Frames, then content (FC) hypothesisNon-meaningful sound sequences produced by infants, especially sequences of consonants and vowels that typically appear between 6 and 10 months of age. At first, babbling is relatively unformed. It begins around 5 to 7 months of age, when a infant’s vocalisations start to appear as consonant-vowel combinations called canonical syllables, some …
Category Archives: Uncategorized
Axon pathway selection
The capacity that the axons of developing neurons have to select particular directions of migration. The first axons to migrate in the embryo are termed pioneering axons that serve as pathways for some, but not all, later developing axons to migrate to their target. They are guided by growth cones at their tips that respond …
Axon retraction (or pruning)
A phenomenon often seen in early normal development, and as with axonal proliferation occurring before birth, where axons extend farther, or to more places or terminal zones, than they will at maturity. They then refine their connections by retracting. Examples include the retraction of corpus callosum collaterals and the elimination of cortical-cortical connections (e.g., layer …
Axon hillock
The conical, tapering area of the axon’s origin from the soma of the neuron (see figure below), and contains microtubules as well as being devoid of Nissl substance. It is here that the graded inputs of inhibitory postsynaptic potentials and excitatory postsynaptic potentials from the dendrites are summated to determine whether an action potential is …
Axon
Nerve cell process transporting outgoing or efferent information away from the cell body (or soma) in the form of an action potential toward a specific target (other neurons; gland; muscle) with which it connects by means of a synapse. Sometimes referred to as a nerve fiber. An axon of a motoneuron can be up to …
Axon collateral
A branch of the main axon that originates at the node of Ranvier. See Axon, Myelin, Nodes of Ranvier
Axillary hair
Hair in the armpits (or axilla); a secondary sex characteristic. In puberty, axillary hair usually appears after pubic hair. In males, its appearance is associated with characteristic body odor, lowering of the voice pitch, and acne. See Adolescent growth spurt, Adolescent voice change, Pitch, Puberty, Secondary sexual characteristics
Avoidance learning
Learning to make a response to a warning signal in order to avoid an aversive event. See Attributional style, Escape learning, Learned helplessness, Learning, Operant (or instrumental) conditioning
Axial muscles
Striated muscles of the axial skeleton (the bones constituting the head and trunk of a vertebrate body; 80 bones in the human). Most often used to refer to muscles belonging to the trunk, especially those that flex the spine as well as move the thorax and abdomen. Dystonia, often present in preterm infants, involves the …
Autosomal dominant condition/disease
Genetic condition caused by one mutated gene located on one of the autosomal (‘non-sex’) chromosomes. One of the parents will usually have the disease as it is dominant in this mode of inheritance. Each child of an affected individual has a 50% chance of being affected, regardless of sex or birth order, and homozygotes for …