"""musculus dilator pupillae"", The ""Nomina Anatomica"" as authorized in 1895 in Basle and in 1935 in Jena used the full Latin expression. Iris dilator muscle The iris dilator muscle (pupil dilator muscle, pupillary dilator, radial muscle of iris, radiating fibers), is a smooth muscle of the eye, running radially in the iris and therefore fit as a dilator. The pupillary dilator consists of a spokelike arrangement of modified contractile cells called myoepithelial cells. These cells are stimulated by the sympathetic nervous system. When stimulated, the cells contract, widening the pupil and allowing for more light to pass through the eye."
"the reception of images, patterns, motion, and color, melanopsin-containing ipRGCs contribute to various reflexive responses of the brain and body to the presence of light. Evidence for melanopsin's physiological light detection has been tested in mice. A mouse cell line that is not normally photosensitive, Neuro-2a, is rendered light-sensitive by the addition of human melanopsin. The photoresponse is selectively sensitive to short-wavelength light (peak absorption ~479 nm), and has an intrinsic photoisomerase regeneration function that is chromatically shifted to longer wavelengths. Melanopsin photoreceptors are sensitive to a range of wavelengths and reach peak light absorption at blue light wavelengths around"
"reflex) or during accommodation. In lower animals, the muscle cells themselves are photosensitive causing iris action without brain input. It is controlled by parasympathetic fibers of the muscarinic acetylcholine receptor (M3) that originate from the Edinger-Westphal nucleus, travel along the oculomotor nerve (CN III), synapse in the ciliary ganglion, and then enter the eye via the short ciliary nerves.. The short ciliary nerves then run forward and pierce the sclera at the back of the eye, traveling between the sclera and the choroid to innervate the iris sphincter muscle. Iris sphincter muscle The iris sphincter muscle (pupillary sphincter, pupillary constrictor,"
"and thus attain their expected acuity; in the dark this is not necessary, so it is chiefly concerned with admitting sufficient light into the eye. When bright light is shone on the eye, light sensitive cells in the retina, including rod and cone photoreceptors and melanopsin ganglion cells, will send signals to the oculomotor nerve, specifically the parasympathetic part coming from the Edinger-Westphal nucleus, which terminates on the circular iris sphincter muscle. When this muscle contracts, it reduces the size of the pupil. This is the pupillary light reflex, which is an important test of brainstem function. Furthermore, the pupil"
"some neurons and hyperpolarize others, allowing photoreceptors to interact in an antagonistic manner. When light hits photoreceptive pigments within the photoreceptor cell, the pigment changes shape. The pigment, called rhodopsin (conopsin is found in cone cells) comprises 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 an increased affinity for the regulatory protein called"
"dark because channels would re-open and allow for the cell to slightly depolarize. Inhibition by neurons also affects activation in synapses. Together with the bleaching of a rod or cone pigment, merging of signals on ganglion cells are inhibited, reducing convergence. Alpha adaptation, ""i.e."", rapid sensitivity fluctuations, is powered by nerve control. The merging of signals by virtue of the diffuse ganglion cells, as well as horizontal and amacrine cells, allow a cumulative effect. Thus that area of stimulation is inversely proportional to intensity of light, a strong stimulus of 100 rods equivalent to a weak stimulus of 1,000 rods."
"directly, or absorbed after diffuse reflections within the eye that mostly miss exiting the narrow pupil. The iris is a contractile structure, consisting mainly of smooth muscle, surrounding the pupil. Light enters the eye through the pupil, and the iris regulates the amount of light by controlling the size of the pupil. The iris contains two groups of smooth muscles; a circular group called the sphincter pupillae, and a radial group called the dilator pupillae. When the sphincter pupillae contract, the iris decreases or constricts the size of the pupil. The dilator pupillae, innervated by sympathetic nerves from the superior"
"ganglion. Postganglionic nerve fibers leave the ciliary ganglion to innervate the ciliary sphincter. Each afferent limb has two efferent limbs, one ipsilateral and one contralateral. The ipsilateral efferent limb transmits nerve signals for direct light reflex of the ipsilateral pupil. The contralateral efferent limb causes consensual light reflex of the contralateral pupil. The optic nerve, or more precisely, the photosensitive ganglion cells through the retinohypothalamic tract, is responsible for the afferent limb of the pupillary reflex; it senses the incoming light. The oculomotor nerve is responsible for the efferent limb of the pupillary reflex; it drives the iris muscles that"
"the dark-adapted human eye is greatest at about 507nm, a blue-green color, while the light-adapted eye is most sensitive about 555nm, a yellow-green; these are the peak locations of the rod and cone (scotopic and photopic, respectively) luminosity functions. The perception of greenness (in opposition to redness forming one of the opponent mechanisms in human color vision) is evoked by light which triggers the medium-wavelength ""M"" cone cells in the eye more than the long-wavelength ""L"" cones. Light which triggers this greenness response more than the yellowness or blueness of the other color opponent mechanism is called green. A green"
"isolated. Separate connectivity is established in the inner plexiform layer so that each connection is parallel. The response of cone cells to light is also directionally nonuniform, peaking at a direction that receives light from the center of the pupil; this effect is known as the Stiles–Crawford effect. Sensitivity to a prolonged stimulation tends to decline over time, leading to neural adaptation. An interesting effect occurs when staring at a particular color for a minute or so. Such action leads to an exhaustion of the cone cells that respond to that color – resulting in the afterimage. This vivid color"
"the retina, which in its entirety comprises ten distinct layers, including an outer layer of pigmented epithelial cells. The only neural cells that are directly sensitive to light are the photoreceptor cells, which are of two types: rods and cones. Rods function mainly in dim light and provide black-and-white vision while cones are responsible for the perception of colour. A third type of photoreceptor, the photosensitive ganglion cells, is important for entrainment and reflexive responses to the brightness of light. Light striking the retina initiates a cascade of chemical and electrical events that ultimately trigger nerve impulses that are sent"
"is based upon the varying sensitivity of different cells in the retina to light of different wavelengths. Humans are trichromatic—the retina contains three types of color receptor cells, or cones. One type, relatively distinct from the other two, is most responsive to light that is perceived as blue or blue-violet, with wavelengths around 450 nm; cones of this type are sometimes called ""short-wavelength cones"", ""S cones"", or ""blue cones"". The other two types are closely related genetically and chemically: ""middle-wavelength cones"", ""M cones"", or ""green cones"" are most sensitive to light perceived as green, with wavelengths around 540 nm, while"
"in the fibrils. The coloration or wavelength of the diffracted light depends on the angle of observation and can be enhanced by covering the meat with translucent foils. Roughening the surface or removing water content by drying causes the structure to collapse, thus, the structural coloration to disappear. Some animals including cephalopods like squid are able to vary their colours rapidly for both camouflage and signalling. The mechanisms include reversible proteins which can be switched between two configurations. The configuration of reflectin proteins in chromatophore cells in the skin of the ""Doryteuthis pealeii"" squid is controlled by electric charge. When"
"the brain would respond if presented with a new color channel. Mice, which normally have only two cone pigments, can be engineered to express a third cone pigment, and appear to demonstrate increased chromatic discrimination, arguing against some of these obstacles; however, the original publication's claims about plasticity in the optic nerve have also been disputed. Humans cannot see ultraviolet light directly because the lens of the eye blocks most light in the wavelength range of 300–400 nm; shorter wavelengths are blocked by the cornea. The photoreceptor cells of the retina are sensitive to near ultraviolet light, and people lacking"
"light (that is, the pigment is most likely to produce a cellular response when it is hit by a photon with the specific wavelength to which that pigment is most sensitive). The three types of cones are L, M, and S, which have pigments that respond best to light of long (especially 560 nm), medium (530 nm), and short (420 nm) wavelengths respectively. Since the likelihood of response of a given cone varies not only with the ""wavelength"" of the light that hits it but also with its ""intensity"", the brain would not be able to discriminate different colors if"
"suspension of the lens of the eye. Ciliary muscle The ciliary muscle is a ring of smooth muscle in the eye's middle layer (vascular layer) that controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humor into Schlemm's canal. It changes the shape of the lens within the eye, not the size of the pupil which is carried out by the sphincter pupillae muscle and dilator pupillae. The ciliary muscle develops from mesenchyme within the choroid and is considered a cranial neural crest derivative. The ciliary muscle receives parasympathetic fibers from the short ciliary nerves"
"respond to hormonal or other stimuli. Following activation of adenylyl cyclase, the resulting cAMP acts as a second messenger by interacting with and regulating other proteins such as protein kinase A and cyclic nucleotide-gated ion channels. Photoactivatable adenylyl cyclase (PAC) was discovered in ""Euglena gracilis"" and can be expressed in other organisms through genetic manipulation. Shining blue light on a cell containing PAC activates it and abruptly increases the rate of conversion of ATP to cAMP. This is a useful technique for researchers in neuroscience because it allows them to quickly increase the intracellular cAMP levels in particular neurons, and"
"gradients, but growth was faster at less steep gradients and was faster up the gradients than down the gradients. Electroactive polymers (EAPs) are also known as artificial muscles. EAPs are polymeric materials and they are able to produce large deformation when applied in an electric field. This provides large potential in applications in biotechnology and robotics, sensors, and actuators. The production of structural colours concerns a large array of oganisms. From bacteria (""Flavobacterium"" strain IR1) to multicellular organisms, (""Hibiscus trionum"", ""Doryteuthis pealeii"" (squid), or ""Chrysochroa fulgidissima"" (beetle)), manipulation of light is not limited to rare and exotic life forms. Different"
"Rhodopsin Rhodopsin (also known as visual purple) is a light-sensitive receptor protein involved in visual phototransduction. It is named after ancient Greek ῥόδον (rhódon) for ""rose"", due to its pinkish color, and ὄψις (ópsis) for ""sight"". Rhodopsin is a biological pigment found in the rods of the retina and is a G-protein-coupled receptor (GPCR). Rhodopsin is extremely sensitive to light, and thus enables vision in low-light conditions. When rhodopsin is exposed to light, it immediately photobleaches. In humans, it is regenerated fully in about 30 minutes, after which rods are more sensitive. Rhodopsin was discovered by Franz Christian Boll in"
"In the human eye, light enters the pupil and is focused on the retina by the lens. Light-sensitive nerve cells called rods (for brightness), cones (for color) and non-imaging ipRGC (intrinsincally photosensitive retinal ganglion cells) react to the light. They interact with each other and send messages to the brain. The rods and cones enable vision. The ipRGCs enable entrainment to the Earth's 24-hour cycle, resizing of the pupil and acute suppression of the pineal hormone melatonin. The retina contains three forms of photosensitive cells, two of them important to vision, rods and cones, in addition to the subset of"
"a neuron in one layer to an adjacent neuron in the same layer), resulting in more complex receptive fields that can be either indifferent to color and sensitive to motion or sensitive to color and indifferent to motion. Mechanism of generating visual signals: The retina adapts to change in light through the use of the rods. In the dark, the chromophore retinal has a bent shape called cis-retinal (referring to a ""cis"" conformation in one of the double bonds). When light interacts with the retinal, it changes conformation to a straight form called trans-retinal and breaks away from the opsin."
"cells responsible for the support and maintenance of the skeleton, as well as pigment cells, mechanoreceptor cells (which detect motion on the animal's surface), and sometimes gland cells which secrete sticky fluids or even toxins. The varied and often vivid colours of echinoderms are produced by the action of skin pigment cells. These are produced by a variable combination of coloured pigments, such as the dark melanin, red carotinoids, and carotene proteins, which can be blue, green, or violet. These may be light-sensitive, and as a result many echinoderms change appearance completely as night falls. The reaction can happen quickly"
"of voluntary eye movement to track objects of interest: smooth pursuit, vergence shifts and saccades. These movements appear to be initiated by a small cortical region in the brain's frontal lobe. This is corroborated by removal of the frontal lobe. In this case, the reflexes (such as reflex shifting the eyes to a moving light) are intact, though the voluntary control is obliterated. Six extraocular muscles facilitate eye movement. These muscles arise from the common tendinous ring in the orbit, the eye cavity, and attach to the eyeball. The six muscles are the lateral, medial, inferior and superior rectus muscles,"
"absorb light at different wavelengths as retinal-bound pigments. Humans have three different photoreceptor proteins (""photopsin"" or ""cone opsins"") which are found in cone cells and which are responsible for colour vision: George Wald received the 1967 Nobel Prize in Physiology or Medicine for his experiments in the 1950s that showed the difference in absorbance by these photopsins (see image). Photopsin Photopsins (also known as Cone opsins) are the photoreceptor proteins found in the cone cells of the retina that are the basis of color vision. Iodopsin, the cone pigment system in chicken retina, is a close analog of the ""visual"
"the neurons' activity, as they are already active. Light at night, on the other hand, when these neurons are inactive, stimulates them and causes them to fire action potentials. The change in electrical activity manifests itself as a phase shift within the organism. Further research led them to find that phase shifting is a calcium-dependent process. They found that lowering extracellular levels of calcium actually prevents the organism from phase shifting in response to light without affecting the response of the neurons to light. Around the same time, while Block and McMahon were conducting this experiment, other scientists discovered how"
"a light-dark cycle. This observation led to the conclusion that neither rods nor cones, located in the outer retina, are necessary for circadian entrainment and that a third class of photoreceptor exists in the mammalian eye. Provencio and colleagues then found in 2000 that melanopsin is also present in mouse retina, specifically in ganglion cells, and that it mediates non-visual photoreceptive tasks. Melanopsin was found to be encoded by Opn4 with orthologs in a variety of organisms. These retinal ganglion cells were found to be innately photosensitive, since they responded to light even while isolated, and were thus named intrinsically"
"eyes and in the deep brain the ciliary photoreceptor cells. The ciliary photoreceptor cells express a ciliary opsin, which is a photopigment maximally sensitive to UV-light (""λ"" = 383 nm). Thus, the ciliary photoreceptor cells react on UV-light and make the larvae swimming down gravitactically. The gravitaxis here is countered by phototaxis, which makes the larvae swimming up to the light coming from the surface. Phototaxis is mediated by the rhabdomeric eyes. The eyes express at least three opsins (at least in the older larvae), and one of them is maximally sensitive to cyan light (""λ"" = 483 nm) so"
"light from its surroundings onto a light-sensitive membrane in the back of the eye, called the retina. The retina is actually part of the brain that is isolated to serve as a transducer for the conversion of light into neuronal signals. Based on feedback from the visual system, the lens of the eye adjusts its thickness to focus light on the photoreceptive cells of the retina, also known as the rods and cones, which detect the photons of light and respond by producing neural impulses. These signals are processed via complex feedforward and feedback processes by different parts of the"
"cones were also able to entrain. However, when melanopsin was knocked out in blind mice without rods and cones, they exhibited “complete loss of photoentrainment of the circadian oscillator, pupillary light responses, photic suppression of arylalkylamine-N-acetyltransferase transcript, and acute suppression of locomotor activity by light.” Provencio concluded that either melanopsin-containing retinal ganglion cells or outer-retinal photoreceptors (rods and cones) are sufficient to induce a response to light. However, in the absence of either rods and cones or melanopsin, melanopsin becomes necessary for photoentrainment of the circadian oscillator and for other photic responses. To further investigate the role of melanopsin in"
"to activate neuronal spike firing. Recently, photoinhibition, the inhibition of neural activity with light, has become feasible with the application of molecules such as the light-activated chloride pump halorhodopsin to neural control. Together, blue-light activated channelrhodopsin-2 and the yellow light-activated chloride pump halorhodopsin enable multiple-color, optical activation and silencing of neural activity. (See also Photobiomodulation) A caged protein is a protein that is activated in the presence of a stimulating light source. In most cases, photo-uncaging is the technique revealing the active region of a compound by the process of photolysis of the shielding molecule (‘cage’). However, uncaging the protein"
"Fasciculation A fasciculation , or muscle twitch, is a small, local, involuntary muscle contraction and relaxation which may be visible under the skin. Deeper areas can be detected by electromyography (EMG) testing, though they can happen in any skeletal muscle in the body. Fasciculations arise as a result of ""spontaneous depolarization"" of a lower motor neuron leading to the synchronous contraction of all the skeletal muscle fibers within a single motor unit. An example of normal spontaneous depolarization is the constant contractions of cardiac muscle, causing the heart to beat. Usually, intentional movement of the involved muscle causes fasciculations to"
"Cone of light The cone of light, or light reflex, is a visible phenomenon which occurs upon examination of the tympanic membrane with an otoscope. Shining light on the tympanic membrane causes a cone-shaped reflection of light to appear in the anterior inferior quadrant. This corresponds to the 4 o'clock to 5 o'clock position in the right eardrum and the 7 o'clock to 8 o'clock position in the left eardrum. The apex of the cone is at the most depressed part of the tympanic membrane, known as the umbo. The absence of a cone of light does not necessarily signify"
"shape of the lens. In the skin, smooth muscle cells cause hair to stand erect in response to cold temperature or fear. Most smooth muscle is of the single-unit variety, that is, either the whole muscle contracts or the whole muscle relaxes, but there is multiunit smooth muscle in the trachea, the large elastic arteries, and the iris of the eye. Single unit smooth muscle, however, is most common and lines blood vessels (except large elastic arteries), the urinary tract, and the digestive tract. However, the terms single- and multi-unit smooth muscle represents an oversimplification. This is due to the"