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Fall 2019: OPT 114 Ocular Anatomy and Physiology > Retinal Cells > Flashcards

Retinal Cells Flashcards

1
Q

3 main types of cells in the retina

A

Epithelial
-RPE

Neurons

  • Photoreceptors
  • Horizontal
  • Bipolar
  • Amacrine
  • Ganglion

Neuroglia

  • Muller
  • Microglial
  • Astrocytes
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2
Q

RPE Is __ to photoreceptors and __ to choroid

A

Outer to photoreceptors

inner to choroid

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3
Q

RPE extends where

A

From the margins of the ON to era serrata

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4
Q

How many RPE and what is their arrangement

A

~5 million cells arranged in a single layer
-Homogeneously sized. (Columnar in the posterior pole- longer and narrower and cuboidal near the ora serrata- this is where it transitions to pigmented epithelium of the ciliary body).

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5
Q

How are RPE bound and what is their structure

A

Apical aspect has microvilli that are associated with the photoreceptor outer segments.
Tight junctions join the apical aspect of adjacent cells, forming a complete barrier. Therefore, RPE regulates what goes too photoreceptors.

Basal aspet is attached to a basement membrane that forms the most inner layer of Bruch’s membrane.

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6
Q

Bruch’s membrane

A

Basement membrane sandwich.

Inner: RPE basement membrane
Collagen
Elastin
Collen
Outer: Choriocapiliaris basement membrane
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7
Q

RPE and melanin

A

Melanin is present with varying density in RPE cells.
Densest in the macula, and denser in darker skinned individuals. Functions to filter UV radiation.
Covers the choroid.

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8
Q

Lipofuscin

A

Trash collected from photoreceptor cells, mainly derived from incompletely digested photoreceptor outer segments.

Present within lysosomes of RPE cells. Composed of flurorescent compounds, lipids and proteins.

Accumulates with age. Known as “wear and tear” pigment.

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9
Q

Xanthophylls

A

Lutein and zeaxanthin.
Type of yellow plant pigment that is found in RPE cells and outer segments of photoreceptor cells.

Act as a filter and absorb short wavelength visible light (blue) to reduce chromatic aberration. May also have antioxidant effect.

Located throughout the retina, but greatest concentration is in the macula. Accumulate from dietary sources.

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10
Q

Two types of xanthophylls

A

Lutein and Zeaxanthin

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11
Q

How do RPE cells transport nutrients to and remove waste from the photoreceptors

A

Nutrients come from the choriocapillaris and waste are given to the choriocapillaris for removal.

Contributes to the blood-retinal barrier.

RPE cells can metabolize and store vitamin A for the photoreceptors to use. Vitamin A is necessary for phototransduction (converting light energy into neural signal).

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12
Q

How do Ions, water, and glucose/lactate travel through RPE cells

A

Since RPE cells have tight junctions, all nutrients must flow through the cell.

Ions travel by ATPase pumps, cotransporters, and ion channels.

Water travels through aquaporins

Glucose and lactate movement occurs by carrier proteins.

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13
Q

Each RPE cell interacts with ___ photoreceptors

A

30-40. Acts to supply them with nutrients and remove waste.

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14
Q

Which vitamin is necessary for phototransduction

A

Vitamin A. RPE cells metabolize and store vitamin A for photoreceptor use.

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15
Q

RPE cells contain numerous lysosomes that enable the cell to ingest as many as ___ discs daily. Undigested material accumulates as deposits of ___.

A

2000

lipofuscin.

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16
Q

What is the interphotoreceptor matrix (IPM) composed of?

A

Composed of GAGs and proteoglycans. Surrounds the apex of RPE cells and the outer and inner segments of photoreceptors.

Has adhesive properties that holds the RPE and photoreceptors in close proximity since one RPE cell is responsible for ~40 photoreceptor cells.

May be partially responsible for orienting photoreceptor outer segments towards the pupil for optimal light capture.

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17
Q

RPE cells produce growth factor. What does the GF do?

A

Helps maintain the choriocapillaris

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18
Q

~___ million rods and highest density in ___

~___ milling cones and highest density in ___

A

120 million rods. high density in peripheral retina

6 million cones. High density in macula with the fovea being exclusively cones.

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19
Q

6 regions of a photoreceptor (inner to outer)

A 
Inner/top, near vitreous humor. 
1. Inner fiber 
2. Cell body
3. Outer fiber 
4. Inner segment 
5. Cilium
6. Outer segment 
Outer/bottom, connected to RPE.
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20
Q

Inner fibers

A

Axons of the photoreceptor at the top of the cell.

The axon terminals are invaginated and contain presynaptic vesicles. (Cones have more invaginations than rods)

Contains synaptic ribbons that hold the vesicles close to the terminal.

Send the neural signal to bipolar and horizontal cells and release the NT glutamate.

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21
Q

Cell body of photoreceptor cells

A

contains the nucleus

22
Q

Outer fiber of the photoreceptor cells

A

Extends from the inner segment to the cell body

23
Q

Inner segment of the photoreceptor cells

A

Produces the components of the outer segment.

Portion closest to the outer segment is called the ellipsoid, which contains numerous mitochondria.

The portion closest to the cell body is called the hyoid, which contains the ER and golgi.

24
Q

Inner segment contains which two components

A

Ellipsoid- portion closest to the outer segment. Contains the mitochondria.
Myoid- portion closest to the cell body. Contains the ER and golgi.

25
Q

Cilium (IS-OS junction)

A

Composed of microtubules (proteins). Connects the inner segment with the outer segment and acts as a conduit for metabolites between the inner and outer segments.

26
Q

Outer segment

A

Closely associated with the RPE. Consists of a stack of flattened discs surrounded by a lipid bilayer membrane.

Each disc contains a visual pigment transmembrane protein. Visual pigment is activated by light with leads to production of a neural signal. = Phototransduction occurs

27
Q

Where does phototransduction occur in a photoreceptor cell

A

Outer segment discs

28
Q

Visual pigments in rods and cones and what light activates them?

A

Rods-
Rhodopsin is the visual pigment. Activated by light at 496 nm (blue green light)

Cones-
3 Different visual pigments contained in cone discs. Activated by light at:
420 nm (blue)
521 nm (green) 
588 nm (red)
29
Q

Differences between outer segments of rods and cones

A

Rods:
Discs are uniform in width. They are gradually displaced outward by the formation of new discs. They are shed regularly (usually in the morning) and are phagocytize by RPE.

Cones:
Discs are wider at the base than the apex.
Have a longer life span than rods.
Unknown how discs are shed and produced.

30
Q

Difference between inner segments of rods and cones

A

Cones have more mitochondria than rods

31
Q

outer fibers differences between rods and cones

A

Cones have a shorter (sometimes absent) outer fiber.

Cone nuclei lie outer to rod nuclei.

32
Q

Inner fiber differences between rods and cones

A

Rods terminate in a rounded, pear shape structure called a spherule. 1 invagination and 2 synaptic ribbons. Up to 5 neuronal terminals (from bipolar and horizontal cells) may be embedded in 1 spherule.

Cones terminate in a broad, flattened structure called a pedicle. 
Several invaginations (4-8) and synaptic ribbons.
3 neuronal terminals from bipolar and horizontal cells are embedded in each invagination.
33
Q

Structure of cone pedicle

  1. How many invaginations?
  2. How many neurons in each invagination? and which type of neurons?
  3. How many ribbons?
A
  1. 4-8 invaginations
  2. 3 neurons in each that are either bipolar or horizontal
  3. many ribbons that hold synaptic vesicles in place containing glutamate
34
Q

Scotopic vision

A

vision in dim light/darkness by rods.

Ability to recognize fine detail is poor.
Color vision is absent.

35
Q

Photopic vision

A

Vision in bright light by cones. Ability to recognize fine detail and discriminate colors

36
Q

Structure of rod sphenule

  1. How many invaginations?
  2. How many neurons in each invagination and which types of neurons?
  3. How many ribbons?
A
  1. 1 invagination
  2. 5 neurons in each invagination that are either bipolar or horizontal
  3. 2 ribbons that hold synaptic vesicles in place containing glutamate.
37
Q

Horizontal cells

A

Found inner to the photoreceptors, closer to the vitreous chamber.

Dendrites extend horizontally and down to receive signals from photoreceptor cells. They modify the neural signal if needed and sometimes send it back to another photoreceptor cell to double check it (if an axon is present).

38
Q

Function is to integrate and regulate the input from several photoreceptors?

A

Horizontal cells. Take in information from many photoreceptor cells and have the ability to modify the signal or send it back to photoreceptors for double checking.

39
Q

how many Bipolar cells and where are they located

A

36 million inner to photoreceptor cells (120 million rods and 6 million cones, not enough for a 1:1 ratio all over)

40
Q

Role of bipolar cells

A

Dendrites of the bipolar cell receives signals from photoreceptors. Axons send the dural signal to amacrine cells, but mostly to ganglion cells. When they synapse with ganglion cells, they release the neurotransmitter glutamate.

41
Q

Amacrine cells location

A

Inner to bipolar cells (between bipolar and ganglion)

42
Q

Amacrine cell role

A

A single process receives signals from bipolar cells and sends signals to ganglion cells. Releases the neurotransmitter GABA or glycine to ganglion ells.

43
Q

how many Ganglion cells

A

1.2 million cells inner to bipolar and amacrine cels

44
Q

Role of ganglion cells

A

They are the final retinal destination of the neural signal.

Their dendrites receive signals from mainly bipolar cells, but also amacrine cells. Axons carry the retinal neural signal to the brain via the optic nerve. They form bundles that converge at the optic disc and form the optic nerve. The optic nerve courses from the eye to the thalamus to synapse in the LGN (in forebrain). They release glutamate here.

45
Q

Pathway of ganglion cells

A

Their dendrites receive signals from mainly bipolar cells, but also amacrine cells. Axons carry the retinal neural signal to the brain via the optic nerve. They form bundles that converge at the optic disc and form the optic nerve. The optic nerve courses from the eye to the thalamus to synapse in the LGN (in forebrain). Here, they release glutamate.

46
Q

Areas of convergence and non-convergence

A

Convergence occurs in the peripheral retina.
~100 rods and 4-6 cones is transferred to each ganglion cell.

In the central macula, there is a 1:1:1 ratio between photoreceptors, bipolar cells, and ganglion cells. No convergence.

47
Q

Which cells release glutamate and which cells release GABA/glyceine

A

GABA and glyceine is released by amacrine cells to the ganglion cells.

Photoreceptors release glutamate to bipolar cells
Bipolar cells release glutamate to ganglion cells
Ganglion bundles (ON) releases glutamate at the LGN.

48
Q

Neuroglial cells (3)

A

Muller cells (predominant), microglial cells, astrocytes

49
Q

How many muller cells

A

~10 million cells that extend from the photoreceptor inner segments to the inner retinal surface.

50
Q

Where are muller cells located

A

Apical aspect is located between the inner segments of the rods and cones. Basal aspect is at the inner retinal surface.

51
Q

Role of muller cells

A

Provide structural support for retinal neurons.
Maintain extracellular pH by absorbing metabolic waste products.
Recycle neurotransmitters released by retinal neurons (glutamate, GABA, glyceine)
Form the inner limiting membrane

52
Q

Inner limiting membrane formed by muller cells- where is it located and what does it consist of.

A

Innermost boundary of the retina.
Consists of termination of Muller cell processes (footplates) covered by a basement membrane. Vitreous is on the other side of it.

Fall 2019: OPT 114 Ocular Anatomy and Physiology (50 decks)

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