The Retina (2).pptx

The Retina (2) Retinal Layers SFO1002 Dr R S Mughal Learning Outcome s • 1. Describe the functional organisation of cells in the retina. • 2. Describe the interactions amongst the different cell types in the retina. • Describe the directional flow of neural information in the retina. Optical Co...

The Retina (2) Retinal Layers SFO1002 Dr R S Mughal Learning Outcome s • 1. Describe the functional organisation of cells in the retina. • 2. Describe the interactions amongst the different cell types in the retina. • Describe the directional flow of neural information in the retina. Optical Coherence Tomography section through the fovea of a normal eye shows a number of different layers (different shades) Ten retinal layers • Outer retina 1. 2. 3. 4. 5. Retinal pigment epithelium (RPE) Photoreceptors External limiting membrane Outer nuclear layer Outer plexiform layer • Inner retina 6. Inner nuclear layer 7. Inner plexiform layer 8. Ganglion cell layer 9. Nerve fibre layer 10.Internal limiting membrane Ten retinal layers • Alternate groupings of retinal neurons and their processes make up the 10 layers. • The names of the layers are descriptive Complete the table Cells in the 10layered retina • Retinal pigment epithelium (RPE) • Photoreceptors (rods and cones) • Bipolar cells • Horizontal cells • Amacrine cells • Interplexiform neuron • Ganglion cell Neuroglial cells – support cells in the retina • Neuroglial cells aren’t actively involved in the transfer of neural signals. • They provide structure and support and have a role in fighting neural tissue infection. • Neuroglial cells in the retina: • Müller cells • Microglia • Astrocytes Müller cells • Extend throughout the retina. • Large neuroglial cells. • Apex of cell in photoreceptor layer. • Basal aspect at the inner retinal surface . • Functions • Structure: Cellular processes fill in empty retinal space. • Support: Cellular processes enclose dendritic processes within synaptic layers. • Separates retina from vitreous: The endfoot (expanded Müller cell process), along the basal aspect contributes to membrane separating retina from vitreous. • Maintain pH: absorb waste products and neurotransmitters in retina and regulate ion concentration. Microglia and Astrocytes • Microglia • Wandering phagocytic cells, that can be found anywhere in the retina. They become active when infection is present or injury has occurred. • Astrocytes • Star-shaped fibrous cells. • Found in inner retina. • Nerve fibre and ganglion cell layers. • Provide support to nerve fibres and retinal capillaries in inner retina. Light passes through all the neural layers to reach photoreceptors • The target of light is the photoreceptors • Phototransduction (conversion of light energy into electrochemical energy begins here) • Light must pass through the inner retinal layers before reaching photoreceptors Direction of information flow in the retina Direction of information flow in the retina • Vertical flow of information • From outer to inner retina • Photoreceptors • Bipolar cells • Ganglion cells • Optic nerve • Intralayer flow of information • Lateral flow • Horizontal cells • Amacrine cells • Interlayer flow of information • From inner to outer retina (feedback) • Interplexiform cells Modification of vertical neural information before it leaves via the optic nerve • Horizontal cells, amacrine cells and interplexiform cells modify the neural signal before information can leave the optic nerve • Horizontal cells • Synapse with photoreceptors, ganglion cells and other horizontal cells • Inhibitory feedback (to cone cells) or feed-forward (to bipolar cells) • Not thought to influence rod cells • Amacrine cells • Synapse with bipolar cells, ganglion cells, interplexiform and other amacrine cells. • Modulates feed-forward information (info that reaches ganglion cells). • Interplexiform neurones • Conveys information between the two plexiform layers • Feeds back information from inner plexiform layer to outer plexiform layer Modification of vertical neural information before it leaves via the optic nerve Supplementary Reading • Remington • Pages 70-74 (Retinal layers)