The inner nuclear layer or layer of inner granules is made up of a number of closely packed cells, of which there are three varieties, viz.: bipolar cells, horizontal cells, and amacrine cells.

Bipolar cells

The bipolar cells, by far the most numerous, are round or oval in shape, and each is prolonged into an inner and an outer process.

They are divisible into rod bipolars and cone bipolars.

• The inner processes of the rod bipolars run through the inner plexiform layer
  Inner plexiform layer
  The inner plexiform layer is an area of the retina that is made up of a dense reticulum of fibrils formed by interlaced dendrites of retinal ganglion cells and cells of the inner nuclear layer. Within this reticulum a few branched spongioblasts are sometimes embedded....
  
   and arborize around the bodies of the cells of the ganglionic layer; their outer processes end in the outer plexiform layer in tufts of fibrils around the button-like ends of the inner processes of the rod granules.

• The inner processes of the cone bipolars ramify in the inner plexiform layer in contact with the dendrites of the ganglionic cells.

Connection types

Midget bipolars are linked to one cone while diffuse bipolars take groups of receptors. Diffuse bipolars can take signals from up to 50 rods or can be a flat cone form and take signals from seven cones. The bipolar cells corresponds to the intermediary cells between the touch and heat receptors on the skin and the medulla or spinal cord.

Horizontal cells

The horizontal cell

Horizontal cell

Horizontal cells are the laterally interconnecting neurons in the outer plexiform layer of the retina of mammalian eyes. They help integrate and regulate the input from multiple photoreceptor cells...

s lie in the outer part of the inner nuclear layer and possess somewhat flattened cell bodies.

Their dendrites divide into numerous branches in the outer plexiform layer, while their axons run horizontally for some distance and finally ramify in the same layer.

Amacrine cells

The amacrine cell

Amacrine cell

Amacrine cells are interneurons in the retina. Amacrine cells are responsible for 70% of input to retinal ganglion cells. Bipolar cells, which are responsible for the other 30% of input to retinal ganglia, are regulated by amacrine cells.-Overview:...

s are placed in the inner part of the inner nuclear layer, and are so named because they have not yet been shown to possess axis-cylinder processes.

Their dendrites undergo extensive ramification in the inner plexiform layer.