Marieb Human Anatomy & Physiology Twelfth Edition Chapter 15 PDF

Marieb Human Anatomy & Physiology Twelfth Edition Chapter 15 The Special Senses PowerPoint® Lecture Slides prepared by Ashley Spring, Ph.D.,...

Marieb Human Anatomy & Physiology Twelfth Edition Chapter 15 The Special Senses PowerPoint® Lecture Slides prepared by Ashley Spring, Ph.D., Eastern Florida State College Copyright © 2025 Pearson Education, Inc. All Rights Reserved Why This Matters Understanding the anatomy and physiology of the eye helps to identify diseases such as glaucoma Copyright © 2025 Pearson Education, Inc. All Rights Reserved Video: Why This Matters (Career Connection) Click here to view ADA compliant video: Why This Matters (Career Connection) https://mediaplayer.pearsoncmg.com/assets/secs_wtm_ch_15_peter_v2 Copyright © 2025 Pearson Education, Inc. All Rights Reserved Special Senses (1 of 2) The sense of touch is one of the general senses, mediated by general receptors (covered in Chapter 13) Special senses of body include: – Vision – Taste – Smell – Hearing – Equilibrium Copyright © 2025 Pearson Education, Inc. All Rights Reserved Special Senses (2 of 2) All use special sensory receptors, which are distinct receptor cells localized in head region – Not like modified nerves of general receptors Copyright © 2025 Pearson Education, Inc. All Rights Reserved Part 1—The Eye and Vision 70% of body’s sensory receptors are in eye Nearly half of cerebral cortex is involved in visual processing Copyright © 2025 Pearson Education, Inc. All Rights Reserved 15.1 The Eye Eye has three layers, a lens, and humors, and is surrounded by accessory structures Small sphere; only one-sixth of surface visible Most of eye enclosed and protected by fat cushion and bony orbit Consists of accessory structures and the eyeball Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Eye and Accessory Structures (1 of 2) Figure 15.1a The eye and accessory structures. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Accessory Structures of the Eye (1 of 7) Accessory structures protect the eye and aid eye function – Eyebrows – Eyelids – Conjunctiva – Lacrimal apparatus – Extrinsic eye muscles Copyright © 2025 Pearson Education, Inc. All Rights Reserved Accessory Structures of the Eye (2 of 7) Eyebrows – Overlie supraorbital margins – Function ▪ Shade eye from sunlight ▪ Prevent perspiration from reaching eye Copyright © 2025 Pearson Education, Inc. All Rights Reserved Accessory Structures of the Eye (3 of 7) Eyelids – Also called palpebrae; thin, skin-covered folds that protect eye anteriorly – Separated at palpebral fissure (slit) – Meet in corners at medial and lateral commissures – Lacrimal caruncle located at medial commissure contains oil and sweat glands – Tarsal plates: supporting connective tissue for folds, as well as anchor orbicularis oculi and levator palpebrae superioris muscles Copyright © 2025 Pearson Education, Inc. All Rights Reserved Accessory Structures of the Eye (4 of 7) Eyelids (cont ) inued – Eyelids blink reflexively every 3–7 seconds ▪ Offers protection from foreign objects and spreads secretions to moisten eye – Eyelashes have follicles that are innervated ▪ Nerve endings initiate reflex blinking – Lubricating glands associated with eyelids ▪ Tarsal (Meibomian) glands – Modified sebaceous glands produce oily secretion that lubricates lid and eye ▪ Ciliary glands between hair follicles are – Modified sweat glands Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Eye and Accessory Structures (2 of 2) Figure 15.1b The eye and accessory structures. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Accessory Structures of the Eye (5 of 7) Conjunctiva – Transparent mucous membrane that produces a lubricating mucous secretion – Palpebral conjunctiva: membrane that lines underside of eyelids – Bulbar conjunctiva: membrane that covers white of eyes (not cornea) ▪ Small blood vessels found in this membrane; seen easily in “bloodshot” eyes – Conjunctival sac: space between palpebral and bulbar conjunctiva ▪ Area where contact lens rests Copyright © 2025 Pearson Education, Inc. All Rights Reserved Accessory Structures of the Eye (6 of 7) Lacrimal apparatus – Consists of lacrimal gland and ducts that drain into nasal cavity – Lacrimal gland is located in orbit above lateral end of eye and secretes lacrimal fluid (tears), a dilute saline solution containing mucus, antibodies, and antibacterial lysozyme – Blinking spreads tears toward medial commissure, where they enter paired lacrimal canaliculi via lacrimal puncta – Tears then drain into lacrimal sac and nasolacrimal duct, which empties into nasal cavity Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Lacrimal Apparatus Figure 15.2 The lacrimal apparatus. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Accessory Structures of the Eye (7 of 7) Extrinsic eye muscles – Six straplike extrinsic eye muscles ▪ Originate from bony orbit and insert on eyeball ▪ Enable eye to follow moving objects, maintain shape of eyeball, and hold it in orbit – Four rectus muscles originate from common tendinous ring; names indicate movements ▪ Superior, inferior, lateral, and medial rectus – Two oblique muscles move eye in vertical plane and rotate eyeball ▪ Superior and inferior oblique muscles Copyright © 2025 Pearson Education, Inc. All Rights Reserved Extrinsic Eye Muscles (1 of 4) Figure 15.3a Extrinsic eye muscles. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Extrinsic Eye Muscles (2 of 4) Figure 15.3b Extrinsic eye muscles. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Extrinsic Eye Muscles (3 of 4) Figure 15.3c Extrinsic eye muscles. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Extrinsic Eye Muscles (4 of 4) Figure 15.3d Extrinsic eye muscles. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 15.1 Chalazion: obstructed tarsal glands that may result in a firm, usually painless bump Sty: painful inflammation of any of the sebaceous glands at the base of an eyelash Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 15.2 Conjunctivitis: inflammation of the conjunctiva resulting in reddened, irritated eyes Pinkeye: conjunctival infection caused by bacteria or viruses – Highly contagious Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 15.3 The nasal cavity mucosa is continuous with mucosa of lacrimal duct system, so a cold or nasal inflammation often causes lacrimal mucosa to swell Swelling constricts the ducts and prevents tears from draining, causing “watery” eyes Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 15.4 Diplopia (double vision): occurs when movements of external muscles of two eyes are not perfectly coordinated – Person cannot properly focus images of same area of the visual field from each eye, so sees two images instead of one – Can result from paralysis, extrinsic muscle weakness, or neurological disorders Strabismus (“cross-eye”): congenital weakness of external eye muscles – Eye rotates medially or laterally – Eyes may alternate focusing on objects, or only controllable eye is used ▪ Brain begins to disregard inputs from deviant eye, which can become functionally blind if not treated early Copyright © 2025 Pearson Education, Inc. All Rights Reserved Structure of the Eyeball Wall of eyeball contains three layers – Fibrous layer – Vascular layer – Inner layer Internal cavity filled with fluids called humors Lens separates internal cavity into anterior and posterior segments Copyright © 2025 Pearson Education, Inc. All Rights Reserved Internal Structure of the Eye (Sagittal Section) (1 of 3) Figure 15.4a Internal structure of the eye (sagittal section). Copyright © 2025 Pearson Education, Inc. All Rights Reserved Eyeball: Fibrous Layer (1 of 2) Fibrous layer – Outermost layer; dense avascular connective tissue – Two regions: sclera and cornea ▪ Sclera – Opaque posterior region – Protects and shapes eyeball – Anchors extrinsic eye muscles – Posteriorly, where optic nerve exits, sclera is continuous with dura mater of brain Copyright © 2025 Pearson Education, Inc. All Rights Reserved Eyeball: Fibrous Layer (2 of 2) Fibrous layer (cont ) inued ▪ Cornea – Transparent anterior one-sixth of fibrous layer Forms clear window that lets light enter and bends light as it enters eye – Epithelium covers both surfaces Outer surface protects from abrasions Inner layer, corneal endothelium, contains sodium pumps that help maintain clarity of cornea – Numerous pain receptors contribute to blinking and tearing reflexes Copyright © 2025 Pearson Education, Inc. All Rights Reserved Eyeball: Vascular Layer (1 of 3) Vascular layer – Middle pigmented layer of eye, also called uvea – Three regions: choroid, ciliary body, and iris ▪ Choroid region – Posterior portion of uvea – Supplies blood to all layers of eyeball – Brown pigment absorbs light to prevent scattering of light, which would cause visual confusion Copyright © 2025 Pearson Education, Inc. All Rights Reserved Eyeball: Vascular Layer (2 of 3) Vascular layer (cont ) inued ▪ Ciliary body – Anteriorly, choroid becomes ciliary body – Thickened ring of tissue surrounding lens – Ciliary muscle is smooth muscle bundles that control shape of lens Ciliary zonule (suspensory ligament) extends from ciliary muscle to lens Encircles lens and holds lens in position – Ciliary processes are radiating folds on the posterior surface of ciliary body secrete fluid for anterior segment of eyeball Copyright © 2025 Pearson Education, Inc. All Rights Reserved Eyeball: Vascular Layer (3 of 3) Vascular layer (cont ) inued ▪ Iris – Colored part of eye that lies between cornea and lens, continuous with ciliary body – Pupil: central opening that regulates amount of light entering eye Close vision and bright light cause sphincter pupillae (circular muscles) to contract and pupils to constrict; parasympathetic control Distant vision and dim light cause dilator pupillae (radial muscles) to contract and pupils to dilate; sympathetic control Changes in emotional state—pupils dilate when subject matter is appealing or requires problem-solving skills Copyright © 2025 Pearson Education, Inc. All Rights Reserved Internal Structure of the Eye (Sagittal Section) (2 of 3) Figure 15.4a Internal structure of the eye (sagittal section). Copyright © 2025 Pearson Education, Inc. All Rights Reserved Internal Structure of the Eye (Sagittal Section) (3 of 3) Figure 15.4b Internal structure of the eye (sagittal section). Copyright © 2025 Pearson Education, Inc. All Rights Reserved Pupil Constriction and Dilation Figure 15.5 Pupil constriction and dilation. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Eyeball: Inner Layer (1 of 7) Inner layer (retina) – Retina originates as an outpocketing of brain – Contains: ▪ Millions of photoreceptor cells that transduce light energy ▪ Neurons ▪ Glial cells – Delicate two-layered membrane ▪ Outer pigmented layer ▪ Inner neural layer Copyright © 2025 Pearson Education, Inc. All Rights Reserved Microscopic Anatomy of the Retina (1 of 4) Figure 15.6a Microscopic anatomy of the retina. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Eyeball: Inner Layer (2 of 7) Inner layer (retina) (cont ) inued – Pigmented layer of the retina ▪ Single-cell-thick lining next to choroid ▪ Extends anteriorly, covering ciliary body and iris ▪ Functions: – Absorbs light and prevents its scattering – Phagocytizes photoreceptor cell fragments – Stores vitamin A Copyright © 2025 Pearson Education, Inc. All Rights Reserved Eyeball: Inner Layer (3 of 7) Inner layer (retina) (cont ) inued – Neural layer of the retina ▪ Transparent layer that runs anteriorly to margin of ciliary body – Anterior end has serrated edges called ora serrata ▪ Composed of three main types of neurons – Photoreceptors, bipolar cells, ganglion cells ▪ Signals spread from photoreceptors to bipolar cells to ganglion cells ▪ Ganglion cell axons exit eye as optic nerve Copyright © 2025 Pearson Education, Inc. All Rights Reserved Eyeball: Inner Layer (4 of 7) Inner layer (retina) (cont ) inued – Neural layer of the retina (cont ) i nued ▪ Optic disc – Site where optic nerve leaves eye – Lacks photoreceptors, so referred to as blind spot ▪ Retina has quarter-billion photoreceptors that are one of two types: – Rods – Cones Copyright © 2025 Pearson Education, Inc. All Rights Reserved Microscopic Anatomy of the Retina (2 of 4) Figure 15.6a Microscopic anatomy of the retina. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Eyeball: Inner Layer (5 of 7) Inner layer (retina) (cont ) inued – Rods ▪ Dim light, peripheral vision receptors ▪ More numerous and more sensitive to light than cones ▪ No color vision or sharp images ▪ Numbers greatest at periphery Copyright © 2025 Pearson Education, Inc. All Rights Reserved Eyeball: Inner Layer (6 of 7) Inner layer (retina) (cont ) inued – Cones ▪ Vision receptors for bright light ▪ High-resolution color vision ▪ Macula lutea area at posterior pole lateral to blind spot – Contains mostly cones ▪ Fovea centralis: tiny pit in center of macula lutea that contains all cones, so is region with best visual acuity – Eye movement allows us to focus in on object so that fovea can pick it up Copyright © 2025 Pearson Education, Inc. All Rights Reserved Microscopic Anatomy of the Retina (3 of 4) Figure 15.6b Microscopic anatomy of the retina. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Microscopic Anatomy of the Retina (4 of 4) Figure 15.6c Microscopic anatomy of the retina. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Eyeball: Inner Layer (7 of 7) Inner layer (retina) (cont ) inued – Two sources of blood supply to retina ▪ Choroid supplies outer third (photoreceptors) ▪ Central artery and vein of retina supply inner two- thirds – Enter/exit eye in center of optic nerve – Vessels are visible in living person Copyright © 2025 Pearson Education, Inc. All Rights Reserved Part of the Posterior Wall (Fundus) of the Right Eye as Seen With an Ophthalmoscope Figure 15.7 Part of the posterior wall (fundus) of the right eye as seen with an ophthalmoscope. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 15.5 Retinal detachment: condition where pigmented and neural layers separate (detach), allowing jellylike vitreous humor to seep between them Can lead to permanent blindness because deprives photoreceptors of nutrients Usually happens when retina is torn during traumatic blow to head or sudden stopping of head during movement (e.g., bungee jumping) Symptom described by victims as “curtain being drawn across the eye” and/or sootlike spots or light flashes Treatment: reattachment of retina with laser surgery Copyright © 2025 Pearson Education, Inc. All Rights Reserved Eyeball: Internal Chambers and Fluids (1 of 3) Internal chambers and fluids – The lens and ciliary zonule separate eye into two segments 1. Posterior segment 2. Anterior segment Copyright © 2025 Pearson Education, Inc. All Rights Reserved Eyeball: Internal Chambers and Fluids (2 of 3) Internal chambers and fluids (cont ) inued – Posterior segment ▪ Contains vitreous humor, a fluid that: – Transmits light – Supports posterior surface of lens – Holds neural layer of retina firmly against pigmented layer – Contributes to intraocular pressure ▪ Vitreous humor forms in embryo and lasts whole lifetime Copyright © 2025 Pearson Education, Inc. All Rights Reserved Eyeball: Internal Chambers and Fluids (3 of 3) Internal chambers and fluids (cont ) inued – Anterior segment ▪ Iris divides anterior segment into two chambers: – Anterior chamber—between cornea and iris – Posterior chamber—between iris and lens ▪ Entire segment contains aqueous humor, a plasma like fluid continuously formed (unlike vitreous humor) by capillaries of ciliary processes – Drains via scleral venous sinus (canal of Schlemm) at sclera-cornea junction – Supplies nutrients and oxygen mainly to lens and cornea but also to retina, and removes wastes Copyright © 2025 Pearson Education, Inc. All Rights Reserved Circulation of Aqueous Humor (1 of 3) Figure 15.8 Circulation of aqueous humor. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Circulation of Aqueous Humor (2 of 3) Figure 15.8 Circulation of aqueous humor. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Circulation of Aqueous Humor (3 of 3) Figure 15.8 Circulation of aqueous humor. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 15.6 Glaucoma: condition in which drainage of aqueous humor is blocked, causing fluid to back up and increase pressure within eye Pressures may increase to dangerous levels and compress retina and optic nerve, leading to blindness Symptoms: few early signs, but late signs include seeing halos around lights and blurred vision Detection: intraocular pressure determined by directing puff of air at cornea and measuring amount of corneal deformation – Test should be done yearly after age 40 Treatment: eye drops that increase rate of aqueous humor drainage or decrease its production; laser therapy or surgery Copyright © 2025 Pearson Education, Inc. All Rights Reserved Eyeball: Lens Lens – Biconvex, transparent, flexible, and avascular – Changes shape to precisely focus light on retina – Two regions: ▪ Lens epithelium: anterior region of cuboidal cells that differentiate into lens fiber cells ▪ Lens fibers: form bulk of lens and are filled with transparent protein crystallin – Lens fibers are continually added, so lens becomes more dense, convex, and less elastic with age Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 15.7 Clouding of lens – Consequence of aging, diabetes mellitus, heavy smoking, frequent exposure to intense sunlight – Some congenital – Crystallin proteins clump – Vitamin C increases cataract formation – Lens can be replaced surgically with artificial lens Copyright © 2025 Pearson Education, Inc. All Rights Reserved Photograph of a Cataract Figure 15.9 Photograph of a cataract. Copyright © 2025 Pearson Education, Inc. All Rights Reserved 15.2 Cornea and Lens Focus Light on the Retina Wavelength and color – Electromagnetic radiation: all energy waves, from long radio waves to short X rays; visible light occupies a small portion in the middle of the spectrum ▪ Light has wavelengths between 400 and 700 nm – Eyes respond only to visible light Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Electromagnetic Spectrum and Photoreceptor Sensitivities (1 of 2) Figure 15.10a The electromagnetic spectrum and photoreceptor sensitivities. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Overview: Light and Optics (1 of 3) Wavelength and color (cont ) i nued – Light: packets of energy (photons or quanta) that travel in wavelike fashion at high speeds – When visible light passes through prism, it is broken up into bands of colors (rainbow) ▪ Red wavelengths are longest and have lowest energy, and violet are shortest and have most energy – Color that eye perceives is a reflection of that wavelength ▪ Grass is green because it absorbs all colors except green ▪ White reflects all colors, and black absorbs all colors Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Electromagnetic Spectrum and Photoreceptor Sensitivities (2 of 2) Figure 15.10b The electromagnetic spectrum and photoreceptor sensitivities. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Overview: Light and Optics (2 of 3) Refraction and lenses – Refraction: bending of light rays ▪ Caused by change in speed of light when light passes from one transparent medium to another, angling path of light to an oblique angle – Example: from liquid to air ▪ Lenses of eyes can also refract light because they are curved on both sides – Convex: thicker in center than at edges – Concave: thicker at edges than in center Copyright © 2025 Pearson Education, Inc. All Rights Reserved Refraction Figure 15.11 Refraction. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Overview: Light and Optics (3 of 3) Refraction and lenses (cont ) inued – Convex lenses bend light passing through it, so that rays converge at focal point ▪ Image formed at focal point is upside-down and reversed from left to right – Concave lenses disperse light, preventing light from being focused Copyright © 2025 Pearson Education, Inc. All Rights Reserved Light Is Focused by a Convex Lens Figure 15.12 Light is focused by a convex lens. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Focusing Light on the Retina (1 of 5) Pathway of light entering eye: cornea, aqueous humor, lens, vitreous humor, entire neural layer of retina, and finally photoreceptors Light is refracted three times along path: (1) entering cornea, (2) entering lens, and (3) leaving lens Majority of refractory power is in cornea; however, it is constant and cannot change focus Copyright © 2025 Pearson Education, Inc. All Rights Reserved Focusing Light on the Retina (2 of 5) Lens is able to adjust its curvature to allow for fine focusing – Can focus for distant vision and for close vision Copyright © 2025 Pearson Education, Inc. All Rights Reserved Focusing for Distant and Close Vision (1 of 3) Figure 15.13a Focusing for distant and close vision. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Focusing Light on the Retina (3 of 5) Focusing for distant vision – Eyes are best adapted for distant vision – Far point of vision: distance beyond which no change in lens shape is needed for focusing ▪ 20 feet for emmetropic (normal) eye ▪ Cornea and lens focus light precisely on retina at this distance – Ciliary muscle is relaxed in distance vision, which causes a pull on ciliary zonule; as a result, lenses are stretched flat Copyright © 2025 Pearson Education, Inc. All Rights Reserved Focusing for Distant and Close Vision (2 of 3) Figure 15.13b Focusing for distant and close vision. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Focusing Light on the Retina (4 of 5) Focusing for close vision – Light from close objects (