Mother of Pearl

Meisje met de parel, Johannes Vermeer, Girl with a Pearl Earring (ca. 1665)

Nacre, also known as "mother of pearl", is an organic-inorganic composite material produced by some molluscs as an inner shell layer; it is also the material of which pearls are composed. It is strong, resilient, and iridescent.

Nacre is secreted by the epithelial cells of the mantle (also known by the Latin word pallium meaning mantle, robe or cloak, adjective pallial, a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass) tissue of various molluscs. The nacre is continuously deposited onto the inner surface of the shell, the iridescent nacreous layer, commonly known as "mother of pearl". The layers of nacre smooth the shell surface and help defend the soft tissues against parasites and damaging debris by entombing them in successive layers of nacre, forming either a blister pearl attached to the interior of the shell or a free pearl within the mantle tissues. The process is called encystation, from κύστις • (kústis) f (genitive κύστεως); bladder. From Proto-Indo-European *(s)kewH- (“to cover”) or from κύω (kúō).

Nacre: from Middle French nacre, from Medieval Latin nacchara, from Arabic نَقَّارَة‎ (naqqāra), from the root ن ق ر‎ (n-q-r). Noun نَقَّارَة • (naqqāra) f (plural نَقَّارَات‎ (naqqārāt) or نَقَاقِير‎ (naqāqīr)) a kind of small drum, the forebear of the European kettledrum (timpanum: tympan/timbale, borrowed from Ancient Greek τύμπανον (túmpanon), from τύπτω (túptō, “I strike, beat”)).

Wednesday, March 10

Pinctada margaritifera, shaped like an ear

"Through irritation, the soul often grows– just like the pearl.

As long as that manifested by the individual stays pure, little harm may come."

― Edgar Cayce (ECRL 254-68)

tympanum: eardrum &/or auris media (middle ear: the cavity in the temporal bone between the eardrum & the inner ear that contains the ossicles & conveys sound to the cochlea.)

A diagram of the anatomy of the human ear.

  Green is the outer ear.

  Red is the middle ear.

  Purple is the inner ear.

➥ audition ≍ irritation of the soul ⬄ vibration & resonance

Balance, cf: Balance (ability) & Equilibrioception

Providing balance, when moving or stationary, is a central function of the ear. The ear facilitates two types of balance: static balance, which allows a person to feel the effects of gravity and dynamic balance, which allows a person to sense acceleration.

Static balance is provided by two ventricles, the utricle and the saccule. Cells lining the walls of these ventricles contain fine filaments, and the cells are covered with a fine gelatinous layer. Each cell has 50–70 small filaments, and one large filament, the kinocilium. Within the gelatinous layer lie otoliths, tiny formations of calcium carbonate. When a person moves, these otoliths shift position. This shift alters the positions of the filaments, which opens ion channels within the cell membranes, creating depolarisation and an action potential that is transmitted to the brain along the vestibulocochlear nerve.

Dynamic balance is provided through the three semicircular canals. These three canals are orthogonal (at right angles) to each other. At the end of each canal is a slight enlargement, known as the ampulla, which contains numerous cells with filaments in a central area called the cupula. The fluid in these canals rotates according to the momentum of the head. When a person changes acceleration, the inertia of the fluid changes. This affects the pressure on the cupula and results in the opening of ion channels. This causes depolarization, which is passed as a signal to the brain along the vestibulocochlear nerve.[9] Dynamic balance also helps maintain eye tracking when moving, via the vestibulo–ocular reflex.