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A. White- Histology > The Eye > Flashcards

Flashcards in The Eye Deck (79):
1

What are the three layers of the eye?

The three layers of the eyeball, from outside to inside: sclera & cornea -> uvea (vascular tunic) -> retina (inner tunic).

2

What are the three layers of the sclera?

The sclera has three layers: episceral (outer), sclera proper (inner), and lamina cribosa.

3

What is the episceral layer of the eye?

Episceral: is the outermost layer of the sclera. It contains collagen, vessels and attaches eyelid to the sclera.

4

What is the sclera proper?

Sclera proper: innermost layer. It contains collagen, and tendons attach to the sclera at this layer. Collagen is parallel to withstand ocular muscles of the eyeball.

5

What is the lamina cribosa?

Lamina cribosa: optic nerve fibers pass through this region. It is continuous with the cornea and is highly vascularized. It is also continuous with the dural lining of the optic nerve.

6

How many layers are in the cornea?

5

7

What are the 5 layers of the cornea?

from inner to outer: corneal endothelium, descemet's membrane, stroma, bowman's membrane, corneal epithelium.

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8

What is the corneal epithelium?

Corneal epithelium: stratified, non-keratinized squamous epithelium. It has 5 – 6 layers and is highly mitotic.

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9

What is the Bowman's membrane?

Bowman’s membrane: is the outer layer of the cornea. It has type I collagen.

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10

What is the corneal stroma?

Corneal stroma: thin layer of collagen fibers that is highly resistant to deformation and trauma.

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11

What is Descemot's membrane?

Descemot’s membrane: collagen bundles separated from the stroma by the endothelium.

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12

What is the corneal endothelium?

Corneal endothelium: single layer of large squamous cells. (simple squamous cells)

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13

What are the 3 layers of the uvea?

Contains the choroid, ciliary body and the iris.

14

What is the choroid?

Choroid: It is anteior to the ora serrata (serrated ring inside the eyball that separates the retina and eyeball). It has highly vascularized loose connective tissue, and the vessels supply nutrients to the outer retina. It also contains Bruh’s glassy membrane, which contains PIGMENTED epithelium.

15

What is the ciliary body?

Ciliary body: an expansion of the choroid. It has two layers – the innermost layer is continuous with the pigmented layer of the retina, and the surface layer is from the sensory layer of the retina. It produces aqueous humor, anchors the lens in place, and contains ciliary muscles that change the shape of the lens (thicker or wider – controlled by parasympathetics).

16

Vitreous humor flows from the ___ chamber to the ___ chamber.

posterior, anterior

17

In order to make a gradient for vitreous humor to flow, what type of organelles are found in the posterior and anterior chamber?

mitochondria

18

What type of capillaries are present near the posterior and anterior chamber?

fenestrated.

19

What canal does the vitreous humor pass through as travels from the posterior to anterior chamber?

Canal of Schlemm

20

The iris makes a border between what chambers of the eye?

posterior and anterior chambers.

21

What do ciliary muscles do?

The ciliary muscles in the ciliary body allow for thickening and flattening of the lens. This allows for accommodation of near and far vision (reracting light), and is assisted by the cornea.

22

How does the lens change when viewing something near to the eye?

For close vision, the ciliary muscle contracts, reducing tension and making the lens thicker.

23

How does the lens change when viewing something far from the eye?

For distant vision, the ciliary muscle relaxes, increasing tension in ligaments and causing the lens to flatten. The tension is produced by ligaments attached to the lens.

24

What do the nonpigmented cells in the ciliary body produce?

vitreous humor.

25

Once nonpigmented cells in the ciliary body produce vitreous humor, where does the vitreous humor go?

to the posterior chamber and veins.

26

What is the function of the iris?

Iris: anterior to the lens. It separates the anterior and posterior chambers. It is angled and made of connective tissue, which is the passageway for aqueous humor. This also surrounds the pupil.

27

What does the outer layer of the iris do?

The iris has a double layer of epithelium. The OUTER has myofilaments that has sympathetic innervation (dilates pupil) and parasympathetic (constricts pupil).

28

What is the inner layer of the iris?

pigmented epithelial cells.

29

If the iris has a large number of melanocytes, what color will the iris be?

dark

30

What are the two regions of the retina?

Retina: has two regions divided by the ora serrata – the optic disc and fovea centralis.

31

What does the optic disc do?

Optic disc: region on posteior side near the optic nerve. It is the blind spot.

32

What does the fovea centralis do?

Fovea centralis: contains cone receptors and yellow pigment. It is an area of acute vision. This has to do with how the cones are angled and how light enters.

33

What is the vitreal chamber?

Vitreal chamber: posterior to lens, contains vitreous body and a gelatinous mass of water, hyaluroinic acid and vitrein. It also contains a hyaloid canal, which is a remnant of an early fetal vessel used for nutrition.

34

How is glaucoma caused?

Glaucoma: increased intraocular pressure due to comprised drainage of aqueous humor from anterior chamber.

35

Pigmented epithelium in the retina comes from what region?

the optic cup.

36

What do the inner and outer segments of the retina do?

Inner and outer segments: outer segments have rhodopsin-containing lamellae (it prevents light from scattering in the eye and focuses it in the right place).

37

What is the external limiting membrane of the retina?

External limiting membrane: is at the junction of the inner and outer segments of rods and cons and outer nuclear layer. It has junctions between rods and cones and Mueller cells (support cells).

38

What are the layers of the retina?

outer nuclear, outer plexiform, inner nuclear, inner plexiform, ganglion cell, optic nerve and internal limiting membrane.

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39

What is the outer nuclear layer?

Outer nuclear: cell bodies of rods and cones (1st order neurons – they are the receptors that light strikes, and they generate action potentials that are send to other neurons).

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40

What is the outer plexiform layer?

Outer plexiform layer: area of syapses between axons of rods and cones and dendrites of bipolar neurons and horizontal cells.

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41

What is the inner nuclear layer?

Inner nuclear layer: cell bodies of bipolar cells (2nd order neurons – receive information from 1st order, sends to third order nucleus). They take image and process it.

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42

What is the inner plexiform layer?

Inner plexiform layer: synapses btween axons of bipolar cells and dendrites of ganglion cells.

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43

What is the ganglion cell layer?

Ganglion cell layer: cell bodies of ganglions (3rd order neurons – used to fine-tune an image).

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44

What is the optic nerve layer?

Optic nerve layer: axons of ganglion cells

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45

What is the internal limiting membrane?

Internal limiting membrane: terminations of Mueller (support) cell processe and their basement membrane.

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46

What types of cells are found in the retina?

ganglion, Mueller, amacrine, horizontal, bipolar and pigmented epithelial cells.

47

What are pigmented epithelial cells?

Pigmented epithelial cells: are adjacent to choroid and synthesize melanin. Their process protect outer segments of rods and cones, which are protosensitive. This region is constantly forming new pigment cells (lamellae), and therefore has phagocytosis to degrade old pigment cells.

48

What are bipolar cells?

Bipolar cells: conducting neurons that synapse with rods and cones.

49

What are horizontal cells?

Horizontal cells: interneurons that connect rods and cones with each other and with bipolar cells.

50

What are amacrine cells?

Amacrine cells: interneurons that connect ganglion cells and bipolar neurons.

51

What are Mueller cells?

Muller cells: neuroglial cells that extend throughout the retina. They form membranes between Muller cells.

52

What are ganglion cells?

Ganglion cells: neurons whose axons form the fibers of the optic nerve.

53

What is the macular lutea?

Macular lutea: yellow region surrounding the fovea with the highest visual acuity.

54

What is the fovea centralis?

Fovea centralis: depressio of the visual axis that has a high density of cone cells. It lacks rod cells and capillaries.

55

What is the optic disc?

Optic disc: region that lacks photoreceptors (e.g. blind spot) and is where the ganglion turns into optic nerve.

56

What are the two types of photoreceptors in the retina?

rods and cones.

57

What pigment do rods use?

rhodopsin; cones use 3 different types of pigment.

58

What are the 3 regions of the rods and cones?

. Rods and cones have a cell body, and inner segment and an outer segment. The inner segment has organelles. The cell body has modified cilium and stacks of disks with photoreceptors. It is also connected by stalk to inner segment.

59

What are rod cell discs?

Rod cell disks: disks detach from cell membrane and become free. They are constantly renewed. Older disks are phagocytosed by surrounding pigmented epithelial cells.

60

Do cone cell discs detach from the cone?

no

61

What does the rod tunic use in low-light conditions?

rhodopsin

62

The rod is responsible for what type of vision?

black and white vision

63

Cone tunics are responsible for what type of vision?

vision in high-light conditions; each cone tunic connects to a bipolar cell.

64

What is rhodopsin?

Rhodopsin: a transmembrane protein with opsin and 11-cis-retinal (Vitamin A derivative).

65

What activates 11-cis-retinal?

A photon (e.g. light). 11-cis-retinal then activates rhodopsin.

66

When rhodopsin is activated, what molecule does it interact with?

transducin (a G-protein)

67

When transducin is activated, what enzymes does it subsequently activate?

cGMP phosphodiesterase

68

The activation of cGMP causes what to happen to the potential of a membrane?

hyperpolarization occurs due to closed Na channels. Calcium concentration is also decreased, which activates recoverin.

69

recoverin activates what enzyme?

guanalyte cyclase; this returns cGMP levels to normal.

70

What is bleaching?

Bleaching: disassembly of rhodopsin into opsin and retinal after light stiumulation.

71

How are photopigments regenerated?

Regeneration of photopigments: 11=trans-retinal is converted back into 11-cis-retinal, which is transported back into the photoreceptor. This recombines with opsin and rhodopsin is regnerated.

72

What are the two components of the lens?

capsule and endothelium

73

What is the capsule?

Capsule: insertion point for suspensory ligament. It contains collagen and type IV collagen and is secreted by subscapular epithelial cells.

74

What is the anterior epithelium?

Anterior epithelium: simple cuboidal epithelium that gives rise to cells that become “lens fibers”.

75

What is the lens nucleus?

Lens nucleus: composed of lens cells that mature into fiber like structures that are devoid of the nucleus and organells, but are filled with proteins.

76

What are the components of the eyelid?

Composed of the anterior surface, palpebral fascia and the palpebran conjuctiva.

77

What is the anterior surface of the eyelid?

The anteior surface is covered with skin. It has sebaceous and sweat glands (Glands of Zeiss and Moll).

78

What is the palpebral fascia?

The palpebral fascia is fibrous and contains sebaceous glands that do not have hair follicles. Theyopen in front of free edge of eyelid and their secretion keeps normal tear film in the eye (Meibomian glands).

79

What is the palpebral conjunctiva?

The palpebra conjuctiva is stratified columnar/squamous epithelium that has goblet cells. It lines the INNER surface of the eyelid and is continuous with the bulbar conjunctiva (covers eyeball).