406
UNIT 3
Organ Systems
Figure 20-15A.
Retinal layers.
H&E,
3
463
There are
10 histologic layers in the retina
; see Figure
20-13B and Synopsis 20-1 for details of the compo-
nents in each layer.
Ganglion cell
Ganglion cell
Cone
Cone
Rod
Rod
10
μ
m
Nerve fiber layer (9)
Ganglion cell layer (8)
Inner plexiform layer (7)
Inner nuclear layer (6)
Outer plexiform layer (5)
Outer limiting layer (3)
Photoreceptor layer (2)
Bruch membrane
Outer nuclear layer (4)
Pigment epithelium
layer (1)
Inner limiting membrane (10)
Ganglion cell
Cone
Rod
A
B
Figure 20-15B.
Scanning electron micrograph of retinal layers.
Freeze-fracture preparation,
3
1,200
This freeze-fracture preparation of the
peripheral retina
shows the three-
dimensional shapes of the various cells in the retina. This section from
the peripheral retina has fewer ganglion cells than the macular retina
illustrated at
left
. Compare Figure 20-13B and C.
T. Yang
Neural
outflow
Light
Nerve fiber layer
Inner plexiform layer
Inner nuclear layer
Outer nuclear layer
Outer plexiform layer
Outer limiting layer
Photoreceptor layer
Pigment
epithelium layer
Ganglion cell layer
Inner limiting
membrane
Ganglion
cell
Müller cell
Müller cell
Amacrine
cell
Bipolar cell
Horizontal
cell
Rod cell
Cone cell
Pigment cell
C
Figure 20-15C.
A representation of the functional retinal
layers.
Light passes through all
retinal layers
to activate the
photore-
ceptor cells
(
rods
and
cones
), and excess light is absorbed by
pigmented epithelial cells. The photoreceptors transduce the
light into electrochemical signals, which pass to the
conduct-
ing neurons
(
bipolar cells
, then
ganglion cells
). Horizontal and
amacrine cells are
association neurons
that have long dendrites.
The dendrites of the
horizontal cells
synapse with photorecep-
tors and contribute to the elaborate neuronal connections in the
outer plexiform layer
. The dendrites of
amacrine cells
are in con-
tact with bipolar and ganglion cells and modulate signals in the
inner plexiform layer
. The ganglion cells collect all visual infor-
mation and send it along their axons in the optic nerve.
Müller
cells
are large supporting neuroglial cells and extend from the
inner limiting membrane
to the
outer limiting membrane
. Their
processes surround all the neuronal elements of the retina.
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