Scientific American: Illusion/Scientific American - Illusion.ISO/pc/illusion/hub_fie.cxt/00065_Field_frep80x.txt

Text File | 1996-12-30 | 1KB | 48 lines

AMACRINE CELLS

    These cells come in an
astonishing variety of shapes
and use an impressive number
of neurotransmitters. There
may be well over twenty
different types. They all have in
common, first, their location,
with their cell bodies in the
middle retinal layer and their
processes in the synaptic zone
between that layer and the
ganglion cell layer; second,
their connections, linking
bipolar cells and retinal
ganglion cells and thus forming
an alternative, indirect route
between them; and, finally,
their lack of axons,
compensated for by the ability
of their dendrites to end
presynaptically on other cells.

    Amacrine cells seem to have
several different functions,
many of them unknown: one
type of amacrine seems to play a
part in specific responses to
moving objects found in retinas
of frogs and rabbits; another
type is interposed in the path
that links ganglion cells to
those bipolar cells that receive
rod input. Amacrines are not
known to be involved in the
center-surround organization
of ganglion-cell receptive
fields, but we cannot rule out
the possibility. This leaves most
of the shapes unaccounted for,
and it is probably fair to say, for
amacrine cells in general, that
our knowledge of their anatomy
far outweighs our
understanding of their
function.