A&P Chapter 15

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Describe the structure and functions of eyebrows, eyelids, conjunctiva, and lacrimal apparatus.

Eyebrows - short, coarse hairs that overlie the supraorbital margins of the skull
shade eye from sunlight
prevent perspiration from reaching eye

Palpebrae (eyelids) - thin, mobile, skin-covered folds
Function-protect eyes anteriorly
eyelashes - project from free margin of each eyelid
initiate reflex blinking
palpebral fissure - slit between eyelids
medial & lateral commissures -angles of the eye
lacrimal caruncle - fleshy elevation containing glands that secrete a whitish, oily secretion, fancifully called Sandman’s eye-sand
tarsal plate - connective tissue sheet that supports eyelid lubricating glands
tarsal glands - modified sebaceous glands; oily secretion keeps eyelids from sticking together
sebaceous glands - more typical oil glands; arise from eyelash follicles
ciliary glands - modified sweat glands; lie between eyelash follicles
levator palpebrae superioris -muscle that raises upper eyelid

Conjunctiva - transparent mucous membrane covering the anterior surface of eye & lining the eyelids; covers only the “whites of eyes”, not the cornea
produces a lubricating mucus that prevents eye from drying out
conjunctivitis - inflammation of the conjunctiva

Lacrimal apparatus - the lacrimal glands & the ducts that drain lacrimal secretions into the nasal cavity
lacrimal glands - located in the orbits above the lateral ends of the eyes; secrete lacrimal secretions
lacrimal secretions (tears) - dilute saline solution containing mucus, antibodies, & lysozyme (enzyme that destroys bacteria)clean & protect eye surface moistens & lubricate eyes
excretory ducts - carry tears from lacrimal glands to eyes tears drain from eyes into the lacrimal sacs then nasolacrimal ducts which empty into the nasal cavity


Describe the 6 extrinsic eye muscles.

Extrinsic eye muscles - six strap-like muscles controlling eye movements & maintaining eyeball shape
originate from bony orbit & insert into outer surface of eye
four rectus muscles (lateral, medial, superior, inferior) - originate from common tendinous ring
two oblique muscles (superior, inferior) - move eye in vertical plane when eye is turned medially by the rectus muscles


List the 3 layers of the eye (most superficial to deepest or deepest to most superficial).

fibrous layer
vascular layer
inner layer (retina)


Describe the fibrous layer of the eye & its structures (sclera, cornea).

Fibrous layer - outermost coat of eye composed of dense avascular connective tissue; two regions

sclera - posterior, glistening white, opaque region
protects & shapes eye anchoring site for extrinsic muscles accommodates optic nerve posteriorly

cornea - anterior, clear region; bulges anteriorly
lets light enter eye; major part of light-bending apparatus epithelial cells continually renew the cornea
extraordinary capacity for generation & repair avascular


Describe the vascular layer of the eye & its structures (choroid, ciliary body, iris, pupil).

Vascular layer (uvea) - pigmented middle layer of eyeball; three regions

choroid - blood vessel-rich, dark brown membrane forming posterior 5/6 of the vascular layer
its blood vessels supply nutrients to all eye layers
melanocytes produce brown pigment helps absorb light

ciliary body - thickened ring of tissue that encircles lens
ciliary muscles - smooth muscle bundles that control lens shape
ciliary zonule (suspensory ligament) - fine fibers that hold lens in place
iris - visible, colored part of eye lying between cornea & lens
two smooth muscle layers; one constricts pupil, the other dilates
pupil - round central opening of iris; regulates amount of light that enters eye
pupils constrict - close vision & bright light
pupils dilate - distant vision, dim light, changes in emotional state
eye color - determined by amount of brown pigment in iris
large amount of pigment - brown or black iris
small amount of pigment - blue, green, or gray iris


Describe the inner layer (retina) of the eye & its structures (pigmented layer, neural layer).

Inner layer (retina) - delicate membrane forming innermost layer; two layers
pigmented layer of the retina - outer layer; pigment cells absorb light & prevent it from scattering, phagocytize fragments of photoreceptors, and store vitamin A
neural layer of the retina - transparent inner layer that contains 3 types of neurons
photoreceptors - sensory neurons that convert light energy
bipolar cells - bipolar neurons; carry signals to ganglion cells
ganglion cells - generate AP’s


Describe the 3 types of neurons in the neural layer.

photoreceptors - sensory neurons that convert light energy
bipolar cells - bipolar neurons; carry signals to ganglion cells
ganglion cells - generate AP’s


Describe the 2 types of photoreceptors.

Rods (purple) - respond to dim light
used for peripheral vision
more numerous
more sensitive to light

Cones (yellow) - respond to bright light
high-resolution color vision
macula lutea - oval region at posterior pole; contains mostly cones
fovea centralis - minute central pit in macula lutea; contains only cones


Explain how blood is supplied to the neural retina.



Compare and contrast aqueous humor and vitreous humor.

anterior segment - in front of the lens
contains aqueous humor (clear, plasma-like fluid) which is continually flowing; supplies nutrients & carries away wastes
subdivided by iris into 2 chambers
anterior chamber - between cornea & iris
posterior chamber - between iris & lens

posterior segment - behind the lens
filled with vitreous humor(clear gel)
transmits light supports lens holds neural layer of retina against pigmented layer
contributes to intraocular pressure


Describe the structure and function of the lens. Explain the effects of aging on the lens.

Lens - biconvex, transparent, flexible, avascular structure that can change shape to allow precisely focus light on the retina

lens fibers - form bulk of lens; cells filled with a transparent protein called crystallin; lens fibers are continually added

Aging effects
lens becomes more compact, denser, & less elastic
presbyopia - lens loses flexibility; impairs ability to focus light properly
cataract - clouding of lens


Define the terms electromagnetic radiation, visible spectrum, refraction, convex lens, and concave lens.

Electromagnetic radiation - emitted wave packets of energy from short gamma rays to long radio waves

Visible spectrum - part of spectrum human eyes can respond to; 400-700 nm
different retinal cones respond to different wavelengths of visible spectrum
420 nm (blue),, 530 nm (green), 560 nm (red)
white light refracted in a prism reveals color components
objects have color because they absorb some wavelengths & reflect others
we see reflected light

Refraction - light passing from one transparent medium to another of different optical density has a change in speed & refracts (bends); faster in less dense medium

Lens - transparent object curved on one or both surfaces
convex lens - thickest in center; light rays bend so they converge (come together) at focal point
concave lens - thicker at the edges; light rays diverge (spread apart)


Explain how light refracts as it passes through the eye.

light passes sequentially through the cornea, aqueous humor, lens, vitreous humor, & entire neural layer of the retina
light is bent 3 times - entering cornea, entering the lens, & leaving the lens
refractory power of cornea & humors is constant
refractory power of lens changes
lens is elastic; curvature & light-bending power changes to allow fine focusing of an object


Contrast focusing for distant vision and focusing for close vision.

Focusing for distant vision
eyes are best adapted for distant vision
ciliary muscles are relaxed & lens is thin(low refractory power)

Focusing for close vision
eyes must make continuous adjustments (3)
accomodation of the lens - accomodation increases the refractory power of the lens when the lens bulges providing a shorter focal length
constriction of the pupils - enhances the effect of accomodation by reducing pupil size
convergence of the eyeballs - directs the eyeballs toward the object being viewed


Define the terms emmetropic eye, myopic eye, and hyperopic eye. Explain correction for nearsightedness and farsightedness.

Emmetropic eye - normal eye; light focuses properly

Myopic eye - eye is too long so focal point is in front of retina; myopia is nearsightedness
hard to focus on far objects
concave lens correction (divergent lens)

Hyperopic eye - eye is too short or cornea is too flat so focal point is behind retina; hyperopia is farsightedness hard to focus on near objects convex lens correction(convergent lens)


Describe the cellular structure of rods and cones.

sensitive to dim light (night vision, peripheral vision)
contain only 1 type of pigment
perceived input is in gray tones only
as many as 100 rods feed into a ganglion cell
results in fuzzy & indistinct images

need bright light for activation (low sensitivity)
each cone has 1 of 3 types of pigment
perceived input is vividly colored
each cone in fovea feeds to single ganglion cell
vision is detailed & has high resolution


Outline differences between rods and cones.

sensitive to dim light (night vision, peripheral vision)
contain only 1 type of pigment
perceived input is in gray tones only
as many as 100 rods feed into a ganglion cell
results in fuzzy & indistinct images

need bright light for activation (low sensitivity)
each cone has 1 of 3 types of pigment
perceived input is vividly colored
each cone in fovea feeds to single ganglion cell
vision is detailed & has high resolution


Explain how retinal and opsins combine to form 4 different visual pigments.

Visual pigment - composed of retinal & opsin
retinal - light-absorbing molecule made from vitamin A

opsins - proteins that are combined with retinal to form four types of visual pigments

depending on the type of opsin to which it is bound, retinal preferentially absorbs different wavelengths of light

when light strikes a pigment, retinal changes shape which in turn changes the shape of opsin, activating it

capture of light by visual pigments is only light-dependent stage

photochemical event initiates chain of chemical & electrical reactions in rods & cones

ultimately, an electrical impulse is transmitted along optic nerve


Explain why we see sharp, colorful images during the day and fuzzy, gray images at night.

Excitation of rods
rhodopsin - deep purple visual pigment
formation & breakdown of rhodopsin
rhodopsin forms & accumulates in the dark
bleaching of the pigment - light absorption by rhodopsin causes retinal to change shape (activate) & eventually detach from opsin

Excitation of cones
photopsins - 3 types; breakdown & regeneration is similar to rhodopsin but brighter light is needed to activate cones
three types of cones - blue cones, green cones, & red cones each has a different opsin
each type is named for the wavelengths it absorbs best
detect primary colors (RGB)
intermediate colors come from activation of more than one type of cone (blue + red = purple; red + green = yellow) all cones activated equally = white


Explain the causes of color blindness. Name the most common type of color blindness.

genetics - most common cause; X-linked trait (more males)
diseases - diabetes, glaucoma
medications - for heart disease, high blood pressure
chemicals - fertilizers, carbon monoxide
age - eyes lose some ability to see color; cataracts

Red-green color blindness - the most common type
lack red or green cones - red & green are seen as same color, red or green depending upon the cone type present anomalous (abnormal) red or green cones


Differentiate between the chemoreceptors for taste and smell.

chemoreceptors - both taste and smell involve sensory receptors that respond to chemicals in an aqueous solution
taste receptors - excited by food chemicals dissolved in saliva
smell receptors - excited by airborne chemicals dissolved in nasal membrane fluids


Describe the structures of the olfactory epithelium, olfactory sensory neurons, and olfactory nerves.

Olfactory epithelium - organ of smell; yellow-tinged patch of pseudostratified epithelium located in the roof of the nasal cavity
olfactory sensory neurons - receptor cells shaped like bowling pins
supporting cells - surround & cushion receptor cells
olfactory stem cells - short cells lying at base of the epithelium; differentiate to form new olfactory sensory neurons

Olfactory sensory neuron - bipolar neuron with a thin apical dendrite that terminates in a knob from which several long cilia radiate
olfactory cilia - increase receptive surface area; nonmotile
mucus - produced by the supporting cells & olfactory glands thinly coats the olfactory epithelium, covering the olfactory cilia functions as a solvent that captures & dissolves airborne odorants replaced every 30-60 days

Olfactory nerve (cranial nerve I) - is formed from the unmyelinated axons of olfactory sensory neurons filaments of the olfactory nerve - bundles of axons that pass through openings in cribriform plate of ethmoid bone to synapse with neurons in the olfactory bulb
olfactory bulbs - distal ends of olfactory tracts


Explain the physiology of smell.

Olfactory receptors respond to several different odor-causing chemicals; we can distinguish ~10, 000 odors
odorant must be volatile (gaseous state) & dissolve in the fluid coating the olfactory epithelium
odorant binds to a G protein-linked receptor; leading to synthesis of cAMP, a second messenger
cAMP opens a cation channel allowing Na+ & Ca2+ to enter the olfactory cilium membrane; causes depolarization of receptor membrane triggering an AP


Differentiate between fungiform, foliate, and vallate papillae on the tongue.

fungiform papillae - mushroom-shaped; scattered over the entire tongue surface

foliate papillae - lateral margins of the tongue

vallate papillae - large round papillae; at the back of tongue


Describe the structure of a taste bud.

Taste bud - flask-shaped structure consisting of two types of epithelial cells

gustatory epithelial cells - receptor cells for taste
gustatory hairs - long microvilli that project from the tips of gustatory epithelial cells through a taste pore to the surface of the epithelium where they are bathed by saliva; receptor membranes of gustatory epithelial cells

basal epithelial cells - stem cells that divide & differentiate into new gustatory epithelial cells
friction & hot foods damage taste buds
taste buds are replaced every 7 to 10 days


List the 5 basic taste sensations and explain what produces each.

sweet - produced by many organic compounds; sugars, saccharin, alcohols, some amino acids, some lead salts(in lead paint)

sour - produced by acids, specifically their hydrogen ions (H+)

salty - produced by metal ions (inorganic salts); table salt

bitter - produced by alkaloids (complex molecules with pharmacologic activity); quinine,nicotine, caffeine, morphine, strychnine

umami - produced by the amino acids glutamate & aspartate; the “beef” taste of steak, the tang of aging cheese,the flavor of MSG monosodium glutamate)


Explain the physiology of taste.

For a chemical to be tasted, it must dissolve in saliva, diffuse into the taste pore, & contact the gustatory hairs

Activation of taste receptors
1. food chemical binds to receptors in gustatory hair membrane
2. membrane is depolarized causing a graded potential
3. neurotransmitter is released from the gustatory epithelial cell
4. neurotransmitter binds to associated sensory dendrites
5. generator potentials are initiated that lead to an action potential

Different gustatory cells have different thresholds for activation
bitter receptors detect substances in minute amounts
other receptors are less sensitive


Describe the anatomical structures of the external ear, middle ear, and internal ear.

external ear & middle ear - involved with hearing only; simple
internal ear - functions in both hearing & equilibrium; complex


Define the terms sound, frequency, hertz, wavelength, pitch, amplitude, loudness, and decibel.

Sound - a pressure disturbance; alternating areas of high & low pressure produced by a vibrating object & propagated by the molecules of the medium

Frequency - number of waves that pass a given point in a given time

hertz - units used to measure sound frequency; waves per second humans hear from 20 to 20,000 hertz

wavelength - distance between 2 consecutive crests or troughs

wavelength and frequency are related; the shorter the wavelength, the higher the frequency

pitch - our perception of frequency
high frequency = high pitch
low frequency = low pitch

Amplitude - height of the sine wave crests; sound’s intensity or energy

energy - pressure differences between compressed & rarefied areas

loudness - our subjective interpretation of sound intensity
high amplitude = loud
low amplitude = soft

decibels (dB) - logarithmic units used to measure loudness
0 dB - threshold for hearing
90 dB - prolonged exposure causes hearing loss
120 dB - threshold for pain


Relate frequency to pitch and amplitude to loudness.

high frequency = high pitch
low frequency = low pitch

high amplitude = loud
low amplitude = soft


Explain the route of sound waves through the ear.



Define the terms deafness, conduction deafness, sensorineural deafness, tinnitus, and Meniere’s syndrome.

Deafness - any degree of hearing loss

conduction deafness - hampering of sound conduction to inner ear fluids-compacted earwax, perforated eardrum, otitis media (middle ear inflammation), otosclerosis

sensorineural deafness - damage to neural structures
age, excessively loud noises, strokes, tumors in auditory cortex

tinnitus - ringing or clicking sound in ears in absence of auditory stimuli
-cochlear nerve degeneration, aspirin

Meniere’s syndrome - labyrinth disorder
causes vertigo, nausea, vomiting, tinnitus, hearing loss


List the 3 types of receptors that contribute to the sense of equilibrium.

Equilibrium - sense dependent on inputs from the inner ear, vision, and stretch receptors of muscles & tendons

Vestibular apparatus - equilibrium receptors in vestibule and semicircular canals
receptors in vestibule - monitor linear acceleration; static equilibrium
receptors in semicircular canals - monitor rotation; dynamic equilibrium


Describe the structure of the static equilibrium receptors in the vestibule.

Static equilibrium receptors - monitor the position of the head in space; respond to linear acceleration


Describe the structure of the dynamic equilibrium receptors in the cochlea.

Dynamic equilibrium receptors - respond to acceleration and deceleration of rotational head movement


Explain in simple terms how static equilibrium is perceived.



Explain in simple terms how dynamic equilibrium is perceived.



Explain the cause of motion sickness.

Motion sickness - due to a sensory input mismatch; visual inputs indicate that your body is fixed with reference to a stationary environment, but your vestibular apparatus detects movement & sends impulses that disagree with the visual information; results in nausea & vomiting