Chapter 15: The Special Senses (A)
how may poles does the eyeball have?
2 (anterior and posterior)
how many layers are in the delicate retina?
2; pigmented and neural layer
how many layer or tunics make up the eyeball?
3 (fibrous, vascular, and inner)
how many times does light bend when it enters the eye?
3; as it enter cornea, and on entering and leaving the lens
how many extrinsic eye muscles are their?
6
what is a transparent object curved on one or both surfaces?
a lens
lens
adjustable focusing apparatus of the eye; supported vertically within the eyeball
what is the function of the pupil?
allows ligh to enter the eye
bulbar conjunctiva
anterior surface of eyeballs (covers white of the eyes)
what is the anterior segemnent filled with?
aqeueous humor
visible spectrum
beam of light despersed when visible light passes through a prism;
why do objects have color?
because they absorb some wavlength and reflect others; things that look white reflect all wavelenghts of light, where black objects absorb them all
what happens to lens as we age?
becomes denser, more convex, and becomes less elastic
what type of pigment does the iris only contain?
brown pigment
how is the eye protected?
by cushion of fat and walls of the bony orbit
what is the function of the deep corneal endothelium of the cornea?
cells have active sodium pumps that maintain clarity of cornea by keeping water content of the cornea low
blood supply to inner two thirds of the eyeball are served by what?
central artery and central vein of the retina
what region of vascular layer is blood vessel rich, dark brown membrane that forms 5/6thh of vascular layer?
choroid
what is the ring of tissue that surrounds the lens and anteriorly is where the choroid changes?
ciliary body
What are ciliary bodies composed of?
ciliary muscles; smooth muscle bundles; controls lens shape
what is vitreous humor?
clear gel the binds water; transmits light; supports posterior surface of lens; hold neural retina against pigmented layer
what is cataracts?
clouding of the lens; occur as consequences of ageing, diabetes, smoking , and exposure to sunlight
Glaucoma
compression of the retina and optic nerve if drainage of aqueous humor is blocked
lens epithelium
confined to anterior lens surface; consists of cuboidal cells that diiferientiate in the lens fibers
lacrimal apparatus
consists of lacrimal gland and ducts that drain excess lacrimal secretions into nasal cavity
lacrimal fluid
contains mucus antibodies and lysozome (enzyme that destroys bacteria); cleanses and protects eye surface as it moistens and lubricates it
what contributes to blinking and tearing reflexes? (cornea or sclera)
cornea
what is the anterior portion of the eye and bulges from its junction with the sclera?
cornea
what part of the eye bends light as it enters the eye?
cornea
where are most pain receptors in eye located?
cornea
superior oblique
depresses eye and turns it laterally
inferior rectus
depresses the eye and turns it medially
what is the function of the dilator papillae (radial muscles)?
distant vision and dim light; contracts; pupils dilate
inferior oblique
elevates the eye and turns it laterally
superior rectus
elevates the eye and turns it medially
tarsal glands
embedded in tarsal plates; modified sebacous glands that produce an oily secretion that lubricates the eyelid and eye and prevents eyelids from sticking together
ciliary zonule
enxtends from ciliary processes to lens; halo of fine fibers that encircle and help hold the lens in its upright position in the eye
what are the accesory structures of the eye?
eyebrows, eyelids, conjunctiva, lacrimal apparatus, and the extrinstic eye muscles
what is composed of dense avascular connective tissue and is the outermost coat of the eye?
fibrous layer
lacrimal caruncle
fleshy elevation at medial commisure; contains sebacous and sweat glands and produces whitish, oily secretion (sometimes collects at medial commisures)
what helps maintain the eyeballs shape?
fluids in eyes internal cavities called humors
what is the function of the sphincter paillae (circular muscles)?
for close vision and bright light; contracts; pupil contrictsq
lens fibers
form bulk of lens; contain no nuclei and few organelles; contain crystallins
what are the functions of the aqueous humor?
forms and drains continually and in constant motion; filtered from capillaries of the ciliary processes; supplies nutrients and oxygen mainly to lens and cornea but also to retina and removes wastes
what is the function of the eyebrows?
help shades the eyes from sunlight and prevent perspiration trickling down the forehead from reaching the eyes
what type of cells play a role in visual processing?
horizontal and amacrine cells
real image
image formed by convex lens; inverted upside down and reveresed from left to right
lacrimal secretion
in lacrimal gland; dilute saline solution (tears), releases by lacrimal gland;
electromagnetic radiation
includes all energy waves from long radio waves to very short gamma waves and x rays with wavelength of 1nm and less
tarsal plates
internal supporting connective tissue sheet of eyelids; anchor orbicularis oculi and levator palpebrae superioris muscles
whats the most anterior protion of the vascular layer, and is the visible colored part of the eye?
iris
what is the macula lutea?
its an oval region lateral to blind spot of each eye
through what paired structures do tears enter to lacrimal puncta?
lacrimal canaliculi
what is the bioconvex transparent flexible structure that can change shape to allow precise focusing of light on the retina?
lens
what are the two regions of the lens?
lens epithelium and lens fibers
convex lens
lens which is thickest at center (camera lens); light rays converge (come together); focal point (intersection of light rays at single point)
lacrimal gland
lies in orbit above the lateral end of the eye
palpebral conjunctiva
lines the eyelids
red wavelenghts
longest and have lowest energy
what is the pupil made out of?
made up of 2 smooth muscle layers with bunches of sticky elastic fibers that congeal into random pattern before birth
what produces the brown pigment in the choroid, that helps about light, preventing it from scattering and reflecting within the eye?
melanocytes
lateral rectus
moves eye laterally
medial rectus
moves the eye medially
refraction
occurs when light ray meets the surface of a different medium at an oblique angle rather then at a right angle (perpendicular)
cones
operate in bright light; provide high acuity color vision
visible light
part of spectrum that our eyes respond to; has wavelenght range of 400 - 700nm. travels in forms of waves
the neural layer of the retina is the innermost transparent layer, that plays a direct role in vision. What 2 types of neurons is it composed of?
photoreceptors, bipolar cells, and ganglion cells
what segement is behind the lens and filled with vitreous humor?
posterior segement
ciliary processes
posterior surface of lens; radiating folds which contain capillaries that secrete the fluid that fills the cavity of the anterior segment of the eyeball
what is the function of the eyelids
protects the eye anteriorly
whats the round central opening of the eye?
pupil
what do eyelash nerve endings initiate
reflex blinking
what type of photoreceptor is more sensitive to light, are more numerous, are dim light and peripheral vision receptors, and do not provide either sharp images or color vision?
rods
what are the photoreceptors in the eye?
rods and cones
what forms posterior portion and bulk of fibrous layer, and is white and opaque
sclera
what are the 2 regions of the fibrous layer?
sclera and cornea
palpebral fissure
seperates the eyelids; meet at medial and lateral angles
violet wavelenghts
shortest and most energetic
what is the pathway of signals in neural layer?
signals are produced in response to light and spread fro, photorecptors in the pigmented layer, to bipolar cells, then to innermost ganglion cells, where action potentials are generated
photons
small particles or packets in which light can also be envisioned
ciliary glands
smaller more typical sebacous glands, and modified sweat glands; associated with eyelash follicles
70% of all sensory receptors are located where?
the eye
what is inside the macula lutea?
the fovea centralis; allows light to pass directly to photoreceptors (enhances visual acuity); contains only cones
what is the inner most layer of the eyeball?
the inner layer (retina)
the anterior segement of the ye is further divided into anterior and posterior chambers by what?
the iris
what divides the eye into two segements?
the lens and the ciliary zonule
the ganglion cells make a right turn an inner face of retina then leave the posterior aspect of eye as what?
the optic nerve
whats the outer layer of the retina that stores vitamin A, absorbs light and prevents its scattering?
the pigmented layer
what forms the middle coat of the eyeball and has 3 regions?
the vascular layer (uvea)
concave lens
thicker at the edges than at the center; diverge light (bend outward) so the light rays move away from each other
what do muscle fibers allow pupil to do?
to act as a reflexiveily activated diaphram to vary pupil size
what is the major function of conjunctivas?
to produce a lubricating mucus that prevents eyes from drying out
conjunctiva
transparent mucous membrane
crystallins
transparent precisely folded protiens; forms body of lens
light
travels in a given medium; speed is constant; speed changes when light passes from one transparent medium into another with different density
blood supply to outer third region of the eye is supplied by what?
vessels in the choroid
reflection
when light bounces off a surface; accounts for most of light reaching our eye
when do the pupils dilate?
when subject matter is appealing or requires problem solving skills
conjunctival sac
where contact lenses lie and eye medications are administered
characteristics of the optic disc
where the optic nerve leaves the eye; weak spot in fundus (posterior wall) of eye; lack photoreceptors; light focused on it cannot be seen
