Squamous cells

flat, paving stone shaped, cells, usually found in the epithelial tissue where the body meets the external environment such as the cervix, skin, vagina, vulva and gastrointestinal tract.  Squamous epithelium is formed from cells of the mucous membrane of the mouth and squamous endothelium lines blood vessels. The outermost layer of our skins is composed …

Spontaneous motor activity

Movements expressed by the embryo or fetus that are not a response to explicit stimulation by an experimenter.  At least some spontaneous movements are generated by activity in the central nervous system, although in intact embryos/fetuses movements may be influenced by uncontrolled sources of environmental stimuli or self-stimulation.  See Central pattern generator (CPG), Motility, Movement, …

Spindle

A structure resembling a spinning-machine spindle that is formed from fine fibers of protein in the cytoplasm of cells at the beginning of metaphase of cell division.  Chromosomes are attached to the spindle fibbers by their centromeres at the equator.  The equator is the widest part of the spindle.  See Centromere, Chromatid, Chromosome, Metaphase

Spinal cord

The component of the central nervous system continuous with the brain stem, and within the protective vertebral column, that extends down the spine, receiving sensory and visceral input, and containing the neurones that connect to muscles.  It contains both tray and white matter (the latter consisting of ascending and descending white fibers) and has 31 …

Spina bifida

A congenital defect in which the spinal column is imperfectly closed so that part of the meninges or spinal cord protrudes, often resulting in hydrocephalus and other neurological disorders.  See Hydrocephalus, Meninges, Neural tube, Spinal cord, Tower test

Sphericity

The condition under which the variance of the difference is constant between any two estimated factor level means in an analysis of variance, but one that is less restrictive than compound symmetry.  As with compound sphericity (of which sphericity is a more general form), it is important in the analysis of variance of repeated measures …

Sphericity assumption

Repeated measures analysis of variance must display the variance pattern of sphericity for proper application (i.e., population variances of the differences between all possible pairs or levels of the independent variable are equal).  This assumption is always met when there are only two levels of a repeated measures factor.  Sphericity is both a necessary and …