In neuroanatomy, a nucleus is a central nervous system structure that is composed mainly of gray matter, and which acts as a hub or transit point for electrical signals in a single neural subsystem. For example, the lateral geniculate nucleus mediates signals in the vertebrate visual system. The vestibular nucleus stores head motion information and guides eye movements via the vestibulo-ocular reflex. Neuroanatomy is the anatomy of the nervous system. ... A diagram showing the CNS: 1. ... Grey matter is a category of nervous tissue with many nerve cell bodies and few myelinated axons. ... A. A schematic view of an idealized action potential illustrates its various phases as the action potential passes a point on a cell membrane. ... Grays FIG. 719– Hind- and mid-brains; postero-lateral view. ... Classes and Clades See below Vertebrates are members of the subphylum Vertebrata (within the phylum Chordata), specifically, those chordates with backbones or spinal columns. ... The visual system is the part of the nervous system which allows organisms to see. ... The nuclei of the vestibular nerve. ... Figure 3 Three-neuron arc, during a head movement to the right. ...

Other examples include the raphe nuclei, which are involved in sleep, and the suprachiasmatic nucleus, which controls the circadian rhythm. All the nerve cell axons terminating on a nucleus tend to employ the same neurotransmitter at their synapses. As a result, the effects of certain psychoactive drugs are concentrated in particular nuclei. Morphine is believed to act via synapses of the arcuate nucleus, for example. The raphe nuclei (Latin for the bit in a fold or seam) is a moderately sized cluster of nuclei found in the brain stem, and releases serotonin to the rest of the brain. ... Sleep is the state of natural rest observed in most mammals, birds, fish, as well as invertebrates such as the fruitfly Drosophila. ... The suprachiasmatic nucleus (SCN) is a nucleus in the hypothalamus situated immediately above the optic chiasm, on either side of the third ventricle. ... A circadian rhythm is a roughly-24-hour cycle in the physiological processes of living beings, including plants, animals, fungi and cyanobacteria. ... Neurons (also called nerve cells) are the primary cells of the nervous system. ... An axon or nerve fiber, is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neurons cell body or soma. ... Chemical structure of D-Aspartic Acid, a common Amino Acid neurotransmitter. ... Illustration of the major elements in a prototypical synapse. ... A psychoactive drug or psychotropic substance is a chemical that alters brain function, resulting in temporary changes in perception, mood, consciousness, or behaviour. ... A psychoactive drug or psychotropic substance is a chemical substance that acts primarily upon the central nervous system where it alters brain function, resulting in temporary changes in perception, mood, consciousness and behavior. ... Morphine (INN) (IPA: ) is a potent opiate analgesic drug and is the principal active agent in opium. ... The arcuate nucleus is an aggregation of neurons in the mediobasal hypothalamus, adjacent to the third ventricle and the median eminence. ...