Rod cell
Cross section of the retina. Rods are visible at far right.
Location	Retina
Function	Low light photoreceptor
Morphology	rod shaped
Presynaptic connections	None
Postsynaptic connections	Bipolar Cells and Horizontal cells

Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of photoreceptor, cone cells. Since they are more light-sensitive, rods are responsible for night vision. Named for their cylindrical shape, rods are concentrated at the outer edges of the retina and are used in peripheral vision. There are about 100 million rod cells in the human retina. Axial organization of the retina (from Cajal, 1911) This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... Human eye cross-sectional view. ... Human eye cross-sectional view. ... Photoreceptor cells are contained in the retina and are responsible for transducing, or converting, light into signals that can be ultimately transmitted to the brain via the optic nerve. ... The term morphology in biology refers to the outward appearance (shape, structure, colour, pattern) of an organism or taxon and its component parts. ... As a part of the retina, the bipolar cell exists between photoreceptors (rod cells and cone cells) and ganglion cells. ... This article or section is incomplete and may require expansion and/or cleanup. ... Photoreceptor cells are contained in the retina and are responsible for transducing, or converting, light into signals that can be ultimately transmitted to the brain via the optic nerve. ... Human eye cross-sectional view. ... Eyes are organs of vision that detect light. ... This article or section does not cite any references or sources. ... Normalised absorption spectra of human cone (S,M,L) and rod (R) cells Cone cells, or cones, are cells in the retina which only function in relatively bright light. ... Peripheral vision is a part of vision that occurs outside the very center of gaze. ...

A rod cell is sensitive enough to respond to a single photon of light, and is about 100 times more sensitive to a single photon than cones. Since rods require less light to function than cones, they are therefore the primary source of visual information at night (scotopic vision). Cone cells, on the other hand, require tens to hundreds of photons to become activated. Additionally, multiple rod cells converge on a single interneuron, collecting and amplifying the signals. However, this convergence comes at a cost to visual acuity (or Image resolution) since the pooled information from multiple cells is less distinct than it would be if the visual system received information from each rod cell individually. The convergence of rod cells also tends to make peripheral vision very sensitive to movement, and is responsible for the phenomenon of individuals seeing something vague occur out of the corner of his or her eye. The word light is defined here as electromagnetic radiation of any wavelength; thus, X-rays, gamma rays, ultraviolet light, infrared radiation, microwaves, radio waves, and visible light are all forms of light. ... Scotopic vision is the monochromatic vision of the eye in dim light. ... An interneuron (also called relay neuron,association neuron or bipolar neuron) is a term used to describe a neuron which has two different common meanings. ... Image resolution describes the detail an image holds. ... The visual system is the part of the nervous system which allows organisms to see. ...

Because they have only one type of light sensitive pigment, rather than the three types that human cone cells have, rods have little, if any, role in color vision. Color is an important part of the visual arts. ...

Rod cells also respond more slowly to light than cones do, so stimuli they receive are added over about 100 milliseconds. While this makes rods more sensitive to smaller amounts of light, it also means that their ability to sense temporal changes, such as quickly changing images, is less accurate than that of cones^[1] However, if multiple flashes of sub-threshold light occurs during the 100 millisecond period, the energy of the flashes of light would summate to produce a light which will reach threshold and send a signal to the brain.

Experiments by George Wald and others showed that rods are more sensitive to the blue area of the spectrum, and are completely insensitive to wavelengths above about 640 nm (red). This fact is responsible for the Purkinje effect, in which blue colors appear more intense relative to reds in darker light, when rods take over as the cells responsible for vision. George Wald (November 18, 1906–April 12, 1997) was an American scientist who is best known for his work with pigments in the retina. ... The Purkinje effect (sometimes called the Purkinje shift, or dark adaptation) is the tendency for the peak sensitivity of the human eye to shift toward the blue end of the color spectrum at low illumination levels. ...

Like cones, rod cells have a synaptic terminal, an inner segment, and an outer segment. The synaptic terminal forms a synapse with another neuron, for example a bipolar cell. The inner and outer segments are connected by a cilium.^[1] The inner segment contains organelles and the cell's nucleus, while the outer segment, which is pointed toward the front of the eye, contains the light-absorbing materials.^[1] Illustration of the major elements in a prototypical synapse. ... As a part of the retina, the bipolar cell exists between photoreceptors (rod cells and cone cells) and ganglion cells. ... cross-section of two motile cilia, showing the 9+2 structure A cilium (plural cilia) or undulipodium (pl. ... Schematic of typical animal cell, showing subcellular components. ... In cell biology, the nucleus is an organelle, found in most eukaryotic cells, which contains most of the cells genetic material. ...

Response to light

Activation of a photoreceptor cell is actually a hyperpolarization; when they are not being stimulated, rods and cones depolarize and release a neurotransmitter spontaneously, and activation of photopigments by light sends a signal by preventing this. Depolarization occurs due to the fact that in the dark, cells have a relatively high concentration of cyclic guanosine 3'-5' monophosphate (cGMP), which opens ion channels (largely sodium channels, though Calcium can enter through these channels as well). The positive charges of the ions that enter the cell down its electrochemical gradient change the cell's membrane potential, cause depolarization, and lead to the release of the neurotransmitter glutamate. Glutamate can depolarize some neurons and hyperpolarize others, allowing photoreceptors to interact in an antagonistic manner. Hyperpolarization has several meanings: In biology, hyperpolarization occurs when a cells membrane potential dips below its resting level. ... In biology, depolarization is the event a cell undergoes when its membrane potential grows more positive with respect to the extracellular solution. ... Chemical structure of D-Aspartic Acid, a common Amino Acid neurotransmitter. ... Cyclic guanosine monophosphate (cGMP) is a second messenger derived from GTP. Cyclic guanosine monophosphate (cGMP) is a cyclic nucleotide derived from guanosine triphosphate (GTP). ... Ion channels are pore-forming proteins that help to establish and control the small voltage gradient that exists across the plasma membrane of all living cells (see cell potential) by allowing the flow of ions down their electrochemical gradient. ... Sodium channels are integral membrane proteins that exist in a cells plasma membrane and regulate the flow of sodium (Na+) ions into it. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Standard atomic weight 40. ... ... In cellular biology, an electrochemical gradient refers to the electrical and chemical properties across a membrane. ... This article or section is in need of attention from an expert on the subject. ... Glutamate is the anion of glutamic acid. ...

When light hits photoreceptive pigments within the photoreceptor cell, the pigment changes shape. The pigment, called rhodopsin (iodopsin is found in cone cells) consists of a large protein called opsin (situated in the plasma membrane), attached to which is a covalently-bound prosthetic group: an organic molecule called retinal (a derivative of vitamin A). The retinal exists in the 11-cis-retinal form when in the dark, and stimulation by light causes its structure to change to all-trans-retinal. This structural change causes it to activate a regulatory protein called transducin, which leads to the activation of cGMP phosphodiesterase, which breaks cGMP down into 5'-GMP. Reduction in cGMP allows the ion channels to close, preventing the influx of positive ions, hyperpolarizing the cell, and stopping the release of neurotransmitters (Kandel et al., 2000). Though cone cells primarily use the transmitter substance acetyl choline, rod cells use a variety. The entire process by which light initiates a sensory response is called visual phototransduction. Transducin is the name given to the G-protein alpha-subunits that are naturally expressed in vertebrate retina rods and cones. ... Visual phototransduction is a process by which light is converted into electrical signals in the rod cells and cone cells of the retina of the eye. ...

Activation of a single molecule of rhodopsin, the photosensitive pigment in rods, can lead to a large reaction in the cell because the signal is amplified. Once activated, rhodopsin can activate hundreds of transducin molecules, each of which in turn activate a phosphodiesterase molecule, which can break down over a thousand cGMP molecules per second.^[1] Thus rods can have a large response to a small amount of light.

As the retinal component of rhodopsin is derived from vitamin A, a deficiency of vitamin A causes a deficit in the pigment needed by rod cells. Consequently, fewer rod cells are able to sufficiently respond in darker conditions, and as the cone cells are poorly adapted for sight in the dark, blindness can result. This is night-blindness.

Table

Comparison of rod and cone cells, from Kandel^[1] Normalised absorption spectra of human cone (S,M,L) and rod (R) cells Cone cells, or cones, are cells in the retina of the eye which only function in relatively bright light. ...

Nyctalopia (literally night blindness) is a condition making it difficult or impossible to see in the dark. ... Blindness is the condition of lacking visual perception due to physiological or psychological factors. ... For the Irish mythological figure, see Naoise. ...

References

1. ^ ^{a b c d e} Kandel E.R., Schwartz, J.H., Jessell, T.M. (2000). Principles of Neural Science, 4th ed., pp.507-513. McGraw-Hill, New York.

See also

• Sensory receptor