Eye Morphology

LaCourse (1981) examined the structure and ultrastructure of Mytilus in detail using light and transmission electron microscopy. He found that there were pigment cells in close membrane association with the PRCs. The arrangement between PRCs and pigment cells was irregular. The PRCs were unpigmented. Their distal ends were covered with many microvilli and one or more cilia with the 9 + 2 arrangement of microtubules in their axonemes. Figure 2.8-3 is an artist's schematic of a slice through the eyecup based on electron microscope photomicrographs. The optic nerve

FIGURE 2.8-1 Artist's line drawing of a transverse section through an eye of M. edulis (from a light micrograph). Object in the eyecup is an artifact; a shrunken ball of mucus and cilia. Scale line is 20 <*=m. (From LaCourse, J.R., Ph.D. dissertation, University of Connecticut, Storrs, 1981. With permission.)

Pigment Cell Line
FIGURE 2.8-2 Transmission electron micrograph of pigment cells (PC) and ciliated sensory cells (SC) on the margin of the eyecup. (■ 3000). (From LaCourse, J.R., Ph.D. dissertation, University of Connecticut, Storrs, 1981. With permission.)

axons are about 1 to 2 ^m in diameter. Note the slender region between the inner nuclear part of the PRCs and the outer section, which contains the cilia and microvilli that project into the eyecup. Each microvillus is about 12 ^m long and 0.15 ^m in diameter. Its interior is lled with granular material and small v esicles about 0.03 ^m in diameter. The microvilli presumably contain the photoreceptor pigments and are the primary transduction sites where captured photons trigger photochemical reactions leading to PRC hyperpolarization. Of the PRCs, LaCourse (1981) comments:

Slender cell processes, passing through the pigmented region contain microtubules and numerous cytoplasmic vesicles as supportive or transportive elements. These processes are without pigment granules and therefore do not function as shading elements. The large nuclear regions of the sensory cells house rich accumulations of glycogen granules, Golgi apparatus, mitochondria, and both smooth and rough endoplasmic reticu-lum. The presence of these organelles indicates the high level of synthetic activity common to visual cells.

Glycogen Granules

FIGURE 2.8-3 Artist's reconstruction of the cells in the Mytilus eyecup based on many TEM micrographs. Key to abbreviations: BL, basal lamella; C, cilia; CV, cytoplasmic vesicles; LP, lipid droplets; M, mitochondria; MT, microtubules; MV, microvilli; NT, axons; PC, pigment cells; PG, pigment granules; PN, pigment cell nucleus; SC, photosensor cell; SER, smooth endoplasmic reticulum; SN, sensory cell nucleus; Z, zonules. (From LaCourse, J.R., Ph.D. dissertation, University of Connecticut, Storrs, 1981. With permission.)

FIGURE 2.8-3 Artist's reconstruction of the cells in the Mytilus eyecup based on many TEM micrographs. Key to abbreviations: BL, basal lamella; C, cilia; CV, cytoplasmic vesicles; LP, lipid droplets; M, mitochondria; MT, microtubules; MV, microvilli; NT, axons; PC, pigment cells; PG, pigment granules; PN, pigment cell nucleus; SC, photosensor cell; SER, smooth endoplasmic reticulum; SN, sensory cell nucleus; Z, zonules. (From LaCourse, J.R., Ph.D. dissertation, University of Connecticut, Storrs, 1981. With permission.)

Was this article helpful?

0 0
Peripheral Neuropathy Natural Treatment Options

Peripheral Neuropathy Natural Treatment Options

This guide will help millions of people understand this condition so that they can take control of their lives and make informed decisions. The ebook covers information on a vast number of different types of neuropathy. In addition, it will be a useful resource for their families, caregivers, and health care providers.

Get My Free Ebook


Post a comment