Alphabetical list

Afferent : Generally, a connection or pathway to a node. 1. The complementary terms afferent and efferent were first used by Unzer (1771; see English translation, 1851, pp. 69, 254) to indicate toward or away from, respectively, the central nervous system (Meckel, 1817) or, conversely, away from or toward the non-neuronal tissues of the body; see Sherrington (1900, p. 784), Clarke & O'Malley (1996, p. 342). These neutral terms avoid functional implications that may or may not be valid; for example, afferent information from the skin may not be sensory if it does not reach the level of consciousness. 2. A connection or projection to a gray matter region, neuron type (Bota & Swanson, 2007), neuron (Waldeyer, 1891), or site. The preferred synonym is input. more details

Afterbrain ( Baer, 1837 ) : Synonym for medulla (Winslow, 1733); term introduced for vertebrates by Baer (1837, p. 107, in the original German, "Nachhirn"). Also see His (1895, p. 162). more details

Amacrine cell ( Cajal, 1899-1904 ) : A neuron (Waldeyer, 1891) characterized by amacrine extensions. They were discovered in the retina (Herophilus, 335-263 BC), in the olfactory bulb (Weitbrecht, 1744), and in the peripheral nervous system (Meckel, 1817) where they are called interstitial cells; they were regarded as having no axon (Kölliker, 1896), and thus "amacrine" (see Cajal, 1899-1904). Examples of neurons with amacrine extensions and/or axon, and/or dendrites (His, 1889) are now known; they are very common in nerve nets. more details

Amacrine connection : A bidirectional connection between two nodes established by amacrine extensions arising in both nodes from specific types of amacrine cells. more details

Amacrine extension : A neuron extension that in a chain normally forms a reciprocal (bidirectional) synapse (Foster & Sherrington, 1897) with a like extension of another neuron (Waldeyer, 1891); that is, an amacrine extension may function as an axon (Kölliker, 1896) or a dendrite (His, 1889) in a chain, conducting in either direction depending on functional activity in the neural network; see Swanson (2003, pp. 23, 243). An amacrine extension may also form unidirectional synapses. A synonym is amacrine process. more details

Amacrine process : Synonym for amacrine extension; see Swanson (2003, pp. 23, 243). more details

Anterior ( Aristotle ) : Rostral (Schulze, 1893) in relation to the longitudinal axis (Barclay, 1803); commonly used in this way for comparative anatomy, as was the case for Aristotle in De Partibus Animalium; see, for example, translation by Ogle (1912, 684b-25). Vicq d'Azyr (1786, pp. 51, 58) first clearly defined the term as in front or toward the face, corresponding in most vertebrates to rostral, and in humans to ventral (Schulze, 1893) or anterior (Galen, c177). Discarding the ambiguous terms anterior and posterior has been urged since at least 1880 (Spitzka, 1880, p. 75). Formal descriptors of position in anatomy can be traced to this statement by Aristotle in De Partibus Animalium, "it is a universal law that, as regards above and below, front and back, right and left, the nobler and more honourable part invariably is placed uppermost, in front, and on the right, rather than in the opposite positions, unless some more important object stands in the way"; see translation by Ogle (1912, 665a; also see 667b, 669b). In Historia Animalium he clarified the problems with positional information in comparative anatomy, "In man, above all other animals, the terms ‘upper' and ‘lower' are used in harmony with their natural positions; for in him, upper and lower have the same meaning as when they are applied to the universe as a whole. In like manner the terms, ‘in front', ‘behind', ‘right' and ‘left', are used in accordance with their natural sense. But in regard to other animals, in some cases these distinctions do not exist, and in others they do, but in a vague way. For instance, the head with all animals is up and above in respect to their bodies; but man alone, as has been said, has, in maturity, this part uppermost in respect to the material universe"; see translation by Thompson (1910, 294a-25). Also see Standring (2008, Fig. 1). more details

Anterior ( Galen, c177 ) : Ventral (Schulze, 1893) in relation to the longitudinal axis (Barclay, 1803); commonly used in this way for human and other primate anatomy, as was the case for Galen; see translation by Singer (1999, p. 129), also see translation by Duckworth (1962, pp. 229, 231). Also see anterior (Aristotle). more details

Anteroposterior axis ( Swanson & Bota, 2010 ) : Often used as synonym for rostrocaudal axis in most vertebrates and for the dorsoventral axis in humans; see Standring (2008, Fig. 1). Application of this old and confusing designation is discouraged; see anterior (Aristotle) and anterior (Galen, c177). Also spelled anterior-posterior axis. more details

Arachnoid ( A ; Blasius, 1666 ) : A delicate membrane resembling a spider's web interposed between dura (Galen, c177) and pia (Galen, c192), and separated from pia by subarachnoid space (Magendie, 1827). It is histologically similar to pia, and the two are often considered together as leptomeninges; see Dorland's (2003), Standring (2008, p. 389). The arachnoid was first illustrated for macrodissected adult humans by Casserio (1627), and described and named by Blasius (1666). more details

Arachnoidea mater : Synonym for arachnoid (Blasius, 1666). more details

Arborization ( Cajal, 1888 ) : Short form of terminal arborization (Cajal, 1888). more details

Architecture ( Swanson & Bota, 2010 ) : The conceptual structure and overall logical organization of a system-here the nervous system (Monro, 1783)-from the point of view of its function or design; see Oxford English Dictionary (1989) and Sherrington (1906, pp. 271, 308). more details

Autonomic ganglia ( GA ; Langley, 1900 ) : A topographic division of vertebrate peripheral ganglia with gray matter regions that are distinguished from the craniospinal ganglia, and for description are divided into paravertebral ganglia, prevertebral ganglia (Gaskell, 1886), and terminal ganglia (Gaskell, 1886). Galen (c173-c192) described at least three pairs; see translations by Duckworth (1962, pp. 217-218), May (1968, pp. 695-696), Smith (1971, p. 179). The term was introduced by Langley (1900, pp. 677-678). more details

Autonomic nerves ( AUN ; Langley, 1898 ) : A topographic division of nerves (Herophilus, c335-280 BC). An autonomic nerve is a vertebrate nerve (Herophilus, c335-280 BC)-and a communicating or anastomotic network of branches (a prevertebral plexus or a terminal plexus) sometimes associated with it-that appears macroscopically to arise in the peripheral nervous system (Meckel, 1817) from an autonomic ganglion (Langley, 1900) rather than a craniospinal nerve. In the second century, Galen-see translations by Singer (1999, p. 142) and Duckworth (1962, p.111)-described at least some of them in animals except humans, and the term was introduced by Langley (1898, p. 241). more details

Axial plane : Synonym for transverse plane (Henle, 1855) in human radiology, also referred to as transaxial and viewed as if from the feet toward the head; see Standring (2005, p. 3). more details

Axon ( Kölliker, 1896 ) : A neuron extension that in a chain normally conducts information away from the dendrites (His, 1889) and/or cell body (Deiters, 1865) to axon terminals (Barker, 1899), the presynaptic compartment (De Camilli et al., 2001) of synapses (Foster & Sherrington, 1897). Most neurons (Waldeyer, 1891) have one axon trunk with a variable number of axon collaterals (Cajal, 1899), and the presynaptic compartment may be (a) an axon varicosity (although not all varicosities form synapses) also called a synapse-of-passage, (b) a terminal-of-passage along the axon trunk or axon collaterals, or (c) an axon terminal (synonym: terminal bouton) at the end of an axon collateral or the axon trunk; see Swanson, 2004, Fig. 5). The axon was probably discovered microscopically in unfixed molluscan material by Dutrochet (1824, Pl. 2, fig. 2; see Van der Loos, 1967, pp. 22-23) and for vertebrates by Remak (1837; his primitive band). Axons were first distinguished clearly from dendrites by Wagner (1846, see Tab. 3, Fig. 43-a; see Van der Loos, 1967, p. 37), and named thus by Kölliker (1896, p. 2). It is common in vertebrates for the axon to arise from the cell body or a dendrite, as first demonstrated microscopically in macerated tissue from the Torpedo electric organ by Wagner (1846, Tab. 3, Fig. 43-c; see Van der Loos, 1967, pp. 38-39). more details

Axon bifurcation : Y-shaped branching of an axon trunk, generating two bifurcation branches (Cajal, 1899); discovered in hagfish Golgi material by Nansen (1887, pp. 158, 213, "dichotomous subdivisions of nerve tubes"), named bifurcation by Cajal (1889, Fig. 3 and p. 91). more details

Axon bifurcation branch : One of the two products of an axon bifurcation; discovered in hagfish Golgi material by Nansen (1887, pp. 158, 213), named bifurcation branch by Cajal (1889, pp. 91, 95). more details

Axon collateral ( Cajal, 1899 ) : A branch of an axon trunk that is typically thinner than the trunk and arises at a roughly right angle. First pointed out by Deiters (1865, Tab. 1, Fig. 1-b; see Van der Loos, 1967, p. 44), Golgi (1873) established their existence with his black reaction and noted their roughly right angle of origin (he called them branches or side fibrils); apparently named by Cajal (1899, p. 329, "collaterals of axons"). A short form is collateral (Waldeyer, 1891). more details

Axon connection ( Bota & Swanson, 2007 ) : A unidirectional connection established by an axon (Kölliker, 1896) or group of axons from a neuron type (Bota & Swanson, 2007) arising in one node and establishing synapses (Foster & Sherrington, 1897) in another node with another neuron or neuron type (Bota & Swanson, 2007). more details

Axon hillock ( Schaffer, 1893 ) : The expanded part of an axon trunk as it arises from the cell body (Deiters, 1865) or dendrite (His, 1889) of a neuron (Waldeyer, 1891), often distinguished by a relative absence of ribosomes; discovered in macerated microdissected ox spinal cord by Dieters (1865, Tab. 1, fig. 1) and named by Schaffer (1893, p. 850). Also see Peters et al. (1991, pp. 101-108). more details

Axon terminal ( Barker, 1899 ) : A swelling-terminal (Cajal, 1899)-at the end of an axon trunk, axon collateral (Cajal, 1899), or terminal arborization (Cajal, 1888) that is presynaptic and usually rather simple although more elaborate configurations are found. First illustrated by Deiters (1865, Tab. 1, Fig. 1-b; Tab. 2, Fig. 6-b; see Van der Loos, 1967, p. 44), first interpreted correctly by Cajal (1888, Tab. I), and named thus by Barker (1899, p. 88, "terminals of one axone"). more details

Axon trunk : The segment of an axon (Kölliker, 1896) that begins at the distal (Barclay, 1803) end of the axon hillock (Schaffer, 1893) and extends distally, typically generating axon collaterals (Cajal, 1899) and remaining the thickest part of the overall axonal arborization; it comes to an abrupt end at a bifurcation (Cajal, 1889), when present. Galen in the second century used the term trunk for nerves (Herophilus, c335-280 BC) as a whole; see translation by May (1968, pp. 554, 572-573). Remak (1838) discovered that axons arise from neurons (Waldeyer, 1891). more details

Axon varicosity : A swelling along an unmyelinated axon-or unmyelinated segment of an axon (Kölliker, 1896)-that may either form a bouton-of-passage, or may not form a synapse (Foster & Sherrington, 1897) but simply reflect the presence of one or more mitochondria with a diameter greater than the axon. Ehrenberg (1833, p. 453; also see Van der Loos, 1967, Fig. 8) described and named varicose fibers, Cajal (1888, p. 4) described and named varicosities of the neural prolongation [axon] in Golgi preparations of avian cerebellum (Aristotle). more details

Axon-of-passage : Segment of an axon (Kölliker, 1896) that passes through a gray matter region without forming synapses (Foster & Sherrington, 1897). Preferable to fiber-of-passage (Cajal, 1894a) because more accurate; also see Cowan et al. (1972, p. 38). more details