SPECIAL SENSES PART 1 (VISION)

smell, taste, sight, and hearing

The other four “traditional” senses—

special senses

The other four “traditional” senses—smell, taste, sight, and hearing—are called

equilibrium

Receptors for a fifth special sense,—are housed in the ear, along with the organ of hearing.

special sense receptors

are either large, complex sensory organs (eyes and ears) or localized clusters of receptors (taste buds and olfactory epithelium).

vision

Of all the senses, the—-has been studied most.

eyes

Nearly 70 percent of all sensory receptors in the body are in the

The optic tracts

carry information from the eyes to the brain and are massive bundles, containing over a million nerve fibers.

The adult eye

is a sphere that measures about 1 inch (2.5 cm) in diameter.

anterior one-sixth of the eye’s surface

Only the—- is normally seen. The rest of it is enclosed and protected by a cushion of fat and the walls of the bony orbit

The accessory structures of the eye

include the extrinsic eye muscles, eyelids, conjunctiva, and lacrimal apparatus.

eyelids

Anteriorly the eyes are protected by the?

medial commissure (canthus) and lateral commissure (canthus)

meet at the medial and lateral corners of the eye, the? (3)

palpebral fissure

The space between the eyelids in an open eye is called the?

eyelashes

Projecting from the border of each eyelid are the?

tarsal glands

Modified sebaceous glands associated with the eyelid edges are the?—These glands produce an oily secretion that lubricates the eye

Ciliary glands

which are modified sweat glands, lie between the eyelashes (cilium=eyelash), and their ducts open at the eyelash follicles.

lacrimal caruncle

On the medial aspect of each eye is the? a raised area containing sebaceous and sweat glands that produce an oily, whitish secretion that also lubricates the eye

conjunctiva

A delicate membrane, the—-lines the eyelids and covers part of the outer surface of the eyeball. It ends at the edge of the transparent cornea by fusing with the corneal epithelium.

conjunctiva

secretes mucus, which helps to lubricate the eyeball and keep it moist

lacrimal apparatus

consists of the lacrimal gland and a number of ducts that drain lacrimal secretions into the nasal cavity.

conjunctivitis

Inflammation of the conjunctiva, called—results in reddened, irritated eyes

Pinkeye

its infectious form caused by bacteria or viruses, is highly contagious.

lacrimal glands

are located above the lateral end of each eye. They continually release a dilute salt solution (tears) onto the anterior surface of the eyeball through several small ducts.

lacrimal canaliculi; lacrimal sac; nasolacrimal duct

sequence of tears flushing;

mucus, antibodies, and lysozyme

what does tears contain?

lysozyme

an enzyme that destroys bacteria. they cleanse and protect the eye surface as they moisten and lubricate it.

“sniffles”

When lacrimal secretion increases substantially, tears spill over the eyelids and fill the nasal cavities, causing congestion and the

“sniffles”

This happens when the eyes are irritated by foreign objects or chemicals and when we are emotionally upset.

the enhanced tearing

acts to wash away or dilute the irritating substance.

“emotional tears”

is poorly understood, but some suspect that crying is important in reducing stress

a cold or nasal inflammation

often causes the lacrimal mucosa to become inflamed and swell. This impairs the drainage of tears from the eye surface, causing “watery” eyes.

Six extrinsic eye muscles (external eye muscles)

are attached to the outer surface of each eye. These muscles produce gross eye movements and make it possible for the eyes to follow a moving object.

Lateral rectus; Medial rectus; Superior rectus; Inferior rectus; Inferior oblique; Superior oblique

Extrinsic muscles of the eye; (6)

Lateral rectus

Moves eye laterally; VI (abducens)

Medial rectus

Moves eye medially; III (oculomotor)

Superior rectus

Elevates eye and turns it medially; III (oculomotor)

Inferior rectus

Depresses eye and turns it medially; III (oculomotor)

Inferior oblique

Elevates eye and turns it laterally; III (oculomotor)

Superior oblique

Depresses eye and turns it laterally; IV (trochlear)

eyeballs

The eye itself, called the—is a hollow sphere

three tunics, or layers,

the eyeball’s wall is compose of?

humors

the interior of the eyeball is filled with fluid called?— that help to maintain its shape.

the lens

the main focusing apparatus of the eye, is supported upright within the eye cavity, dividing it into two chambers.

fibrous layer

The outermost layer, called the—consists of the protective sclera and the transparent cornea.

protective sclera and the transparent cornea

the outermost layer, called the fibrous layer consists of? (2)

sclera

is seen anteriorly as the “white of the eye.” The central anterior portion of the fibrous layer is crystal clear.

cornea

This “window” is the—through which light enters the eye. The— is well supplied with nerve endings.

cornea

Most are pain fibers, and when the— is touched, blinking and increased tear production occur. Even so, the— is the most exposed part of the eye, and it is very vulnerable to damage.

cornea

is the only tissue in the body that is transplanted from one person to another without the worry of rejection. Because it has no blood vessels, it is beyond the reach of the immune system.

vascular layer

The middle, or—of the eyeball, has three distinguishable regions

choroid

Most posterior is the—a blood-rich nutritive tunic that contains a dark pigment. The pigment prevents light from scattering inside the eye.

ciliary body

Moving anteriorly, the choroid is modified to form two smooth muscle structures, the—

ciliary body

is attached to the lens by a suspensory ligament called the ciliary zonule, and the iris.

ciliary zonule and the iris.

ciliary body is attached to the lens by a suspensory ligament called the? (2)

pupil

The pigmented iris has a rounded opening, the—through which light passes.

iris

Circularly and radially arranged smooth muscle fibers form the—which acts like the diaphragm of a camera.

iris

it regulates the amount of light entering the eye so that we can see as clearly as possible in the available light.

Cranial nerve III (oculomotor)

what controls the muscles of the iris?

the circular muscles contract, and the pupil constricts, or gets smaller

In close vision and bright light, what happens?

the radial fibers contract to enlarge (dilate) the pupil, which allows more light to enter the eye.

In distant vision and dim light, what happens?

sensory layer

The innermost—eye is the delicate two-layered retina, which extends anteriorly only to the ciliary body.

delicate two-layered retina

The innermost sensory layer of the eye is the—which extends anteriorly only to the ciliary body.

The outer pigmented layer of the retina

is composed of pigmented cells that, like those of the choroid, absorb light and prevent light from scattering inside the eye.

The outer pigmented layer of the retina

They also act as phagocytes to remove dead or damaged receptor cells and store vitamin A needed for vision.

The transparent inner neural layer of the retina

contains millions of receptor cells, the rods and cones, which are called photoreceptors because they respond to light.

photoreceptors

the rods and cones, which are called—because they respond to light.

bipolar cells and then ganglion cells

Electrical signals pass from the photoreceptors via a two-neuron chain (2)

optic nerve

before leaving the retina via the—and being transmitted to, and interpreted by, the optic cortex. The result is vision.

optic cortex

before leaving the retina via the optic nerve and being transmitted to, and interpreted by, the—. The result is vision.

optic disc

The photoreceptor cells are distributed over the entire retina, except where the optic nerve leaves the eyeball; this site is called the—

blind spot in our vision

Since there are no photoreceptors at the optic disc, it results in a?

optic disc

When light from an object is focused on the—, the object disappears from our view and we cannot see it.

The rods and cones

which are not evenly distributed in the retina?

rods

are densest at the periphery, or edge, of the retina and decrease in number as the center of the retina is approached.

rods

allow us to see in gray tones in dim light, and they provide our peripheral vision.

night blindness

Anything that interferes with rod function hinders our ability to see at night. This condition, called

night blindness

dangerously impairs our ability to drive safely at night.

night blindness

Its most common cause is prolonged vitamin A deficiency, which eventually causes the neural retina to deteriorate.

Vitamin A

is one of the building blocks of the pigments the photoreceptor cells need to respond to light.

Vitamin A supplements

will restore function if taken before degenerative changes in the neural retina occur.

cones

are discriminatory receptors that allow us to see the details of our world in color under bright light conditions. They are densest in the center of the retina and decrease in number toward the retinal edge (the opposite of rods).

fovea centralis

Lateral to each blind spot is the—a tiny pit that contains only cones

fovea centralis

Consequently, this is the area of greatest visual acuity, or point of sharpest vision, and anything we wish to view critically is focused on the—

three

how many varieties of cones are there?

“red cones”

this is the only cone population to respond to red light at all, so these are called the

intermediate colors

Impulses received at the same time from more than one type of cone by the visual cortex are interpreted as— similar to what occurs when two colors of paint are mixed.

white

When all three cone types are stimulated, we see?

yellow

If someone shines red light into one of your eyes and green into the other, you will see?

“mixing”

If someone shines red light into one of your eyes and green into the other, you will see yellow, indicating that the— and interpretation of colors occur in the brain, not in the retina.

brain

interpretation of colors occur in the—, not in the retina.

total color blindness

Lack of all three cone types results in—

partial color blindness

whereas lack of one cone type leads to—

red-green color blindness

Most common is the lack of red or green receptors, which leads to two varieties of?

Red and green

are seen as the same color—either of the two, depending on the cone type present

X (female) sex chromosome,

Because the genes regulating color vision are on the?

sex-linked condition

Because the genes regulating color vision are on the X (female) sex chromosome, color blindness is a—It occurs almost exclusively in males.

Light entering the eye

focused on the retina by the lens, a flexible biconvex crystal-like structure

the lens

is held upright in the eye by the ciliary zonule attached to the ciliary body

Cataracts

the loss of lens transparency, cause vision to become hazy and distorted and can eventually cause blindness.

Cataracts

Other risk factors for forming—include diabetes mellitus, frequent exposure to intense sunlight, and heavy smoking.