1. The retina contains different layers and cell types that work together to convert light stimuli into neural signals. Photoreceptors detect light and hyperpolarize, bipolar cells exhibit spatial antagonism, and ganglion cells generate action potentials that are transmitted to the brain. 2. Within the retina, there are two main types of bipolar cells (on-center and off-center) and two main types of ganglion cells (midget and parasol) that differ in their receptive field properties and transmission of sustained vs. transient responses. 3. The different retinal cell types form pathways through the lateral geniculate nucleus to the visual cortex that allow for the processing of visual information like spatial resolution, color

1. Functional Retinal Physiology
PRESENTER
Archana Sharma
Bachelor in optometry
23rd Batch (Second year )

2. Different layers of retina

3. Functional retinal physiology can be studied by either :
A. Extracellular recording :
- Microelectrode placed in close proximity to a neuron.
- Records action potentials.
B. Intracellular recording :
- Microelectrode pierces the neuron’s membrane.
- Records membrane potential
( degree of depolarization or hyperpolarization )

4. Receptive fields of ganglion cells
• Area which influences the neural activity of the cell.
• Records action potential from ganglion cell by extracellular recording
method.
Maintained discharge (Spontaneous activity )
- Action potential which occur in absence of stimulus.
• Have center-surround organization.
• A ganglion cell is not responsive to diffuse illumination.

5. Spatial antagonism ( Lateral inhibition )

6. In graph,
A = Cell’s maintained discharge
B = Receptive field center
C = Border between center and
surround
D = Receptive field surround
E = Termination of cell’s receptive field

7. Photoreceptor
• Convert radiant energy into electrical activity ( Phototransduction ).
• Resting membrane potential= -50mV
• When exposed to light, hyperpolarized to -70mV
• Produces graded potential not action potential.
• Under dark , it releases neurotransmitter glutamate.

8. • During dark , Na+ ions flows into the outer segment of rods through
sodium channels so called dark current producing slight
depolarization.
• Absorption of light by rhodopsin initiates a series of events that
blocks the Na+ ions and the resultant hyperpolarization of the outer
segment occurs.
• Rhodopsin = Opsin + Chromophore

9. Rod hyperpolarization
11-cis retinal 11-trans retinal Transducin (protein)
Phosphodiesterase ( protein )
Breaks up cGMP into GMP
Na+ pores close
Rod hyperpolarization
Photon
Activates
Activates
Fig : Flowchart showing the stages that leads to rod hyperpolarization.

10. Horizontal cells
• 2 classes of Horizontal cells : H1 and H2
• H1 cells: receives inputs from M- & L- cones and little from S- cones
• H2 cells: strong connection with S-cones also receives input from M-
& L- cones.
• Shows graded response.
• Manifests substantial spatial summation.

11. Horizontal cells

12. Bipolar cells
• First retinal cells to display spatial antagonism
• Like photoreceptors and Horizontal cells, do not generate action
potential
• Based on receptive field , 2 types :
1. On-centre bipolar cell (depolarization- excitation) : Invaginating
synapse
2. Off-centre bipolar cell (hyperpolarization- inhibition) : Conventional
flat synapse .

13. • On- and off - center bipolar cells synapse with photoreceptor in outer
plexiform layer ( OPL ).
• On- and off- center bipolar cells synapse with ganglion cells in the
inner plexiform layer ( IPL ) .
• Also classified as :
1. Midget bipolar cell
2. Diffuse bipolar cell
3. S-cone bipolar cell

14. What causes bipolar cell to have on- and off-center
arrangement in OPL ???
• Glutamate released by photoreceptors has different effects on the
two classes of bipolar cells.
• Under dark conditions, photoreceptors continuously release
neurotransmitter.
• Light stimulation causes hyperpolarization of the receptor and
consequent reduction in the release of neurotransmitter.

15. • Role of glutamate
- On center bipolar cell – inhibitory - reduction in release of
glutamate causes excitation (depolarization)
- Off center bipolar cell – excitatory - reduction in its release causes
inhibition (hyperpolarization)

16. Midget bipolar cell
- In central and midperipheral retina :
Receives input from single M- and L- cones.
High spatial resolution (visual acuity)
- In peripheral retina:
Receives input from all cones
(Spatial summation).
– Exhibit color opponency (both on- and off- centres)
– Have smaller soma and less extensive dendritic trees.

17. Diffuse bipolar cell
• Are non- color opponent.
• Receptive field center is formed by 5-10 M- and L- cones .
• Surround receives inputs from H1 cells which have input
from M and L cones .
• Spectral sensitivity of center is very similar to that of surround.

18. Color opponency of Midget bipolar cell
• A single cone forms the receptive field centre in central and mid
peripheral retina .
• The surround is apparently formed by input from H1 horizontal
cells.
• The midget bipolar cells manifests a different spectral sensitivity
in its surround that its centre causing color opponency.

19. Amacrine cells
• Like bipolar cells ,shows a centre- surround organization
• Has critical role in coding movement (time related
characteristics of neural response)
• First retinal neuron to display action potentials

20. Ganglion cells
• Classified as :
1. Midget ganglion cells (Parvo cells )
2. Parasol ganglion cells ( Magno cells )
3. Small – bistratified ganglion cells
• Generate action potential similar to amacrine cells , don’t decay and
reach to dorsal lateral geniculate nucleus (dLGN)
• This action potential is increased by myelin sheath along the ganglion
cell zones.

21. • On-center midget bipolar cells synapse with on- center midget
ganglion cells.
• Off- center midget bipolar cells synapse with off- center midget
ganglion cells
• On-center diffuse bipolar cells synapse with on- center parasol
ganglion cells.
• Off- center diffuse bipolar cells synapse with off- center parasol
ganglion cells

22. Midget ganglion cell
• In Central and Mid - peripheral retina :
- Receives input from only one midget bipolar cell and only one cone
- Limited spatial summation and high spatial resolution.
• In Peripheral retina :
- Receives input from more than one bipolar cell
- Increased spatial summation and decreased spatial resolution.
• Midget ganglion cells forms a sustained response- substantial input
from sustained amacrine cells

23. Parasol ganglion cells
• Have larger receptive field and synapse with more than one diffused
bipolar cells.
• These cells respond transiently to a flash of light- substantial input
from transient amacrine cells.

25. • Axons of midget , parasol and bistratified ganglion cells synapse in
the LGN.
• Forms interdependent parvo, magno and konio pathway through
striate cortex, visual area 2 and specialized higher cortical centers.
• Some ganglion cells project to the superior colliculus (control eye
movements).
• Some ganglion cells project to suprachiasmatic nucleus (SCN) of
hypothalamus responsible for circadian rhythm.

26. THANK YOU !!!