Circadian oscillator. A circadian clock, or circadian oscillator, is a biochemical mechanism that oscillates with a period of 24 hours and is coordinated with the day-night cycle.
Circadian clocks are the central mechanisms which drive circadian rhythms. They consist of three major components: The clock is reset as the environment changes through an organism's ability to sense external time cues of which the primary one is light. Circadian oscillators are ubiquitous in tissues of the body where they are synchronized by both endogenous and external signals to regulate transcriptional activity throughout the day in a tissue-specific manner.[1] The circadian clock is intertwined with most cellular metabolic processes and it is affected by organism aging.[2] The basic molecular mechanisms of the biological clock have been defined in vertebrate species, Drosophila melanogaster, plants, fungi, bacteria,[3][4] and presumably also in Archaea.[5][6][7] Transcriptional and translational control[edit]
Hebbian theory. Hebbian theory is a theory in neuroscience which proposes an explanation for the adaptation of neurons in the brain during the learning process.
It describes a basic mechanism for synaptic plasticity, where an increase in synaptic efficacy arises from the presynaptic cell's repeated and persistent stimulation of the postsynaptic cell. Introduced by Donald Hebb in his 1949 book The Organization of Behavior,[1] the theory is also called Hebb's rule, Hebb's postulate, and cell assembly theory. Hebb states it as follows: "Let us assume that the persistence or repetition of a reverberatory activity (or "trace") tends to induce lasting cellular changes that add to its stability.… When an axon of cell A is near enough to excite a cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A's efficiency, as one of the cells firing B, is increased.
Hebbian engrams and cell assembly theory[edit] Principles[edit] Biological thermodynamics. Biological thermodynamics is the quantitative study of the energy transductions that occur in and between living organisms, structures, and cells and of the nature and function of the chemical processes underlying these transductions.
Biological thermodynamics may address the question of whether the benefit associated with any particular phenotypic trait is worth the energy investment it requires. History[edit] German-British medical doctor and biochemist Hans Krebs' 1957 book Energy Transformations in Living Matter (written with Hans Kornberg)[1] was the first major publication on the thermodynamics of biochemical reactions.
In addition, the appendix contained the first-ever published thermodynamic tables, written by Kenneth Burton, to contain equilibrium constants and Gibbs free energy of formations for chemical species, able to calculate biochemical reactions that had not yet occurred. The focus of thermodynamics in biology[edit] Energy Transformation in Biological Systems[edit] where: Towards complete functional and structural imaging of cortical circuits. Neocortex. A representative column of neocortex.
Cell body layers are labeled on the left, and fiber layers are labeled on the right. Anatomy[edit] The neocortex consists of the grey matter, or neuronal cell bodies and unmyelinated fibers, surrounding the deeper white matter (myelinated axons) in the cerebrum. The neurons of the neocortex are also arranged in vertical structures called neocortical columns. These are patches of the neocortex with a diameter of about 0.5 mm (and a depth of 2 mm).
The neocortex is derived embryonically from the dorsal telencephalon, which is the rostral part of the forebrain. Evolution[edit] The neocortex is the newest part of the cerebral cortex to evolve (hence the prefix "neo"); the other parts of the cerebral cortex are the paleocortex and archicortex, collectively known as the allocortex. Neocortex ratio[edit] Pyramidal Neurons.