HMO202

Question 1

What are the 10 retinal layers? tell in order of direction of incident light.

Answer 1

1. Internal limiting membrane.
2. nerve fibre layer
3. ganglion cell layer
4. inner plexiform layer
5. inner nuclear layer
6. outer plexiform layer
7. outer nuclear layer.
8. external limiting membrane.
9. Photoreceptor layer.
10. retinal pigment epithelium (RPE)

Direction of light 1–>10. inner and outer segment are given w.r.t to the centre of the eye. inner being closest to centre of the eye and outer being furthest away

Question 2

What are 4 main processing stages of visual pathway

Answer 2

layer of retina can be grouped into 4 main processing stages in visual pathway.

1.photoreception
2.transmission of signal to bipolar cell.
3.transmission of signal to ganglion cell.
4. transmission to the optic nerve
Different condition affect different parts of the retina differently.

Question 3

how do retinal neurons interact to form light pathway to the brain

Answer 3

light reaches photoreceptors –> activates them in outer segment–> this signal travels along the photoceptors through the cell body of the photoreceptor to the synapse with the bipolar cell at thr outer plexiform layer- the signal then travels along the bipolar cell to synapse with the ganglion cell. the axons of the ganglion cell form the optic nerve that is directly connected with the brain.

Question 4

what are neurotransmitters in retina?

Answer 4

Chemical messengers that transmit
messages from a nerve cell across
the synapse to a target cell.
the target can be another nerve cell, muscle etc.

influences neuron either by exciting or inhibiting

Question 5

what is a receptive field?

Answer 5

an “area in which
stimulation leads to response of a particular
sensory neuron”

each neuron has a receptive field that covers part of an area in our field of vision.

presence of appropriate stimulus will activate the receptive field. the response/stimulus provided by the receptive field (RF)depends on where the light falls in the RF.
2 types of RF
on-centre, off-surround and off-centre, on-surround

Question 6

what are photoreceptors?

Answer 6

photoreceptors are light sensors that respond to light by the process of transduction. photons are capture

Question 7

what is the function of horizontal cells

Answer 7

Horizontal cells at the OPL provide lateral
inhibition, through a mechanism of
feedback channel which helps in
modulating the photoreceptor response.
• Two physiological types of horizontal
cells.
• Luminosity type- respond to changes in
intensity
• Chromaticity type- respond to changes in
wavelength.

Responsible for modulating
brightness (hyperpolarizing
potentials)
• Inhibiting responses under high
light conditions (GABA)
• Summation of responses under
low light (Glutamate)
• Responsible for maximising
contrast
• Colour opponency

Question 8

what are amacrine cells?

Answer 8

• responsible for beginning of motion perception
• responsible for modulating brightness
• interact with bipolar cell and ganglion cells

Question 9

what is the difference between bipolar and amacrine cells

Answer 9

bipolar cells cannot detect motion perception whereas amacrine cells can

Question 10

what are ganglion cells, their roles etc

Answer 10

• The ganglion cell collects the
visual signal from photoreceptors
via two intermediate neuron types:
bipolar cells and amacrine cells.

• Ganglion cells are the final
neurons which then transmit the
visual signal via its axons in the
optic nerve to dLGN and then to
the primary visual cortex

the way ganglion cells synapse with bipolar cells determine the type of receptive field it will have

• responsible for shape and motion of object
• ganglion cells do not participate in image formation.

Question 11

what pathway do the ganglion cells take?

Answer 11

• The ganglion cell axons run in
the nerve fiber layer above the
inner limiting membrane
towards the optic nerve head in
an arcuate form.
• Inner retina and ganglion cells
are displaced in foveal pit to
form the foveal slope.

Question 12

when is maximum excitement or response achieved by receptive field?

Answer 12

if the receptive field is on-centre, off-surround of a ganglion cell then;

if the centre is illuminated by light maximum response is achieved. the opposite is the case for off-centre on-centre receptive field.

Question 13

what are glial cells

Answer 13

support cells

three types: Muller cells, astroglia, microglia

Question 14

what is function of astrogila?

Answer 14

-provide nutrional support to neurons.
-form blood-brain barrier
-Help maintain the right potassium concentration by taking
up excess

Question 15

what is the function of muller cells

Answer 15

found in INL
-clear neural waste, such as co2 and ammonia.
-protect neurons form exposure excess neurotransmitter
-though to synthesize retinoic acid.
-involved in retinal glucose metabolism, providing them with nutrition,
-

Question 16

what is the role of microglia?

Answer 16

• Roles in:
• retinal homeostasis,
• recovery from injury after trauma to the retina
• progression of disease
• phagocytosis of degenerating
retinal neurons.