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 Part A

Chemical Senses  Chemical senses – gustation (taste) and olfaction (smell)  Chemoreceptors respond to chemicals in aqueous solution

Taste Buds Figure 15.1

Taste Sensations  Sweet – sugars, saccharin, alcohol, some amino acids  Salt – metal ions  Sour – hydrogen ions  Bitter – alkaloids such as quinine and nicotine  Umami – elicited by the amino acid glutamate  Taste is 80% smell

Gustatory Pathway Figure 15.2

Figure 15.3  Olfactory epithelium  Olfactory receptor cells  bipolar neurons Sense of Smell

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

Structure of the Eyeball Figure 15.8a

The Retina: Ganglion Cells and the Optic Disc Figure 15.10b

Sensory Tunic: Retina Figure 15.10a

Light  Electromagnetic radiation – energy waves from short gamma rays to long radio waves  Our eyes respond to a small portion of this spectrum called the visible spectrum  Different cones in the retina respond to different wavelengths of the visible spectrum

Rods  Absorb all wavelengths of visible light  Sensitive to dim light  Perceived input is only gray tones  Sum of visual input from many rods feeds into a single ganglion cell  Results in fuzzy and indistinct images

Cones  Need bright light for activation (have low sensitivity)  Have pigments that furnish a vividly colored view  Each cone synapses with a single ganglion cell  Vision is detailed and has high resolution

Figure Functional Anatomy of Photoreceptors

Chemistry of Visual Pigments  Retinal is a light-absorbing molecule  synthesized from vitamin A  Two isomers: 11-cis and all-trans  Combines with opsin proteins to form visual pigments  Isomerization of retinal initiates electrical impulses in the optic nerve

Excitation of Rods  Cones  Visual pigments are retinal + opsins  blue, green, & red opsins

Phototransduction Figure 15.22

Adaptation  Adaptation to bright light (going from dark to light) involves:  Dramatic decreases in retinal sensitivity – rod function is lost  Switching from the rod to the cone system – visual acuity is gained  Adaptation to dark is the reverse  Cones stop functioning in low light  Rhodopsin accumulates in the dark and retinal sensitivity is restored

Visual Pathways Figure 15.23

The Ear: Hearing and Balance Figure 15.25a (eustachian tube)

Middle Ear (Tympanic Cavity) Figure 15.25b

Inner Ear  Bony & membranous labyrinths  Vestibule, semicircular canals, cochlea Figure 15.27

The Cochlea Figure 15.28

Properties of Sound  Amplitude – intensity of a sound measured in decibels (dB)  Loudness – subjective interpretation of sound intensity Figure 15.29

Transmission of Sound to the Inner Ear Figure 15.31

Resonance of the Basilar Membrane Figure 15.32

Excitation of Hair Cells in the Organ of Corti  Bending cilia:  Opens mechanically gated ion channels  Causes a graded potential and the release of a neurotransmitter (probably glutamate)  The neurotransmitter causes cochlear fibers to transmit impulses to the brain, where sound is perceived

Auditory Pathways Figure  Pitch is interpretation of position of cochlear nuclei neurons stimulated  Loudness is due to varying thresholds of cochlear cells & # of cells stimulated  Localization is perceived by superior olivary nuclei

Mechanisms of Equilibrium and Orientation  Vestibular apparatus – equilibrium receptors in the semicircular canals and vestibule  Maintains our orientation and balance  Vestibular receptors monitor static equilibrium  Semicircular canal receptors monitor dynamic equilibrium

Anatomy of Maculae  Sensory receptors for static equilibrium  Contain supporting cells & hair cells  Hair cells have stereocilia & kinocilium embedded in otolithic membrane  Otolithic membrane  Jellylike mass studded with tiny CaCO 3 stones called otoliths  Utricule hairs - horizontal movement  Saccule hairs - vertical movement

Effect of Gravity on Utricular Receptor Cells  Otolithic movement in the direction of the kinocilia:  Depolarizes vestibular nerve fibers  Movement in the opposite direction:  Hyperpolarizes vestibular nerve fibers  From this information, the brain is informed of the changing position of the head

Crista Ampullaris and Dynamic Equilibrium  In ampulla of each semicircular canal  Responds to angular movements - dynamic equilibrium  Each crista has support cells and hair cells that extend into a gel-like mass called the cupula  Dendrites of vestibular nerve fibers encircle the base of the hair cells

Crista Ampullaris and Dynamic Equilibrium Figure 15.37b

Activating Crista Receptors & Rotational Sensation  Cristae respond to changes in velocity of rotational head movements  Directional bending of hair cells in the cristae causes:  Depolarizationson on one side  Hyperpolarizations on the other side