Clinical Anatomy and Physiology of the Visual System E-Book by Lee Ann Remington & Denise Goodwin

Author:Lee Ann Remington & Denise Goodwin [Remington, Lee Ann & Goodwin, Denise]
Language: eng
Format: epub
ISBN: 9780323711692
Publisher: Elsevier Health Sciences
Published: 2021-06-24T22:00:00+00:00

Fig. 8.19 Schematic of ON and OFF bipolar pathways. The OFF bipolar dendrite synapses on the flat part of the cone. The ON bipolar dendrite synapses within the photoreceptor invagination. The OFF bipolar axon terminates in sublamina a, and the ON bipolar axon terminates in sublamina b. The AII amacrine cell relays rod signals to both ON and OFF ganglion cells.

Bipolar axons end in the inner plexiform layer. One synaptic configuration is a dyad, which consists of a synapse between a bipolar axon and two postsynaptic elements, either two amacrine processes or one amacrine process and one ganglion dendrite. ON and OFF bipolar axons terminate in different tiers of the inner plexiform layer. OFF bipolars synapse in the outer tier, sublamina a (nearest the inner nuclear layer), and ON bipolars synapse in the inner tier, sublamina b, closest to the ganglion cell layer.78 Rod bipolars do not synapse with ganglion cells directly but with amacrine cells. Thus the rod signal must pass through a four neuron chain (see Fig. 8.19).

Bipolar cells transfer information to retinal ganglion cells, which are the first cells in the visual pathway to respond with an action potential. Once a threshold is reached, the ganglion cell responds, and a signal is sent to higher central nervous system locations. All other retinal neurons give graded responses, the intensity of which is determined by the intensity of the stimulus.

The P ganglion cells terminate in the parvocellular layers of the lateral geniculate nucleus, are associated with cone bipolar cells, and carry color information. The P1 cells, also called midget ganglion cells, are concentrated in central retina and constitute 80% of the ganglion cell population.78 M ganglion cells project to the magnocellular layers of the lateral geniculate nucleus. They have also been called parasol ganglion cells because of their large spreading dendritic trees. Because they have such expansive processes and cover a large area of retina, they can respond rapidly to moving or changing stimuli.

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