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66 Cards in this Set

  • Front
  • Back
What is our dominant sense?
Vision
What percent of all the sensory receptors in the body are in the eyes (and nealy half of the cerebral cortex os involved in some aspect of visual processing)?
70%
What is the diamete of the adult eye?
2.5 cm
How much of the eye's surface is visible?
The anterior one-sixth
T or F, only a small potion of the eyes tissues are actually invloved in photoreception
True
What are the accessory structures of the eye?
eyebrows
eyelids
conjunctiva
lacrimal apparatus
extrinsic eye muscles
What is deep to the eyebrows?
parts of the orbicularis oculi and corrugator muscles
Contraction of the orbicularis muscle does what?
"DEPRESSES the EYEBROW"
The corrugator moves the eyebrow how?
medially
What is another name for eyelids?
"palpebrae"
What is the name of the eyelid split?
palpebral fissure
What are the medial and lateral ends of the eye called?
canthi
the medial canthus sports a fleshy elevation called the?
lacrimal caruncle
What are tarsal plate?
they are connective tissue sheets that support the eyelids internally

-they also anchor the orbicularis oculi and levator palpebrae superioris muscles that run within the eyelid
When does the orbicularis muscle encircle the eye?
when it contract the eye closed
What are the several types of glands associated with the eyelids?
-tarsal glands (Meibomian glands)

-ciliary glands
Describe tarsal glands.
Tarsal glands are also called Meibomian glands and are embedded in the tarsal plates, and their ducts open at the eyelid edge posterior to the eyelashes. These modified sebaceous glands produce an oily secretion that lubricates the eyelid and the eye and prevents the eyelids from sticking together
Describe ciliary glands.
they are associated with the eyelash follicles and are smaller, more typical sebaceous glands, and modified sweat glands, called ciliary glands which lie between the hair follicles
What is the conjunctiva?
it is a transparent mucous membrane that lines the eyelids as the palpebral conjunctiva and reflects (folds back( over the anterior surface of the eyeball as the bulbar conjuntiva.

It covers only the white part of the eye, not the cornea.

It is very thin, and blood vessels are clearly visible beneath it.
What is the difference between the palpebral and bulbar conjunctiva?
Palpebral Conjuctiva = eyelids

Bulbar Conjunctiva = (white of) eyeball
What is the major function of the conjunctiva?
to produce a lubricating mucus that prevents the eye from drying out
What does the lacrimal apparatus consist of?
the lacrimal gland ad the ducts that drain excess lacrimal secretions into the nasal cavity
Where is the lacrimal gland located?
it lies in the orbit above the lateral end of the eye and is visable through the conjunctiva when the lid is everted
What does the lacrimal gland secrete?
it continually releases a dilute saline solution called lacrimal secretion (tears) into the superior part of the conjuntival sac through several small excretory ducts
Explain the pathways of tears.
"blinking spreads tears down and across medially to the MEDIAL COMMISSURE, where they enter the PAIRED LACRIMAL CANALICULI (via two tiny openings called LACRIMAL PUNCTA, visible as tiny red dots on the medial margin of each eyelid), the tears then drain intothe LACRIMAL SAC and then into the NASOLACRIMAL DUCT which empties into the nasal cavity at the INFERIOR NASAL MEATUS"
Describe lacrimal secretion.
it contains:
mucus
antibodies
lysozyme (an enzyme that destroys bacteria)

it cleans and protects the eye as it moistens and lubricates it
Where do the exrinsic eye muscles originate and insert?
- they originate from the bony orbit and insert into the outer surface of the eyeball

- they allow the eye to follow a moving object and maintain the shape of the eyeball and hold it in shape
Where do the four rectus muscles originate and insert?
they originate from a common tendinous ring, the annular ring, at the back of the orbit

- they insert on the eyeball

-their names clear indicate their loctions and actions:
superior, inferior, lateral, and medial rectus muscles
What plane do the two oblique muscles of the eyeballs move in when the eyeball is already turned medially by the rectus muscles?
VERTICAL PLANE
Describe the superior oblique muscle of the eye.
(it originates in common with the rectus muscles) it runs along the medial wall of the orbit, and then makes a right angle turn and passes through a fibrocartilaginous loop suspended from thE frontal bone called the TROCHLEA before inserting on the SUPEROLATERAL aspect of the eyeball

-"IT ROTATES THE EYE UP AND LATERALLY"
Describe the inferior oblique muscle of the eye.
it originates from the medial orbit surface and runs laterally and obliquely to insert on the inferolateral eye surface

-"IT ROTATES THE EYE UP AND LATERALLY"
Why do we need the two oblique muscles?
the superior and inferior recti cannot elevate or depress the without also turning it medially because they approach the eye from a POSTEROMEDIAL DIRECTION

-the obliques are necessary to elevate or depress the eye by canceling out the medial pull of the superior and inferior rectus muslces
All extrinsic eye muscles are are served by the oculomotor nerves(CN 3) except what two muscles?
- lateral rectus

- superior oblique

- (which are innervated by abducens-CN 6 and trochlear-CN 4)
How are the extrinsic eye muscles able to be the most precisely and rapidly controlled skeletal muscles in the body?
they have high AXON-to-FIBER RATIO!!!

-the motor units if these muscles contain only 8-12 muscles calls and in some cases as few as two or three
Describe the structure of the eyeball.
-the eyeball is a sightly irregular hollow sphere with an anterior and posterior pole

- its wall is composed of three layers:
fibrous layer
vascular layer
sensory layer

- the interior cavity is filled with fluids called HUMORS that help to maintain its shape

-the LENS, is supported vertically within the internal cavity dividing it into anterior and posterior segments, or cavities
What are the structures of the fibrous layer of the eye?
- the fiberous layer is the outmost layer of the eye and is AVASCULAR

- it contains the SCLERA and the CORNEA
Describe the sclera.
- forms the posterior portion and the bulk of the fibrous layer, it is glistening white and opaque

- seen anteriorly as the white of the eye, the tough tendon-like sclera protects and shapes the eyeball and provides a sturdy anchoring site for the extrinsic eye muscles

- posteriorly, where the sclera is pierced by the optic nerve, it is continuous with the dura mater of the brain
Describe the cornea.
- consists of the anterior sixth of the fibrous layer which is modified to form the transparent cornea, which bulges anteriorly from its junction with the sclera

- lets light enter the eye and is a major part of the light-bending apparatus of the eye

-it is covered by epithelial sheets on both faces and merges with the bulbar conjunctiva at the scalera-cornea junction

- the inner face of the cornea contains deep corneal endothelium where its cells have active sodium pumps that maintain the clarity of the cornea by keeping the water of the cornea low
Why is the cornea special?
1- has many nerve endings (mostly pain receptors)

2- when touched, it causes blinking and increases tears

3- even though it is the most exposed part of the eye, it is very vulnerable to damage

4- has extrordinary regeneration capacity

5- "IT IS THE ONLY TISSUE IN THE BODY THAT CAN BE TRANSPLANTED WITH LITTLE TO NO POSSIBILITY OF REJECTION,
BECAUSE IT HAS NO BLOOD VESSELS, IT IS BEYOND THE REACH OF THE IMMUNE SYSTEM!"
Describe the middle layer of the eye.
- the vascular layer is also called the UVEA

- it is pigmented

- it has three layers:
choroid
ciliary body
iris
Describe the choroid.
- it is highly vascular, dark brown membrane that forms the posterior five-sixths of the uvea

- its blood vessels provide nutrition to all eye layers

- its brown pigment, produced by melanocytes, helps absorb light, preventing it from scattering and reflecting within the eye (which would cause visual confusion)

-the choroid is incomplete posteriorly where the optic nerve leaves the eye

- anteriorly it becomes the ciliary body
Describe the ciliary body.
- a thickened ring of tissue that encircles the lens

- part of the vascular (middle) layer of the eye that is formed from the choroid

- it consists chiefly of the interlacin smooth muscle bundles called CILIARY MUSCLES, which control lens shape

- near the lens, its posterior surface is thrown into radiating folds called CILIARY PROCESSES, which contain the capillaries that secrete the fluid that fills the cavity of the anterior segment of the eyeball

- the CILIARY ZONULE (suspensory ligament) extends from the capillary processes to the lens: this halo of fine fibers encircles ans helps hold the lens in its upright position in the eye
Describe the iris.
- part of the vascular (middle) layer of the eye

- it is the visible colored part of the eye and the most ANTERIOR part of the UVEA

- shaped like a flattened doughnut, it lies between the CORNEA and the LENS and is continous with the ciliary body posteriorly

- it round central opening, the pupil, allows light to enter the eye

- the iris is made up of two smooth muscle layers with bundles of sticky elastic fibers that congeal into a random pattern before birth

- the iris's muscle fibers allow it to act as a reflecively activated diaphragm to vary pupil size
Describe the iris's role in close versus distant vision.
close vision and bright light:
the sphincter pupillae (circular muscles) contract and the pupil constricts

distant and dim light:
the dilator pupillae (radial muscles) contract and the pupil dilates, allowing more light to enter the eye
Pupillary dilation and constriction are controlled by what?
Sympathetic and Parasympathetic fibers
When do our pupil tend to dilate?
- subject is appealing
- in response to fear
- during problem solving

- on the other hand, boredom or subject matter that is personally repulsive causes pupil constriction
T or F, the iris contains only brown pigment?
True!

- blue and other colored eyes are a result of small pigment that is restricted to posterior surface of the iris, which causes shorter wavelengths of light
What is the OUTER PIGMENTED LAYER of the retina for?
- it abuts the choroid and extends anteriorly to cover the ciliary body and the posterior face of the iris

- the single pigmented epithelial cells (like those of the choroid), ABSORB LIGHT and prevent it from scattering in the eye

- act as PHAOGOCYTES to remove dead or damaged photoreceptor cells and store vitamin as needed by the phtoreceptor cells
What is the INNER NEURAL LAYER of the retina for?
- as called ORA SERRATA

- the neural layer of the retina plays a direct role in vision
From the posterior to the anterior, what are the three main types of neurons in the neural layer?
- photoreceptors

- bipolar cells

- ganglion cells
WHERE THE OPTIC NERVE EXISTS THE EYE!!
THE OPTIC DISK !!

- it is also called the blind spot b/c it lacks photoreceptors, so light focused on it cannot be seen

- the brain uses FILLING to deal with the adsence of input
Describe Rods.
- they are part of the quarter-billion photoreceptors found in the neural retinas

- they are more numerous then cones and are DIM-LIGHT and PERIPHERAL VISION RECEPTORS

- THEY ARE FAR MORE SENSITIVE TO LIGHT THAN CONES ARE, BUT THEY DO NOT PROVIDE EITHER SHARP IMAGES OR COLOR VISION

- this is why color are indistinct and edges of objects appear fuzzy in dim light and at the edges of out visual field
Describe Cones.
- also, they are part of the quarter-billion photoreceptors found in the neural retinas

- operate in bright light and provide high-acuity color vision

- lateral to the blind spot of the eye and directly at the posterior pole is the MACULA LUTEA with pit in its center called the FOVEA CENTRALIS, which contains mostly CONES
The retina periphery contains mostly?
Rods!

- which continouosly decreases in density from there to the macula

- only the fovea has sufficient cone density to provide detailed color vision, so anything we wish to view critically is focused on the foveae (if we want to focus on rapidly moving images, our eyes must flick rapidly to provide foveae with images of different partsof the visual field)
What is seen with an ophthalmoscope exam of the inner eye?
the blood supply to the neural retina which receives it from 2 sources:

-CHOROID (to outer third)
-CENTRAL ARTERY and CENTRAL VEIN OF THE RETINA (to inner 2/3's)
The posterior segment (between iris and lens) of the eye is filled with what?
VITREOUS HUMOR -clear gel that binds tremendous amounts of water that:

1-transmits light
2-supports the posterior surface of the lens and holds the neural rentina firmly against the pigmented layer
3- contributes to intraocular pressure, helping to counteract the pulling force of the exrinsic eye muscles

- is formed in the embryo and lasts a lifetime
The anterior segment (between cornea and iris) of the eye is filled with what?
AQUEOUS HUMOR - a clear fluid similar to blood plasma

- it forms and drains continually and is in constant motion

- it normally maintains intraocular pressure of about 16 mm Hg, which helps support the eyeball internally

- it supplies nutrients and oxygen to the lens and cornea and to some cells of the retina, and it carries away their metabolic wastes
What is the shape of the lens?
BICONVEX and it can change shape to allow precise focusing of light on the retina
Where is the lens?
posterior to the iris, held in place by ciliary zonule

- like the cornea it is avascular b/c blood vessels interfere eith transparency
What order does light pass from the air to the eye?
ON FINAL!

CORNEA
AQUEOUS HUMOR
LENS
VITREOUS HUMOR

THEN THROGH ENTIRE THICKNESS OF THE NEURAL LAYER OF THE RETINA TO EXCITE THE PHOTORECEPTORS THAT ABUT THE PIGMENTED LAYER
How many times is light bent as it enters the cornea and enters and leaves the lens?
light is bent three times
T or F, the reflactory period of the humors and cornea is constant yet the lens is high elastic and can easily change shape
True
Rods versus Cones
Rods:
1- very sensitive and best for night and peripheral vision
2- only percieve GREY tones

Cones:
1- low sensitivity (need bright light for activation)
2- have one of three different pigments that furnish a vividly colored view of the world
T or F, are rods 100 times less senstive than cones?
False, rods are more sensitive than cones
What is in the fibrous layer of the eye?
cornea and sclera
Where are the blood vessels of the eye?
In the retina!