ommatidium


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Related to ommatidium: Rhabdomere

ommatidium

(ŏm′ə-tĭd′ē-əm)
n. pl. ommatid·ia (-ē-ə)
One of the optical units, consisting of photoreceptors and usually one or more lenses, that make up a compound eye of an insect or a crustacean.

om′ma·tid′i·al (-ē-əl) adj.

ommatidium

(pl. ommatidia) any of the numerous facets which make up the compound eye of insects and other arthropods. Each ommatidium has its own lens and is composed of a group of retinal cells surrounded by pigment cells. The light-sensitive part of the ommatidium is the RHABDOM, and on its receiving a stimulus a photochemical reaction takes place which results in impulses being sent to the optic nerve.

ommatidium 

One of the visual elements of the compound eye of arthropods. It is hexagonal in shape and about ten times longer than its diameter. It consists of a corneal facet below which is a crystalline cone which collects light and a sensory area called the rhabdom, all of it being enclosed in a dark pigment.
References in periodicals archive ?
Bactrocera dorsalis had a smaller eye width and a smaller individual square ommatidium area than the other 2 species, and the largest number of ommatrichia.
saltator, like some other amphipods, possesses an undifferentiated cornea, a fused-type rhabdom attached to the crystalline cone, and five retinula cells in each ommatidium (Ball, 1977; Meyer-Rochow, 1978; Hallberg et al.
With the high magnification of a stereomicroscope, we identified the ommatidium whose optic axis was aligned with that of the microscope.
Normally, all photoreceptors in a single ommatidium view an identical receptive field, which may be imaged onto several photoreceptor types for spectral or polarizational analysis.
After isolating the response of a single optic nerve fiber, we align the animal so that the optic axis of the recorded ommatidium views the center of the pattern.
The video frames were taken 6 s after the beginning of the response records (arrows), when the grey-black edge of the cylinder began to enter the field of view of the recorded ommatidium from the right.
Figure 1A shows the intensity response functions for a single dark-adapted ommatidium during the day and at night.
A second eccentric cell located in the same ommatidium generated much smaller action potentials ([approximately]2.
Biometrical data of the constituent parts of one representative central ommatidium of the compound eye of the two crustaceans are given in Table I.
The former study, however, illuminated the entire retina, whereas the latter study limited the stimulus to a single ommatidium.
The average area occupied by an individual ommatidium was then measured and the number of ommatidia calculated from the total retinal area.
Illumination of a single ommatidium in the retina generally evokes slow depolarizing potentials (0-5 mV) in association with a single train of action potentials (20-60 mV) in the compartment, whereas illumination of the entire retina elicits slow hyperpolarizing potentials (5-15 mV) and a spike train of reduced rate.