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Commissure
A commissure () is the location at which two objects abut or are joined. The term is used especially in the fields of anatomy and biology. * The most common usage of the term refers to the brain's commissures, of which there are five. Such a commissure is a bundle of commissural fibers as a tract that crosses the midline at its level of origin or entry (as opposed to a decussation of fibers that cross obliquely). The five are the anterior commissure, posterior commissure, corpus callosum, commissure of fornix (hippocampal commissure), and habenular commissure. They consist of fibre tracts that connect the two cerebral hemispheres and span the longitudinal fissure. In the spinal cord there are the anterior white commissure, and the gray commissure. ''Commissural neurons'' refer to neuronal cells that grow their axons across the midline of the nervous system within the brain and the spinal cord. * ''Commissure'' also often refers to cardiac anatomy of heart valves. In the hear ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anterior Commissure
The anterior commissure (also known as the precommissure) is a white matter tract (a bundle of axons) connecting the two temporal lobes of the cerebral hemispheres across the midline, and placed in front of the columns of the fornix. In most existing mammals, the great majority of fibers connecting the two hemispheres travel through the corpus callosum, which is over 10 times larger than the anterior commissure, and other routes of communication pass through the hippocampal commissure or, indirectly, via subcortical connections. Nevertheless, the anterior commissure is a significant pathway that can be clearly distinguished in the brains of all mammals. The anterior commissure plays a key role in pain sensation, more specifically sharp, acute pain. It also contains decussating fibers from the olfactory tracts, vital for the sense of smell and chemoreception. The anterior commissure works with the posterior commissure to link the two cerebral hemispheres of the brain and als ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Decussation
Decussation is used in biological contexts to describe a crossing (due to the shape of the Roman numeral for ten, an uppercase 'X' (), ). In Latin anatomical terms, the form is used, e.g. . Similarly, the anatomical term chiasma is named after the Greek uppercase 'Χ' (chi). Whereas a decussation refers to a crossing within the central nervous system, various kinds of crossings in the peripheral nervous system are called chiasma. Examples include: * In the brain, where nerve fibers obliquely cross from one lateral side of the brain to the other, that is to say they cross at a level other than their origin. See for examples Decussation of pyramids and sensory decussation. In neuroanatomy, the term ''chiasma'' is reserved for crossing of- or within nerves such as in the optic chiasm. * In botanical leaf taxology, the word ''decussate'' describes an opposite pattern of leaves which has successive pairs at right angles to each other (i.e. rotated 90 degrees along the st ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fornix (neuroanatomy)
The fornix (from lat, fornix, lit=arch) is a C-shaped bundle of nerve fibers in the brain that acts as the major output tract of the hippocampus. The fornix also carries some afferent fibers to the hippocampus from structures in the diencephalon and basal forebrain. The fornix is part of the limbic system. While its exact function and importance in the physiology of the brain are still not entirely clear, it has been demonstrated in humans that surgical transection—the cutting of the fornix along its body—can cause memory loss. There is some debate over what type of memory is affected by this damage, but it has been found to most closely correlate with recall memory rather than recognition memory. This means that damage to the fornix can cause difficulty in recalling long-term information such as details of past events, but it has little effect on the ability to recognize objects or familiar situations. Structure The fibers begin in the hippocampus on each side of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Labial Commissure Of Mouth
The commissure is the corner of the mouth, where the vermillion border The vermilion border (sometimes spelled vermillion border), also called margin or zone, is the normally sharp demarcation between the lip and the adjacent normal skin. It represents the change in the epidermis The epidermis is the outermost o ... of the superior labium (upper lip) meets that of the inferior labium (lower lip). The commissure is important in facial appearance, particularly during some functions, including smiling. As such it is of interest to dental surgeons. Diseases that involve the commissure include angular chelitis. See also * Commissure Lips {{anatomy-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Canthi
The canthus (pl. canthi, palpebral commissures) is either corner of the eye where the upper and lower eyelids meet. More specifically, the inner and outer canthi are, respectively, the medial and lateral ends/angles of the palpebral fissure. The bicanthal plane is the transversal plane linking both canthi and defines the upper boundary of the midface. Etymology The word ' is the Latinized form of the Ancient Greek ('), meaning 'corner of the eye'. Population distribution The eyes of those of East Asian and some Southeast Asian people tend to have the inner canthus veiled by the epicanthus. In the Caucasian or double eyelid, the inner corner tends to be exposed completely. Commissures * The ''lateral palpebral commissure'' (commissura palpebrarum lateralis; external canthus) is more acute than the medial, and the eyelids here lie in close contact with the bulb of the eye. * The ''medial palpebral commissure'' (commissura palpebrarum medialis; internal canthus) is prolonged ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Commissural Fiber
The commissural fibers or transverse fibers are axons that connect the two hemispheres of the brain. In contrast to commissural fibers, association fibers connect regions within the same hemisphere of the brain, and projection fibers connect each region to other parts of the brain or to the spinal cord. Structure The commissural fibers make up tracts that include the corpus callosum, the anterior commissure, and the posterior commissure. Corpus callosum The corpus callosum is the largest commissural tract in the human brain. It consists of about 200-300 million axons that connect the two cerebral hemispheres. The corpus callosum is essential to the communication between the two hemispheres. A recent study of individuals with agenesis of the corpus callosum suggests that the corpus callosum plays a vital role in problem solving strategies, verbal processing speed, and executive performance. Specifically, the absence of a fully developed corpus callosum is shown to have a si ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beak
The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for eating, preening, manipulating objects, killing prey, fighting, probing for food, courtship, and feeding young. The terms ''beak'' and '' rostrum'' are also used to refer to a similar mouth part in some ornithischians, pterosaurs, cetaceans, dicynodonts, anuran tadpoles, monotremes (i.e. echidnas and platypuses, which have a beak-like structure), sirens, pufferfish, billfishes and cephalopods. Although beaks vary significantly in size, shape, color and texture, they share a similar underlying structure. Two bony projections – the upper and lower mandibles – are covered with a thin keratinized layer of epidermis known as the rhamphotheca. In most species, two holes called ''nares'' lead to the respiratory system. Etymology Although the word "beak" was, in the past, generally restricted to the sharpened ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Biology
Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary information encoded in genes, which can be transmitted to future generations. Another major theme is evolution, which explains the unity and diversity of life. Energy processing is also important to life as it allows organisms to move, grow, and reproduce. Finally, all organisms are able to regulate their own internal environments. Biologists are able to study life at multiple levels of organization, from the molecular biology of a cell to the anatomy and physiology of plants and animals, and evolution of populations.Based on definition from: Hence, there are multiple subdisciplines within biology, each defined by the nature of their research questions and the tools that they use. Like other scientists, biologists use t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eyelid
An eyelid is a thin fold of skin that covers and protects an eye. The levator palpebrae superioris muscle retracts the eyelid, exposing the cornea to the outside, giving vision. This can be either voluntarily or involuntarily. The human eyelid features a row of eyelashes along the eyelid margin, which serve to heighten the protection of the eye from dust and foreign debris, as well as from perspiration. "Palpebral" (and "blepharal") means relating to the eyelids. Its key function is to regularly spread the tears and other secretions on the eye surface to keep it moist, since the cornea must be continuously moist. They keep the eyes from drying out when asleep. Moreover, the blink reflex protects the eye from foreign bodies. The appearance of the human upper eyelid often varies between different populations. The prevalence of an epicanthic fold covering the inner corner of the eye account for the majority of East Asian and Southeast Asian populations, and is also found ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Abut
Premises are land and buildings together considered as a property. This usage arose from property owners finding the word in their title deeds, where it originally correctly meant "the aforementioned; what this document is about", from Latin ''prae-missus'' = "placed before". In this sense, the word is always used in the plural, but singular in construction. Note that a single house or a single other piece of property is "premises", not a "premise", although the word "premises" is plural in form; e.g. "The equipment is on the customer's premises", never "The equipment is on the customer's premise". Law relating to premises Liability of owner of premises in tort Transfer of ownership of premises Premises registration Premises registration is "a way to locate where livestock or dead animals are kept or congregated." [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Brachiopod
Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection. Two major categories are traditionally recognized, articulate and inarticulate brachiopods. The word "articulate" is used to describe the tooth-and-groove structures of the valve-hinge which is present in the articulate group, and absent from the inarticulate group. This is the leading diagnostic skeletal feature, by which the two main groups can be readily distinguished as fossils. Articulate brachiopods have toothed hinges and simple, vertically-oriented opening and closing muscles. Conversely, inarticulate brachiopods have weak, untoothed hinges and a more complex system of vertical and oblique (diagonal) muscles used to keep the two valves aligned. In many brachiopods, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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