NEURAL FUNCTIONS OF RETINA Physiology Lecture SlideshowNEURAL FUNCTIONS OF RETINA Physiology Lecture Slideshow
  • Rods and cones
  • Horizontal cells
  • Bipolar cells
  • Amacrine cells
  • Ganglion cells
  • Interplexiform cells
  • Rods and cones– Photoreceptors
  • Horizontal Cells—Inhibitory cells
  • Bipolar Cells– Depolarising/Hyperpolarising
  • Amacrine Cells—30 types
  • Ganglion cells—W, X and Y cells

Visual Pathway in Retina

  • Cone vision– foveal portion of retina
    – 3 cell pathway
    – Cones → bipolar cells → Ganglion cells
    – New and fast system
  • Rod vision– peripheral retina
    – 4 cell pathway
    – Cones → bipolar cells → amacrine cells →
    Ganglion cells
    – New and fast system


  • Glutamate
  • Amacrine cells secrete 8 types of NT
    – GABA
    – Glycine
    – Dopamine
    – Acetylcholine
    – Indolamine

Signal Transmission in Retina

  • Ganglion cells and amacrine cells
    – True action potential
  • Amacrine cells, horizontal cells and
    – Electrotonic conduction
    – Graded Potential


  • Rods and cones
  • Transmits signals to outer plexiform layer
  • Synapse with bipolar and horizontal cells

Horizontal cells

  • Transmits signals horizontally to bipolar cells
  • In the outer plexiform layer
  • Transmits inhibitory signals laterally
  • Plays role in lateral connectivity along with
    amacrine cells
  • Synapse with dendrites of bipolar cells and
    cell bodies of rods and cones
  • Obeys phenomena of lateral inhibition
  • Lateral inhibition– transmission of visual
    patterns with proper visual contrast
  • Light strikes eye– central area excited
  • Outer zone–inhibited by lateral inhibition via
    horizontal cells
  • amacrine cells also contribute in lateral
  • Enhancement of visual contrast

Bipolar Cells

  • 2 types
    – Hyperpolarizing cells
    – Depolarizing cells
  • 1
    st order neuron in visual pathway
  • Cells respond to glutamate released by rods
    and cones in their specific manner
  • Bipolar (Depolarizing) cells takes excitation
    from rods and cones
  • Bipolar (Hyperpolarizing) cells takes signals
    from horizontal cells
  • Half of the cells transmit positive signals and
    rest half sends negative signals
  • Contributes in lateral inhibition and provides
    contrast border in the image

Amacrine Cells

  • 30 types
  • Functions
  1. Conduction Pathway (Rod vision)
  2. Offset image
  3. Respond to change in illumination
  4. Directional sensitivity
  5. Visual image analysis

Ganglion cells

  • 1.6 million
  • 60 rods and 2 cones converge on ganglion cell
    – Central fovea
    – Peripheral retina
  • 3 types
    – W Cells
    – X Cells
    – Y Cells

W cells

  • 40 per cent of all the ganglion cells
  • Small, diameter less than 10 micrometers
  • Transmit signals in optic nerve fibers at slow velocity
    of 8m/sec
  • Ganglion cells receive most of excitation from rods
    transmitted via bipolar and amacrine cells
  • Have broad fields in the peripheral retina because
    dendrites of ganglion cells spread widely in the inner
    plexiform layer, receiving signals from broad areas
  • W cells are sensitive for detecting directional
    movement in the field of vision
  • Important for crude rod vision in dark

X Cells

  • Most numerous of the ganglion cells
  • 55 per cent of the total
  • Medium diameter, 10-15 micrometers
  • Transmit signals in their optic nerve fibers at 14 m/sec
  • Small fields because their dendrites do not spread
    widely in the retina
  • Signals represent discrete retinal locations
  • Fine details of visual image are transmitted
  • Every X cell receives input from at least one cone
  • X cell responsible for all color vision

Y cells

  • Largest and least numerous (5%) , up to 35
    micrometers in diameter
  • Transmit their signals at 50 m/sec or faster
  • Broad dendritic fields—from widespread
    retinal areas
  • Y ganglion cells also respond to rapid changes
    in the visual image

P and M cells

  • 20 types of retinal ganglion cells
  • Magnocellular(M) and Parvocellular(P) cells
  • P cells
    – Beta cells project in to parvocellular cell layer of
    lateral geniculate nucleus of thalamus
  • M cells
    – Project in to magnocellular cell layer of lateral
    geniculate nucleus of thalamus
    – Relays information from optic tract to visual cortex

Ganglion cells

P Cells

  • Smaller receptive field
  • Conduct impulses
  • Sustained color stimuli
  • Sensitive to color
    stimulus and fine details
  • Not sensitive to black
    and white

M Cells

  • Larger receptive field
  • Conduct impulses
  • Rapidly changing color
  • Not sensitive to color
  • Sensitive to black and

On-off Response

Rapid impulses for a fraction of a second when a light is first turned on and decreasing rapidity in the next fraction of a second.

On-off Response

Ganglion cell showing lateral to the spot of light, cell is markedly inhibited Light is turned on—lateral inhibition

On-off Response

  • Ganglion cells are excited by changes in light intensity
  • Light is turned off, opposite effects occur–“on- off” and “off-on” responses
  • Phenomena occur depolarizing and hyperpolarizing bipolar cells
  • Temporary responses are also contributed by the amacrine cells

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