«By far the most important venomous insects are members of the order Hymenoptera, including bees, wasps, and ants. They vary in size from minute to large (up to 60 mm in body length). The abdomen and thorax are connected by a slender pedicle that may...» Document abstract
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SummaryBy far the most important venomous insects are members of the order Hymenoptera, including bees, wasps, and ants. They vary in size from minute to large (up to 60 mm in body length). The abdomen and thorax are connected by a slender pedicle that may be quite long in certain wasps and ants. Bees and most wasps are winged as adults; ants are wingless, except for sexually mature adults during part of the life cycle. Mouthparts are adapted for chewing but in some species are modified for sucking. The life cycle includes egg, larva, and pupa stages before emergence of adults. Immature stages may be protected and provided with food by the adult. Both animal and plant foods are used. Many species are parasitic on other arthropods. All ants and many species of bees and wasps are social insects. Colonies range in size from a few dozen individuals to many thousands. In cold climates, most individuals die in autumn, leaving the fertilized females to winter over and found new colonies in the spring.
Table of Contents- The honeybee (Apis mellifera) is one of the few domesticated insects and is maintained in hives in many countries.
- The first escapes from hives occurred in the state of São Paulo in 1957, and the "Brazilian killer bees," or "Africanized bees," have spread widely.
- Bumblebees (Bombus and related genera) are a largely holarctic group often found in quite cold environments.
- Solitary wasps are predators, feeding largely on other insects and spiders.
- Ants are social insects, worldwide in distribution over a wide range of habitats. Many ants sting, and others have repugnant secretions.
- Multiple stings often result from disturbance of a nest, as the first insects encountered release alarm pheromones that incite aggressive behavior in other members of the colony.
- Intense pain after stings by hornets and other social wasps is largely caused by serotonin and acetylcholine, which constitute 1% to 5% of dry venom weight.
- Ant venoms show great variation. Those of more primitive ants (subfamilies Ponerinae, Myrmicinae, and Dorylinae) resemble venoms of social wasps, containing kininlike peptides, enzymes, and unidentified proteins.
«Lice are small wingless insects that are ectoparasites of mammals. They are mostly host specific, and two species are human parasites: Pthirus pubis (pubic louse) and Pediculus humanus, with two varieties, P. h. capitis (head louse) and P. h....» Document abstract
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SummaryLice are small wingless insects that are ectoparasites of mammals. They are mostly host specific, and two species are human parasites: Pthirus pubis (pubic louse) and Pediculus humanus, with two varieties, P. h. capitis (head louse) and P. h. corporis (body louse). They are obligatory parasites, subsisting on blood from the host, and have mouthparts modified for piercing and sucking. The mouthparts are drawn into the head of the louse when not in use.
The adult head louse is about 2 to 4 mm long with an elongated body that is flattened dorsoventrally. The head is only slightly narrower than the thorax. The three pairs of legs are about equal in length and possess delicate hooks at the distal extremities. The entire life is spent on the host's body. The eggs (nits) are deposited on hair shafts, generally one nit to a shaft. The nits hatch in about 1 week, and the freshly hatched larvae, which must feed within 24 hours of hatching or die, mature in about 15 to 16 days. The adult female lives for approximately 1 month and may deposit more than 100 eggs during her reproductive life. Body lice are slightly larger than head lice but are similar in appearance with a similar life cycle, although the nits are deposited on fibers of clothing. Head lice and body lice interbreed.
The adult head louse is about 2 to 4 mm long with an elongated body that is flattened dorsoventrally. The head is only slightly narrower than the thorax. The three pairs of legs are about equal in length and possess delicate hooks at the distal extremities. The entire life is spent on the host's body. The eggs (nits) are deposited on hair shafts, generally one nit to a shaft. The nits hatch in about 1 week, and the freshly hatched larvae, which must feed within 24 hours of hatching or die, mature in about 15 to 16 days. The adult female lives for approximately 1 month and may deposit more than 100 eggs during her reproductive life. Body lice are slightly larger than head lice but are similar in appearance with a similar life cycle, although the nits are deposited on fibers of clothing. Head lice and body lice interbreed.
Table of Contents- The adult head louse is about 2 to 4 mm long with an elongated body that is flattened dorsoventrally
- Lice are found wherever people are found. Able to exist only briefly away from the human body, lice are spread by close personal contact and by sharing of clothing and bedding.
- The head louse localizes on the scalp and rarely on other hairy areas of the body.
- The body louse lives chiefly in the seams of clothing and is rarely seen on the skin.
- Treatment of all types of lice strives to eradicate lice and nits and prevent reinfestation.
- Body lice may be treated with the same medications, but parasites and nits are not generally found on the skin.
«Mites make up the largest group in the class Arachnida. Most are small arthropods, and many are barely visible. Mites have two body regions, a small cephalothorax and a larger, unsegmented abdomen. The cephalothorax and abdomen are broadly joined,...» Document abstract
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SummaryMites make up the largest group in the class Arachnida. Most are small arthropods, and many are barely visible. Mites have two body regions, a small cephalothorax and a larger, unsegmented abdomen. The cephalothorax and abdomen are broadly joined, giving most mites an oblong to globular appearance. Newly hatched larvae have three pairs of legs, and larvae acquire a fourth pair after the first molt. Mites are highly diverse. Some are parasitic, with both vertebrates and invertebrates serving as hosts; some are scavengers, some feed on plants, and many are free living and predaceous. Although most species are oviparous, some are ovoviviparous, and a few are viviparous. They occur worldwide and frequently in great numbers. Mites have been associated with disease transmission, allergies, and dermatologic manifestations. Of the approximately 35,000 species, about 50 are known to cause human skin lesions, and most of the cutaneous lesions are caused by mites feeding or burrowing in the skin. Since children and adults of all races are susceptible to these ubiquitous arthropods, they are responsible for considerable morbidity. The mites of medical importance are some of the sarcoptic mites, some of the trombiculid mites, a number of other acariform mites that infest organic substances such as grains and produce, and the gamasid mites that are vectors of several rickettsial and viral diseases. Dermatologic manifestations of mite bites may be seasonal, as with the trombiculids; individual cases or outbreaks of varying magnitude may be related to contact with mites that infest animals or various foods. Epidemics may occur, as is presently the case with scabies.
Table of Contents- The human scabies mite is Sarcoptes scabiei var. hominis, an obligate human parasite that completes its entire life cycle in and on the epidermis of humans.
- Severe nocturnal pruritus is the hall-mark of scabies. Itching also may be provoked by any sudden warming of the body and generally does not involve the face.
- Diagnosis is based on the combination of nocturnal pruritus and cutaneous findings and is confirmed by microscopic examination of burrow contents.
- A number of topical treatments are available. In most cases a single overnight application of 5% permethrin cream (Elimite) is curative.
- Control of scabies outbreaks in nursing homes and similar epidemic situations can be almost insurmountable because of the number of patients and contacts that must be treated simultaneously.
- Humans develop itchy papules, often with some urtication, and scratching may give rise to varying degrees of secondary infection.
- Treatment is symptomatic and consists of topical antipruritic agents, corticosteroids, systemic antihistamines, and occasionally, pulse therapy with systemic corticosteroids.
«Common: Eastern White Pine
Scientific: Pinus strobus
Derivation of name: Latin name for pine from Greek "pitus" / incense-bearing or a gum-yielding tree (pitchy) or [sic] Greek "strobus" (cone) [1]
Also known as: white pine, northern white...» Document abstract
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SummaryCommon: Eastern White Pine
Scientific: Pinus strobus
Derivation of name: Latin name for pine from Greek "pitus" / incense-bearing or a gum-yielding tree (pitchy) or [sic] Greek "strobus" (cone) [1]
Also known as: white pine, northern white pine, northern pine, ship-mast pine, soft pine, pin blanc, and Weymouth pine [2]
Table of Contents- Family Pinacea
- More detail of Subgenus Strobus
- Close relatives
- How to identify White Pine
- Place/Habitat
- Conservation Status
- Associated Animals
- Mycorrhizae
- Folk-Medicinal Properties
- Economic Importance
- Evolutionary History
- Biggest white pine on record
«The past several decades have witnessed a veritable explosion of knowledge about the central nervous system (CNS), and in no area has this been as impressive as in peptide neurobiology. Numerous peptide neurotransmitter candidates have been...» Document abstract
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SummaryThe past several decades have witnessed a veritable explosion of knowledge about the central nervous system (CNS), and in no area has this been as impressive as in peptide neurobiology. Numerous peptide neurotransmitter candidates have been identified and characterized, their CNS distributions mapped, and their genes cloned. The tenet “one neuron-one transmitter” erroneously attributed to Dale has been convincingly refuted with numerous demonstrations of neurons containing multiple peptides or combinations of peptide and nonpeptide neurotransmitters. Additionally, since the early 1980s there has been an embarrassment of riches in the form of knowledge about neurotransmitter receptor diversity, diversity of receptor-effector coupling, and neurotransmitter transporters. These discoveries have not yet been fully integrated into what is known about normal or aberrant CNS function, although dysfunction at virtually any level could conceivably lead to neuropsychiatric deficits.
Table of Contents- By definition, a neuropeptide is a chain of two or more amino acids linked by peptide bonds, and differs from other proteins only in the length of the amino acid chain.
- Many of the known behavioral effects of neuropeptides are observed only after their direct injection into the CNS because most peptides do not penetrate the blood-brain barrier in amounts sufficient to produce effects before being inactivated by serum and tissue enzymes that degrade them.
- The tertiary structure for recognition is also used by the immune system for the production of specific antibodies, as well as by biological receptors.
- Neuropeptides are found throughout the CNS, as well as in various peripheral organs, such as the gastrointestinal tract, pancreas, and adrenal glands.
- In the cortex of rats SRIF is found in some of the large stellate-shaped neurons and in abundance among the fusiform-shaped, nonpyramidal neurons of layers II to V, and particularly in layer V of the sensory cortex.
- Through the use of retrograde tracing methods and dual staining techniques, several pathways for certain peptides have now been delineated.
- Some of the noradrenergic locus ceruleus neurons, in turn, project to the hypothalamic paraventricular nucleus where their input increases CRF synthesis and release.
- The neurotensin-neuromedin N gene was originally cloned from canine ileal mucosa, and complementary deoxyribonucleic acid (cDNA) probes constructed against this form were used to clone the rat gene.
«Neuropeptide receptors have undergone the same process of discovery and characterization that receptors for other neurotransmitters have enjoyed. The process begins with the pharmacological characterization of the receptor's physicochemical binding...» Document abstract
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SummaryNeuropeptide receptors have undergone the same process of discovery and characterization that receptors for other neurotransmitters have enjoyed. The process begins with the pharmacological characterization of the receptor's physicochemical binding properties by assessing the affinity of various metabolically derived and synthetic peptide fragments, and the native molecule, for the receptor binding site found in membrane preparations. Peptide receptor locations are mapped with radioactive or fluorescent tags that are inserted into peptide molecules, which often contain substituted amino acids at the most vulnerable peptidase cleavage sites. Previously, once the peptide receptor was characterized pharmacologically, it was usually purified from some relatively enriched biological tissue source or brain region by affinity column chromatography. After it had been purified, binding parameters and activity were recharacterized for the reconstituted purified receptor protein and structural information obtained by X-ray crystallography. This process was closely followed in the purification of the neurotensin-neuromedin N receptor.
Table of Contents- The neurotensin receptor was first characterized by photoaffinity labeling and cross-linking of radioiodinated ligands, which resulted in two labeled subunits of about 49 Kd and 51 Kd from rat brain synaptosomes.
- The much more powerful tools of molecular biology have been utilized more recently.
- Neuropeptide receptors have been associated with just about every type of second messenger signal transduction system that has been identified.
- Peptides are degraded to smaller fragments, and eventually to single amino acids, by specific enzymes termed peptidases.
- The metabolism of TRH has been investigated fairly completely, principally because of the limited number of fragments that can be generated from a tripeptide.
- The peptides involved in neuroendocrine regulation have cell bodies residing in the hypothalamus that receive feedback from all levels of the endocrine axes.
- Regional differences in CRF receptor regulation by corticosterone have also been reported, which have been shown to partly result from differential glycosylation of the CRF receptor.
- Alzheimer's Disease Dementia of the Alzheimer's Type represents up to two thirds of the demented population encountered in clinical practice, and over half of the nursing home beds in the United States are currently occupied by such patients.
- The CRF-containing interneurons of the cortex are also consistently depleted in Alzheimer's disease. As with SRIF, subcortical areas containing CRF neurons may be spared, but unlike SRIF, CRF receptors are increased in number (up-regulated) with no change in affinity.
- Corticotropin-Releasing Factor After a search spanning nearly three decades, CRF was isolated and characterized in 1981 as a 41-amino acid peptide.
- A series of studies have demonstrated significant elevations of CRF concentrations in the CSF of drug-free patients with major depression or following suicide.
- Like many other neuropeptide transmitters, central administration of SRIF produces a variety of behavioral and physiological effects.
- Decreased neurotensin concentrations in CSF have been reported in several populations of patients with schizophrenia when compared to controls or patients with other psychiatric disorders.
«Resting Membrane Potential In nerve cells, potassium ions (K+) are at higher concentration inside the membrane than outside whereas the opposite is true for sodium (Na+), calcium (Ca2+), and chloride (Cl–) ions (Fig. 1.9-1). The bulk solutions on...» Document abstract
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SummaryResting Membrane Potential In nerve cells, potassium ions (K+) are at higher concentration inside the membrane than outside whereas the opposite is true for sodium (Na+), calcium (Ca2+), and chloride (Cl–) ions (Fig. 1.9-1). The bulk solutions on either side of the membrane are electrically neutral, with most of the intracellular negative charge being contributed by large organic anions (acids and proteins). The differential distribution of ions across neuronal membranes results in part from the action of membrane pumps that use energy from adenosine triphosphate (ATP) to drive ions against a concentration gradient into or out of the cell. The best characterized pump is the Na+-K+ adenosine triphosphatase (ATPase) that transports 3 Na+ out of and 2 K+ into the cell during each cycle. Because an unequal amount of charge is moved during each cycle, the pump is electrogenic and produces an electrochemical potential across the membrane that makes the inside of the membrane negative with respect to the outside. Na+-K+ ATPase activity is a major contributor to brain energy utilization, with as much as 40 percent of brain oxygen consumption resulting from pump activity required to reestablish ionic homeostasis following action potential firing and synaptic transmission. The cardiac glycosides digoxin (Lanoxin) and ouabain are effective inhibitors of Na+-K+ ATPase in the heart and improve myocardial contractility by depolarizing cardiac myocytes and increasing intracellular Ca2+.
Table of Contents- At rest, neuronal membranes are permeable to K+ and Cl– and to a lesser extent to Na+, partly because of the flow of ions through nongated leakage channels.
- For each ion in solution there is a specific membrane potential at which the opposing forces of the electrical gradient and concentration gradient are balanced.
- Because ions do not directly penetrate the lipid membrane but rather flow through ion channels, the ion channels can be thought of as variable resistors.
- Active Membrane Properties: Action Potentials Changes in membrane potential have important effects on excitability because certain ion channels are activated (gated) by voltage changes.
- Many axons are encased in myelin sheaths that allow them to send action potentials over longer distances.
«In its simplest form, the postsynaptic response to neurotransmitter release can be mediated by a single protein complex. For example, nicotinic acetylcholine receptors are self-contained stimulus-response modules that both detect a stimulus,...» Document abstract
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SummaryIn its simplest form, the postsynaptic response to neurotransmitter release can be mediated by a single protein complex. For example, nicotinic acetylcholine receptors are self-contained stimulus-response modules that both detect a stimulus, acetylcholine, and generate a response, passage of ion currents. In a similar vein, other members of this superfamily of ionotropic receptors, including g-aminobutyric acid (GABA) and glutamate receptors, have the ability to function in a manner that is independent of the intracellular signaling pathways discussed. Thus, in contrast to growth factor or G-protein–coupled receptors, which often recruit elaborate cascades to elicit a response, the simplicity of self-sufficient ionotropic receptor complexes represents an optimal design for achieving reliability, precision, and speed. However, this view of ionotropic receptors as insulated from their social environment has had to be abandoned in the face of overwhelming evidence that this class of receptors is dynamically regulated by intraneuronal signaling pathways. Although these receptors do not rely on intraneuronal signaling pathways to operate ion channels, because these channels are an intrinsic feature of the receptor complex the linkage between ligand binding and ion channel gating is nevertheless subject to regulation by the network of intraneuronal signaling pathways just described. For example, phosphorylation of the GABA or glutamate receptors modulates their response to ligand exposure.
Table of Contents- Long-Term Depression The principle that ion channels are regulated by second messenger pathways is of central importance in considering how neuronal responses are altered by experience.
- Long-Term Potentiation The notion that coactivation of multiple second messenger pathways can have a qualitatively different impact than any one individually is also borne out in another well-known model of synaptic plasticity, long-term potentiation.
- This unusual property of NMDA receptors provides a molecular mechanism for conferring associative properties on long-term potentiation.
- Role of Phosphorylation The associative property of this model of synaptic plasticity has focused attention on deciphering the intraneuronal signaling pathways that mediate the long-term change in synaptic transmission triggered by NMDA receptor stimulation.
- Actions of Psychotropic Drugs In addition to providing insight into the molecular mechanism underlying synaptic plasticity, studies of intraneuronal signaling pathways are also directly relevant to deciphering the mode of action of psychotropic drugs.
- Evidence supporting this theory has been provided by recent studies demonstrating that opiate withdrawal is attenuated in transgenic animals that are deficient in CREB.
«Classes of Neurotransmitters Much of the information transfer between neurons in the CNS occurs via chemical synapses. These synapses use a variety of messengers (neurotransmitters) that are released in a Ca2+-dependent fashion from presynaptic...» Document abstract
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SummaryClasses of Neurotransmitters Much of the information transfer between neurons in the CNS occurs via chemical synapses. These synapses use a variety of messengers (neurotransmitters) that are released in a Ca2+-dependent fashion from presynaptic terminals and act on specific protein receptors to produce biochemical and excitability changes in the receiving cell. There are two primary groups of neurotransmitters—low–molecular-weight amines and neuroactive peptides. These agents act on two classes of receptors, ligand-gated ion channels, at which the binding of the transmitter directly opens ion channels in the membrane, and G protein coupled receptors. The activated G protein then acts on ion channels or alters biochemical second-messenger systems. Physiologists classify synaptic transmission according to the speed of transmission (fast or slow) and according to the nature of the response (excitatory or inhibitory).
Table of Contents- Currently, there are nine low–molecular-weight amines that serve as neurotransmitters.
- Conductance Mechanisms Underlying Neurotransmitter Actions
- Structure of Neurotransmitter Receptors Considerable information now exists about the primary structure of neurotransmitter receptors.
- The ligand-gated ion channels gated by extracellular ATP (called P2X receptors) are exceptions to the scheme described above and have structures more typical of the inwardly rectifying K+ channels.
- G-protein coupled receptors have a distinctly different structure from the ligand-gated ion channels.
«Structure and Function of Voltage-Gated Ion Channels Voltage-gated ion channels allow the flow of ions in response to changes in membrane voltage and are key elements in neuronal excitation and inhibition. Although ion channels can usually pass more...» Document abstract
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SummaryStructure and Function of Voltage-Gated Ion Channels Voltage-gated ion channels allow the flow of ions in response to changes in membrane voltage and are key elements in neuronal excitation and inhibition. Although ion channels can usually pass more than a single type of ion, voltage-gated channels are named according to the predominant ion that flows when the channel is open. Ion channels that are selective for Na+, K+, Ca2+, or Cl– have been described in neuronal membranes. Certain ion channels that are gated directly by chemical neurotransmitters such as glutamate and acetylcholine are selective for Na+, K+, and Ca2+ but exclude Cl– and are called nonselective cationic channels.
Table of Contents- Sodium (Na+) Channels Na+ channels are primarily responsible for the fast upstroke of action potentials, although in some neurons Na+ channels also contribute to lower-level depolarizations and pacemaker firing.
- Relations between primary protein structure and ion channel function in Na+ channels have been examined using mutations of specific amino acid residues.
- The net effect is similar to the scorpion toxins. Finally, certain local anesthetic drugs, including lidocaine and procaine, block Na+ channels by binding reversibly to sites within the hydrophobic regions of the ion channel.
- Delayed-rectifier channels open slowly and show little inactivation during prolonged depolarizations.
- M channels represent a class of K+ channels that are activated in a time- and voltage-dependent fashion but are blocked by the neurotransmitter, acetylcholine, acting at muscarinic receptors.
- KATP channels exist in the CNS and appear to be involved in regulating the release of certain neurotransmitters and perhaps in determining the response of some neurons to changes in intracellular energy levels.
- Calcium (Ca2+) Channels Because Ca2+ is involved in numerous cellular events including enzyme activation, gene expression, and neurotransmitter release, the regulation of intracellular Ca2+ levels is of major importance to neurons.
- Most structural information about Ca2+ channels comes from skeletal muscle HVA Ca2+ channels.
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