Retina and RPE Part 2 Flashcards
How many bipolar cells are in the retina?
35.7 million
What is the primary function of bipolar cells?
transmit signals from photoreceptors to ganglion cells, between which they are interposed
Within which layer of the neurosensory retina can bipolar cells be found?
cell bodies are in the inner nuclear layer
oriented in a radial fashion parallel to the photoreceptors
What is the arrangement of bipolar clels dendrites?
single or multiple dendrites pass outwards to synapse principally with photoreceptors (but also horizontal cells)
What are the 2 types of cells which bipolar cell dendrites synapse with?
- photoreceptors (principally)
- horizontal cells
What is the arrangement of bipolar cells’ axons?
passes inwards and synapses with ganglion and amacrine cells
What are the 2 types of cells which bipolar cells’ axons synapse with?
- ganglion cells
- amacrine cells
What is the ratio of cones : bipolar cells : ganglion cells in the foveal region of the central retina?
1 : 1: 1
What is the ratio of bipolar cells : rods cells in the peripheral retina?
1 bipolar cell receives stimuli from 50-100 rods
What does the ratio of bipolar cells : photoreceptors correspond to in the retina?
corresponds to decreasing visual acuity present in the peripheral retina
the summation of stimuli is a crucial factor in the sensitivity of the rod system to low levels of stimulation
How many subtypes of bipolar cells exist in humans?
9 morphological subtypes
- 1 rod bipolar type
- 8 cone bipolar types
- 5 types of diffuse cone bipolars
- 3 types of midget bipolars
What are the 3 types of midget bipolar cells?
- invaginating midget bipolar cells
- flat midget bipolar cells
- blue cone-specific bipolar cells (blue S-cone)
What proportion of all bipolar cells is accounted for by rod bipolar cells?
20%
What is the distribution of rod bipolar cells in the retina?
- have a small receptive field or dendritic tree in the central retina (15 μm wide, 10–20 rods)
- larger in the peripheral retina (30 μm and 30–50 rods)
Where are rod bipolar cells most dense?
around the fovea
How many rods are contacted by rod bipolar cells in the periphery?
up to 50
What type of cells do rod bipolar cells synapse with?
AII amacrine cells
&, only rarely, with diffuse ganglion cells
What is the role of diffuse cone bipolar cells?
concerned with converging information from many cones
What is the arrangement of diffuse cone bipolar cells?
Their dendrites fan out (up to 70–100 μm) to end in clusters of between five and seven cone pedicles (can be as high as 15–20)
In what region is overlap of diffuse cone bipolar cells extensive?
the perifoveal region
Which of the types of bipolar cells is smallest?
invaginaing midget bipolar cells
What are the connections formed by invaginating midget bipolar cells?
dendrites penetrate the base of a single cone pedicle (occasionally two) to form a central element in triads
What is the ratio of midge bipolar cells to cones like?
near 1:1 midget bipolar cells to cones, decreases peripherally
What are 2 types of cells that dendrites of invaginating midget bipolar cells may synapse with?
- amacrine cells
- midget ganglion cells
What is the arrangement of flat midget bipolar cells? What type of cells do they connect?
connect single cones with single midget ganglion cells or more rarely may connect several cones
How do flat midget bipolar cells differ from invaginaing midget bipolar cells?
they are similar except flat midget bipolar cell dendrites do not invaginate deeply into the cone pedicle
What type of bipolar cells can most cones be in contact with?
can be in contact with flat and invaginating midget bipolar cells, as well as diffuse cone bipolar cells
What type of contacts with other cells are made by blue cone-specific bipolar cells (blue S-cone)?
only a limited number of cones in their territory - specifically blue cones (it is suggested)
Where are the cell bodies of most ganglion cells located?
innermost nucleated layer of the retina (ganglion cell layer) situated between the nerve fibre layer and the inner plexiform layer
In addition to the ganglion cell layer, where are other displaced ganglion cells sometimes found?
inner nuclear layer
What do ganglion cells represent in the visual pathway?
they are the last neuronal link in the retinal component of the visual pathway
What layer are formed by ganglion cell axons?
nerve fibre layer on the innermost surface of the retina
Where do ganglion cell axons synapse?
on cells in the lateral geniculate nucleus of the thalamus
What separates and sheaths bundles formed by ganglion cell axons?
glial cells
What structure is formed by bundles of ganglion cell axons?
optic nerve
Via which structure do ganglion cells exit from the gloe and enter the optic nerve?
lamina cribrosa
What changes about the ganglion cell axons once they exit via the lamina cribrosa?
the axons become myelinated with oligodendrocytes
How many layers of ganglion cell bodies exist in the central retina/ fovea vs the peripheral retina?
- up to 7 layers in the central retina/fovea (ganglion cell layer is 60–80 μm thick)
- as few as 1 layer in the peripheral retina (10–20 μm thick)