Neurophys 6

Front 1

Most of the light bending (focusing) occurs at the
level of

Back 1

the curved cornea not the lens

Front 2

Myopic eye
near sighted, parallel light rays become

Back 2

focused at
an area before the retina

Front 3

Myopic eye can be fixed with what type of lens

Back 3

A concave lens should fix
it.

Front 4

Hypermetrophic

Back 4

eye is an eye too short, rays get
focused at s point behind the retina

Front 5

Hypermetrophic can be fixed by

Back 5

a convex lens
should fix it

Front 6

In a relaxed eye the lens are in

Back 6

in a flattened position which is the same position
as when we focus far aw

Front 7

Flattened shape takes
place because

Back 7

because the lens is covered in a sheet with tension

Front 8

When focusing on something close the
retina becomes

Back 8

rounded this happens because there are muscles attached to the sheet and act to relieve the tension of the sheet.

Front 9

This change in btw
flattened and rounded shapes is called the

Back 9

processes of accommodation.

Front 10

Presbyopia is the

Back 10

inability of lens to change shape (remains in relatively flattened position)

Front 11

The retinal pigment epithelial cells have a lot of

Back 11

melanin the idea is that if light doesn't get caught
by its proper receptor, you don't want it to be
bouncing around so this black blanket of melanin
traps it. Behind this layer is this choroid

Front 12

layers that light has to go through

Back 12

Outer Nuclear Layer (ONL)
Nuclei of photoreceptors
Outer Plexiform Layer (OPL)
Outer synaptic layer
Inner Nuclear layer (INL)
Cell bodies of bipolar, horizontal and
amacrine cells
Inner Plexiform layer (IPL)
Inner synaptic layer
Ganglion cell layer (GCL)

Front 13

The flow of visual info goes from

Back 13

photo receptors,
bipolar cells, ganglion cells

Front 14

The area where the
nuclei of photo receptor cells are is known as

Back 14

Outer nuclear layer

Front 15

Area where photoreceptors
make synapses with secondary axons is called

Back 15

The outer plexiform layer

Front 16

Area with cell bodies of
bipolar, horizontal and amacrine cells is k

Back 16

Inner nuclear layer

Front 17

Area where bipolar cells
make synapse connection is

Back 17

Inner plexiform layer

Front 18

Area of body of ganglion cell is known as

Back 18

ganglion cell layer

Front 19

In the inner most portions of the retina astrocytes

Back 19

lay the tract for blood supply to develop

Front 20

Muller cells are

Back 20

radial glial cells that run across the length of all the layers, they form an outer limiting membrane and inner limiting membrane

Front 21

Foveal specialization

Back 21

at fovea, only photoreceptors present;
other cells pushed to side; thought to decrease light scatter
and increase visual acuity.

Front 22

Human retina is highly

Back 22

rod dominant

Front 23

At the fovea
there are only photoreceptors. All the other cells
are pushed aside this is for light not to be

Back 23

get
disturbed as it gets to the fovea..this is why the
retina has he highest visual acuity cause light gets
straight to the

Front 24

At the fovea there's one
photoreceptor cell synapsing with

Back 24

one bipolar cells
which synapses with one ganglion cell so this is one
to one relay of info

Front 25

Rods most concentrated in

Back 25

periphery

Front 26

In periphery, much “convergence”
of communication

Back 26

many
photoreceptors to a few bipolar
cells to even less ganglion cells

Front 27

Light goes to fovea pit. The fovea is only a couple of
microns long, so how do we deal with having our
highest visual acuity being relatively small

Back 27

We
are always moving our head to focus on what we
really want to see.

Front 28

Retinitis pigmentosa is a diseased in which

Back 28

you can lose vision without even know it

Front 29

Glaucoma is

Back 29

the lost of cell ganglion in the cell periphery

Front 30

Rods are active most in

Back 30

dim light.

Front 31

On the periphery there's lousy visual
acuity because

Back 31

photoreceptors synapse with
multiple bipolar cells, so that they can't tell where
the light is coming from as a consequence the
spatial resolution is poor..why is it this way?
Because under dim light the rods achieve
sensitivity by recruiting the response of many
photoreceptors sacrificing visual acuity to pick up visual sensitivity.

Front 32

. In retinit pigmentosa the fovea gets hit and the cones

Back 32

get lost and rods remain, so we still have peripheral vision which is not very useful for visual acuity

Front 33

In the photoreceptor outer segment there are
disks, each one of these disk have

Back 33

rhodopsin

Front 34

The
disks are made of of lipid bilayer and inserted in
them there are

Back 34

we see the rhodopsin molecule made up of 2
components aa segment that goes across the
bilayer 7 times and a lighht sensory molecule
called retinal and it has a bent characteristic in its
resting state before ready to absorb light

Front 35

When
light gets turned on, retinal

Back 35

retinal has a conformational
change and becomes straight and kicks out apsin
and becomes active

Front 36

Once the photon is absorbed an
enzymatic cascade is activated that alters

Back 36

the flow of ions through the plasma membrane of the receptor

Front 37

Oddly, the receptors hyperpolarized
when they absorbed the photon because

Back 37

Na channels are closed gprotein and activated the gprotein alpha
subunit goes on and activates cGMP
phophodiesterase and it takes cGMP and makes a
5gmp..Na channel is a cgmp dependent. When
photon is absorbed cgmp is degraded and Na
channel closes leading to hyperpolarization.
segment is rich in mitochondria.

Front 38

Invertebrate response to light

Back 38

light > ^ action potentials; brighter > more spikes

Front 39

Vertebrate photoreceptor response is

Back 39

is hyperpolarizing and graded
Brighter light > greater hyperpolarization (up to saturation at ~ -70 mV)

Front 40

In dark, cell is depolarized
by a continual

Back 40

influx of
sodium through the outer
segment (the “dark
current”)

Front 41

Sodium is pumped out in

Back 41

inner segment and
potassium pumped in by
Na/K/ATPase pump

Front 42

Inner segment has
many, many

Back 42

mitochondria to supply
ATP for the pump

Front 43

Absorption of light by
visual pigment leads to

Back 43

closure of outer segment
channels

Front 44

In the dark there's an influx of Na into the
photoreceptor and the cell continues to

Back 44

to depolarize
dark current

Front 45

Lots of Na/k atpase pumps on

Back 45

inner membrane

Front 46

When Na channels close no more

Back 46

dark current and what sets the membrane potential are
the k channels

Front 47

In vertebrate photoreceptor,
light absorbed by visual
pigment leads to

Back 47

Activation of G- protein
(transducin) >
Activation of PDE >
Decrease in cGMP >
Closure of channels >
Hyperpolarization >
Decrease in neurotransmitter
Release (!)

Front 48

Photoreceptors can adapt and adjust their response range to

Back 48

a very
large range of background intensity (10 orders of magnitude (!))

Front 49

Addition of a background light shifts

Back 49

the response operating range
respond over new ranges of light intensity
(example - from movie theater to sandy volleyball court)

Front 50

The intensity to which the rods respond changes as
light

Back 50

goes from high to low, at one point the rods
give out and the cones take over for brighter lights.

Front 51

Cones also change to intensity ranges (adaption
process) . How does this affect us.?

Back 51

When light is
really low we need about 6 photons to see it as
background light increases takes more and more
light to see it. There's a point in which rods give up
and cones take over and this is called the rod-cone
break

Front 52

Going from a very bright place to a dim lit
place it takes time for the

Back 52

other words they become
more sensitive to only a few photons

Front 53

When in the
dark and trying to find a star we should look

Back 53

look 18
degrees to the side of the fovea because cones are
not used in the dark but rods which are more
concentrated in the periphery

Front 54

From dark to sandy beach: as
intensity of background light ^,
it takes

Back 54

more light to see a
difference

Front 55

From beach to dark with time:
we become

Back 55

more and more
sensitive to light with time

Front 56

A few other interesting features in retina:

Back 56

Motion-selective ganglion cells
Color-sensitive cells seen in INL (bipolars & horizontal cells)

Front 57

Rod pathway

Back 57

Rods > bipolar > amacrine > ganglion cells

Front 58

Cone pathway

Back 58

Cones > bipolar > ganglion cells

Front 59

Visual pigment regeneration

Back 59

a key role of the retinal pigment
epithelial cells (RPE cells) & carrier proteins (e.g., IRBP)

Front 60

After some time the old retinal dissociated from
apsin which is light sensitive. We need to restore
the inactivated retinal otherwise we go blind..how do we do this?

Back 60

blind. The
old retinal or transretinal leaves the photoreceptor
and it gets carried by a specific protein irbp and
puts into the retinal pigment cell where it is stored
and the enzymes in this place covert the old retinal
to the 11 cys retinal and it goes back to the
photoreceptor to associate with apsin so that light
ca be seen again

Front 61

Problems in retinal epithelial
segements can lead to blindness because the
ability to restore retinal

Back 61

is lost. Retinal is a variant
of vit a. If not enough vit we go blind. Shark liver
has lots of vit a.

Front 62

Photoreceptors,
horizontal cells and
bipolar cells all give
graded responses to

Back 62

light

Front 63

Some amacrine cells
show action potentials
All ganglion cells show
action potentials

Back 63

Because we need a signal that doesn't decay
with long distances. Graded potential degrade with
distance. Horizontal and amacrine cells have
graded potentials because cells are close together

Front 64

Ganglion cells care about

Back 64

differences meaning visual contrast, so differences
btw light and dark not big lights

Front 65

On ganglion cells
when stimulated with light with a dark center, it
decreases the action potentials, a small light
produces

Back 65

large actions potentials and large light
doesn't produce action potentials

Front 66

An off center ganglion, small light theres a

Back 66

decrease in AP if we put a dark center in the light
there is action potential

Front 67

“Off” bipolar cells:
typical ionotropic

Back 67

glutamate receptors
that allow influx of Na, Ca – keep cells
depolarized when glu is present

Front 68

“On” bipolar cells:
metabotropic

Back 68

receptors hypothesized
To be kept closed by glutamate

Front 69

glutamate is
photoreceptor neurotransmitter
&
light decreases

Back 69

glutamate release
from photoreceptors onto bipolar
cells in both cases

Front 70

Hyperpolarization in the photoreceptors is
converted to

Back 70

depolarization by the on center bipolar cells

Front 71

On On center ganglia As the light creates an action
potential potential, but as the light becomes
broader in spatial dimension, the ap decreases.
How does that happen?

Back 71

Without the surround
response creates an ap on the ganglion. Now when
the stimulu elicits the response of the surround
response Here's where we have the impact of the
horizontal cells. Horizontal cells believed to inhibit
photoreceptor Keeping them tonically
hyperpolarized. The surrounding photoreceptor
gets hyperpolarized which leads to
hyperpolarization of the horizontal cell that
relieves the tonic inhibition of the photoreceptors
to which the horizontal cell is attached to and the
photoreceptor depolarizes, so glutamate can't be
released because hyperpolarization is needed when
dealing with on center ganglion. This is known as
lateral inhibition and it helps improve visual contrast

Front 72

overwhelmed with and nts and
no changes can be achie

Back 72

On graph b A compound has been given which
blocks Neurotransmitter release From the
photoreceptor to the second order Neuron cell So
then the system is

Front 73

wave.
So under conditions in which photoreceptors
seemed to be acting fine but they can't get their
message across bipolar cells, there is no

Back 73

B wave so you wouldnt be able to see

Front 74

a-wave
b-wave
c-wave
d-wave

Back 74

photoreceptor origin
inner retinal activity
Pigment epithelial cells function
off response (inner retina)