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The Special Senses
Part A
Human Anatomy & Physiology, Sixth Edition
Elaine N. Marieb
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
15
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
Sense of Smell
 Olfactory epithelium
 Olfactory receptor cells
 bipolar neurons
Figure 15.3
Olfactory Transduction Process
Odorant
binding
protein
Inactive
Odorant
chemical
Na+
Active
Na+ influx
causes
depolarization
ATP
Adenylate
cyclase
cAMP
Cytoplasm
Depolarization of
olfactory receptor
cell membrane
triggers action
potentials in axon
of receptor
Figure 15.4
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
Functional Anatomy of Photoreceptors
Figure 15.19
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
(eustachian tube)
Figure 15.25a
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
 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
Figure 15.34
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 CaCO3 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