Neurochemistry of retina

- KSHITIJ SHIVHARE

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INTRODUCTION

• Retina is a multilayered sensory tissue that lines the back of the eye.

• It contains millions of light receptors that captures light rays and convert them into electrical impulses.

• These impulses travel along the optic nerve to the brain where they are turned to images.

Gross Anatomy

Retina extends from the optic disc to the ora serrata.

Ora serrata is the last region where the retina ends and ciliary body starts; it consists of tooth like projections.

Layers of Retina• Retinal Pigment Epithelium (RPE)• Photoreceptor layer (Rods And Cones) • External Limiting Membrane• Outer Nuclear layer• Outer Plexiform Layer• Inner Nuclear Layer• Inner Plexiform Layer• Ganglion Cell Layer• Nerve Fiber Layer• Internal Limiting Membrane

Neurochemistry

How light signals is transfer to area 17 of brain

HOW FIRST IMPULSE WILL GENERATE?

• Metarhodopsin II (called as activated rhodopsin)

• The activate transducin (GTP) will active the phosphodiesterase (PDE)

• (PDE) will catalyses conversion of cGMP ( Cyclic guanosine monophosphate ) and convert cGMP to GMP(in light) which is leading to reduction of concentration of cGMP

• The reduction of cGMP ( Cyclic guanosine monophosphate ) is responsible for producing the ELECTRICAL response

• Which is the first impulse that has generated

• This process of changing the information to electrical impulses is known as transduction

HOW INFORMATION WILL TRANSFER?

Information transmission b/w retinal neurons occurs by

1. ion channel activity at gap junction or by

2. Neurotransmitters

NEUROTRANSMITTERS

2 type:1. Excitatory 2. inhibitoryGlutamate excitatory neurotransmitter release by

photoreceptors Bipolar _ ganglion

GLYCIN & GABA

Inhibitory neurotransmitters GABA release from amacrine & horizontal GLYCINE effect on ganglion and horizontal

• In addition to neurotransmitters we have neuromodulator that can alter or change neuron transmission

1. DOPAMINE ( function as neuro. )2. NITRIC ACID3. RETINOIC ACID ( metabolite of vitamin A,

retinol )

• EX) dopamine can change the conductance of gap junction b/w horizontal cells and change in back ground illumination

LIGHT SIGNALS

DIRECT ROUTE

o Direct route of light signals passing through retina (ON_centre)mechanism

RETINAL NEUROCHEMISTRY

Cone photoreceptors↓Bipolar cells↓Ganglion cells↓ LGB ( lateral geniculate body, recieves visual impulses )↓Primary visual cortex area 17

INDIRECT ROUTEo In dark both photoreceptors will release their

neurotransmitterso Partial inhibition of activated ganglion cells o Include light signlas received by neighbor cone

cello It will happen for better VA o (OFF_CENTRE) Cell

INDIRECT ROUTE

Rod photoreceptor↓Glutamate NTRod bipolar cell (Synapse 1)↓Glutamate NTAmacrine cell (Synapse 2)↓Indoleamine NTCone bipolar cell (Synapse 3)↓Glutamate NTGanglion cell (Synapse 4)

REFERENCE

• 1. Neurochemistry of the Retina - ScienceDirect [Internet]. Sciencedirect.com. 2016 [cited 7 July 2016]. Available from: http://www.sciencedirect.com/science/book/9780080254852

• 2. Shichi H. Physiological Background. Lippincott-Raven [Internet]. 1999 [cited 7 July 2016];. Available from: http://www.ncbi.nlm.nih.gov/books/NBK28019/

Thank You.