Photoreceptor

(redirected from Photoreceptors)
Also found in: Dictionary, Medical, Wikipedia.
Related to Photoreceptors: Mechanoreceptors, Chemoreceptors

photoreceptor

[¦fōd·ō·ri′sep·tər]
(physiology)
A highly specialized, light-sensitive cell or group of cells containing photopigments.

Photoreceptor

 

a light-detecting, light-sensitive structure capable of generating physiological, that is, nerve or receptor, signals in response to the absorption of photons by its pigment molecules.

In a broad sense, the term “photoreceptor” is applied to all light-sensitive structures, ranging from the stigmata of unicellular organisms and from individual photosensitive cells scattered over the bodies of such organisms as worms and lancelets to the specialized visual cells of the eye, the complex organ of photoreception in animals and man. Photoreceptors also include various structures—such as the chloroplasts of plants, the plastids of algae, and the chromatophores of bacteria—that contain pigments and are responsible for such photobiological processes as photosynthesis, phototropism, phototaxis, and photoperiodism.

In the retina of the eye in man and other vertebrates the photoreceptors are the highly differentiated visual cells known as rod cells and cone cells; in invertebrates the retinular cells are photoreceptors. The photosensitive element of photoreceptor cells— the photoreceptor membrane—contains phospholipids and rhodopsin, which is a visual pigment that absorbs light. In the photoreceptors of vertebrates the photoreceptor membranes form the outer segments of the rods and cones; in invertebrates the photoreceptor membranes form numerous finger-like protruberances called microvilli; the densely packed system of the microvilli is called the rhabdomere of the visual cell.

The outer segment in vertebrates consists of numerous (up to 15,000 in deepwater fishes) disks or very flat sacs measuring about 160 angstroms in thickness and from 1–2 to 6–8 micrometers in diameter, depending on the species of animal. The disks are oriented strictly perpendicularly to the long axis of the cell. In the rods they float in the cytoplasm, since they are severed from the outer cell membrane; in the majority of the cones they maintain their connection with the membrane. In the rods, but not in the cones, the outer segment is continuously renewed through the formation of new apical disks and the atrophy and phagocytosis of the old ones.

Owing to the strict orientation of visual-pigment molecules in the photoreceptor membrane and to the special tubular packing of the membrane in the cell, many invertebrates are able to discern the direction of polarization of light and to orient themselves according to the light. The rods of vertebrates are the receptors of twilight, or scotopic, vision; the cones are responsible for day, or photopic, vision and for color vision. The compound eyes of insects are also capable of distinguishing color.

REFERENCES

See references under .

M. A. OSTROVSKII [27–1760–1 ]

References in periodicals archive ?
The cells frequently fail to mature into functional RPE capable of supporting photoreceptors.
Follow-up studies in mice identified key molecules that interact with RPGR to maintain the structure of photoreceptors.
They are ocelli consisting of a single lens below which lie elongated photoreceptors with rhabdoms located close to the base of the lens (Fig.
In RP, which affects approximately 100,000 Americans and 1 in 4,000 persons worldwide, rod-specific genetic mutations cause rod photoreceptor cells to dysfunction and degenerate over time.
They enhance vision by absorbing scattered light and ensure survival of photoreceptor cells by delivering nutrients.
Disruption of the photoreceptor IS/OS junction was observed.
These results demonstrate that gestational lead exposure resulting in blood lead levels of 10 [micro]g/dL alters retinal development by selectively promoting the development of rod photoreceptor cells and bipolar cells.
The new system mimics the complex behavior of photoreceptor cells, creating a more natural message for the ganglion cells to interpret.
A research study is showing promise that adult stem cells within the retina can be chemically induced to regenerate photoreceptors and restore vision in people suffering from conditions such as age-related macular degeneration (AMD) and retinitis pigmentosa (RP).
Animals with no backbone-invertebrates--often sport photoreceptors shaped like microscopic bottle brushes.
The cells were able to integrate with the retina to become new cone photoreceptors.
healthy cone and rod photoreceptors, the light-detectors at the back of the