A small region of the brain located just beneath the thalamus making up the floor of the third cerebral ventricle, and also the lower region of the diencephalon. The pituitary gland is attached to the bottom of the hypothalamus by a slender stalk (the infundibulum) as shown in the figure below. It is responsible for …
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Hypothesis
A conjecture or tentative explanation of certain facts that is testable empirically and then supported or rejected by the findings (i.e., on the basis of one or other inferential statistic). It is also a term applied in cognitive psychology to strategies for solving problems or making decisions such as participants in experiments inferring what sort …
Hypothalamic-pituitary-adrenal (HPA) axis
A complex and important physiological pathway between brain and peripheral structures whereby the amount of steroids released from the adrenal glands is controlled by a negative feedback mechanism involving release of peptides from the anterior pituitary gland (adrenocorticotropic hormone, ACTH) and the hypothalamus (corticotrophin-releasing factor, CRF) as shown in the figure below. Peptide release is …
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Hypomorphic nervous system
A smaller than normal nervous system, usually due to fewer cells. In the developing embryo, it is the inhibition of differentiation, typically due to a genetic mutation. See Differentiation (embryology), Embryo, Hypoplasia, Morphogenesis
Hypoplasia
Reduced size owing to the underdevelopment of all or part of an organ (see figure below for an example). Moderate to severe hypoplasia in a child with the Goldenhar-Golin syndrome (also known as Oculuoauricular dysplasia), which is a congenital birth defect involving deformities of the face, usually on one side. It is a rare congenital …
Hypomere
The ventrolateral portion of a myotome (the middle portions of a mesodermic somite, forming muscles innervated by the ventral rami of the spinal nerves. See Dermomyotome, Epimere, Mesoderm, Myotome, Somites, Ventral
Hypertonia
More a description than a diagnosis (as hypotonia), it presents as a marked increase in muscle tension (or tone) with spasticity or rigidity. If the latter, the muscles are unable to stretch through a full range of motion that is velocity dependent as is typical of people with Parkinson’s disease (who can also show lead …
Hypoglycemia
A lower than normal level of sugar (glucose) in the blood, usually diagnosed when whole blood glucose levels are lower than 20-40 mg/dl. Glucose supply to the brain is probably more important for brain metabolism than oxygen in the newborn. This is because oxygen consumption is relatively low in the newborn brain and minimal in cerebral …
Hyperextension
A posture in which the neck and trunk are overextended (i.e., curved too much backwards), and which can be seen in preterm infants. It can cause upper airway obstruction. It may also affecting the development of reaching and grasping. See Dystonia, Posture, Preterm infant
Hyperbilirubinemia
excessive accumulation of bilibrubin in the blood and tissues that leads to jaundice. It is a rich reddish bile pigment that is thought to be produced by a breakdown in the manufacture of haemoglobin, and the resultant unconjugated bilibrubin cannot be removed by the immature liver. It can cross the blood-brain barrier, and in excessive …