Bipolar Cell

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Bipolar cells are a class of neurons that are primarily utilized as sensory afferents, carrying signal from the various sense organs towards higher level processing areas. Within the retina, bipolar cells act as the signal couriers between the photoreceptors that react to light stimuli and the ganglion cells that carry these signals out of the eye and into the cortex. Bipolar cells are so-called because they have two polar extensions that protrude from opposite ends of the soma. One of these extensions extends to a single photoreceptor (either a rod or cone) while the other delivers the processed signal to the dendritic arbors of the ganglion cells.

There are at least nine morphological types of cone bipolar (CB) and one type of rod bipolar (RB) cells in the mammalian retina. They have distinctive morphology from amacrine cells and ganglion cells, characterized by varicose axon terminals in the IPL.

Bipolar cells differ in their dendritic branching pattern, the number of cones contacted, and the stratification level of their axons in the IPL. A type of BPs, in general, occupy two strata of the IPL to tile up the entire space of the strata, with little overlapping region between different BPs.

Physiology

Processing Activity

The ON and OFF center circuits within the retina are a product of the either sign-conserving or sign-reversing synapse that the bipolar cell shares with its paired photoreceptor. Sign-conserving synapses result in an OFF center while sign-reversing synapses produce an ON center. The surround portion of the center/surround functionality is dependent upon the aggregate signals from surrounding horizontal and amacrine cells.

Unlike other neurons, bipolar cells do not transmit signals by way of action potentials. They instead make use of a potential gradient that can be modulated by the connecting horizontal and amacrine cells.

Electrophysiology

  • Sign-conserving vs. Sign-reversing details


Anatomy

Location

Shape

Connections

Molecules

Open questions / status / relevance to eyewire

References