Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Human Anatomy & Physiology, Sixth Edition Elaine N. Marieb PowerPoint ® Lecture Slides prepared by Vince Austin, University of Kentucky 15 The Special Senses Vision, Taste, Smell

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Eye and Associated Structures  70% of all sensory receptors are in the eye  Most of the eye is protected by a cushion of fat and the bony orbit  Accessory structures include eyebrows, eyelids, conjunctiva, lacrimal apparatus, and extrinsic eye muscles

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Eye and Accessory structures

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Eyebrows Eyelids  Coarse hairs that overlie the supraorbital margins  Functions include:  Shading the eye  Preventing perspiration from reaching the eye Eyelids Protect the eye anteriorly  Palpebral fissure – separates eyelids  Canthi – medial and lateral angles (commissures)

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Palpebrae (Eyelids)  Eyelashes  Project from the free margin of each eyelid  Initiate reflex blinking  Lubricating glands associated with the eyelids  Meibomian glands and sebaceous glands  Ciliary glands lie between the hair follicles

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Lacrimal Apparatus (tear ducts) Lacrimal gland and associated ducts  Lacrimal glands secrete tears  Tears  Contain mucus, antibodies, and lysozyme  Drain into the nasolacrimal duct

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Extrinsic Eye Muscles  Six straplike extrinsic eye muscles  Enable the eye to follow moving objects  Maintain the shape of the eyeball

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Structure of the Eyeball  A slightly irregular hollow sphere with anterior and posterior poles  The wall is composed of three tunics – fibrous, vascular, and sensory  The internal cavity is filled with fluids called humors  The lens separates the internal cavity into anterior and posterior segments

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Structure of the Eyeball Figure 15.8a

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Vascular Tunic: Iris  The colored part of the eye  Pupil – central opening of the iris  Regulates the amount of light entering the eye during:  Close vision and bright light – pupils constrict  Distant vision and dim light – pupils dilate  Changes in emotional state – pupils dilate when the subject matter is appealing or requires problem-solving skills

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Pupil Dilation and Constriction Figure 15.9

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Sensory Tunic: Retina  Two-layered membrane  Pigmented layer – the outer layer that absorbs light and prevents its scattering  Neural layer, which contains:  Photoreceptors  Bipolar cells and ganglion cells  Amacrine and horizontal cells

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings The Retina: Ganglion Cells and the Optic Disc  Ganglion cell axons:  Run along the inner surface of the retina  Leave the eye as the optic nerve  The optic disc:  Is the site where the optic nerve leaves the eye  Lacks photoreceptors (the blind spot)

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings The Retina: Photoreceptors  Rods:  Respond to dim light  Are used for peripheral vision  Cones:  Respond to bright light  Have high-acuity color vision  Are found in the macula lutea  Are concentrated in the fovea centralis

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Key Points in Phototransduction

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Signal Transduction in Retina

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Channels open in the DARK- continuous release of neurotransmitter from photoreceptor- release of neurotransmitter from photoreceptor hyperpolarizes bipolar calcium channels to close- no neurotransmitter release Light- closes channels in photoreceptor/opens calcium channels in bipolar cell- neurotransmitter released- action potential in optic nerve

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Taste Buds Most of the 10,000 or so taste buds are found on the tongue  There are five (maybe 6) basic taste sensations  Sweet – sugars, saccharin, alcohol, and some amino acids  Salt – metal ions  Sour – hydrogen ions  Bitter – alkaloids such as quinine and nicotine  Umami – elicited by the amino acid glutamate  Lipids? ?

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Taste Transduction  The stimulus energy of taste is converted into a nerve impulse (action potential) by:  Na + influx in salty tastes  H + in sour tastes (by directly entering the cell, by opening cation channels, or by blockade of K + channels)  Gustducin in sweet and bitter tastes

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Gustatory Pathway Figure 15.2

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Influence of Other Sensations on Taste  Taste is 80% smell  Thermoreceptors, mechanoreceptors, nociceptors also influence tastes  Temperature and texture enhance or detract from taste

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Sense of Smell  The organ of smell is the olfactory epithelium, which covers the superior nasal concha  Olfactory receptor cells are bipolar neurons with radiating olfactory cilia  Olfactory receptors are surrounded and cushioned by supporting cells  Basal cells lie at the base of the epithelium

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Sense of Smell Figure 15.3

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Physiology of Smell  Olfactory receptors respond to several different odor-causing chemicals  When bound to ligand these proteins initiate a G protein mechanism, which uses cAMP as a second messenger  cAMP opens Na + and Ca 2+ channels, causing depolarization of the receptor membrane that then triggers an action potential

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Olfactory Pathway  Impulse sent to:  The olfactory cortex (what is that smell)  The hypothalamus, amygdala, and limbic system (emotional component of smell

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Olfactory Transduction Process Figure 15.4 Odorant binding protein Odorant chemical Na + Cytoplasm Inactive Active Na + influx causes depolarization Adenylate cyclase ATP cAMP Depolarization of olfactory receptor cell membrane triggers action potentials in axon of receptor