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Cephalopod Eye
Cephalopods, as active marine predators, possess sensory organs specialized for use in aquatic conditions.Budelmann BU. "Cephalopod sense organs, nerves and the brain: Adaptations for high performance and life style." Marine and Freshwater Behavior and Physiology. Vol 25, Issue 1-3, Page 13-33. They have a camera-type eye which consists of an iris, a circular lens, vitreous cavity (eye gel), pigment cells, and photoreceptor cells that translate light from the light-sensitive retina into nerve signals which travel along the optic nerve to the brain. For the past 140 years, the camera-type cephalopod eye has been compared with the vertebrate eye as an example of convergent evolution, where both types of organisms have independently evolved the camera-eye trait and both share similar functionality. Contention exists on whether this is truly convergent evolution or parallel evolution. Unlike the vertebrate camera eye, the cephalopods' form as invaginations of the body surface (rath ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 then processes that image within the retina and sends nerve impulses along the optic nerve to the visual cortex to create visual perception. The retina serves a function which is in many ways analogous to that of the film or image sensor in a camera. The neural retina consists of several layers of neurons interconnected by synapses and is supported by an outer layer of pigmented epithelial cells. The primary light-sensing cells in the retina are the photoreceptor cells, which are of two types: rods and cones. Rods function mainly in dim light and provide monochromatic vision. Cones function in well-lit conditions and are responsible for the perception of colour through the use of a range of opsins, as well as high-acuity vision used fo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Orthogonal
In mathematics, orthogonality is the generalization of the geometric notion of '' perpendicularity''. By extension, orthogonality is also used to refer to the separation of specific features of a system. The term also has specialized meanings in other fields including art and chemistry. Etymology The word comes from the Ancient Greek ('), meaning "upright", and ('), meaning "angle". The Ancient Greek (') and Classical Latin ' originally denoted a rectangle. Later, they came to mean a right triangle. In the 12th century, the post-classical Latin word ''orthogonalis'' came to mean a right angle or something related to a right angle. Mathematics Physics * In optics, polarization states are said to be orthogonal when they propagate independently of each other, as in vertical and horizontal linear polarization or right- and left-handed circular polarization. * In special relativity, a time axis determined by a rapidity of motion is hyperbolic-orthogonal to a space axi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eye Development
Eye formation in the human embryo begins at approximately three weeks into embryonic development and continues through the tenth week.Ort, D., David, H."Development of the Eye" Retrieved 22 April 2015. Cells from both the mesodermal and the ectodermal tissues contribute to the formation of the eye. Specifically, the eye is derived from the neuroepithelium, surface ectoderm, and the extracellular mesenchyme which consists of both the neural crest and mesoderm. Neuroepithelium forms the retina, ciliary body, iris, and optic nerves. Surface ectoderm forms the lens, corneal epithelium and eyelid. The extracellular mesenchyme forms the sclera, the corneal endothelium and stroma, blood vessels, muscles, and vitreous. The eye begins to develop as a pair of optic vesicles on each side of the forebrain at the end of the 4th week of pregnancy. Optic vesicles are outgrowings of the brain which make contact with the surface ectoderm and this contact induces changes necessary for f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pax6
Paired box protein Pax-6, also known as aniridia type II protein (AN2) or oculorhombin, is a protein that in humans is encoded by the ''PAX6'' gene. Function PAX6 is a member of the Pax gene family which is responsible for carrying the genetic information that will encode the Pax-6 protein. It acts as a "master control" gene for the development of eyes and other sensory organs, certain neural and epidermal tissues as well as other homologous structures, usually derived from ectodermal tissues. However, it has been recognized that a suite of genes is necessary for eye development, and therefore the term of "master control" gene may be inaccurate. Pax-6 is expressed as a transcription factor when neural ectoderm receives a combination of weak Sonic hedgehog (SHH) and strong TGF-Beta signaling gradients. Expression is first seen in the forebrain, hindbrain, head ectoderm and spinal cord followed by later expression in midbrain. This transcription factor is most noted for its ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bilateria
The Bilateria or bilaterians are animals with bilateral symmetry as an embryo, i.e. having a left and a right side that are mirror images of each other. This also means they have a head and a tail (anterior-posterior axis) as well as a belly and a back (ventral-dorsal axis). Nearly all are bilaterally symmetrical as adults as well; the most notable exception is the echinoderms, which achieve secondary pentaradial symmetry as adults, but are bilaterally symmetrical during embryonic development. Most animals are bilaterians, excluding sponges, ctenophores, placozoans and cnidarians. For the most part, bilateral embryos are triploblastic, having three germ layers: endoderm, mesoderm, and ectoderm. Except for a few phyla (i.e. flatworms and gnathostomulids), bilaterians have complete digestive tracts with a separate mouth and anus. Some bilaterians lack body cavities (acoelomates, i.e. Platyhelminthes, Gastrotricha and Gnathostomulida), while others display primary body cavi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nautilus Pompilius
The chambered nautilus (''Nautilus pompilius''), also called the pearly nautilus, is the best-known species of nautilus. The shell, when cut away, reveals a lining of lustrous nacre and displays a nearly perfect equiangular spiral, although it is not a golden spiral. The shell exhibits countershading, being light on the bottom and dark on top. This is to help avoid predators, because when seen from above, it blends in with the darkness of the sea, and when seen from below, it blends in with the light coming from above. The range of the chambered nautilus encompasses much of the south Pacific; It has been found near reefs and on the seafloor off of the coasts of Australia, Japan, and Micronesia. The eyes of the chambered nautilus, like those of all ''Nautilus'' species, are more primitive than those of most other cephalopods; the eye has no lens and thus is comparable to a pinhole camera. The species has about 90 cirri (referred to as "tentacles", see ) that do not have sucke ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cuttlefish
Cuttlefish or cuttles are marine molluscs of the order Sepiida. They belong to the class Cephalopoda which also includes squid, octopuses, and nautiluses. Cuttlefish have a unique internal shell, the cuttlebone, which is used for control of buoyancy. Cuttlefish have large, W-shaped pupils, eight arms, and two tentacles furnished with denticulated suckers, with which they secure their prey. They generally range in size from , with the largest species, the giant cuttlefish (''Sepia apama''), reaching in mantle length and over in mass. Cuttlefish eat small molluscs, crabs, shrimp, fish, octopus, worms, and other cuttlefish. Their predators include dolphins, sharks, fish, seals, seabirds, and other cuttlefish. The typical life expectancy of a cuttlefish is about 1–2 years. Studies are said to indicate cuttlefish to be among the most intelligent invertebrates. [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Squid
True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting these criteria. Like all other cephalopods, squid have a distinct head, bilateral symmetry, and a mantle. They are mainly soft-bodied, like octopuses, but have a small internal skeleton in the form of a rod-like gladius or pen, made of chitin. Squid diverged from other cephalopods during the Jurassic and occupy a similar role to teleost fish as open water predators of similar size and behaviour. They play an important role in the open water food web. The two long tentacles are used to grab prey and the eight arms to hold and control it. The beak then cuts the food into suitable size chunks for swallowing. Squid are rapid swimmers, moving by jet propulsion, and largely locate their prey by sight. They are among the most intelligent o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Octopus Vulgaris
The common octopus (''Octopus vulgaris'') is a mollusc belonging to the class Cephalopoda. ''Octopus vulgaris'' is one of the most studied of all octopus species, and also one of the most intelligent. It ranges from the eastern Atlantic, extends from the Mediterranean Sea and the southern coast of England, to the southern coast of South Africa. It also occurs off the Azores, Canary Islands, and Cape Verde Islands. The species is also common in the Western Atlantic. The common octopus hunts at dusk. Crabs, crayfish, and bivalve molluscs (two-shelled, such as cockles) are preferred, although the octopus eats almost anything it can catch. It is able to change colour to blend in with its surroundings, and is able to jump upon any unwary prey that strays across its path. Using its beak, it is able to break into the shells of shelled molluscs. Training experiments have shown the common octopus can distinguish the brightness, size, shape, and horizontal or vertical orientation of objects ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bathyteuthis
''Bathyteuthis'' is the singular genus of squid in the family Bathyteuthidae, encompassing three species. ''Bathyteuthis'' species are found scattered throughout the world’s oceans at mesopelagic to bathypelagic depths, commonly between 700 and 2,000 meters. They are found in deep-sea territories and can be spotted on the coast of New England. The genus contains bioluminescent species. Description ''Bathyteuthis'' are deep reddish maroon in colour and small in size, with none exceeding 80 mm in mantle length. The arms on ''Bathyteuthis'' are short, joined by a low, fleshy web, with suckers arranged in irregular rows (two proximally increasing to four distally). Tentacular clubs are short and narrow, with 8-10 longitudinal series of numerous, minute suckers. Buccal connectives have small suckers attached to the dorsal border of the ventral arms (arms IV). Fins are small, round and separate. The head has eyes turned slightly to the front. Suckers lack circularis muscles. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cone Cell
Cone cells, or cones, are photoreceptor cells in the retinas of vertebrate eyes including the human eye. They respond differently to light of different wavelengths, and the combination of their responses is responsible for color vision. Cones function best in relatively bright light, called the photopic region, as opposed to rod cells, which work better in dim light, or the scotopic region. Cone cells are densely packed in the fovea centralis, a 0.3 mm diameter rod-free area with very thin, densely packed cones which quickly reduce in number towards the periphery of the retina. Conversely, they are absent from the optic disc, contributing to the blind spot. There are about six to seven million cones in a human eye (vs ~92 million rods), with the highest concentration being towards the macula. Cones are less sensitive to light than the rod cells in the retina (which support vision at low light levels), but allow the perception of color. They are also able to perceive ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rod Cell
Rod cells are photoreceptor cells in the retina of the eye that can function in lower light better than the other type of visual photoreceptor, cone cells. Rods are usually found concentrated at the outer edges of the retina and are used in peripheral vision. On average, there are approximately 92 million rod cells (vs ~6 million cones) in the human retina. Rod cells are more sensitive than cone cells and are almost entirely responsible for night vision. However, rods have little role in color vision, which is the main reason why colors are much less apparent in dim light. Structure Rods are a little longer and leaner than cones but have the same basic structure. Opsin-containing disks lie at the end of the cell adjacent to the retinal pigment epithelium, which in turn is attached to the inside of the eye. The stacked-disc structure of the detector portion of the cell allows for very high efficiency. Rods are much more common than cones, with about 120 million rod cells comp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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