteinG protein activates adenylate cyclase to generate cAMPcAMP opens Na+ channels to initiate depolarization. Information on number of action potentials decoded by olfactorybulbs.

Animals have greater numbers of receptors thus better sense of smellUsually 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

Figure 15.23b

(b) Enlarged section of a circumvallate papilla.

Taste bud

Circumvallate papilla

Figure 15.23a

(a) Taste buds are associated with fungiform, foliate, and circumvallate (vallate) papillae.

Fungiform papillae

Epiglottis

Palatine tonsil

Foliate papillae

Lingual tonsil

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

Tastebuds

Circumvallate papilla

Fungiform papilla

Filiform papillae

The structure and representative locationsof the three types of lingual papillae. Tastereceptors are located in taste buds, whichform pockets in the epithelium of fungiform or circumvillate papillae.

Figure 15.23c

Taste fibersof cranialnerve

Connectivetissue

Gustatory(taste) cells

Tastepore

Gustatoryhair

Stratifiedsquamousepitheliumof tongue

(c) Enlarged view of a taste bud.

Basalcells

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 ReceptorsReceptor cell

Stimulusremoved

Stimulus

Threshold

Receptor depolarization

Stimulus

Receptorcell

Synapse

Axon ofsensoryneuron

Stimulus

Axon

Actionpotentials

Generator potential

Synapticdelay

to CNS

Figure 17-2 Olfactory and Gustatory Receptors

Salt receptors and sour receptors are chemically gated ion channels whose stimulation produces depolarization of the cell.

Salt and Sour Receptors

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, and Umami Receptors

Sour,salt Gated ion

channel

Resting plasmamembrane

Channel opens

Depolarizedmembrane

Sweet,bitter, orumami Membrane

receptor

ActiveG protein

InactiveG protein

ActiveG protein

Inactive2nd messenger

Active2nd messenger

Depolarization of membranestimulates release of chemicalneurotransmitters.

Activation of second messengers stimulates release of chemical neurotransmitters.

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 tongueMaps differ somewhat , but generally

Actions of the Major Tastants

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