© 2015 Pearson Education, Inc.

The Senses Special senses Smell Taste Sight Hearing Equilibrium
© 2015 Pearson Education, Inc.

The Eye and Vision 70 percent of all sensory receptors are in the eyes
Each eye has over 1 million nerve fibers Protection for the eye Most of the eye is enclosed in a bony orbit A cushion of fat surrounds most of the eye © 2015 Pearson Education, Inc.

Accessory Structures of the Eye
Eyelids and eyelashes Conjunctiva Lacrimal apparatus Extrinsic eye muscles © 2015 Pearson Education, Inc.

Figure 8.1 Surface anatomy of the eye and accessory structures.
Site where conjunctiva merges with cornea Eyebrow Eyelid Eyelashes Pupil Palpebral fissure Lacrimal caruncle Medial commissure (canthus) Lateral commissure (canthus) Sclera (covered by conjunctiva) Iris Eyelid

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 © 2015 Pearson Education, Inc.

Figure 8.1 Surface anatomy of the eye and accessory structures.
Site where conjunctiva merges with cornea Eyebrow Eyelid Eyelashes Pupil Palpebral fissure Lacrimal caruncle Medial commissure (canthus) Lateral commissure (canthus) Sclera (covered by conjunctiva) Iris Eyelid

Lacrimal apparatus  lacrimal gland and ducts Lacrimal gland—produces lacrimal fluid; situated on lateral aspect of each eye Lacrimal canaliculi—drain lacrimal fluid from eyes medially Lacrimal sac—provides passage of lacrimal fluid towards nasal cavity Nasolacrimal duct—empties lacrimal fluid into the nasal cavity © 2015 Pearson Education, Inc.

Function of the lacrimal apparatus Protects, moistens, and lubricates the eye Empties into the nasal cavity Lacrimal secretions (tears) contain: Dilute salt solution Mucus Antibodies Lysozyme (enzyme that destroys bacteria) © 2015 Pearson Education, Inc.

Figure 8.2a Accessory structures of the eye.
Lacrimal gland Excretory duct of lacrimal gland Conjunctiva Anterior aspect Eyelid Eyelashes Tarsal glands (a) Eyelid

Figure 8.2b Accessory structures of the eye.
Lacrimal gland Lacrimal sac Excretory ducts of lacrimal gland Lacrimal canaliculus Nasolacrimal duct Inferior meatus of nasal cavity Nostril (b)

Figure 8.3a Extrinsic muscles of the eye.
Superior oblique muscle Superior oblique tendon Superior rectus muscle Conjunctiva Lateral rectus muscle Optic nerve Inferior rectus muscle Inferior oblique muscle (a)

Figure 8.3b Extrinsic muscles of the eye.
Trochlea Superior oblique muscle Superior oblique tendon Axis at center of eye Superior rectus muscle Inferior rectus muscle Medial rectus muscle Lateral rectus muscle (b)

Figure 8.3c Extrinsic muscles of the eye.
Controlling cranial nerve Name Action Lateral rectus Moves eye laterally VI (abducens) Medial rectus Moves eye medially III (oculomotor) Superior rectus Elevates eye and turns it medially III (oculomotor) Inferior rectus Depresses eye and turns it medially III (oculomotor) Inferior oblique Elevates eye and turns it laterally III (oculomotor) Superior oblique Depresses eye and turns it laterally IV (trochlear) (c)

Structure of the Eye Layers forming 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 © 2015 Pearson Education, Inc.

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 and vein of the retina (canal of Schlemm) Vitreous humor Optic disc (blind spot) (in posterior segment) (a)

Figure 8.4b Internal anatomy of the eye (sagittal section).
Vitreous humor in posterior segment Ciliary body Iris Retina Margin of pupil Choroid Aqueous humor Sclera Fovea centralis (in anterior segment) Optic disc Lens Optic nerve Cornea Ciliary zonule (b)

Structure of the Eye: The Fibrous Layer
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 © 2015 Pearson Education, Inc.

Structure of the Eye: Vascular Layer
Choroid is a blood-rich nutritive layer in the posterior of the eye Pigment prevents light from scattering Modified anteriorly into two structures: Ciliary body—smooth muscle attached to lens by ciliary zonule (suspensory ligament) Iris—regulates amount of light entering eye Pigmented layer that gives eye color Pupil—rounded opening in the iris © 2015 Pearson Education, Inc.

Structure of the Eye: Sensory Layer
Retina contains two layers Outer pigmented layer absorbs light and prevents it from scattering Inner neural layer Contains receptor cells (photoreceptors) Rods Cones © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

Figure 8.5a The three major types of neurons composing the retina.
Pigmented layer of retina Rod Cone Bipolar cells Ganglion cells Pathway of light (a)

Figure 8.5b The three major types of neurons composing the retina.
Pigmented layer of retina Neural layer of retina Central artery and vein of retina Optic disc Sclera Optic nerve Choroid (b)

Neurons of the retina and vision 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 © 2015 Pearson Education, Inc.

Light absorption by cone populations
Figure 8.6 Sensitivities of the three cone types to the different wavelengths of visible light. Visible light 560 nm (red cones) 530 nm (green cones) 420 nm (blue cones) Light absorption by cone populations Wavelength (nanometers)

Lens Biconvex crystal-like structure
Held in place by a suspensory ligament attached to the ciliary body © 2015 Pearson Education, Inc.

Lens Cataracts result when the lens becomes hard and opaque with age
Vision becomes hazy and distorted Eventually causes blindness in affected eye Risk factors include: Diabetes mellitus Frequent exposure to intense sunlight Heavy smoking © 2015 Pearson Education, Inc.

Figure 8.7 Photograph of a cataract.

Two Segments, or Chambers, of the Eye
Lens divides the eye into two chambers: Anterior (aqueous) segment Anterior to the lens Contains aqueous humor Posterior (vitreous) segment Posterior to the lens Contains vitreous humor © 2015 Pearson Education, Inc.

Figure 8.4b Internal anatomy of the eye (sagittal section).
Vitreous humor in posterior segment Ciliary body Iris Retina Margin of pupil Choroid Aqueous humor Sclera Fovea centralis (in anterior segment) Optic disc Lens Optic nerve Cornea Ciliary zonule (b)

Anterior Segment 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 © 2015 Pearson Education, Inc.

Posterior Segment Vitreous humor
Gel-like substance posterior to the lens Prevents the eye from collapsing Helps maintain intraocular pressure © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

Fovea centralis Macula Blood vessels Optic disc Retina Lateral Medial
Figure 8.8 The posterior wall (fundus) of the retina as seen with an ophthalmoscope. Fovea centralis Macula Blood vessels Optic disc Retina Lateral Medial

Pathway of Light Through the Eye
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 distance vision (over 20 feet away) Accommodation—the lens must change shape to focus on closer objects (less than 20 feet away) © 2015 Pearson Education, Inc.

Light from distant source Focal point
Figure 8.9 Relative convexity of the lens during focusing for distant and close vision. Retina Light from distant source Focal point (a) Light from near source Focal point Retina (b)

Figure 8.10 Real image (reversed left to right, and upside down) formed on the retina.

Visual Fields and Visual Pathways
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 Optic tracts Contain fibers from the lateral side of the eye on the same side and the medial side of the opposite eye © 2015 Pearson Education, Inc.

Visual Fields and Visual Pathways
Overlap of the visual fields, and inputs from both eyes to each optic cortex provide for depth perception © 2015 Pearson Education, Inc.

Pathway of Nerve Impulses into Brain
The pathway of nerve impulses from the retina of the eye into the brain: Optic nerve Optic chiasma Optic tract Thalamus Optic radiation Visual cortex in occipital lobe of brain © 2015 Pearson Education, Inc.

Figure 8.11 Visual fields of the eyes and visual pathway to the brain.
Fixation point Right eye Left eye Optic nerve Optic chiasma Optic tract Optic radiation Thalamus Occipital lobe (visual cortex)

Eye Reflexes Internal muscles are controlled by the autonomic nervous system Photopupillary reflex: bright light causes pupils to constrict through action of radial, circular, and ciliary muscles Accommodation pupillary reflex: viewing close objects causes accommodation Viewing close objects causes convergence (eyes moving medially) © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

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” © 2015 Pearson Education, Inc.

A Closer Look 8.2 Bringing Things into Focus.
Focal plane Correction None required Concave lens (a) Emmetropic eye (b) Myopic eye (nearsighted) Convex lens (c) Hyperopic eye (farsighted)

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 © 2015 Pearson Education, Inc.

Homeostatic Imbalances of the Eyes
Night blindness—inhibited rod function that hinders the ability to see at night Color blindness—genetic conditions that result in the inability to see certain colors Due to the lack of one type of cone (partial color blindness) © 2015 Pearson Education, Inc.

Homeostatic Imbalances of the Eyes
Glaucoma—can cause blindness due to increasing pressure within the eye Hemianopia—loss of the same side of the visual field of both eyes; results from damage to the visual cortex on one side only © 2015 Pearson Education, Inc.

The Ear Houses two senses: Receptors are mechanoreceptors
Hearing Equilibrium (balance) Receptors are mechanoreceptors Different organs house receptors for each sense © 2015 Pearson Education, Inc.

Anatomy of the Ear The ear is divided into three areas:
External (outer) ear Middle ear (tympanic cavity) Inner ear (bony labyrinth) © 2015 Pearson Education, Inc.

Figure 8.12 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 (malleus) Anvil (incus) Stirrup (stapes) External acoustic meatus (auditory canal) Auditory ossicles

The External Ear Involved in hearing only
Structures of the external ear Auricle (pinna) External acoustic meatus (auditory canal) Narrow chamber in the temporal bone Lined with skin and ceruminous (wax) glands Ends at the tympanic membrane (eardrum) © 2015 Pearson Education, Inc.

The Middle Ear (Tympanic Cavity)
Air-filled cavity within the temporal bone Involved only in the sense of hearing Located between tympanic membrane and oval window and round window © 2015 Pearson Education, Inc.

The Middle Ear (Tympanic Cavity)
Two tubes are associated with the inner ear: The opening from the auditory canal is covered by the tympanic membrane The pharyngotympanic, or auditory, tube connects the middle ear with the throat Allows for equalizing pressure during yawning or swallowing This tube is otherwise collapsed © 2015 Pearson Education, Inc.

Bones of the Middle Ear (Tympanic Cavity)
Three bones (ossicles) span the cavity: Malleus (hammer) Incus (anvil) Stapes (stirrup) Function Vibrations from tympanic membrane move the hammer  anvil  stirrup  oval window of inner ear © 2015 Pearson Education, Inc.

Inner Ear or Bony Labyrinth
Includes sense organs for hearing and balance Filled with perilymph Contains a maze of bony chambers within the temporal bone: Cochlea Vestibule Semicircular canals Membranous labyrinth is suspended in perilymph and contains endolymph © 2015 Pearson Education, Inc.

Organs of Equilibrium Equilibrium receptors of the inner ear are called the vestibular apparatus Vestibular apparatus has two functional parts: Static equilibrium Dynamic equilibrium © 2015 Pearson Education, Inc.

Semicircular canals Ampulla Vestibular nerve Vestibule (a)
Figure 8.14a Structure and function of the crista ampullaris (dynamic equilibrium receptor region). Semicircular canals Ampulla Vestibular nerve Vestibule (a)

Static Equilibrium Maculae—receptors in the vestibule
Report on the position of the head Send information via the vestibular nerve Anatomy of the maculae Hair cells are embedded in the otolithic membrane Otoliths (tiny stones) float in a gel around the hair cells Movements cause otoliths to bend the hair cells © 2015 Pearson Education, Inc.

Membranes in vestibule
Figure 8.13a 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 of cranial nerve VIII (a)

Force of gravity Otolithic membrane Otoliths Hair cell Head upright
Figure 8.13b Structure and function of maculae (static equilibrium receptors). Force of gravity Otolithic membrane Otoliths Hair cell Head upright Head tilted (b)

Dynamic Equilibrium These receptors respond to angular or rotary movements Crista ampullaris (in the ampulla of each semicircular canal)—dynamic equilibrium receptors are located in the semicircular canals Tuft of hair cells covered with cupula (gelatinous cap) If the head moves, the cupula drags against the endolymph © 2015 Pearson Education, Inc.

Semicircular canals Ampulla Vestibular nerve Vestibule (a)
Figure 8.14a Structure and function of the crista ampullaris (dynamic equilibrium receptor region). Semicircular canals Ampulla Vestibular nerve Vestibule (a)

Cupula of crista ampullaris (b)
Figure 8.14b Structure and function of the crista ampullaris (dynamic equilibrium receptor region). Ampulla Endolymph Cupula of crista ampullaris (b)

Direction of body movement (c)
Figure 8.14c Structure and function of the crista ampullaris (dynamic equilibrium receptor region). Flow of endolymph Cupula Nerve fibers Direction of body movement (c)

Dynamic Equilibrium Action of angular head movements
The movement of the cupula stimulates the hair cells An impulse is sent via the vestibular nerve to the cerebellum © 2015 Pearson Education, Inc.

Organs of 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 © 2015 Pearson Education, Inc.

Figure 8.15a Anatomy of the cochlea.
Temporal bone Perilymph in scala vestibuli Spiral organ of Corti Vestibular membrane Afferent fibers of the cochlear nerve Temporal bone Cochlea duct (contains endolymph) Perilymph in scala tympani (a)

Figure 8.15b Anatomy of the cochlea.
Vestibular membrane Hair (receptor) cells of spiral organ of Corti Tectorial membrane Fibers of the cochlear nerve Supporting cells Basilar membrane (b)

Mechanism of Hearing Vibrations from sound waves move tectorial membrane Hair cells are bent by the membrane An action potential starts in the cochlear nerve Impulse travels to the temporal lobe Continued stimulation can lead to adaptation © 2015 Pearson Education, Inc.

Mechanism of 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 © 2015 Pearson Education, Inc.

Figure 8.16 Route of sound waves through the ear.
EXTERNAL EAR MIDDLE EAR INTERNAL EAR Auditory canal Ear- drum Hammer, anvil, stirrup Oval window Fluids in cochlear canals Pinna Upper and middle lower Pressure Spiral organ of Corti stimulated Time One vibration Amplitude Amplification in middle ear

Figure 8.17 Activation of the cochlear hair cells.
Stapes Fibers of sensory neurons Scala vestibuli Oval window Perilymph Round window Scala tympani Basilar membrane Cochlear duct (a) Fibers of basilar membrane Apex (long, floppy fibers) Base (short, stiff fibers) 20,000 2, (High notes) (Low notes) (b) Frequency (Hz)

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) © 2015 Pearson Education, Inc.

Chemical Senses: Taste and Smell
Both senses use chemoreceptors Stimulated by chemicals in solution Taste has four types of receptors Smell can differentiate a large range of chemicals Both senses complement each other and respond to many of the same stimuli © 2015 Pearson Education, Inc.

Olfaction—The Sense of Smell
Olfactory receptors are in roof of nasal cavity Olfactory receptors 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 Interpretation of smells is made in the cortex © 2015 Pearson Education, Inc.

Figure 8.18 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 mucosa Olfactory receptor cell Olfactory hairs (cilia) Mucus layer (a) Route of inhaled air containing odor molecules (b)

Taste Buds and the Sense of Taste
Taste buds house the receptor organs Locations of taste buds Most are on the tongue Soft palate Cheeks © 2015 Pearson Education, Inc.

Taste Buds and the Sense of Taste
The tongue is covered with projections called papillae Filiform papillae—sharp with no taste buds Fungiform papillae—rounded with taste buds Circumvallate papillae—large papillae with taste buds Taste buds are found on the sides of papillae © 2015 Pearson Education, Inc.

Figure 8.19a Location and structure of taste buds.
Epiglottis Palatine tonsil Lingual tonsil Fungiform papillae (a)

Figure 8.19b Location and structure of taste buds.
Vallate papilla Taste buds (b)

Structure of Taste Buds
Gustatory cells are the receptors Possess gustatory hairs (long microvilli) Hairs are stimulated by chemicals dissolved in saliva © 2015 Pearson Education, Inc.

Structure of Taste Buds
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 © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

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 Congenital ear problems usually result from missing pinnas and closed or missing external acoustic meatuses © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

Eye problems Strabismus—“crossed eyes”; results from unequal pulls by the external eye muscles in babies Ophthalmia neonatorum—conjunctivitis resulting from gonorrhea in the mother; baby’s eyelids are swollen, and pus is produced © 2015 Pearson Education, Inc.

Problems of aging associated with vision include presbyopia, glaucoma, cataracts, and arteriosclerosis of the eye’s blood vessels Presbyopia—“old vision” results from decreasing lens elasticity that accompanies aging © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

© 2015 Pearson Education, Inc.

Similar presentations

Presentation on theme: "© 2015 Pearson Education, Inc."— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

© 2015 Pearson Education, Inc.

Similar presentations

Presentation on theme: "© 2015 Pearson Education, Inc."— Presentation transcript:

Similar presentations

About project

Feedback