lens placode

Examples of lens placode in the following topics:

• Development of Vision

  • The epithelium thickens to form the lens placode.
  • The lens differentiates and invaginates until it detaches from the epithelium.
  • This vesicle is subsequently invaginated by further inductions from the chordamesoderm, and induces the ectoderm that thickens (lens placode) and further invaginates to a point that detaches from the ectoderm and forms a neurogenic placode.
  • The lens placode is triggered by the chordamesoderm to invaginate and form the optic cup, composed of an outer layer of neural retina and inner layer of pigmented retina that unite and form the optic stalk .
  • Some cells in the lens vesicle will form the cornea and the lens vesicle will develop completely to form the definitive lens.

• Development of Hearing and Balance

  • The human inner ear develops during week four of embryonic development from the auditory placode, a thickening of the ectoderm that gives rise to the bipolar neurons of the cochlear and vestibular ganglions.
  • As the auditory placode invaginates towards the embryonic mesoderm, it forms the auditory vesicle or otocysts.

• Autonomic Interactions

  • Dilates pupils and relaxes the ciliary muscle to the lens, allowing more light to enter the eye and far vision.
  • Causes constriction of the pupil and contraction of the ciliary muscle to the lens, allowing for closer vision.

• Divisions of the Autonomic Nervous System

  • The PSNS typically functions in contrast to the SNS by dilating the blood vessels leading to the GI tract, causing constriction of the pupil and contraction of the ciliary muscle to the lens to enable closer vision, and stimulating salivary gland secretion, in keeping with the rest and digest functions.

• Optic (II) Nerve

  • The light reflex refers to the constriction of both pupils that occurs when light is shone into either eye; the accommodation reflex refers to the swelling of the lens of the eye that occurs when one looks at a near object, as in reading.

• Tissues and Aging

  • Age-related changes in vision include the cornea becoming thicker and less curved; the anterior chamber decreasing in size and volume; the lens becoming thicker and more opaque, and also gaining rigidity and losing elasticity; the ciliary muscles atrophy and the pupil constricts; and there is also a reduction of rods and nerve cells of the retina .

• Marfan Syndrome

  • Dislocation of the lens in one or both eyes can also occur in an individual with Marfan's.

• Tissue Development

  • The ectoderm forms the central nervous system, the lens of the eye, cranial and sensory nerves, the ganglia and nerves, pigment cells, head connective tissues, the epidermis, hair, and mammary glands.

• Function and Physiology of the Spinal Nerves

  • Dilates pupils and relaxes the ciliary muscle to the lens for far vision.