Chp 50-52 (Optic of Vision, Neuro function of Retina)

Question 1

Define Eye

Answer 1

1. Organs of the Visual system
2. Detects light and convert it into electro-chemical impulses in neurons
3. Regulates the light intensity through a diaphragm, focuses it through an adjustable assemly of lenses to form an image-convering the image to electrical signals and transmits these signals to the brain.

NOTE: the eye is not shaped like a perfect sphere

Question 2

The Wall of the Eye consists of 3 concentric layers:

Answer 2

1. outer layer- (cornea, conjunctiva, sclera)
2. Middle layer- (Iris,Ciliary body, choroid plexus)
3. Inner Layer- (retina)

Question 3

Discuss the anatomy of the Eye in detail:

Answer 3

1. Eye is made up of 3 coats or layers
2. spaces of the eye are filled with the aqueous humor antriorly (between cornea and lens)
3. the vitreous body= a clear jelly-like substance composed of water and proteins = behind the lens, filing the entire posterior cavity.
4. the lens is suspended to the ciliary body by the suspensory ligament (zonule of zinn) made up of hundreds of fine transparent fibers which transmit muscular forces to change the shape of the lens for focusing.

Question 4

What is the average normal intraocular pressure and does it remain constant?

Answer 4

1. 15mm Hg, with a range from 12 to 20 mm Hg
2. Intraocular pressure remains constant in the normal eye, usually within + or - mm Hg of its normal level.

Question 5

Define Glaucoma and normal range of intraocular pressure:

Answer 5

is a group of eye conditions that damage the optic nerve. This damage is often caused by pathologically high intraocular pressure in the eye.

Pressure rises acutely to 60 to 70 mm Hg.

NOTE: pressure rising above 25 to 30 mm Hg can cause loss of visoin when maintaing for long periods due to compression on the axons of the optic nerve

Question 6

what changes the curvature of the lens and what is this process called?

Answer 6

changing of the Curvature of the lens is carried out by the Ciliary Muscles surrounding the lens.

This process is calld “Accomodation”

Question 7

In children the refractive power of the lens of the eye can be increased voluntarily from _____ to _____

Answer 7

20 diopters to 34 dipters

Question 8

Fun Fact:

how many estimated suspensory ligaments are attached radially around the lens, pulling the lens edges toward the outer circle of the eyeball?

Answer 8

70 Ligaments

Question 9

light energy enters the eye through what anatomical structure?

Answer 9

Through:

cornea

pupil

then lens

Question 10

T or F

The lens shape is changed for near focus (accomodation) and is controlled by the Ciliary Muscle.

Answer 10

True

Question 11

Name the light sensitive cells of the Retina

Answer 11

Photoreceptors: Cones and Rods

Question 12

Photons of light falling on the light-sensitive cells of the retina are converted into what?

Answer 12

Converted into electrical signals that are transmitted to the brain by the optic nerve and interpreted as sight and vision

Question 13

What type of Nerves control “accomodation”?

Answer 13

Parasympathetic Nerves

Question 14

The ciliary muscle is controlled almost entirely by what nerve signals?

Answer 14

Parasympathetic Nerve signals

Question 15

Parasympathetic nerve signals are transmitted to the eye through what cranial nerves?

Answer 15

Through Cranial Nerve III from the third nerve nucleus in the brain stem

Question 16

Define Emmetropia

Answer 16

Normal Eye

Question 17

Define Presbiopia

Answer 17

• the loss of accommmodatin by the lens
• lens begins to lose its intrinsic elastic properties and becomes less responsive and unable to focus on near objects (corrected with bifocal lens)

Question 18

Define Myopia

Answer 18

• Nearsightedness
• due to an eye that is elongated from front to back causign light rays to focus in front of the retina (corrected with concave lens)

Question 19

Define Hyperopia

Answer 19

• Farsightedness
• due to an eyeball that is too short from top to bottom, causing light rays to focus behing the retina (correction with a convex lens)

Question 20

Define Astigmatism

Answer 20

-caused by substantial difference in the curvature over different planes through the eye, resulting light rays entering the eye form diffent directions are focused at differnt points (corrected with the use of cylindrical lens)

Question 21

Define Cataracts:

Answer 21

• Condition comonly affecting the eye(s) of older people
• A cloudy or opaque area or areas in the lens
• some of the lens fibers become denatured
• the same protein coagulate to form opaque areas in place of normal transparent protein fibers
• Condition correction= surgical removal of the lens replaced by a powerful Convex Lens in front of the eye

Question 22

The “Retina” contains what 2 major types of light-sensitive photoreceptor cells used for vision?

name and what are they responsible for?

Answer 22

-Rods = are mainly responsible for black and white vision and vision in the Dark

-Cones = responsible for Color Vison

Question 23

Rods are responsoble for?

Contain what type of pigment?

Answer 23

• responsoble for low-light monochrome vision (black and white)
• Contain pigment “Rhodopsin” (visual Purple) which is sensitive at low light intensity but saturates at higher (photopic) intensities

Note: distibution is not present fovea and blind spot

Note: Rod density is greater in the peripheral retina than in the central retina

Question 24

Cones are responsible for?

where are they mostly found?

Answer 24

• responsoble for color vision
• require brighter light to function
• 3 types of cones (red,green,blue)
• mostly concentrated in and near the fovea

Question 25

Photochemistry of Vison: the outer segment of the rod that projects into the pigment layer of the retina has a concentration of \_\_\_\_% of the ____ \_\_\_\_ pigment called _____ or visual purple.

Answer 25

40% Light sinsitive pigment Rhodopsin

Question 26

Rhodopsin is composed of what proteins?

Answer 26

-this substance is a combination of the protein ***"Scotopsin" the carotenoid pigment 11- cis retinal***

Question 27

The primary visual cortex lies in the ____ \_\_\_\_ area, extending forward from the ____ \_\_\_\_ on the medial aspect of each occipital cortex (area #17)

Answer 27

1. Calcarine Fissure Area 2. occipital pole

Question 28

Name the Layers of Retina from the outside to the inside: (total of 9)

Answer 28

(1) pigmented layer, (2) layer of rods and cones projecting to the pigment, (3) outer nuclear layer containing the cell bodies of the rods and cones, (4) outer plexiform layer, (5) inner nuclear layer, (6) inner plexiform layer, (7) ganglionic layer, (8) layer of optic nerve fibers, inner limiting membrane (9) inner limiting membrane

Question 29

Rods and Cones (photosensors) are found in which layer of the eye? What else can be found in this layer?

Answer 29

Under the Pigmented epithelium The outer layer Additional: Outer layer of ***Granular Cells***

Question 30

What type of cranular cells are present in the "Inner Layer" of the eye ?

Answer 30

1. Horizontal cells 2. Bipolar Cells 3. Amacrine Cells 4. Ganglion Cells

Question 31

What can be found in the Nerve Fiber layer of the Eye?

Answer 31

Optic Nerve

Question 32

What is the importance of ***Foveal Region*** of the Retina ?

Answer 32

- Is important for ***" Acute and Detailed Vision"*** - fovea is a minute area in the ***center of the retina***, - is composed almost entirely of ***cones*** - these ***cones*** have a special structure that ***aids their detection of detail in the visual image.***

Question 33

T or F the *photochemicals* in the *cones* have almost exactly the same chemical composition as that of *rhodopsin* in the *rods.* the only difference is that the protein portions, or the *opsins-called photopsins* in the *cones* - are slightly different from the *scotopsin of the rods.*

Answer 33

True

Question 34

What is the chemical composition found in the rods? The Proten portion is known as?

Answer 34

Chemical composition ***Rhodopsin*** Protein ***Scotopsin***

Question 35

Protein portion of the photochemcals known as ***Photopsin*** is found in the ? And is the only difference found in the chemical compositon "protein portion" as that of *Scotopsin of the ?*

Answer 35

***Cones*** ***Rods***

Question 36

Name the *Color pigments* of *Cones* These color pigments show peak absorbencies at *light wavelents of*...provide each

Answer 36

1. Red (570) 2. Blue (445) 3. Green (535)

Question 37

The absorbtion curve for the *Rhodopsin* of the *Rods* shows a peak at ______ nanometers .

Answer 37

*505 nanometers*

Question 38

Name the different neuronal cell types :

Answer 38

1. Photoreceptors 2. Horisontal cells 3. biporal cells 4. amacrine cells 5. ganglion cells

Question 39

Photoreceptors

Answer 39

The photoreceptors: ***rods and cones*** -which *transmit signals* to the *outer plexiform layer*, where they *synapse with bipolar cells* and *horizontal cells*

Question 40

Horizonatal Cells

Answer 40

The ***horizontal cells,*** which *transmit signals horizontall* in the *outer plexiform layer* from the *rods and cones to bipolar cells*

Question 41

Bipolar cells

Answer 41

The ***bipolar cells*** *transmit signals vertically* from the *rods, cones,* and *horizontal cells* to the *inner plexiform layer*, where they *synapse with ganglion cells and amacrine cells*

Question 42

Amacrine cells

Answer 42

***amacrine cells***, which *transmit signals* in *two directions,* *either directly from bipolar cells to ganglion cells* or *horizontally within the inner plexiform layer* *from axons of the bipolar cells to dendrites of the ganglion cells or to other amacrine cells*

Question 43

Ganglion cells

Answer 43

***ganglion cells***, which *transmit output signals* from *the retina through the optic nerve into the brain*

Question 44

describe the *Visual pathway*

Answer 44

The *visual nerve signals leave* the *retinas* through the ***optic nerves***. At the ***optic chiasm***, the optic nerve fibers from the nasal halves of the retinas cross to the opposite sides, where they join the fibers from the opposite temporal retinas to form the ***optic tracts.*** The fibers of each optic tract then synapse in the ***dorsal lateral geniculate nucleus*** of the thalamus, and from there, ***geniculocalcarine fibers*** pass by way of the ***optic radiation*** (also called the geniculocalcarine tract) to the ***primary visual cortexin*** the calcarine fissure area of the medial occipital lobe

Question 45

Visual fibers also pass to several older areas of the brain: describe

Answer 45

(1) from the optic tracts to the suprachiasmatic nucleus of the hypothalamus, presumably to control circadian rhythms that synchronize various physiologic changes of the body with night and day; (2) into the pretectal nuclei in the midbrain, to elicit reflex movements of the eyes to focus on objects of importance and to activate the pupillary light reflex; (3) into the superior colliculus, to control rapid directional movements of the two eyes; (4) into the ventral lateral geniculate nucleus of the thalamus and surrounding basal regions of the brain, presumably to help control some of the body's behavioral functions.

Question 46

The *primary visual cortex* *lies* in the ____ \_\_\_\_\_\_area, extending forward from the ____ \_\_\_\_on the medial aspect of each occipital cortex. This area is the terminus of ____ \_\_\_\_\_\_ signals from the eyes.

Answer 46

***calcarine fissure area*** ***occipital pole*** ***direct visual*** signals .

Question 47

The ***fovea*** is responsible for the highest degree of What ?

Answer 47

***Visual Acuity*** - *macula* is the region that the *retinal fovea* transmits its signals. - Based on retinal area, the *fovea* has *several hundred* times as *much representation in the primary visual cortex as do the most peripheral portions of the retina*

Question 48

What is the *Secondary visual* area called and where can it be found?

Answer 48

***visual association areas*** -lies *lateral, anterior, superior, and inferior* to the ***primary visual cortex.*** Most of these areas also fold outward over the lateral surfaces of the occipital and parietal cortex. Secondary signals are transmitted to these areas for analysis of visual meanings.

Question 49

The ***secondary visual areas***, also called ***visual association areas***, lie lateral, anterior, superior, and inferior to the primary visual cortex.. These ***Secondary signals*** are transmitted to these areas for analysis of WHAT?

Answer 49

***visual meanings***