An act that can be of help, aid, or assistance to another person. The behavior can take different forms, such as physical, verbal, intellectual, emotional, social, economic, and spiritual. See Agressive behavior
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Prosencephalon
Also known as the forebrain, in contrast to the midbrain (mesencephalon) and the hindbrain (rhombocephalon) as indicated in figure below (together with other other primary structures that make up the central nervous system). The prosencephalon ultimately participates in the control of a number of functions (e.g., eating, emotional displays, internal temperature, sleep). It becomes evident during the …
Proprioception
Sensory information about position and movement of body parts relative to gravity available via sensory receptors (i.e., proprioceptors) in joints, muscle and skin as well as the vestibular system. Closing the eyes and touching the nose with the index finger relies almost entirely on proprioception (it is difficult, if not impossible though, to isolate completely …
Proper noun
A noun that refers to a unique individual, place or organization. During early childhood, children learn the meanings of proper and common nouns and the syntactical difference between them. There is longstanding evidence that children first discriminate among individuals and learn how to name them, but for other classes of objects (e.g., toys) they first learn names …
Prophase
Discounting interphase in meiosis, it is the first phase of three parts (early, mid and late) of cell division in which chromosomes contract and divide along their length into chromatids, except for the centromeres. By late prophase, the two chromosomes begin to move apart and align in pairs as the nuclear membrane has already broken …
Prone infant sleep position
Refers to infants sleeping on their stomachs, which is now known to increase the chances of the infant dying from sudden infant death syndrome (SIDS). See Sudden infant death syndrome (SIDS, cot or crib death), Supine infant sleep position
Proliferative cells
During embryonic development, cells differentiate very rapidly, becoming increasingly specialized, with the rate of proliferation decreasing over time. Some, such as human cardiac muscle cells, are then not able to divide again, while others are required to replace lost cells (e.g., epithelial cells, skin fibroblasts) via, for example, apoptosis. All told, cell proliferation amounts to a careful …
Proliferative ventricular zone
A transient region of the embryonic brain with active cell division and where neurons and radial glia cells are produced from ectodermal cells. It is referred to as the ventricular zone in that it lines the ventricular system in which cerebrospinal is produced. During neurogenesis, newly generated cells migrate to their final destinations from the ventricular zone. They …
Prolactin
A peptide hormone, also known as the luteotropic hormone and the ‘milk hormone’ in everyday language. It is produced in the pituitary gland and best known for its role in the lactation of mammals in response to suckling of the young after birth (other production sites include the uterus, the brain, breasts, prostate gland, skin and adipose …
Progress zone
The zone consists of mesodermal cells and is situated underneath the apical ectodermal ridge of the vertebrate limb bud (see figure below). It acts to provide positional information that enables cells to develop into a limb. The transmission of this information appears to depend on the time the cells spend in the zone during outgrowth of the …