Development of the Sensory Retina

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Questions and Answers

At what week of development does the future fovea start to form?

22 weeks (correct)

25 weeks

18 weeks

30 weeks

Which cells migrate away from the centre of the future fovea during foveal development?

Ganglion cells and photoreceptors

Bipolar cells and horizontal cells

Inner nuclear layer cells and then ganglion cells

Ganglion cells and then inner nuclear layer cells (correct)

What is the primary mechanism determining peripheral cell density in the retina?

Migration towards the fovea and apoptosis of photoreceptors

Expansion and migration of retinal cells

Differentiation of bipolar cells and horizontal cells

Migration away from the fovea and apoptosis of ganglion cells (correct)

What is the characteristic of the fovea that differentiates it from the peripheral retina?

Higher density of cones, particularly L- and M-cones Signup and view all the answers

When do changes in cell density due to retinal expansion and migration continue to occur in the retina?

For a limited period after birth, but not for some years Signup and view all the answers

What is the layer in the retina where vertical networks in the inner and outer retina are interconnected?

Outer plexiform layer (OPL) Signup and view all the answers

What is the direction of the developmental gradient in the formation of the sensory retina?

From the centre to the periphery Signup and view all the answers

Which type of cell is the first to differentiate in the retina during week 9?

Ganglion cells Signup and view all the answers

What is the order of formation of the neural layers in the retina?

Nerve fibre layer, Marginal zone, Inner neuroblastic layer Signup and view all the answers

When do the last rods, Műller’s cells, and bipolar cells form in the human retina?

Postnatally Signup and view all the answers

Which phase of synapse formation in the peripheral retina involves the formation of synapses between retinal ganglion cells and amacrine cells?

The first phase Signup and view all the answers

What is the name of the layer that forms after the inner neuroblastic layer in the retina?

Transient layer of Chievitz Signup and view all the answers

At 4.5 months, what is the characteristic arrangement of cone nuclei in the outer nuclear layer?

Aligned adjacent to the RPE Signup and view all the answers

What is the primary site of synapse formation in the retina at 4.5 months?

Between bipolar cell dendrites and cone pedicles Signup and view all the answers

At 5.5 months, what is the morphology of the ganglion cell layer?

Thinned out to one or two layers Signup and view all the answers

What is the primary function of Műller fibres in the inner plexiform layer?

Supporting bipolar, ganglion, and amacrine cells Signup and view all the answers

What is the characteristic feature of photoreceptor outer segments at 4.5 months?

Not yet formed Signup and view all the answers

What is the origin of bipolar and horizontal cells in the inner nuclear layer?

Outer neuroblastic layer Signup and view all the answers

Study Notes

Retinal Development

At 4.5 months, retinal lamination is essentially complete, with layers including RPE, photoreceptors, outer plexiform layer, inner nuclear layer, inner plexiform layer, ganglion cell layer, and nerve fibres.
At this stage, large cone nuclei are aligned adjacent to the RPE, and primitive lamellar synapses are established between bipolar cell dendrites and cone pedicles.

Formation of the Retina

By 5.5 months, the retina has progressed, with growing photoreceptor outer segments projecting between RPE and external limiting membrane.
The outer nuclear layer consists of 6-7 layers of nuclei, with cones aligned to the external limiting membrane.
The outer plexiform layer has a linear arrangement of synapses between bipolar cells and rod spherules.

Foveal Development

The fovea is the first part of the retina to develop but the last to mature, starting to form at approximately 22 weeks.
The future fovea initially appears as a thickened layer of ganglion cell nuclei, which will later give way to the foveal pit.
Cell migration plays a crucial role in foveal development, with ganglion and inner nuclear layer cells migrating away from the centre of the future fovea.
Cones, particularly L- and M-cones, migrate into the fovea, increasing central cone density.

Retinal Cell Density

Retinal cell density is determined by expansion, migration, and apoptosis.
Foveal cell density is primarily a result of migration and lack of expansion.
Peripheral cell density is due to a combination of migration away from the fovea, greater retinal expansion, and apoptosis of ganglion cells.

Formation of the Sensory Retina

The retina has a centre-to-periphery developmental gradient, starting from the site of the future fovea and extending outward.
Differentiation begins at about week 9 with the formation of ganglion cells, then horizontal cells and cones.
By week 10, the first amacrine cells, rods, Müller's cells, and bipolar cells form.
The same waves of cell development are apparent in the periphery, but begin later.
The last rods, Müller's cells, and bipolar cells in the human retina are formed postnatally.

Synaptogenesis

Synapse formation follows the same plan, occurring first in the fovea, about a week after the first cells in a given region are born, then spreading outward to the periphery.
The formation of synapses between the major neuronal classes of the retina occurs in three major phases, starting with retinal ganglion cells and amacrine cells forming the earliest functional circuits of the inner plexiform layer.

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Description

Learn about the formation of the sensory retina, including the center to periphery developmental gradient and the timeline of cell differentiation.