A midget cell is one type of
retinal ganglion cell
A retinal ganglion cell (RGC) is a type of neuron located near the inner surface (the ganglion cell layer) of the retina of the eye. It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and reti ...
(RGC). Midget cells originate in the
ganglion cell layer
The ganglion cell layer (ganglionic layer) is a layer of the retina
The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focus ...
of the
retina
The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which the ...
, and project to the
parvocellular layers of the
lateral geniculate nucleus
In neuroanatomy, the lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, ventral projec ...
(LGN). The axons of midget cells travel through the
optic nerve
In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived fro ...
and
optic tract
In neuroanatomy, the optic tract () is a part of the visual system in the brain. It is a continuation of the optic nerve that relays information from the optic chiasm to the ipsilateral lateral geniculate nucleus (LGN), pretectal nuclei, and su ...
, ultimately synapsing with
parvocellular cell
Parvocellular cells, also called P-cells, are neurons located within the parvocellular layers of the lateral geniculate nucleus (LGN) of the thalamus. "''Parvus''" is Latin for "small", and the name "parvocellular" refers to the small size of t ...
s in the LGN. These cells are known as midget retinal ganglion cells due to the small sizes of their
dendritic trees and cell bodies. About 80% of RGCs are midget cells. They receive inputs from relatively few rods and cones. In many cases, they are connected to midget
bipolar cells
A bipolar neuron, or bipolar cell, is a type of neuron that has two extensions (one axon and one dendrite). Many bipolar cells are specialized sensory neurons for the transmission of sense. As such, they are part of the sensory pathways for smell, ...
, which are linked to one cone each.
These neurons show roughly circular
receptive fields
The receptive field, or sensory space, is a delimited medium where some physiological stimuli can evoke a sensory neuronal response in specific organisms.
Complexity of the receptive field ranges from the unidimensional chemical structure of od ...
with antagonistic center and surround; this property is known as spatial opponency and these neurons are typically divided into ON- or OFF-center, depending on whether they are excited or inhibited by photons falling on the center of their receptive fields.
Most of these cells are chromatically opponent, meaning that long- and medium-wavelength visible light (commonly approximated to red and green, respectively) exert opposing effects on the center and the surround.
For instance, a chromatically opponent L-ON midget cell would be excited (and more likely to spike action potentials) if light of long wavelength falls on the cone or cones in the center of its receptive field but would be inhibited by medium-wavelength light falling on the surround of its receptive field.
However, not all midget cells are chromatically opponent.
They have slow
conduction velocity
In neuroscience, nerve conduction velocity (CV) is an important aspect of nerve conduction studies. It is the speed at which an electrochemical impulse propagates down a neural pathway. Conduction velocities are affected by a wide array of factor ...
and are very responsive to high temporal frequencies (i.e. rapidly and low spatial frequencies).
See also
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Bistratified cell Bistratified ganglion cell can refer to either of two kinds of retinal ganglion cells whose cell body is located in the ganglion cell layer of the retina, the small-field bistratified ganglion cell, also known as small bistratified cell (SBC), and ...
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Parasol cell
A parasol cell, sometimes called an M cell or M ganglion cell, is one type of retinal ganglion cell (RGC) located in the ganglion cell layer of the retina. These cells project to magnocellular cells in the lateral geniculate nucleus (LGN) as part ...
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Photosensitive ganglion cell
Intrinsically photosensitive retinal ganglion cells (ipRGCs), also called photosensitive retinal ganglion cells (pRGC), or melanopsin-containing retinal ganglion cells (mRGCs), are a type of neuron in the retina of the mammalian eye. The presence ...
References
External links
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{{Eye anatomy
Visual system
Nervous tissue cells