Toxin injections made from a chemical produced by bacteria that temporarily paralyse muscle by acting on nerve impulse transmission. They produce reduction of hypertonicity by reversible denervation. Although this toxin exerts this effect on most nerve cells, it acts preferentially on cholinergic nerve endings. Dose-response experiments indicate that the vertebrate neuromuscular junction is the site …
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Boss (or bride of sevenless)
The gene coding for the seven less ligand and required for the development of the R7 cell in each ommatidium (one of the single eyes forming the compound eye) in the fly eye. More specifically, activation of a membrane receptor tyrosine kinase (seven less) in the R7 precursor by the ligand bride of sevenless present …
Body awareness
Attention directed to human bodies, including both one’s own and that of another person. This awareness can concern either the features/appearance of the body or the dynamics of human body movement and posture. Sometimes body awareness is restricted to proprioception. Based on proprioception (and touch) some (e.g., Philippe Rochat) claim that human newborns already demonstrate …
Bone Morphogenetic Proteins (BMPs)
Members of the transforming growth factor-beta (TGF-b) superfamily of proteins that have been shown to play important roles during embryological growth and development of many different organ systems (particularly the patterning of ventral mesoderm), as well as in tissue repair in postnatal life. Since 1988, more than 16 different human BMPs have been identified. Recent …
Blood Oxygenation Level Dependent Contrast (BOLD signal)
The blood oxygen level dependent signal that serves as the basis for current methods in fMRI. First used to generate functional images of the human brain in the early 1990s, BOLD fMRI uses the intrinsic paramagnetic signal ofdeoxyhemoglobin (dHB) to detect local hemodynamic changes in blood flow associated with neuronal activity. Because it is strongly …
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Bock’s profile analysis
A variant of multivariate repeated measures analysis of variance, in which time-adjacent means are compared. If changes are significant in one of these comparisons but not in others that will indicate the period in time during which change was most pronounced. Thus, it can help to identify the time span during which change is most …
Blastula
The first stage in the development of an embryo,formed by cleavage of the zygote. It consists of a hollow sphere containing undifferentiated dividing cells (blastomeres), which form a layer (blastoderm) around a central cavity (blastocoele). In mammals, the embryo at this stage is referred to as the blastocyst (see figure below). Blastula showing the blastomeres …
Blastomere
A totipotent, undifferentiated cell produced by cleavage of a fertilised egg up to the last blastula stage of early embryonic development (see figure below). It is blastomeres that are used for in-vitro fertilisation. A set of blastomeres on Day 4 forms a morula See Adhesion molecules, Blastula, Cleavage, Embryogenesis, Gastrulation, Morula
Blastopore
A temporary opening on the surface of gastrula through which the internal cavity (the archenteron) communicates with the exterior (see figure below). Its dorsal lip in amphibians was shown by Hans Spemann (1869-1941) to be the site of induction of overlying tissue during gastrulation. It is the source of the dorsalizing proteins chord in and …
Birth prevalence
Cases of a specified condition that can be identified by a given age. Excludes cases that cannot be ascertained because they die before the condition is recognised, as well as those that outgrow the condition by the given age and those who migrate in. Includes cases who die after being diagnosed and those who migrate …