AP II

•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

ciliary body

-Anteriorly, choroid becomes ciliary body -Thickened ring of tissue surrounding lens -Consists of smooth muscle bundles, ciliary muscles, that control shape of lens -Capillaries of ciliary processes secrete fluid for anterior segment of eyeball -Ciliary zonule (suspensory ligament) extends from ciliary processes to lens •Holds lens in position

lens

-Biconvex, transparent, flexible, and avascular -Changes shape to precisely focus light on retina

Iris

-Colored part of eye that lies between cornea and lens, continuous with ciliary body

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 secretion (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

Refraction and lenses (cont.)

-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

•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

eyelids contain

-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

Focusing Light on the Retina (cont)

-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 muscles are completely relaxed in distance vision, which causes a pull on ciliary zonule; as a result, lenses are stretched flat

Structure of the eyeball (3 layers)

-Fibrous layer -Vascular layer -Inner layer Internal cavity filled with fluids called humors Lens separates internal cavity into anterior and posterior segments.

Wavelength and color (cont.)

-Light: packets of energy (photons or quanta) that travel in wavelike fashion at high speeds -When visible light passes through spectrum, 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

vascular layer

-Middle pigmented layer of eye, also called uvea -Three regions: choroid, ciliary body, and iris

•Fibrous layer

-Outermost layer; dense avascular connective tissue -Two regions: sclera and cornea

•Eyebrows

-Overlie supraorbital margins -Function Shade eye from sunlight Prevent perspiration from reaching eye

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

Refraction and lenses

-Refraction: bending of light rays §Due to change in speed of light when it passes from one transparent medium to another and path of light is at 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

Optic disc

-Site where optic nerve leaves eye -Lacks photoreceptors, so referred to as blind spot

•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

•Internal chambers and fluids

-The lens and ciliary zonule separate eye into two segments 1. Posterior segment 2. Anterior segment

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

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

Special senses of body include

-Vision -Taste -Smell -Hearing -Equilibrium

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

Sound is generally perceived in the occipital lobe of the cerebral cortex.

False

The structure that allows equalization of the pressure in the middle ear with that outside the body is the external auditory meatus.

False

-Anterior segment

Iris divides anterior segment into two chambers: -Anterior chamber—between cornea and iris -Posterior chamber—between iris and lens

Which statement about sound localization is not true?

It requires processing at the cortical level.

Select one of the following that best describes the effect of breathing deeply and slowly to recognize a scent.

More air containing the odor is brought into contact with the olfactory epithelium.

Which of the following is true about photoreceptors?

Rods absorb light throughout the visual spectrum but confer only gray tone vision.

How do rods and cones differ functionally?

Rods operate mostly in dim light and provide noncolor vision with relatively low acuity. Cones provide high-acuity color vision in bright light. For other differences between rods and cones

Name the cranial nerves that serve the sense of taste.

Taste is served by cranial nerves VII (facial), IX (glossopharyngeal), and X (vagus)

Focusing for Distant and Close Vision

The ciliary muscle and the ciliary zonule focus an image by changing the shape of the lens. *They are arranged sphincterlike around the lens *Ciliary muscle contraction loosens the ciliary zonule fibers and relaxation tightens them

Which of the following is not a characteristic of olfactory receptor cells?

They are unipolar neurons.

In order for sound to reach the spiral organ (of Corti), the auditory ossicles must vibrate the oval window and set the endolymph in motion.

True

Light passes through the entire thickness of the neural layer of the retina to excite the photoreceptors.

True

The extrinsic eye muscle motor units contain only 8 to 12 muscle cells and in some cases as few as 2 or 3 muscle cells.

True

The function of the lens of the eye is to allow precise focusing of light on the retina.

True

When we move from darkness to bright light, retinal sensitivity is lost, but visual acuity is gained.

True

Blockage of the scleral venous sinus might result in (a) a sty, (b) glaucoma, (c) conjunctivitis, (d) a cataract.

a

Nearsightedness is more properly called (a) myopia, (b) hyperopia, (c) presbyopia, (d) emmetropia.

a

Which sequence best describes a normal route for the flow of tears from the eyes into the nasal cavity? (a) lacrimal canaliculi, lacrimal sacs, nasolacrimal ducts; (b) lacrimal ducts, lacrimal canaliculi, nasolacrimal ducts; (c) nasolacrimal ducts, lacrimal canaliculi, lacrimal sacs.

a

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

Of the neurons in the retina, the axons of which of these form the optic nerve? (a) bipolar cells, (b) ganglion cells, (c) cone cells, (d) horizontal cells.

b

Olfactory nerve filaments are found (a) in the optic bulbs, (b) passing through the cribriform plate of the ethmoid bone, (c) in the optic tracts, (d) in the olfactory cortex.

b

Pitch is to frequency of sound as loudness is to (a) quality, (b) intensity, (c) overtones, (d) all of these.

b

The structure that allows pressure in the middle ear to be equalized with atmospheric pressure is the (a) pinna, (b) pharyngotympanic tube, (c) tympanic membrane, (d) oval window.

b

Which reactions occur when a person looks at a distant object? (a) pupils constrict, ciliary zonule (suspensory ligament) relaxes, lenses become less convex; (b) pupils dilate, ciliary zonule becomes taut, lenses become less convex; (c) pupils dilate, ciliary zonule becomes taut, lenses become more convex; (d) pupils constrict, ciliary zonule relaxes, lenses become more convex.

b

The ciliary body does not:

belong to the anterior chamber of the eye.

Information from balance receptors goes directly to the:

brain stem reflex centers.

Accessory glands that produce an oily secretion are the (a) conjunctiva, (b) lacrimal glands, (c) tarsal glands.

c

Otoliths (ear stones) are (a) a cause of deafness, (b) a type of hearing aid, (c) important in equilibrium, (d) the rock-hard petrous part of the temporal bones.

c

The phenomenon of dark adaptation is best explained by the fact that (a) rhodopsin does not function in dim light, (b) rhodopsin breakdown occurs slowly, (c) rods exposed to intense light need time to generate rhodopsin, (d) cones are stimulated to function by bright light.

c

The transmission of sound vibrations through the internal ear occurs chiefly through a) nerve fibers, (b) air, (c) fluid, (d) bone.

c

Which of the following is not a possible cause of conduction deafness? (a) impacted cerumen, (b) middle ear infection, (c) cochlear nerve degeneration, (d) otosclerosis.

c

Receptors for hearing are located in the

cochlea.

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

retinal detachment

condition where pigmented and neural layers separate (detach), allowing jellylike vitreous humor to seep between them •Can lead to permanent blindness •Usually happens when retina is torn during traumatic blow to head or sudden stopping of head during movement (example: bungee jumping) •Symptom described by victims as "curtain being drawn across the eye" and/or sootlike spots or light flashes

The mucous membrane that lines the eyelids and is reflected over the anterior surface of the eyeball is the ___________.

conjunctiva

Nasal cavity mucosa

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

Taste buds are found on the (a) anterior part of the tongue, (b) posterior part of the tongue, (c) palate, (d) all of these.

d

The blind spot of the eye is (a) where more rods than cones are found, (b) where the macula lutea is located, (c) where only cones occur, (d) where the optic nerve leaves the eye.

d

The portion of the fibrous layer that is white and opaque is the (a) choroid, (b) cornea, (c) retina, (d) sclera.

d

Which of the following statements does not correctly describe the spiral organ? (a) Sounds of high frequency stimulate hair cells at the basal end, (b) the "hairs" of the receptor cells are embedded in the tectorial membrane, (c) the basilar membrane acts as a resonator, (d) the more numerous outer hair cells are largely responsible for our perception of sound.

d

One complication from having only one eye would be

depth perception.

Fibers of the olfactory nerve project through the cribriform plate of the _____ bone.

ethmoid

vitreous humor

forms in embryo and lasts whole lifetime

Give the correct term for someone that can see at far distance but not close up.

hyperopia

Conjunctivitis

inflammation of the conjunctiva resulting in reddened, irritated eyes

Dark adaptation:

involves accumulation of rhodopsin.

Chalazion

obstructed tarsal glands that may result in a firm, usually painless bump

Diplopia (double vision)

occurs when movements 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

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 Retina has quarter-billion photoreceptors that are one of two types: -Rods -Cones

Sty

painful inflammation of any of the sebaceous glands at the base of an eyelash

The bending of light rays is called

refraction.

Olfactory cells and taste buds are normally stimulated by:

substances in solution.

The eye muscle that elevates the eye is the:

superior rectus.

The lateral wall of the middle ear is formed primarily by the _______bone.

temporal

The blind spot of the eye is:

where the optic nerve leaves the eye.

Sclera

white of the eye -Opaque posterior region -Protects and shapes eyeball -Anchors extrinsic eye muscles -Posteriorly, where optic nerve exits, sclera is continuous with dura mater of brain

blood supply to retina

§Central artery and vein of retina supply inner two-thirds -Enter/exit eye in center of optic nerve -Vessels are visible in living person

-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

-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

Lens 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

-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

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

Eye and Vision

•70% of body's sensory receptors are in eye •Half of cerebral cortex is involved in visual processing

Accessory Structures of the Eye (1 of 8)

•Accessory structures protect the eye and aid eye function •Structures include: -Eyebrows -Eyelids -Conjunctiva -Lacrimal apparatus -Extrinsic eye muscles

Focusing Light on the Retina

•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 -Can focus for distant vision and for close vision

The eye

•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

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

Pinkeye

•conjunctival infection caused by bacteria or viruses -Highly contagious