the special senses

accessory structures of the eye include: (5 things)

• eyebrows

• eyelids

• eyelashes

• lacrimal apparatus

• extrinsic eye muscles

lacrimal apparatus

group of structures that produces and drains lacrimal fluid (tears)

function of extrinsic eye muscles

moving the eye

wall of the eye layers (3; from superficial to deepest)

1. fibrous tunic

2. vascular tunic

3. retina

the fibrous tunic is composed of the ________ and ___________

sclera and cornea

sclera

posterior 5/6 of the fibrous tunic (“white” of the eye)

cornea

anterior 1/6 of the fibrous tunic (transparent portion that covers iris and helps focus)

the vascular tunic is composed of the _________, _____________, and _____

choroid, ciliary body, and iris

is the choroid vascular or avascular? why?

vascular bc it nourishes the retina

the choroid contain melanocytes because:

melanin helps absorb stray light

the ciliary body produces ___________, and is involved in:

aqueous humor; changing the lens shape

the iris is between the ________ and _____

cornea and lens

the iris contains: (2 things)

• melanocytes

• circular and radial smooth muscle fibers

function of the iris (+ how)

regulating amount of light entering the eyeball through the pupil

• does this by dilating or constricting the pupil

the retina is the ___________ layer of the vascular tunic, can be viewed with _______________, and contains ________________ that convert _____ _____ into _________ ________

the retina is the innermost layer of the vascular tunic, can be viewed with an ophthalmoscope, and contains photoreceptors that convert light rays into nerve impulses

types of photoreceptors (+ what they allow us to see)

• rods: shades of grey in dim light

• cones (blue, green, red): produce color vision in brighter light

is the majority of our vision mediated by rods or cones?

cones

• loss of cones means legal blindness

blind spot (+ alt. name)

= optic disc

place where optic nerve II leaves the retina and there are no rods or cones

macula lutea

center of the posterior retina that contains only cones

fovea centralis

center of the macula and area of highest resolution

• point where image should be focused

lens (what is it + function)

biconvex, elastic structure that helps focus images on the retina

the interior of the eyeball contains the ________ and __________ cavities

anterior; posterior

anterior cavity of the inner eye is anterior to the ______ and is filled with ____________ _________

anterior cavity of the inner eye is anterior to the lens and is filled with aqueous humor

chambers of the anterior cavity (+ their position relative to other structures)

• anterior chamber: between cornea and iris

• posterior chamber: between iris and len

how often is aqueous humor replaced in the anterior cavity, and why

every 90 minutes to maintain intraocular pressure

the posterior cavity contains the __________ chamber, which contains the _________ body

vitreous; vitreous

refraction of light rays (+what structures of the eye it involves)

bending of light as it passes through the cornea and lens, then comes into exact focus on the central fovea of the retina

accommodation

the process of an image being focused on the retina: curvature of the elastic lens increases (becomes more spherical) as a result of looking at an object closer, which increases refraction

emmetropic

a normal eye / vision

myopia (what + why)

nearsightedness

• eyeball too long or lens too thick so image converges in front of retina

hyperopia (alt. name + what + why)

= hypermetropia; farsightedness

• eyeball too short or lens too thin means image converges behind retina

astigmatism

either cornea or lens has irregular curvature

binocular vision

the ability for both eyes to focus on one set of objects

convergence

allows for binocular vision: movement of the two eyeballs so that a close object strikes the same point on both retinas

strabismus

misalignment of eyes, basically a condition that interferes with binocular vision

how does hearing work

the ear converts sound vibrations into electrical signals (nerve impulses)

parts of the external ear (2 portions)

• auricle / pinna (helix + lobule)

• external auditory canal

which structure separates the middle ear from the external ear

tympanic membrane

the middle ear contains: (3 things)

• auditory ossicles

• tensor tympani (muscle)

• stapedius muscles

auditory ossicles (3)

• malleus

• incus

• stapes

muscles of the middle ear + function

tensor tympani and stapedius muscles attach to the auditory ossicles and dampen noise

the internal (inner) ear contains: (2 structures)

• cochlea

• vestibular apparatus

cochlea (what is it, what does it do)

series of fluid-filled channels that transmit vibrations to the spiral organ (organ of Corti), which results in nerve impulses

organ of Corti (+ alt. name)

= spiral organ

and organ that receives vibrations from the cochlea and causes nerve impulses

structures making up the vestibular apparatus (3)

• semicircular ducts

• utricle

• saccule

vestibular apparatus function

propagating nerve impulses in order to maintain equilibrium