Exercise 17-The Special Senses/Anatomy of the Eye

Special Sense Receptors
large, complex sensory organs (eyes and ears)
or, localized clusters of receptors (taste buds and olfactory epithelium)

Medial Commisure and Lateral Commisure
the medial and lateral junctions of the upper and lower eyelids

Conjunctiva
a mucous membrane that lines the internal surface of the eyelids and continues over the anterior surface of the eyeball to the outer edge or the cornea, where it fuses with the corneal epithelium.
secretes mucus which lubricates the eyeball

Conjunctivitis
inflammation of the conjunctiva
often accompanied by redness of the eye

Ciliary Glands
modified sweat glands
lie between the eyelashes and help lubricate the eyeball.
An inflammation of one of these is called a sty

Tarsal Glands
posteror to the eyelashes
secrete an oily substance

Lacrimal Apparatus
consists of lacrimal glands (which lie superior and lateral to each eye) and a system of ducts.
Lacrimal glands continually release a dilute salt solution (tears) onto the anterior surface of the eyeball through several small ducts. Tears flush across eyeball into lacrimal canals, into lacrimal sac, then into nasolacrimal duct

Fibrous Tunic
protective outermost part of eye composed of dense connective tissue
contains: sclera (white of eye) and cornea (where light enters)

Uvea
the vascular tunic
choroid- blood-rich posterior part, contains a dark pigment that prevents light from scattering within the eye. Leads to ciliary body, iris, pupil

Ciliary Body
modified part of the choroid. where the lens is attached.

Iris
pigmented part; composed of circularly and radially arranged smooth muscle fibers. acts like the diaphragm of a camera to regulate the amount of light entering the eye.
circular muscles contract in close vision and bright light (pupil contracts)
Radial fibers contract in distant vision and in dim light (enlarges the pupil)

Sensory Tunic
the delicate retina.
transparent neural layer-extends anteriorly only to the ciliary body.
contains rods and cones

Rods and Cones
photoreceptors which begin the chain of electrical events that pass from the photoreceptors to bipolar cells, and then to ganglion cells

Optic Disc
blind spot
the photoreceptor cells are distributed all over the neural retina, except here, where the optic nerve leaves the eyeball

macula Lutea
an area of high cone density
lateral to each blind spot
yellow spot

Fovea Centralis
a minute pit about .5 mm in diameter, which contains only cones and is the area of greatest visual acuity

Lens
focuses light entering the eye on the retina.
held upright in the eye by a suspensory ligament attached to the ciliary body.
divided into two segments

Anterior Segment
anterior to the lens.
contains a clear, watery fluid called the aqueous humor (this is continually formed by the capillaries of the ciliary body. helps to maintain the intraocular pressure of the eye, also provides nutrients)

Posterior Segment
behind the lens, filled with gel-like vitreous humor/vitreous body (reinforces the posterior part of the eyeball, helps to keep the retina pressed firmly against the wall of the eyeball)

Scleral Venous Sinus
a drainage duct located at the junction of the sclera and cornea

accommodation
the ability of the eye to focus specifically for close objects (less than 20 feet)

Real Image
the image formed on the retina as a result of the light-bending activity of the lens.
reversed from left to right, inverted, and smaller than the object

Myopia
nearsightedness
the image normal focuses in front of the retina.
can see close objects without difficulty, but distant objects are blurred or indistinct.
correction requires a concave lens, causing the light reaching the eye to diverge

Hyperopia
farsightedness.
if the image focuses behind the retina.
need convex lenses to boost converging power of lens for close vision

Astigmatism
irregularities in the curvatures of the lens and/or the cornea.
blurred vision problem.

Presbyopia
“old vision”
when the elasticity of the lens dramatically decreases with age.
difficulty in focusing for near/close vision.
can be tested with near point of accommodation-about 10cm in young adults, closer in children and farther in old age

Visual Acuity
sharpness of vision.
generally tested by a Snellen eye chart

Convergence
medial eye movement
extrinsic eye muscles responsible for this–controlled by the somatic nervous system
essential for near vision

The eyeball is wrapped in adipose tissue within the bony orbit. What is the function of the adipose tissue? To package, protect, and cushion the eyeball in the bony orbit. Why does one often have to blow one’s nose after …

sclera (frontal area of eye) white portion of the eye; tough fibrous membrane; maintains the shape of the eyeball; serves as protective covering for the eye. optic nerves (frontal area of eye) receives impulses from the retina and transmits them …

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Eyebrows Prevent perspiration from getting in eye, shade eye from direct sunlight Eyelids and lashes Protect eyes from foreign objects by blinking, keeps eyes lubricated with tears WE WILL WRITE A CUSTOM ESSAY SAMPLE ON ANY TOPIC SPECIFICALLY FOR YOU …

Olfactory receptors Roof of nasal passages / neurons with long cilia / chemical must be dissolved in mucus for detection / impulses are transmitted via the olfactory nerve / smell Cortex Interpretation of smells is made in the… WE WILL …

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