Essentials of Human Anatomy & Physiology Chapter 8 Special Senses PDF

Chapter 8 Special Senses Lecture Presentation by Patty Bostwick-Taylor Florence-Darlington Technical College © 2018 Pearson Education, Ltd.  Spe...

Chapter 8 Special Senses Lecture Presentation by Patty Bostwick-Taylor Florence-Darlington Technical College © 2018 Pearson Education, Ltd.  Special Senses ▪ Special senses include: ▪ Smell ▪ Taste ▪ Sight ▪ Hearing ▪ Equilibrium ▪ Special sense receptors ▪ Large, complex sensory organs ▪ Localized clusters of receptors © 2018 Pearson Education, Ltd.  Part I: The Eye and Vision ▪ 70 percent of all sensory receptors are in the eyes ▪ Each eye has over 1 million nerve fibers carrying information to the brain © 2018 Pearson Education, Ltd.  Anatomy of the Eye ▪ Accessory structures include the: ▪ Extrinsic eye muscles ▪ Eyelids ▪ Conjunctiva ▪ Lacrimal apparatus © 2018 Pearson Education, Ltd. Figure 8.1 Surface anatomy of the eye and accessory structures. Site where Eyebrow conjunctiva Eyelid merges with cornea Eyelashes Palpebral Pupil fissure Lacrimal caruncle Lateral Medial commissure commissure (canthus) (canthus) Iris Sclera (covered by Eyelid conjunctiva) © 2018 Pearson Education, Ltd.  External and Accessory Structures ▪ Eyelids ▪ Meet at the medial and lateral commissure (canthus) ▪ Eyelashes ▪ Tarsal glands produce an oily secretion that lubricates the eye ▪ Ciliary glands are located between the eyelashes © 2018 Pearson Education, Ltd.  External and Accessory Structures ▪ Conjunctiva ▪ Membrane that lines the eyelids and eyeball ▪ Connects with the transparent cornea ▪ Secretes mucus to lubricate the eye and keep it moist © 2018 Pearson Education, Ltd.  External and Accessory Structures ▪ Lacrimal apparatus = lacrimal gland + ducts ▪ Lacrimal gland—produces lacrimal fluid (tears); situated on lateral end of each eye ▪ Tears drain across the eye into the lacrimal canaliculi, then the lacrimal sac, and into the nasolacrimal duct, which empties into the nasal cavity © 2018 Pearson Education, Ltd.  External and Accessory Structures ▪ Tears contain: ▪ Dilute salt solution ▪ Mucus ▪ Antibodies ▪ Lysozyme (enzyme that destroys bacteria) ▪ Function of tears ▪ Cleanse, protect, moisten, lubricate the eye © 2018 Pearson Education, Ltd. Figure 8.2a Accessory structures of the eye. Lacrimal Excretory duct gland of lacrimal gland Conjunctiva Anterior aspect Eyelid Eyelashes Tarsal glands (a) Eyelid © 2018 Pearson Education, Ltd. Figure 8.2b Accessory structures of the eye. Lacrimal Lacrimal sac gland Excretory ducts of lacrimal gland Lacrimal canaliculus Nasolacrimal duct Inferior meatus of nasal cavity Nostril (b) © 2018 Pearson Education, Ltd.  External and Accessory Structures ▪ Extrinsic eye muscles ▪ Six muscles attach to the outer surface of the eye ▪ Produce gross eye movements © 2018 Pearson Education, Ltd. Figure 8.3a Extrinsic muscles of the eye. Superior oblique muscle Superior oblique tendon Superior rectus muscle Conjunctiva Lateral rectus muscle Optic Inferior Inferior nerve rectus oblique (a) muscle muscle © 2018 Pearson Education, Ltd. Figure 8.3b Extrinsic muscles of the eye. Trochlea Superior oblique muscle Superior oblique tendon Axis at Superior center of rectus muscle eye Inferior rectus muscle Medial rectus muscle Lateral rectus muscle Common (b) tendinous ring © 2018 Pearson Education, Ltd. Figure 8.3c Extrinsic muscles of the eye. (c) © 2018 Pearson Education, Ltd.  Internal Structures: The Eyeball ▪ Three layers, or tunics, form the wall of the eyeball ▪ Fibrous layer: outside layer ▪ Vascular layer: middle layer ▪ Sensory layer: inside layer ▪ Humors are fluids that fill the interior of the eyeball ▪ Lens divides the eye into two chambers © 2018 Pearson Education, Ltd. Figure 8.4a Internal anatomy of the eye (sagittal section). Sclera Ciliary body Choroid Ciliary zonule Retina Cornea Fovea centralis Iris Pupil Optic nerve Aqueous humor (in anterior segment) Lens Scleral venous sinus Central artery (canal of Schlemm) and vein of Vitreous humor the retina (in posterior segment) Optic disc (blind spot) (a) © 2018 Pearson Education, Ltd. Figure 8.4b Internal anatomy of the eye (sagittal section). Ciliary body Vitreous humor in posterior segment Iris Margin Retina of pupil Choroid Sclera Aqueous humor Fovea centralis (in anterior segment) Optic disc Lens Optic nerve Cornea Ciliary zonule (b) © 2018 Pearson Education, Ltd.  Internal Structures: The Eyeball ▪ Fibrous layer = sclera + cornea ▪ Sclera ▪ White connective tissue layer ▪ Seen anteriorly as the “white of the eye” ▪ Cornea ▪ Transparent, central anterior portion ▪ Allows for light to pass through ▪ Repairs itself easily ▪ The only human tissue that can be transplanted without fear of rejection © 2018 Pearson Education, Ltd.  Internal Structures: The Eyeball ▪ Vascular layer ▪ Choroid is a blood-rich nutritive layer that contains a pigment (prevents light from scattering) ▪ Choroid is modified anteriorly into two smooth muscle structures ▪ Ciliary body ▪ Iris—regulates amount of light entering eye ▪ Pigmented layer that gives eye color ▪ Pupil—rounded opening in the iris © 2018 Pearson Education, Ltd.  Internal Structures: The Eyeball ▪ Sensory layer ▪ Retina contains two layers 1. Outer pigmented layer absorbs light and prevents it from scattering 2. Inner neural layer contains receptor cells (photoreceptors) ▪ Rods ▪ Cones © 2018 Pearson Education, Ltd.  Internal Structures: The Eyeball ▪ Sensory layer (continued) ▪ Electrical signals pass from photoreceptors via a two- neuron chain ▪ Bipolar neurons ▪ Ganglion cells ▪ Signals leave the retina toward the brain through the optic nerve ▪ Optic disc (blind spot) is where the optic nerve leaves the eyeball ▪ Cannot see images focused on the optic disc © 2018 Pearson Education, Ltd. Figure 8.5a The three major types of neurons composing the retina. Pigmented layer of retina Rod Cone Bipolar cells Ganglion Pathway cells of light (a) © 2018 Pearson Education, Ltd. Figure 8.5b The three major types of neurons composing the retina. Pigmented layer of Neural layer retina of retina Central artery and vein of retina Optic disc Sclera Optic (b) nerve Choroid © 2018 Pearson Education, Ltd.  Internal Structures: The Eyeball ▪ Sensory layer (continued) ▪ Rods ▪ Most are found toward the edges of the retina ▪ Allow vision in dim light and peripheral vision ▪ All perception is in gray tones © 2018 Pearson Education, Ltd.  Internal Structures: The Eyeball ▪ Sensory layer (continued) ▪ Cones ▪ Allow for detailed color vision ▪ Densest in the center of the retina ▪ Fovea centralis–lateral to blind spot ▪ Area of the retina with only cones ▪ Visual acuity (sharpest vision) is here ▪ No photoreceptor cells are at the optic disc, or blind spot © 2018 Pearson Education, Ltd.  Internal Structures: The Eyeball ▪ Sensory layer (continued) ▪ Cone sensitivity ▪ Three types of cones ▪ Each cone type is sensitive to different wavelengths of visible light © 2018 Pearson Education, Ltd.  Internal Structures: The Eyeball ▪ Lens ▪ Flexible, biconvex crystal-like structure ▪ Held in place by a suspensory ligament attached to the ciliary body © 2018 Pearson Education, Ltd. Figure 8.4a Internal anatomy of the eye (sagittal section). Sclera Ciliary body Choroid Ciliary zonule Retina Cornea Fovea centralis Iris Pupil Optic nerve Aqueous humor (in anterior segment) Lens Scleral venous sinus Central artery (canal of Schlemm) and vein of Vitreous humor the retina (in posterior segment) Optic disc (blind spot) (a) © 2018 Pearson Education, Ltd.  Internal Structures: The Eyeball ▪ Lens divides the eye into two chambers 1. Anterior (aqueous) segment ▪ Anterior to the lens ▪ Contains aqueous humor, a clear, watery fluid 2. Posterior (vitreous) segment ▪ Posterior to the lens ▪ Contains vitreous humor, a gel-like substance © 2018 Pearson Education, Ltd. Figure 8.4a Internal anatomy of the eye (sagittal section). Sclera Ciliary body Choroid Ciliary zonule Retina Cornea Fovea centralis Iris Pupil Optic nerve Aqueous humor (in anterior segment) Lens Scleral venous sinus Central artery (canal of Schlemm) and vein of Vitreous humor the retina (in posterior segment) Optic disc (blind spot) (a) © 2018 Pearson Education, Ltd. Figure 8.4b Internal anatomy of the eye (sagittal section). Ciliary body Vitreous humor in posterior segment Iris Margin Retina of pupil Choroid Sclera Aqueous humor Fovea centralis (in anterior segment) Optic disc Lens Optic nerve Cornea Ciliary zonule (b) © 2018 Pearson Education, Ltd.  Internal Structures: The Eyeball ▪ Aqueous humor ▪ Watery fluid found between lens and cornea ▪ Similar to blood plasma ▪ Helps maintain intraocular pressure ▪ Provides nutrients for the lens and cornea ▪ Reabsorbed into venous blood through the scleral venous sinus, or canal of Schlemm © 2018 Pearson Education, Ltd.  Internal Structures: The Eyeball ▪ Vitreous humor ▪ Gel-like substance posterior to the lens ▪ Prevents the eye from collapsing ▪ Helps maintain intraocular pressure © 2018 Pearson Education, Ltd.  Internal Structures: The Eyeball ▪ Ophthalmoscope ▪ Instrument used to illuminate the interior of the eyeball and fundus (posterior wall) ▪ Can detect diabetes, arteriosclerosis, degeneration of the optic nerve and retina © 2018 Pearson Education, Ltd. Figure 8.7 The posterior wall (fundus) of the retina as seen with an ophthalmoscope. Fovea Macula Blood Optic disc Retina centralis vessels Lateral Medial © 2018 Pearson Education, Ltd.  Physiology of Vision ▪ Pathway of light through the eye and light refraction ▪ Light must be focused to a point on the retina for optimal vision ▪ Light is bent, or refracted, by the cornea, aqueous humor, lens, and vitreous humor ▪ The eye is set for distant vision (over 20 feet away) ▪ Accommodation—the lens must change shape to focus on closer objects (less than 20 feet away) © 2018 Pearson Education, Ltd.  Physiology of Vision ▪ Pathway of light through the eye and light refraction (continued) ▪ Image formed on the retina is a real image ▪ Real images are: ▪ Reversed from left to right ▪ Upside down ▪ Smaller than the object © 2018 Pearson Education, Ltd. Figure 8.9 Real image (reversed left to right, and upside down) formed on the retina. © 2018 Pearson Education, Ltd.  Physiology of Vision ▪ Visual fields and visual pathways to the brain ▪ Optic nerve ▪ Bundle of axons that exit the back of the eye carrying impulses from the retina ▪ Optic chiasma ▪ Location where the optic nerves cross ▪ Fibers from the medial side of each eye cross over to the opposite side of the brain © 2018 Pearson Education, Ltd.  Physiology of Vision ▪ Visual fields and visual pathways to the brain (continued) ▪ Optic tracts ▪ Contain fibers from the lateral side of the eye on the same side and the medial side of the opposite eye ▪ Synapse with neurons in the thalamus ▪ Optic radiation ▪ Axons from the thalamus run to the occipital lobe ▪ Synapse with cortical cells, and vision interpretation (seeing) occurs © 2018 Pearson Education, Ltd.  Physiology of Vision ▪ Summary of the pathway of impulses from the retina to the point of visual interpretation 1. Optic nerve 2. Optic chiasma 3. Optic tract 4. Thalamus 5. Optic radiation 6. Optic cortex in occipital lobe of brain © 2018 Pearson Education, Ltd. Figure 8.10 Visual fields of the eyes and visual pathway to the brain (inferior view). Fixation point Right eye Left eye Optic nerve Optic Optic chiasma tract Optic radiation Thalamus Occipital lobe (visual cortex) © 2018 Pearson Education, Ltd.  Physiology of Vision ▪ Visual fields ▪ Each eye “sees” a slightly different view ▪ Field of view overlaps for each eye ▪ Binocular vision results and provides: ▪ Depth perception (three-dimensional vision) © 2018 Pearson Education, Ltd.  A Closer Look ▪ Emmetropia—eye focuses images correctly on the retina ▪ Myopia (nearsightedness) ▪ Distant objects appear blurry ▪ Light from those objects fails to reach the retina and are focused in front of it ▪ Results from an eyeball that is too long © 2018 Pearson Education, Ltd.  A Closer Look ▪ Hyperopia (farsightedness) ▪ Near objects are blurry, whereas distant objects are clear ▪ Distant objects are focused behind the retina ▪ Results from an eyeball that is too short or from a “lazy lens” © 2018 Pearson Education, Ltd.  A Closer Look ▪ Astigmatism ▪ Images are blurry ▪ Results from light focusing as lines, not points, on the retina because of unequal curvatures of the cornea or lens © 2018 Pearson Education, Ltd. A Closer Look 8.2 Bringing Things into Focus. Focal Correction plane None required Concave lens (a) Emmetropic eye (b) Myopic eye (nearsighted) Convex lens (c) Hyperopic eye (farsighted) © 2018 Pearson Education, Ltd.  Physiology of Vision ▪ Eye reflexes ▪ Convergence: reflexive movement of the eyes medially when we focus on a close object ▪ Photopupillary reflex: bright light causes pupils to constrict ▪ Accommodation pupillary reflex: viewing close objects causes pupils to constrict © 2018 Pearson Education, Ltd.  Part II: The Ear: Hearing and Balance ▪ Ear houses two senses 1. Hearing 2. Equilibrium (balance) ▪ Receptors are mechanoreceptors ▪ Different organs house receptors for each sense © 2018 Pearson Education, Ltd.  Anatomy of the Ear ▪ The ear is divided into three areas 1. External (outer) ear 2. Middle ear 3. Internal (inner) ear © 2018 Pearson Education, Ltd. Figure 8.11 Anatomy of the ear. External (outer) ear Middle ear Internal (inner) ear Vestibulocochlear nerve Auricle (pinna) Semicircular canals Oval window Cochlea Vestibule Round window Pharyngotympanic (auditory) tube Tympanic membrane (eardrum) Hammer Anvil Stirrup (malleus) (incus) (stapes) External acoustic meatus Auditory ossicles (auditory canal) © 2018 Pearson Education, Ltd.  Anatomy of the Ear ▪ External (outer) ear ▪ Auricle (pinna) ▪ External acoustic meatus (auditory canal) ▪ Narrow chamber in the temporal bone ▪ Lined with skin and ceruminous (earwax) glands ▪ Ends at the tympanic membrane (eardrum) ▪ External ear is involved only in collecting sound waves © 2018 Pearson Education, Ltd.  Anatomy of the Ear ▪ Middle ear cavity (tympanic cavity) ▪ Air-filled, mucosa-lined cavity within the temporal bone ▪ Involved only in the sense of hearing ▪ Located between tympanic membrane and oval window and round window © 2018 Pearson Education, Ltd.  Anatomy of the Ear ▪ Middle ear cavity (tympanic cavity) (continued) ▪ Pharyngotympanic tube (auditory tube) ▪ Links middle ear cavity with the throat ▪ Equalizes pressure in the middle ear cavity so the eardrum can vibrate © 2018 Pearson Education, Ltd.  Anatomy of the Ear ▪ Middle ear cavity (tympanic cavity) (continued) ▪ Three bones (ossicles) span the cavity 1. Malleus (hammer) 2. Incus (anvil) 3. Stapes (stirrup) ▪ Function ▪ Transmit vibrations from tympanic membrane to the fluids of the inner ear ▪ Vibrations travel from the hammer → anvil → stirrup → oval window of inner ear © 2018 Pearson Education, Ltd. Figure 8.11 Anatomy of the ear. External (outer) ear Middle ear Internal (inner) ear Vestibulocochlear nerve Auricle (pinna) Semicircular canals Oval window Cochlea Vestibule Round window Pharyngotympanic (auditory) tube Tympanic membrane (eardrum) Hammer Anvil Stirrup (malleus) (incus) (stapes) External acoustic meatus Auditory ossicles (auditory canal) © 2018 Pearson Education, Ltd.  Anatomy of the Ear ▪ Internal (inner) ear ▪ Includes sense organs for hearing and balance ▪ Bony labyrinth (osseous labyrinth) consists of: ▪ Cochlea ▪ Vestibule ▪ Semicircular canals ▪ Bony labyrinth is filled with perilymph ▪ Membranous labyrinth is suspended in perilymph and contains endolymph © 2018 Pearson Education, Ltd. Figure 8.11 Anatomy of the ear. External (outer) ear Middle ear Internal (inner) ear Vestibulocochlear nerve Auricle (pinna) Semicircular canals Oval window Cochlea Vestibule Round window Pharyngotympanic (auditory) tube Tympanic membrane (eardrum) Hammer Anvil Stirrup (malleus) (incus) (stapes) External acoustic meatus Auditory ossicles (auditory canal) © 2018 Pearson Education, Ltd.  Equilibrium ▪ Equilibrium receptors of the inner ear are called the vestibular apparatus ▪ Vestibular apparatus has two functional parts 1. Static equilibrium 2. Dynamic equilibrium © 2018 Pearson Education, Ltd. Figure 8.13a Structure and function of the crista ampullaris (dynamic equilibrium receptor region). Semicircular canals Ampulla Vestibular nerve Vestibule (a) © 2018 Pearson Education, Ltd.  Static Equilibrium ▪ Maculae—receptors in the vestibule ▪ Report on the position of the head ▪ Help us keep our head erect ▪ Send information via the vestibular nerve (division of cranial nerve VIII) to the cerebellum of the brain ▪ Anatomy of the maculae ▪ Hair cells are embedded in the otolithic membrane ▪ Otoliths (tiny stones) float in a gel around hair cells ▪ Movements cause otoliths to roll and bend hair cells © 2018 Pearson Education, Ltd. Figure 8.12a Structure and function of maculae (static equilibrium receptors). Membranes in vestibule Otoliths Otolithic membrane Hair tuft Hair cell Supporting cell Nerve fibers of vestibular division (a) of cranial nerve VIII © 2018 Pearson Education, Ltd. Figure 8.12b Structure and function of maculae (static equilibrium receptors). Force of Otolithic Otoliths gravity membrane Hair cell Head upright Head tilted (b) © 2018 Pearson Education, Ltd.  Dynamic Equilibrium ▪ Crista ampullaris ▪ Responds to angular or rotational movements of the head ▪ Located in the ampulla of each semicircular canal ▪ Tuft of hair cells covered with cupula (gelatinous cap) ▪ If the head moves, the cupula drags against the endolymph ▪ Hair cells are stimulated, and the impulse travels the vestibular nerve to the cerebellum © 2018 Pearson Education, Ltd. Figure 8.13a Structure and function of the crista ampullaris (dynamic equilibrium receptor region). Semicircular canals Ampulla Vestibular nerve Vestibule (a) © 2018 Pearson Education, Ltd. Figure 8.13b Structure and function of the crista ampullaris (dynamic equilibrium receptor region). Ampulla Endolymph Cupula of crista (b) ampullaris © 2018 Pearson Education, Ltd. Figure 8.13c Structure and function of the crista ampullaris (dynamic equilibrium receptor region). Flow of endolymph Cupula Nerve fibers Direction of body (c) movement © 2018 Pearson Education, Ltd.  Hearing ▪ Spiral organ of Corti ▪ Located within the cochlear duct ▪ Receptors = hair cells on the basilar membrane ▪ Gel-like tectorial membrane is capable of bending hair cells ▪ Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe © 2018 Pearson Education, Ltd. Figure 8.14a Anatomy of the cochlea. Temporal Perilymph in scala vestibuli bone Spiral Vestibular organ of membrane Corti Afferent fibers of the cochlear nerve Temporal bone Cochlear duct (contains Perilymph in endolymph) scala tympani (a) © 2018 Pearson Education, Ltd. Figure 8.14b Anatomy of the cochlea. Vestibular Hair (receptor) Tectorial membrane cells of spiral membrane organ of Corti Fibers of Basilar Supporting the cochlear membrane cells nerve (b) © 2018 Pearson Education, Ltd.  Hearing ▪ Pathway of vibrations from sound waves ▪ Move by the ossicles from the eardrum to the oval window ▪ Sound is amplified by the ossicles ▪ Pressure waves cause vibrations in the basilar membrane in the spiral organ of Corti ▪ Hair cells of the tectorial membrane are bent when the basilar membrane vibrates against it ▪ An action potential starts in the cochlear nerve (cranial nerve VIII), and the impulse travels to the temporal lobe © 2018 Pearson Education, Ltd.  Hearing ▪ High-pitched sounds disturb the short, stiff fibers of the basilar membrane ▪ Receptor cells close to the oval window are stimulated ▪ Low-pitched sounds disturb the long, floppy fibers of the basilar membrane ▪ Specific hair cells further along the cochlea are affected © 2018 Pearson Education, Ltd. Figure 8.15 Route of sound waves through the ear. EXTERNAL EAR MIDDLE EAR INTERNAL EAR Auditory Ear- Hammer, Oval Fluids in cochlear canals Pinna canal drum anvil, stirrup window Upper and middle lower Pressure Spiral organ Time Amplitude Amplification One of Corti in middle ear vibration stimulated © 2018 Pearson Education, Ltd. Figure 8.16 Activation of the cochlear hair cells. Stapes Fibers of Scala sensory vestibuli neurons Oval Perilymph window Round Scala Basilar Cochlear window tympani membrane duct (a) Fibers of basilar membrane Apex Base (short, (long, stiff fibers) floppy fibers) 20,000 2,000 200 20 (High notes) (Low notes) (b) Frequency (Hz) © 2018 Pearson Education, Ltd.  Hearing and Equilibrium Deficits ▪ Deafness is any degree of hearing loss ▪ Conduction deafness results when the transmission of sound vibrations through the external and middle ears is hindered ▪ Sensorineural deafness results from damage to the nervous system structures involved in hearing ▪ Ménière’s syndrome affects the inner ear and causes progressive deafness and perhaps vertigo (sensation of spinning) © 2018 Pearson Education, Ltd.  Part III: Chemical Senses: Smell and Taste ▪ Chemoreceptors ▪ Stimulated by chemicals in solution ▪ Taste has five types of receptors ▪ Smell can differentiate a wider range of chemicals ▪ Both senses complement each other and respond to many of the same stimuli © 2018 Pearson Education, Ltd.  Olfactory Receptors and the Sense of Smell ▪ Olfactory receptors are in roof of nasal cavity ▪ Olfactory receptor cells (neurons) with long cilia known as olfactory hairs detect chemicals ▪ Chemicals must be dissolved in mucus for detection by chemoreceptors called olfactory receptors ▪ Impulses are transmitted via the olfactory filaments to the olfactory nerve (cranial nerve I) ▪ Smells are interpreted in the olfactory cortex © 2018 Pearson Education, Ltd. Figure 8.17 Location and cellular makeup of the olfactory epithelium. Olfactory bulb Cribriform plate of ethmoid bone Olfactory tract Olfactory filaments of the olfactory nerve Supporting cell Olfactory Olfactory receptor mucosa cell Olfactory hairs Mucus layer (a) (cilia) Route of inhaled air containing odor molecules (b) © 2018 Pearson Education, Ltd.  Taste Buds and the Sense of Taste ▪ Taste buds house the receptor organs ▪ Locations of taste buds ▪ Most are on the tongue ▪ Soft palate ▪ Superior part of the pharynx ▪ Cheeks © 2018 Pearson Education, Ltd.  Taste Buds and the Sense of Taste ▪ The tongue is covered with projections called papillae that contain taste buds ▪ Vallate (circumvallate) papillae ▪ Fungiform papillae ▪ Filiform papillae © 2018 Pearson Education, Ltd. Figure 8.18a Location and structure of taste buds. Epiglottis Palatine tonsil Lingual tonsil Foliate papillae Fungiform papillae (a) © 2018 Pearson Education, Ltd. Figure 8.18b Location and structure of taste buds. Vallate papilla Taste buds (b) © 2018 Pearson Education, Ltd.  Taste Buds and the Sense of Taste ▪ Gustatory cells are the taste receptors ▪ Possess gustatory hairs (long microvilli) ▪ Gustatory hairs protrude through a taste pore ▪ Hairs are stimulated by chemicals dissolved in saliva © 2018 Pearson Education, Ltd. Figure 8.18c Location and structure of taste buds. Epithelium of tongue Taste bud Connective tissue Surface of the tongue Gustatory (taste) cell Basal cell Sensory nerve fiber Gustatory hairs (microvilli) emerging from a taste pore (c) © 2018 Pearson Education, Ltd.  Taste Buds and the Sense of Taste ▪ Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas ▪ Facial nerve (cranial nerve VII) ▪ Glossopharyngeal nerve (cranial nerve IX) ▪ Vagus nerve (cranial nerve X) ▪ Taste buds are replaced frequently by basal cells © 2018 Pearson Education, Ltd.  Taste Buds and the Sense of Taste ▪ Five basic taste sensations ▪ Sweet receptors respond to sugars, saccharine, some amino acids ▪ Sour receptors respond to H+ ions or acids ▪ Bitter receptors respond to alkaloids ▪ Salty receptors respond to metal ions ▪ Umami receptors respond to the amino acid glutamate or the beefy taste of meat © 2018 Pearson Education, Ltd.  Part IV: Developmental Aspects of the Special Senses ▪ Special sense organs are formed early in embryonic development ▪ Maternal infections during the first 5 or 6 weeks of pregnancy may cause visual abnormalities as well as sensorineural deafness in the developing child © 2018 Pearson Education, Ltd.  Part IV: Developmental Aspects of the Special Senses ▪ Vision requires the most learning ▪ The infant has poor visual acuity (is farsighted) and lacks color vision and depth perception at birth ▪ The eye continues to grow and mature until age 8 or 9 © 2018 Pearson Education, Ltd.  Part IV: Developmental Aspects of the Special Senses ▪ Age-related eye issues ▪ Presbyopia—“old vision” results from decreasing lens elasticity that accompanies aging ▪ Causes difficulty to focus for close vision ▪ Lacrimal glands become less active ▪ Lens becomes discolored ▪ Dilator muscles of iris become less efficient, causing pupils to remain constricted © 2018 Pearson Education, Ltd.  Part IV: Developmental Aspects of the Special Senses ▪ The newborn infant can hear sounds, but initial responses are reflexive ▪ By the toddler stage, the child is listening critically and beginning to imitate sounds as language development begins ▪ Age-related ear problems ▪ Presbycusis—type of sensorineural deafness that may result from otosclerosis ▪ Otosclerosis—ear ossicles fuse ▪ Congenital ear problems usually result from missing pinnas and closed or missing external acoustic meatuses © 2018 Pearson Education, Ltd.  Part IV: Developmental Aspects of the Special Senses ▪ Taste and smell are most acute at birth and decrease in sensitivity after age 40 as the number of olfactory and gustatory receptors decreases © 2018 Pearson Education, Ltd.