The epithelium lining the seminiferous tubules composed of primary male germ cells (SPERMATOGONIA) and supporting SERTOLI CELLS. As SPERMATOGENESIS proceeds, the developing germ cells migrate toward the lumen. The adluminal compartment, the inner two thirds of the tubules, contains SPERMATOCYTES and the more advanced germ cells.
Supporting cells projecting inward from the basement membrane of SEMINIFEROUS TUBULES. They surround and nourish the developing male germ cells and secrete ANDROGEN-BINDING PROTEIN and hormones such as ANTI-MULLERIAN HORMONE. The tight junctions of Sertoli cells with the SPERMATOGONIA and SPERMATOCYTES provide a BLOOD-TESTIS BARRIER.
A specialized barrier, in the TESTIS, between the interstitial BLOOD compartment and the adluminal compartment of the SEMINIFEROUS TUBULES. The barrier is formed by layers of cells from the VASCULAR ENDOTHELIUM of the capillary BLOOD VESSELS, to the SEMINIFEROUS EPITHELIUM of the seminiferous tubules. TIGHT JUNCTIONS form between adjacent SERTOLI CELLS, as well as between the ENDOTHELIAL CELLS.
A functional system which includes the organisms of a natural community together with their environment. (McGraw Hill Dictionary of Scientific and Technical Terms, 4th ed)
The restriction of a characteristic behavior, anatomical structure or physical system, such as immune response; metabolic response, or gene or gene variant to the members of one species. It refers to that property which differentiates one species from another but it is also used for phylogenetic levels higher or lower than the species.
The branch of science concerned with the interrelationship of organisms and their ENVIRONMENT, especially as manifested by natural cycles and rhythms, community development and structure, interactions between different kinds of organisms, geographic distributions, and population alterations. (Webster's, 3d ed)
Male germ cells derived from the haploid secondary SPERMATOCYTES. Without further division, spermatids undergo structural changes and give rise to SPERMATOZOA.
The non-genetic biological changes of an organism in response to challenges in its ENVIRONMENT.
Direct contact of a cell with a neighboring cell. Most such junctions are too small to be resolved by light microscopy, but they can be visualized by conventional or freeze-fracture electron microscopy, both of which show that the interacting CELL MEMBRANE and often the underlying CYTOPLASM and the intervening EXTRACELLULAR SPACE are highly specialized in these regions. (From Alberts et al., Molecular Biology of the Cell, 2d ed, p792)
The single family of PRIMATES in the infraorder TARSII, suborder HAPLORHINI. It is comprised of one genus, Tarsius, that inhabits southern Sumatra, Borneo, Sulawesi, and the Philippines.
Microscopy using an electron beam, instead of light, to visualize the sample, thereby allowing much greater magnification. The interactions of ELECTRONS with specimens are used to provide information about the fine structure of that specimen. In TRANSMISSION ELECTRON MICROSCOPY the reactions of the electrons that are transmitted through the specimen are imaged. In SCANNING ELECTRON MICROSCOPY an electron beam falls at a non-normal angle on the specimen and the image is derived from the reactions occurring above the plane of the specimen.
The properties of a pathogen that makes it capable of infecting one or more specific hosts. The pathogen can include PARASITES as well as VIRUSES; BACTERIA; FUNGI; or PLANTS.
Preparation for electron microscopy of minute replicas of exposed surfaces of the cell which have been ruptured in the frozen state. The specimen is frozen, then cleaved under high vacuum at the same temperature. The exposed surface is shadowed with carbon and platinum and coated with carbon to obtain a carbon replica.
Specialized junctions at which a neuron communicates with a target cell. At classical synapses, a neuron's presynaptic terminal releases a chemical transmitter stored in synaptic vesicles which diffuses across a narrow synaptic cleft and activates receptors on the postsynaptic membrane of the target cell. The target may be a dendrite, cell body, or axon of another neuron, or a specialized region of a muscle or secretory cell. Neurons may also communicate via direct electrical coupling with ELECTRICAL SYNAPSES. Several other non-synaptic chemical or electric signal transmitting processes occur via extracellular mediated interactions.
Keratins, Type I
Remains, impressions, or traces of animals or plants of past geological times which have been preserved in the earth's crust.
A family of Primates of the suborder Strepsirhini containing six genera. The family is distributed in parts of Africa, India, Asia, and the Philippines. The six genera are: Arctocebus (golden potto), GALAGO (bush babies), Loris (slender loris), Nycticebus (slow loris), and Perodicticus (potto). Lorises and pottos are relatively common except for Arctocebus, the golden potto. All are arboreal and nocturnal.
Molecular Sequence Data
Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.
Insects of the family Formicidae, very common and widespread, probably the most successful of all the insect groups. All ants are social insects, and most colonies contain three castes, queens, males, and workers. Their habits are often very elaborate and a great many studies have been made of ant behavior. Ants produce a number of secretions that function in offense, defense, and communication. (From Borror, et al., An Introduction to the Study of Insects, 4th ed, p676)
Anemia characterized by a decrease in the ratio of the weight of hemoglobin to the volume of the erythrocyte, i.e., the mean corpuscular hemoglobin concentration is less than normal. The individual cells contain less hemoglobin than they could have under optimal conditions. Hypochromic anemia may be caused by iron deficiency from a low iron intake, diminished iron absorption, or excessive iron loss. It can also be caused by infections or other diseases, therapeutic drugs, lead poisoning, and other conditions. (Stedman, 25th ed; from Miale, Laboratory Medicine: Hematology, 6th ed, p393)
The various physical methods which include wind, insects, animals, tension, and water, by which a plant scatters its seeds away from the parent plant.
Plant Physiological Phenomena
The physiological processes, properties, and states characteristic of plants.
The class Insecta, in the phylum ARTHROPODA, whose members are characterized by division into three parts: head, thorax, and abdomen. They are the dominant group of animals on earth; several hundred thousand different kinds having been described. Three orders, HEMIPTERA; DIPTERA; and SIPHONAPTERA; are of medical interest in that they cause disease in humans and animals. (From Borror et al., An Introduction to the Study of Insects, 4th ed, p1)
A plant genus of the family FABACEAE. The gums and tanning agents obtained from Acacia are called GUM ARABIC. The common name of catechu is more often used for Areca catechu (ARECA).
In some animals, the jaws together with their horny covering. The beak usually refers to the bill of birds in which the whole varies greatly in form according of the food and habits of the bird. While the beak refers most commonly to birds, the anatomical counterpart is found also in the turtle, squid, and octopus. (From Webster, 3d ed & Storer, et al., General Zoology, 6th ed, p491, 755)
The process of germ cell development in the male from the primordial germ cells, through SPERMATOGONIA; SPERMATOCYTES; SPERMATIDS; to the mature haploid SPERMATOZOA.
The part of CENTRAL NERVOUS SYSTEM that is contained within the skull (CRANIUM). Arising from the NEURAL TUBE, the embryonic brain is comprised of three major parts including PROSENCEPHALON (the forebrain); MESENCEPHALON (the midbrain); and RHOMBENCEPHALON (the hindbrain). The developed brain consists of CEREBRUM; CEREBELLUM; and other structures in the BRAIN STEM.
Sugar-rich liquid produced in plant glands called nectaries. It is either produced in flowers or other plant structures, providing a source of attraction for pollinating insects and animals, as well as being a nutrient source to animal mutualists which provide protection of plants against herbivores.
In evolutionary theory, overlapping geographic distribution of diverging species. In sympatric GENETIC SPECIATION, genetic diversion occurs without geographic separation.
A group of islands in Melanesia constituting a French overseas territory. The group includes New Caledonia (the main island), Ile des Pins, Loyalty Island, and several other islet groups. The capital is Noumea. It was discovered by Captain Cook in 1774 and visited by various navigators, explorers, and traders from 1792 to 1840. Occupied by the French in 1853, it was set up as a penal colony 1864-94. In 1946 it was made a French overseas territory. It was named by Captain Cook with the 5th and 6th century A.D. Latin name for Scotland, Caledonia. (From Webster's New Geographical Dictionary, 1988, p830 & Room, Brewer's Dictionary of Names, 1992, p375)
Use of sound to elicit a response in the nervous system.
Multicellular, eukaryotic life forms of kingdom Plantae (sensu lato), comprising the VIRIDIPLANTAE; RHODOPHYTA; and GLAUCOPHYTA; all of which acquired chloroplasts by direct endosymbiosis of CYANOBACTERIA. They are characterized by a mainly photosynthetic mode of nutrition; essentially unlimited growth at localized regions of cell divisions (MERISTEMS); cellulose within cells providing rigidity; the absence of organs of locomotion; absence of nervous and sensory systems; and an alternation of haploid and diploid generations.
Insect members of the superfamily Apoidea, found almost everywhere, particularly on flowers. About 3500 species occur in North America. They differ from most WASPS in that their young are fed honey and pollen rather than animal food.
Duty to Recontact
The ethical and/or legal obligation of a health provider or researcher to communicate with a former patient or research subject about advances in research relevant to a treatment or to a genetic or other diagnostic test provided earlier, or about proposed new uses of blood or tissue samples taken in the past for another purpose.
Cell surface proteins that bind acetylcholine with high affinity and trigger intracellular changes influencing the behavior of cells. Cholinergic receptors are divided into two major classes, muscarinic and nicotinic, based originally on their affinity for nicotine and muscarine. Each group is further subdivided based on pharmacology, location, mode of action, and/or molecular biology.
Order of mammals whose members are adapted for flight. It includes bats, flying foxes, and fruit bats.
An interdisciplinary study dealing with the transmission of messages or signals, or the communication of information. Information theory does not directly deal with meaning or content, but with physical representations that have meaning or content. It overlaps considerably with communication theory and CYBERNETICS.
The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the NERVOUS SYSTEM.
Any of numerous burrowing mammals found in temperate regions and having minute eyes often covered with skin.
The sequence of transfers of matter and energy from organism to organism in the form of FOOD. Food chains intertwine locally into a food web because most organisms consume more than one type of animal or plant. PLANTS, which convert SOLAR ENERGY to food by PHOTOSYNTHESIS, are the primary food source. In a predator chain, a plant-eating animal is eaten by a larger animal. In a parasite chain, a smaller organism consumes part of a larger host and may itself be parasitized by smaller organisms. In a saprophytic chain, microorganisms live on dead organic matter.
Geographic variety, population, or race, within a species, that is genetically adapted to a particular habitat. An ecotype typically exhibits phenotypic differences but is capable of interbreeding with other ecotypes.
Investigative technique commonly used during ELECTROENCEPHALOGRAPHY in which a series of bright light flashes or visual patterns are used to elicit brain activity.
An order of wholly aquatic MAMMALS occurring in all the OCEANS and adjoining seas of the world, as well as in certain river systems. They feed generally on FISHES, cephalopods, and crustaceans. Most are gregarious and most have a relatively long period of parental care and maturation. Included are DOLPHINS; PORPOISES; and WHALES. (From Walker's Mammals of the World, 5th ed, pp969-70)
An order of small, wingless parasitic insects, commonly known as lice. The suborders include ANOPLURA (sucking lice); AMBLYCERA; ISCHNOCERA; and Rhynchophthirina (elephant and warthog lice).
A plant genus of the family ZYGOPHYLLACEAE. It is sometimes called chaparral but that is a generic word which is used with a number of other plants. Members contain NORDIHYDROGUAIARETIC ACID.
Small oviparous fishes in the family Cyprinodontidae, usually striped or barred black. They are much used in mosquito control.
A heterodimeric protein that is a cell surface antigen associated with lymphocyte activation. The initial characterization of this protein revealed one identifiable heavy chain (ANTIGENS, CD98 HEAVY CHAIN) and an indeterminate smaller light chain. It is now known that a variety of light chain subunits (ANTIGENS, CD98 LIGHT CHAINS) can dimerize with the heavy chain. Depending upon its light chain composition a diverse array of functions can be found for this protein. Functions include: type L amino acid transport, type y+L amino acid transport and regulation of cellular fusion.
Extensions of the nerve cell body. They are short and branched and receive stimuli from other NEURONS.
The relationship between an invertebrate and another organism (the host), one of which lives at the expense of the other. Traditionally excluded from definition of parasites are pathogenic BACTERIA; FUNGI; VIRUSES; and PLANTS; though they may live parasitically.
Amino Acid Sequence
Paired sense organs connected to the anterior segments of ARTHROPODS that help them navigate through the environment.
The ability or act of sensing and transducing ACOUSTIC STIMULATION to the CENTRAL NERVOUS SYSTEM. It is also called audition.
Anchoring points where the CYTOSKELETON of neighboring cells are connected to each other. They are composed of specialized areas of the plasma membrane where bundles of the ACTIN CYTOSKELETON attach to the membrane through the transmembrane linkers, CADHERINS, which in turn attach through their extracellular domains to cadherins in the neighboring cell membranes. In sheets of cells, they form into adhesion belts (zonula adherens) that go all the way around a cell.
The region of the cerebral cortex that receives the auditory radiation from the MEDIAL GENICULATE BODY.
Ability to determine the specific location of a sound source.
Members of the group of vascular plants which bear flowers. They are differentiated from GYMNOSPERMS by their production of seeds within a closed chamber (OVARY, PLANT). The Angiosperms division is composed of two classes, the monocotyledons (Liliopsida) and dicotyledons (Magnoliopsida). Angiosperms represent approximately 80% of all known living plants.
Tool Use Behavior
Modifying, carrying, or manipulating an item external to itself by an animal, before using it to effect a change on the environment or itself (from Beck, Animal Tool Behavior, 1980).
Body Weights and Measures
Membrane-bound compartments which contain transmitter molecules. Synaptic vesicles are concentrated at presynaptic terminals. They actively sequester transmitter molecules from the cytoplasm. In at least some synapses, transmitter release occurs by fusion of these vesicles with the presynaptic membrane, followed by exocytosis of their contents.
The 8th cranial nerve. The vestibulocochlear nerve has a cochlear part (COCHLEAR NERVE) which is concerned with hearing and a vestibular part (VESTIBULAR NERVE) which mediates the sense of balance and head position. The fibers of the cochlear nerve originate from neurons of the SPIRAL GANGLION and project to the cochlear nuclei (COCHLEAR NUCLEUS). The fibers of the vestibular nerve arise from neurons of Scarpa's ganglion and project to the VESTIBULAR NUCLEI.
Financial Management, Hospital
Loss of the tooth substance by chemical or mechanical processes
Ecological and Environmental Phenomena
Differential and non-random reproduction of different genotypes, operating to alter the gene frequencies within a population.
Contraceptive Agents, Male
The distal terminations of axons which are specialized for the release of neurotransmitters. Also included are varicosities along the course of axons which have similar specializations and also release transmitters. Presynaptic terminals in both the central and peripheral nervous systems are included.
Plant cell inclusion bodies that contain the photosynthetic pigment CHLOROPHYLL, which is associated with the membrane of THYLAKOIDS. Chloroplasts occur in cells of leaves and young stems of plants. They are also found in some forms of PHYTOPLANKTON such as HAPTOPHYTA; DINOFLAGELLATES; DIATOMS; and CRYPTOPHYTA.
A group of cold-blooded, aquatic vertebrates having gills, fins, a cartilaginous or bony endoskeleton, and elongated bodies covered with scales.
Lower lateral part of the cerebral hemisphere responsible for auditory, olfactory, and semantic processing. It is located inferior to the lateral fissure and anterior to the OCCIPITAL LOBE.
A highly conserved 76-amino acid peptide universally found in eukaryotic cells that functions as a marker for intracellular PROTEIN TRANSPORT and degradation. Ubiquitin becomes activated through a series of complicated steps and forms an isopeptide bond to lysine residues of specific proteins within the cell. These "ubiquitinated" proteins can be recognized and degraded by proteosomes or be transported to specific compartments within the cell.
A set of genes descended by duplication and variation from some ancestral gene. Such genes may be clustered together on the same chromosome or dispersed on different chromosomes. Examples of multigene families include those that encode the hemoglobins, immunoglobulins, histocompatibility antigens, actins, tubulins, keratins, collagens, heat shock proteins, salivary glue proteins, chorion proteins, cuticle proteins, yolk proteins, and phaseolins, as well as histones, ribosomal RNA, and transfer RNA genes. The latter three are examples of reiterated genes, where hundreds of identical genes are present in a tandem array. (King & Stanfield, A Dictionary of Genetics, 4th ed)
The act of feeding on plants by animals.
Analysis of Variance
The largest family of snakes, comprising five subfamilies: Colubrinae, Natricinae, Homalopsinae, Lycodontinae, and Xenodontinae. They show a great diversity of eating habits, some eating almost anything, others having a specialized diet. They can be oviparous, ovoviviparous, or viviparous. The majority of North American snakes are colubrines. Among the colubrids are king snakes, water moccasins, water snakes, and garter snakes. Some genera are poisonous. (Goin, Goin, and Zug, Introduction to Herpetology, 3d ed, pp321-29)
PASSERIFORMES of the suborder, Oscines, in which the flexor tendons of the toes are separate, and the lower syrinx has 4 to 9 pairs of tensor muscles inserted at both ends of the tracheal half rings. They include many commonly recognized birds such as CROWS; FINCHES; robins; SPARROWS; and SWALLOWS.
Sequence Analysis, DNA
NEURAL PATHWAYS and connections within the CENTRAL NERVOUS SYSTEM, beginning at the hair cells of the ORGAN OF CORTI, continuing along the eighth cranial nerve, and terminating at the AUDITORY CORTEX.
Any of numerous winged hymenopterous insects of social as well as solitary habits and having formidable stings.
Area of the OCCIPITAL LOBE concerned with the processing of visual information relayed via VISUAL PATHWAYS.
A dimension of auditory sensation varying with cycles per second of the sound stimulus.
Pattern Recognition, Visual
Derived from TELENCEPHALON, cerebrum is composed of a right and a left hemisphere. Each contains an outer cerebral cortex and a subcortical basal ganglia. The cerebrum includes all parts within the skull except the MEDULLA OBLONGATA, the PONS, and the CEREBELLUM. Cerebral functions include sensorimotor, emotional, and intellectual activities.
Wormlike or grublike stage, following the egg in the life cycle of insects, worms, and other metamorphosing animals.
The common chimpanzee, a species of the genus Pan, family HOMINIDAE. It lives in Africa, primarily in the tropical rainforests. There are a number of recognized subspecies.
55-kDa antigens found on HELPER-INDUCER T-LYMPHOCYTES and on a variety of other immune cell types. CD4 antigens are members of the immunoglobulin supergene family and are implicated as associative recognition elements in MAJOR HISTOCOMPATIBILITY COMPLEX class II-restricted immune responses. On T-lymphocytes they define the helper/inducer subset. CD4 antigens also serve as INTERLEUKIN-15 receptors and bind to the HIV receptors, binding directly to the HIV ENVELOPE PROTEIN GP120.
The brain stem nucleus that receives the central input from the cochlear nerve. The cochlear nucleus is located lateral and dorsolateral to the inferior cerebellar peduncles and is functionally divided into dorsal and ventral parts. It is tonotopically organized, performs the first stage of central auditory processing, and projects (directly or indirectly) to higher auditory areas including the superior olivary nuclei, the medial geniculi, the inferior colliculi, and the auditory cortex.
Wound Closure Techniques
Microscopy, Electron, Scanning
Microscopy in which the object is examined directly by an electron beam scanning the specimen point-by-point. The image is constructed by detecting the products of specimen interactions that are projected above the plane of the sample, such as backscattered electrons. Although SCANNING TRANSMISSION ELECTRON MICROSCOPY also scans the specimen point by point with the electron beam, the image is constructed by detecting the electrons, or their interaction products that are transmitted through the sample plane, so that is a form of TRANSMISSION ELECTRON MICROSCOPY.
Economic aspects of the field of medicine, the medical profession, and health care. It includes the economic and financial impact of disease in general on the patient, the physician, society, or government.
Subcellular structures found in nerve cell bodies and DENDRITES. They consist of granular endoplasmic reticulum (ENDOPLASMIC RETICULUM, ROUGH) and RIBOSOMES.
Symbiotic combination (dual organism) of the MYCELIUM of FUNGI with the roots of plants (PLANT ROOTS). The roots of almost all higher plants exhibit this mutually beneficial relationship, whereby the fungus supplies water and mineral salts to the plant, and the plant supplies CARBOHYDRATES to the fungus. There are two major types of mycorrhizae: ectomycorrhizae and endomycorrhizae.
Infections of the brain caused by arthropod-borne viruses (i.e., arboviruses) primarily from the families TOGAVIRIDAE; FLAVIVIRIDAE; BUNYAVIRIDAE; REOVIRIDAE; and RHABDOVIRIDAE. Life cycles of these viruses are characterized by ZOONOSES, with birds and lower mammals serving as intermediate hosts. The virus is transmitted to humans by the bite of mosquitoes (CULICIDAE) or TICKS. Clinical manifestations include fever, headache, alterations of mentation, focal neurologic deficits, and COMA. (From Clin Microbiol Rev 1994 Jan;7(1):89-116; Walton, Brain's Diseases of the Nervous System, 10th ed, p321)
Evoked Potentials, Auditory
Image Processing, Computer-Assisted
The measurement of subcutaneous fat located directly beneath the skin by grasping a fold of skin and subcutaneous fat between the thumb and forefinger and pulling it away from the underlying muscle tissue. The thickness of the double layer of skin and subcutaneous tissue is then read with a caliper. The five most frequently measured sites are the upper arm, below the scapula, above the hip bone, the abdomen, and the thigh. Its application is the determination of relative fatness, of changes in physical conditioning programs, and of the percentage of body fat in desirable body weight. (From McArdle, et al., Exercise Physiology, 2d ed, p496-8)
Branch-like terminations of NERVE FIBERS, sensory or motor NEURONS. Endings of sensory neurons are the beginnings of afferent pathway to the CENTRAL NERVOUS SYSTEM. Endings of motor neurons are the terminals of axons at the muscle cells. Nerve endings which release neurotransmitters are called PRESYNAPTIC TERMINALS.
Task Performance and Analysis
Filamentous proteins that are the main constituent of the thin filaments of muscle fibers. The filaments (known also as filamentous or F-actin) can be dissociated into their globular subunits; each subunit is composed of a single polypeptide 375 amino acids long. This is known as globular or G-actin. In conjunction with MYOSINS, actin is responsible for the contraction and relaxation of muscle.
A genus of vibrioid or rod-shaped cells which are motile by polar flagella. Internal photosynthetic membranes are present as lamellar stacks and contain bacteriochlorophyll a or b and carotenoids. Growth occurs photoautotrophically under anaerobic conditions. (From Bergey's Manual of Determinative Bacteriology, 9th ed)
The SKELETON of the HEAD including the FACIAL BONES and the bones enclosing the BRAIN.