Power Point Lecture Slides Prepared by Patty BostwickTaylor

The Senses • Special senses • Smell • Taste • Sight • Hearing •

The Eye and Vision • A. 70 percent of all sensory receptors are in the eyes • B. Each eye has over a million nerve fibers • C. Protection for the eye • Most of the eye is enclosed in a bony orbit • A cushion of fat surrounds most of the eye • Which bones make up the eye orbit? ? © 2012 Pearson Education, Inc.

Site where conjunctiva merges with cornea Eyebrow Eyelid Eyelashes Pupil Lateral canthus Iris Eyelid

Accessory Structures of the Eye • A. Eyelids • Meet at the medial and lateral commissure (canthus) • B. Eyelashes • Tarsal glands produce an oily secretion that lubricates the eye • Ciliary glands are located between the eyelashes- modified sweat glands © 2012 Pearson Education, Inc.

Accessory Structures of the Eye • C. Conjunctiva • Membrane that lines the eyelids • Connects to the outer surface of the eye • Secretes mucus to lubricate the eye and keep it moist • What is pink eye? © 2012 Pearson Education, Inc.

Accessory Structures of the Eye • D. Lacrimal apparatus = lacrimal gland + ducts • 1. Lacrimal gland—produces lacrimal fluid; situated on lateral aspect of each eye • 2. Lacrimal canaliculi—drain lacrimal fluid from eyes medially • 3. Lacrimal sac—provides passage of lacrimal fluid towards nasal cavity • 4. Nasolacrimal duct—empties lacrimal fluid into the nasal cavity © 2012 Pearson Education, Inc.

Lacrimal gland Excretory duct of lacrimal gland Conjunctiva Anterior aspect (a) © 2012 Pearson

Lacrimal gland Excretory ducts of lacrimal gland Lacrimal sac Lacrimal canaliculus Nasolacrimal duct Nostril

Accessory Structures of the Eye • 5. Function of the lacrimal apparatus • Protects, moistens, and lubricates the eye • Empties into the nasal cavity • 6. Lacrimal secretions (tears) contain: • Dilute salt solution • Mucus • Antibodies • Lysozyme (enzyme that destroys bacteria) © 2012 Pearson Education, Inc.

Accessory Structures of the Eye • G. Extrinsic eye muscles • 1. Six muscles attach to the outer surface of the eye • 2. Produce eye movements • How is the human eye musculature different than a cow eye’s? © 2012 Pearson Education, Inc.

Superior oblique muscle Superior oblique tendon Superior rectus muscle Conjunctiva Lateral rectus muscle Optic

Trochlea Superior oblique muscle Superior oblique tendon Axis at center of eye Superior rectus muscle Inferior rectus muscle Why are the eye muscles named this way? Medial rectus muscle Lateral rectus muscle (b) © 2012 Pearson Education, Inc. Figure 8. 3 b

© 2012 Pearson Education, Inc. Figure 8. 3 c

Structure of the Eye • Layers forming the wall of the eyeball • 1. Fibrous layer • Outside layer Why were the layers • 2. Vascular layer of the eye called • Middle layer “tunics” in the past? • 3. Sensory layer • Inside layer © 2012 Pearson Education, Inc.

Ciliary body Ciliary zonule Cornea Iris Pupil Aqueous humor Lens canal of Schlemm Vitreous humor (a) © 2012 Pearson Education, Inc. Sclera Choroid Retina Fovea centralis (macula) Optic nerve Central artery and vein of the retina Optic disc (blind spot) Figure 8. 4 a

Ciliary body Iris Margin of pupil Aqueous humor ( Lens Cornea Ciliary zonule Vitreous humor Retina Choroid Sclera Fovea centralis Optic disc Optic nerve (b) © 2012 Pearson Education, Inc. Figure 8. 4 b

Structure of the Eye: The Fibrous Layer • 1. Sclera • White connective tissue layer • Seen anteriorly as the “white of the eye” • 2. Cornea • Transparent, central anterior portion • Allows for light to pass through • Repairs itself easily Why? • The only human tissue that can be transplanted without fear of rejection © 2012 Pearson Education, Inc.

Structure of the Eye: Vascular Layer • 1. Choroid is a blood-rich nutritive layer in the posterior of the eye • Pigment prevents light from scattering • 2. Modified anteriorly into two structures • a. Ciliary body—smooth muscle attached to lens • b. Iris—regulates light entering eye • Pigmented layer that gives eye color • Pupil—rounded opening in the iris © 2012 Pearson Education, Inc.

Structure of the Eye: Sensory Layer • 1. Retina contains two layers: • Outer pigmented layer • Inner neural layer 2. Contains receptor cells (photoreceptors) • Rods • Cones © 2012 Pearson Education, Inc.

1. Do you recognize anything? 2. What do the axons of the ganglion cells form? See next page if needed. Pigmented layer of retina Rod Cone Bipolar cells Ganglion cells © 2012 Pearson Education, Inc. (a) Pathway of light Figure 8. 5 a

Pigmented Neural layer of of retina Central artery and vein of retina Optic disc

Structure of the Eye: Sensory Layer • Neurons of the retina and vision • A. Rods • 1. Most are found towards the edges of the retina • 2. Allow dim light vision and peripheral vision • 3. All perception is in gray tones © 2012 Pearson Education, Inc.

Structure of the Eye: Sensory Layer • Neurons of the retina and vision • B. Cones • 1. Allow for detailed color vision • 2. Densest in the center of the retina • 3. Fovea centralis–lateral to blind spot • Area of the retina with only cones • Visual acuity (sharpest vision) is here • C. No photoreceptor cells are at the optic disc, or blind spot © 2012 Pearson Education, Inc.

Structure of the Eye: Sensory Layer • Cone sensitivity • A. Three types of cones • B. Different cones are sensitive to different wavelengths • C. Color blindness is the result of the lack of one cone type © 2012 Pearson Education, Inc.

Light absorption by cone populations 560 nm (red cones) 530 nm (green cones) 420

Lens • A. Biconvex crystal-like structure • B. Held in place by a suspensory

Ciliary body Ciliary zonule Cornea Iris Pupil Aqueous humor Lens canal of Schlemm Vitreous humor (a) © 2012 Pearson Education, Inc. Sclera Choroid Retina Fovea centralis (macula) Optic nerve Central artery and vein of the retina Optic disc (blind spot) Figure 8. 4 a

Lens- no notes! • 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 © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Figure 8. 7

Two Segments, or Chambers, of the Eye - No Notes • Anterior (aqueous) segment • Anterior to the lens • Contains aqueous humor • Posterior (vitreous) segment • Posterior to the lens • Contains vitreous humor © 2012 Pearson Education, Inc.

Anterior Segment • A. Aqueous humor • 1. Watery fluid found between lens and cornea • 2. Similar to blood plasma • 3. Helps maintain intraocular pressure • 4. Provides nutrients for the lens and cornea • 5. Reabsorbed into venous blood through the scleral venous sinus, or canal of Schlemm © 2012 Pearson Education, Inc.

Posterior Segment • B. Vitreous humor • 1. Gel-like substance posterior to the lens

Macula Fovea centralis Lateral © 2012 Pearson Education, Inc. Blood Optic disc Retina vessels

Pathway of Light Through the Eye • A. Light must be focused to a point on the retina for optimal vision • B. The eye is set for distance vision (over 20 feet away) • C. Accommodation—the lens must change shape to focus on closer objects (less than 20 feet away) © 2012 Pearson Education, Inc.

Retina Light from distant source Focal point (a) Light from near source Focal point

Pathway of Light Through the Eye • D. Image formed on the retina is a real image • E. Real images are: • Reversed from left to right • Upside down • Smaller than the object © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc. Figure 8. 10

Visual Fields and Visual Pathways • A. 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 • B. Optic tracts • Contain fibers from the lateral side of the eye on the same side and the medial side of the opposite eye © 2012 Pearson Education, Inc.

Fixation point Right eye Left eye Optic nerve Optic chiasma Optic tract Optic radiation

Pathway of vision from light entering pupil to occipital lobe of brain…. Light →Cornea→ Aqueous humor → Pupil → Lens → Vitreous Humor → Absorbed by Pigment/Choroid → Retina [Rods/Cones Electrical signal → Bipolar cells → Ganglion cells] →Optic nerve II→ Optic tract **→ Thalamus → Occipital lobe (visual cortex) **Axons from both eyes due to crossing over Slide 8. 28 © 2012 Pearson Education, Inc.

A Closer Look • Emmetropia—eye focuses images correctly on the retina • A. Myopia (nearsighted) • 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 © 2012 Pearson Education, Inc.

A Closer Look • B. Hyperopia (farsighted) • Near objects are blurry while distant objects are clear • Distant objects are focused behind the retina • Results from an eyeball that is too short or from a “lazy lens” © 2012 Pearson Education, Inc.

Focal plane Correction None required Concave lens (a) Emmetropic eye (b) Myopic eye (nearsighted)

A Closer Look • C. Astigmatism • Images are blurry • Results from light

Homeostatic Imbalances of the Eyes • D. Night blindness—inhibited rod function that hinders the ability to see at night • E. 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) • F. Cataracts—when lens becomes hard and opaque, our vision becomes hazy and distorted © 2012 Pearson Education, Inc.

Homeostatic Imbalances of the Eyes • G. Glaucoma—can cause blindness due to increasing pressure within the eye • H. Hemianopia—loss of the same side of the visual field of both eyes; results from damage to the visual cortex on one side only © 2012 Pearson Education, Inc.

The Ear • A. Houses two senses • Hearing • Equilibrium (balance) • B.

Anatomy of the Ear • The ear is divided into three areas • A.

External (outer) ear Middle ear Internal (inner) ear Vestibulocochlear Nerve (auditory) Pinna Semicircular canals Oval window (auricle) Cochlea Vestibule Round window Auditory tube Tympanic membrane Auditory canal © 2012 Pearson Education, Inc. malleus incus stapes Auditory ossicles Figure 8. 12

The External Ear • A. Involved in hearing only • B. Structures of the external ear • 1. Pinna (auricle) • 2. Auditory Canal (External acoustic meatus) • Narrow chamber in the temporal bone • Lined with skin and ceruminous (wax) glands • Ends at the tympanic membrane © 2012 Pearson Education, Inc.

The Middle Ear (Tympanic Cavity) • A. Air-filled cavity within the temporal bone • B. Only involved in the sense of hearing • When does the middle ear fill with fluid? Is that bad or good? ? © 2012 Pearson Education, Inc.

The Middle Ear (Tympanic Cavity) • Two tubes are associated with the middle ear • The opening from the auditory canal is covered by the tympanic membrane • The auditory tube connecting the middle ear with the throat • Allows for equalizing pressure during yawning or swallowing • This tube is otherwise collapsed • Why do pacifier-babies get more ear infections? ? © 2012 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 eardrum move the malleus incus stapes inner ear © 2012 Pearson Education, Inc.

External (outer) ear Middle ear Internal (inner) ear Vestibulocochlear Nerve (auditory) Pinna Semicircular canals Oval window (auricle) Cochlea Vestibule Round window Auditory tube Tympanic membrane Auditory canal © 2012 Pearson Education, Inc. malleus incus stapes Auditory ossicles Figure 8. 12

Inner Ear or Bony Labyrinth • A. Includes sense organs for hearing and balance • B. Filled with perilymph • C. Contains a maze of bony chambers within the temporal bone • Cochlea • Vestibule • Semicircular canals (balance only!) © 2012 Pearson Education, Inc.

External (outer) ear Middle ear Internal (inner) ear Vestibulocochlear Nerve (auditory) Pinna Semicircular canals Oval window (auricle) Cochlea Vestibule Round window Auditory tube Tympanic membrane Auditory canal © 2012 Pearson Education, Inc. malleus incus stapes Auditory ossicles Figure 8. 12

Organs of Hearing • Organ of Corti • A. Located within the cochlea • B. Receptors = hair cells on the basilar membrane • C. Gel-like tectorial membrane is capable of bending hair cells • D. Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe © 2012 Pearson Education, Inc.

Mechanism of Hearing • A. Vibrations from sound waves move tectorial membrane • B. Hair cells are bent by the membrane • C. An action potential starts in the cochlear nerve • Impulse travels to the temporal lobe • D. Continued stimulation can lead to adaptation • Why do you notice a repetitive sound? © 2012 Pearson Education, Inc.

EXTERNAL EAR Auditory canal Eardrum Hammer, Oval anvil, stirrup window INTERNAL EAR Fluids in cochlear canals Upper and middle lower Pressure Pinna MIDDLE EAR One Amplitude vibration © 2012 Pearson Education, Inc. Amplification in middle ear Spiral organ Time of Corti stimulated Figure 8. 16

Spiral organ of Corti Temporal bone Perilymph in scala vestibuli Vestibular membrane Afferent fibers of the cochlear nerve Temporal bone Cochlear duct (contains Perilymph in endolymph) scala tympani (a) © 2012 Pearson Education, Inc. Figure 8. 15 a

Hair (receptor) cells of spiral organ of Corti Basilar membrane Tectorial membrane Supporting cells

Pathway of sound waves from pinna to temporal lobe of brain…. . • pinna → external auditory canal → tympanic membrane vibration → (malleus → incus → stapes) → oval window → fluids of inner ear movement (perilymph) → Organ of Corti (basilar/tectorial membranes → hair cells) → Electrical impulse and neurotransmitter release → auditory nerve (VIII) → temporal lobe © 2012 Pearson Education, Inc. Slide 8. 40

Mechanism of Hearing- No notes! • 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 © 2012 Pearson Education, Inc.

Fibers of Stapes Scala sensory vestibuli neurons Perilymph Oval window Round window Scala Basilar Cochlear tympani membrane duct (a) Fibers of basilar membrane Apex (long, floppy fibers) Base (short, stiff fibers) 20, 000 (High notes) © 2012 Pearson Education, Inc. (b) 2, 000 200 Frequency (Hz) 20 (Low notes) Figure 8. 17

Organs of Equilibrium • A. Equilibrium receptors of the inner ear are called the vestibular apparatus • B. Vestibular apparatus has two functional parts • Static equilibrium • Dynamic equilibrium © 2012 Pearson Education, Inc.

Semicircular canals Ampulla Vestibular nerve Vestibule (a) © 2012 Pearson Education, Inc. Figure 8.

Membranes in vestibule Otoliths Otolithic membrane Hair tuft Hair cell Supporting cell (a) ©

Otolithic membrane Head upright Otoliths Force of gravity Hair cell Head tilted (b) ©

Endolymph Ampulla Flow of endolymph Cupula of crista ampullaris (b) © 2012 Pearson Education,

Chemical Senses: Taste and Smell • A. Both senses use chemoreceptors • 1. Stimulated by chemicals in solution • 2. Taste has five types of receptors • 3. Smell can differentiate a large range of chemicals • B. Both senses complement each other and respond to many of the same stimuli © 2012 Pearson Education, Inc.

Olfaction—The Sense of Smell Receptors: Neurons with long cilia (1000’s) • Chemicals must be dissolved in mucus for detection • Location: Olfactory receptors are in the roof of the nasal cavity • Impulses are transmitted via the olfactory nerve (I) • Interpretation of smells is made in the olfactory cortex (tied to limbic system) © 2012 Pearson Education, Inc.

Olfactory bulb Cribriform plate of ethmoid bone Olfactory tract Olfactory filaments of the olfactory nerve Supporting cell Olfactory receptor cell Olfactory mucosa (a) Mucus layer Route of inhaled air containing odor molecules Olfactory hairs (cilia) (b) © 2012 Pearson Education, Inc. Figure 8. 18

The Sense of Taste • Receptors: Taste buds- Only 4 types (gustatory cells with long microvillisubstances must be dissolved) • Location of taste buds • Most are on the tongue • Soft palate • Cheeks © 2012 Pearson Education, Inc.

Epiglottis Palatine tonsil Lingual tonsil Fungiform papillae (a) © 2012 Pearson Education, Inc. Figure

Circumvallate papilla Taste buds © 2012 Pearson Education, Inc. (b) Figure 8. 19 b

Structure of Taste Buds • Nerves (different places = different nerves) • Facial nerve • Glossopharyngeal nerve • Vagus nerve • Brain Area- gustatory cortex (insular/frontal lobes) © 2012 Pearson Education, Inc.

Taste Sensations • Sweet receptors (sugars) • Saccharine • Some amino acids • Sour receptors • Acids • Bitter receptors Umami- Glutamate • Alkaloids • Salty receptors **No “spicy” sense • Metal ions © 2012 Pearson Education, Inc.

Developmental Aspects of the Special Senses • A. Formed early in embryonic development • B. Eyes are outgrowths of the brain • C. All special senses are functional at birth © 2012 Pearson Education, Inc.

Developmental Aspects of the Special Senses • Eye problems • A. Strabismus—“crossed eyes” results from unequal pulls by the external eye muscles in babies • B. Ophthalmia neonatorum—conjunctivitis resulting from mother having gonorrhea. Baby’s eyelids are swollen and pus is produced © 2012 Pearson Education, Inc.