A+P Week #5 - Part Two / The Special Senses

Describe the pathway of aqueous humor?

Aqueous humor is formed by filtration from the capillaries in the ciliary processes. Aqueous humor flows from the posterior chamber through the pupil into the anterior chamber. Some also flows through the vitreous humor. Aqueous humor is reabsorbed into the venous blood by the scleral venous sinus.

Plexiform layer

Areas that separate the layers of the neurons

What is the intermediate cell between a rod / cone cell and a ganglion cell?

Bipolar cell

Rods - describe What is rhodospin? How does light effect it? What are the component parts of rhodospin?

Bipolar photoreceptor cells; black and white version Found over most of retina, but not in fovea. More sensitive to light than cones. Protein rhodopsin changes shape when struck by light; and eventually separates into its two components: opsin and retinal. Retinal can be converted to vitamin A from which it was originally derived. In the absence of light, opsin and retinal recombine to form rhodopsin.

Cones - describe?

Bipolar receptor cells Responsible for color vision and visual acuity Numerous in fovea and macula lutea; few over the rest of the retina. As light intensity decreases so does our ability to see color. Visual pigment is iodopsin. Three types exist that respond to blue, red, and green light. Overlap in response to light, thus interpretations of gradation of color possible.

Retinal detachment

Can result in complete blindness

Cataract

Clouding of lens

Iris - describe

Colored part of the eye. Controls light entering the pupil. Smooth muscle determines the size of the pupil.

Macular degeneration

Common in older people, loss in acute vision

Ciliary body - describe

Composed of: ciliary muscle, ciliary ring, and ciliary processes. Aqueous humor is produced by the capillaries of the ciliary processes. ciliary processes are attached to the suspensory ligaments of the lens ciliary muscles control lens shape

Astigmatism

Cornea or lens not uniformly curved

Presbyopia

Degeneration of accommodation ability. Corrected by reading glasses.

Axons carrying information from the nasal part of the visual field go where? (In the optic chiasma)

Do NOT cross

Diabetes relation to eyesight problem?

Dysfunction of peripheral circulation can lead to eyesight problems

True or false: The retina is composed of three layers; an outer vascular layer, a middle layer of pigmented epithelium and an inner neural layer.

False

True or false: Images focused on the retina are right side up

False. Images are focused on the retina inverted.The cerebrum interprets the image as being right side up.

Hyperopia

Farsightedness Image focused behind retina

Three tunics of the eye from superficial to deep

Fibrous: sclera and cornea Vascular: choroid, ciliary body, and iris Nervous: retina

Identify the structural and functional characteristics of the cornea. x4?

Focuses light Transparent Allows light to enter eye Refracts light

Functions of the vitreous humor?

Helps maintain intraocular pressure Holds lens and retina in place Refracts light

Functions of aqueous humor?

Helps maintain intraocular pressure Supplies nutrients to the structures bathed by it Contributes to the refraction of light

Rhodopsin and it's relation to light. Light and dark adaptation.

In bright light, more rhodopsin is broken down into Vitamin A, protecting the eye and making it less sensitive to light. In darker conditions, more rhodopsin is produced so the eye is more sensitive to light. Takes eyes a while to accommodate when going from dark to light and vice versa because of these chemical changes that must occur.

Glaucoma

Increased intraocular pressure by aqueous humor build-up

Light can _____ the visual processing of the rod cells.

Inhibit

Strabismus

Lack of parallelism of light paths through eyes Retina is in the wrong position

Lens focuses light on _______ and ______ .

Macula lutea Fovea centralis

What characterizes the vascular tunic?

Middle layer. Contains most of the blood vessels of the eye: branches off the internal carotid arteries. Contains melanin.

Where do the axons go once they pass through the optic chiasma?

Most travel to the lateral geniculate nuclei of the thalamus. Some branches synapse in the superior colliculi

Myopia

Nearsightedness Focal point too near lens, image focused in front of retina.

Place the tunics of the eyeball in order, beginning with the innermost layer.

Nervous tunic Vascular tunic Fibrous tunic

What are the functions of the aqueous humor?

Nourishes the cornea Maintains pressure in the eye Refracts light Maintains the shape of the eye

Pigmented layer (retina) describe?

Outer pigmented layer. Simple cuboidal epithelium Pigment of this layer and choroid help to separate sensory cells and reduce light scattering.

What are the two layers of the retina?

Pigmented layer and Neural layer

Name the part of the eye which enhances visual acuity by reducing light scattering.

Pigmented layer of the retina

Identify the functions of the sclera

Provides a point of attachment for the extrinsic eye muscles Maintains the shape of the eye Protects internal structures

Rod Cell Hyperpolarization Pathway

Rod cell is unstimulated in dark conditions. Resting membrane potential is relatively non-polarized at -30 Exposure of light forces open Na+ channels to close (we do not need to know the mechanism) and resting membrane potential to hyperpolarize to approx. -35

Compare rods and cones

Rod: Cylindrical Photoreceptive molecule: Rhodopsin Function: noncolor vision; vision under conditions of low light Location: over most of retina; none in fovea centralis Cones: Conical Photoreceptive molecule: Iodopsin Function: color vision, visual acuity Location: numerous in fovea centralis and macula; sparse over rest of retina.

When Rod cells are not stimulated they ______ and when they are stimulated they ______.

Rods are unusual sensory cells: when not stimulated they are depolarized (no poles!). Light causes them to hyper-polarize (more negative inner charge)

The special senses include? x5

Smell Taste Sight Hearing Balance

When thinking about lens accommodation and the ciliary muscle: contraction vs. relaxation, what is important to keep in mind?

This is a concentric muscle. Therefore, relaxation increases the distant / tension. And contraction reduces the distance / tension.

Neural layer of the retina

Three layers of neurons: Photoreceptors, bipolar neurons, and the ganglionic neurons

Describe the cornea?

Transparent window continuous anteriorly with the sclera. CT tissue matrix containing collagen elastic fibers and proteoglycans *More proteoglycans than the sclera for the absorption of water; a high water content would scatter light. Layer of stratified squamous epithelium on the outer surface. Collagen fibers are small, thus transparent. Avascular, transparent, allows light to enter the eye; bends and refracts light. Does have sensory nerve innervation

Crystalline lens - describe?

Transparent, biconvex Held by suspensory ligaments attached to ciliary muscles Changes shape as ciliary muscles contract and relax Anterior surface lined with simple cuboidal epithelial cells Posterior region contains long, columnar epithelial cells called lens fibers The cells on the periphery are the youngest. The inner part is composed of "older" cells. *Loose nuclei and other organelles can be found in the "old" inner layers. *Accumulates proteins called crystallines over time. Covered by an elastic transparent capsule.

Explain the concept of binocular vision?

Visual fields partially overlap yielding Makes depth perception possible.

Fovea centralis

area of greatest visual acuity; photoreceptor cells are tightly packed

Focusing

causing light to converge

Pupils _____ in bright light and ____ in dim light.

constrict dilate

Axons carrying information from the temporal part of the visual field go where? (In the optic chiasma)

cross and project to the opposite side of the brain

Neural layer (retina) describe?

inner layer of rod and cone cells - sensitive to light

What are the three parts of the vascular tunic?

iris, ciliary body, choroid

Axons from the right nasal retina project to the ______ side of the cerebrum and axons from the right temporal retina project to the ______ side of the cerebrum.

left, right

The transparent, biconvex structure in the eye is called the _____.

lens

Convergence

light striking a convex surface light will bend and "converge" upon hitting a convex object.

The fovea centralis is found in the center of a yellow spot on the retina called the ______ lutea.

macula

Sum of visual input from _____ rods feeds into a single ganglion cell.

many

A concave lens corrects ______.

myopia

Emmetropia

normal resting condition of the lens. Ciliary muscle is relaxed. Lens is flat.

After passing through the lens, light from each half of a visual field projects to the ______ side of the retina.

opposite due to the biconvex lens This makes the "wording" of related questions a freakin nightmare... :(

Far point of vision

point at which lens does not have to thicken to focus. 20 feet or more from eye

Focal point

point where light rays converge and cross

Visible light

portion of the electromagnetic spectrum detected by the human eye. ROY G BIV

Idopsin is similar to _____ . Except?

rhodospin - except it is stimulated by light instead of inhibited.

Eyebrows - function?

shade; prevent sweat from getting into the eye

Each cone synapses (indirectly) with a ____ ganglion cell.

single cones exhibit little or no convergence. NOT the same with rod cells

What allows for dark sight adaption?

Changes in the amount of available rhodopsin. Also you could say, the recombination of retinal and opsin.

The glands of the eyelashes and eyelid. What are they + explain their function?

Ciliary glands - modified sweat glands that empty into hair follicles. Meibomian glands - are the tiny oil glands which line the margin of the eyelids (the edges which touch when the eyelids are closed). These glands secrete oil which coats the surface of our eyes and keeps the water component of our tears from evaporating (drying out)

Near vision - describe what is going on? Explain the concept of convergence?

Ciliary muscles contract due to parasympathetic input. (CN III) This contraction reduces tension in the suspensory ligaments. This more convex lens is capable of greater light refraction. Contracted - reduced tension Pupil constriction - the fine tuning (varies the depth of focus) Convergence - as objects move close to the eye, eyes are rotated medially due to reflex contraction of the medial rectus muscles.

Distant vision - describe what is going on in relation to the lens.

Ciliary muscles in the ciliary body are relaxed. Tension in the suspensory ligaments is high. Lens is flattened Relaxed - high tension Remember the ciliary muscle is concentric. Therefore, relaxation causes expansion of the ring.

Fibrous tunic Component parts?

Sclera and Cornea

Pigmented layer of the retina

Single layer of cells; filled with melanin. Deep to the neural layer

The nasal part of the retina refers to what part of the visual field?

Temporal part... So TRICKY....

The main part of the vascular tunic is?

The choroid layer

What is the near point of vision?

The closest point at which an object can be held and seen without appearing blurred

How does the lens accommodate?

The lens changes shape causing the adjustment of the focal point on the retina.

Describe the location of the lens.

The lens is suspended between the posterior chamber and vitreous chamber by suspensory ligaments.

The fovea centralis is the focal point for?

The light that is "directly" entering your eye. Where you are looking directly - not necessarily your periphery.

Describe the choroid of the eye.

The melanin-pigmented portion of the vascular tunic associated with the sclera

The final destination of the optic tracts is?

The occipital lobe (visual cortex)

What is the fovea centralis?

The portion of the retina with the greatest visual acuity

Describe the structure of the retina.

The retina is composed of an outer pigmented layer and an inner neural layer.

The iris is composed of how many muscles? How do these muscles function?

Two The sphincter pupillae (an inner circular muscle) constricts the pupil upon contraction. (Parasympathetic) Dilator pupillae (the outer circular muscle) dilates the pupil upon contraction. (Sympathetic)

Describe the sclera?

White outer layer Maintains shape, protects internal structures, provides muscle attachment point, and it is continuous with the cornea. Composed of dense collagenous CT with elastic fibers. *Collagen fibers are large and opaque (not transparent).

Each visual field is divided into?

a temporal and a nasal half

scleral venous sinus (canal of Schlemm) - function?

absorbs aqueous humor back into the venous blood

A black object absorbs _____ .

all wavelengths of visible light

A white object reflects?

all wavelengths of visible light

Where is the aqueous humor found?

anterior and posterior chambers

Describe the anterior segment of the eye?

anterior to the lens; filled with aqueous humor. Anterior chamber: between the cornea and iris Posterior chamber: between the iris and lens

choroid layer (vascular tunic) - describe?

associated with the sclera. Very thin, pigmented.

An optic tract consists of?

axons that have passed through the optic chiasma

Refraction

bending of light

Depolarization of rods causes depolarization of?

bipolar cells causing depolarization of ganglion cells.

Optic disc

blind spot. Area through which blood vessels enter the eye and where nerve processes from sensory retina meet and exit from eye.

Macula lutea

small yellow spot

The nasal visual field projects to the _____ retina and the temporal visual field projects to the ______ retina.

temporal, nasal

When a convex lens forms an image, the image is ______ .

upside down and reversed right to left