Lotensin

By D. Gorok. Bethel College, Newton, Kansas.

Primary care: Benign paroxysmal po- canals are the most frequently affected buy 10 mg lotensin with mastercard. Recent studies have provided evidence for a fifth taste While the functional receptor categories are well de- modality, one that is called umami, or savoriness. Its recep- fined, it is much more difficult to determine what kind of tors are stimulated quite specifically by glutamate ions, stimulating chemical will produce a given taste sensation. Glutamate ions can and the intensity of the perception depends on the degree CHAPTER 4 Sensory Physiology 87 Microvilli Tight junction substances bind to specific G protein-coupled receptors Epithelium and activate phospholipase C to increase the cell concen- tration of inositol trisphosphate, which promotes calcium Taste pore release from the endoplasmic reticulum. Sweet substances also act through G protein-coupled receptors and cause in- creases in adenylyl cyclase activity, increasing cAMP, which, in turn, promotes the phosphorylation of membrane potassium channels. The resulting decrease in potassium conductance leads to depolarization. In the case of the umami taste, there is evidence of specific G protein-cou- pled receptors in the cell membranes of sensory taste cells. Compared with that of many other animals, the human sense of smell is not particularly acute. Nevertheless, we can distinguish 2,000 to 4,000 different odors that cover a wide range of chemical species. The re- ceptor organ for olfaction is the olfactory mucosa, an area 2 of approximately 5 cm located in the roof of the nasal cav- Synapse Basal ity. Normally there is little air flow in this region of the Supporting cell nasal tract, but sniffing serves to direct air upward, increas- cell Sensory ing the likelihood of an odor being detected. In contrast to the taste sensory cells, the ol- factory cells are neurons and, as such, are primary recep- FIGURE 4. The afferent nerve synapse with the basal tentacular) cells, and tight junctions bind the cells areas of the sensory cells. Most sweet substances are organic; sugars, espe- (dendrite) cially, tend to produce a sweet sensation, although thresh- olds vary widely. By comparison, the apparent sweetness of saccharin, an artificial sweetener, is 600 times as great as that of sucrose, although it is not a sugar. Unfortunately, Tight the salts of lead are also sweet, which can lead to ingestion junction of toxic levels of this poisonous metal.

The lower heart rate tracellular space than if the sodium concentration of the and core temperature and the higher sweat rate are the three sweat is high (Table 29 purchase lotensin 5mg with amex. Other consequences are dis- classical signs of heat acclimatization (Fig. Heat acclimatization is transient, disappearing in a few weeks if not maintained by repeated heat exposure. The Changes in Fluid and Electrolyte Balance Also components of heat acclimatization are lost in the order in Occur With Heat Acclimatization which they were acquired; the cardiovascular changes de- During the first week, total body water and, especially, cay more quickly than the reduction in exercise core tem- plasma volume increase. Later, the fluid changes seem to diminish or disappear, although the cardiovascular adaptations persist. In an unacclimatized person, sweating RESPONSES TO COLD occurs mostly on the chest and back, but during acclimati- The body maintains core temperature in the cold by mini- zation, especially in humid heat, the fraction of sweat se- mizing heat loss and, when this response is insufficient, in- creted on the limbs increases to make better use of the skin creasing heat production. An unacclimatized person who is the chief physiological means of heat conservation in hu- sweating profusely can lose large amounts of sodium. Furred or hairy animals also can increase the thick- acclimatization, the sweat glands become able to conserve ness of their coat and, thus, its insulating properties by sodium by secreting sweat with a sodium concentration as making the hairs stand on end. This effect is mediated through aldos- erection, makes a negligible contribution to heat conserva- terone, which is secreted in response to sodium depletion tion in humans, but manifests itself as gooseflesh. The sweat glands re- spond to aldosterone more slowly than the kidneys, requir- ing several days; unlike the kidneys, the sweat glands do Blood Vessels in the Shell Constrict not escape the influence of aldosterone when sodium bal- to Conserve Heat ance has been restored, but continue to conserve sodium for as long as acclimatization persists. The constriction of cutaneous arterioles reduces skin blood The cell membranes are freely permeable to water, so flow and shell conductance. Constriction of the superficial that any osmotic imbalance between the intracellular and limb veins further improves heat conservation by diverting extracellular compartments is rapidly corrected by the venous blood to the deep limb veins, which lie close to the movement of water across the cell membranes (see Chapter major arteries of the limbs and do not constrict in the cold.

Despite this it has also been shown to reduce fast inhibitory postsynaptic potentials (IPSPs) in the rat lateral amygdala probably by presynaptic A1 inhibitory effect on GABA release (Henbockel and Pap 1999) lotensin 5 mg cheap. Adenosine has also been considered to play a role in sleep induction (Chapter 22). Recently much interest has been shown in the possible neuroproctive effects of adenosine but the responses are complex. Thus A3 agonists can offer some protection given chronically before ischaemic challenge but given acutely post-challenge they can be neurotoxic (see Jacobsen 1998). HISTAMINE The belief that histamine (HT) has a central effect stems from the knowledge that all the classical antihistamines (H1 receptor antagonists) used to treat allergic reaction, such as hay fever, caused marked sedation if, like mepyramine and promethazine, they can cross the blood±brain barrier, but fail to do so if, like terfenedine and cetirizine, they do not. The major problem in establishing histamine as a transmitter in the CNS has been the difficulty in demonstrating its actual presence in neurons rather than just in the invading mast cells, in which it is concentrated and from which it is released in the periphery during allergic reactions. The development of immunohistochemical methods for the visualisation of histamine, and its synthesising enzyme histidine decarboxylase, now show there to be definite histaminergic nerves (see Tohyama et al. These are concentrated in the tuberomammillary nucleus in the posterior hypothalamus, not only in the rat but also in humans, and like the other monoaminergic systems (NA and 5- HT) they give off long highly branched axons which ascend in the medial forebrain bundle projecting to the cerebral cortex and hippocampus. Most histamine neurons also contain other transmitters such as GABA, substance P or enkaphalin. The whole brain concentration of histamine is relatively low (50±70 ng/g) but there is much evidence for its central action (see Schwartz et al. Histidine is a poor substrate for the L-amino- acid decarboxylase responsible for DA and NA synthesis. The synthesis of histamine in the brain can be increased by the administration of histidine, so its decarboxylase is presumably not saturated normally, but it can be inhibited by a fluoromethylhistidine. No high-affinity neuronal uptake has been demonstrated for histamine although after initial metabolism by histamine N-methyl transferase to 3-methylhistamine, it is deaminated by intraneuronal MAOB to 3-methylimidazole acetic acid (Fig. A Ca2‡-dependent KCl-induced release of histamine has been demonstrated by micro- dialysis in the rat hypothalamus (Russell et al.

They pass superiorly through the transverse foramina of the cervical vertebrae and enter the skull through the foramen magnum purchase lotensin 5mg with mastercard. Within the cranium, the Arteries of the Neck and Head two vertebral arteries unite to form the basilar artery at the level The common carotid arteries course upward in the neck along of the pons. The basilar artery ascends along the inferior surface the lateral sides of the trachea (fig. Each common carotid of the brain stem and terminates by forming two posterior cere- artery branches into the internal and external carotid arteries bral arteries that supply the posterior portion of the cerebrum slightly below the angle of the mandible. The posterior communicating arteries this area, a pulse can be detected (see fig. At the base of are branches that arise from the posterior cerebral arteries and the internal carotid artery is a slight dilation called the carotid participate in forming the cerebral arterial circle (circle of Willis) sinus. The carotid sinus contains baroreceptors, which monitor surrounding the pituitary gland. Surrounding the carotid sinus are the carotid bodies, small neurovascular organs that contain chemoreceptors, which respond to chemical changes in the blood. Circulatory System © The McGraw−Hill Anatomy, Sixth Edition Body Companies, 2001 562 Unit 6 Maintenance of the Body Superficial temporal a. Circulatory System © The McGraw−Hill Anatomy, Sixth Edition Body Companies, 2001 Chapter 16 Circulatory System 563 FIGURE 16. The cerebral arterial circle (circle of Willis) consists of the arteries that ring the pituitary gland. Each internal carotid artery arises from the common areas or structures they serve. The principal vessels that arise carotid artery and ascends in the neck until it reaches the base of from the external carotid artery are the following: the skull, where it enters the carotid canal of the temporal bone. Three of the more important roid gland; ones are the ophthalmic artery (see fig. The in- ternal carotid arteries are connected to the posterior cerebral ar- • the lingual artery, which provides extensive vasculariza- teries at the cerebral arterial circle.

Chronic pain with insidious onset dysesthetic extremity pain bandlike pain in torso or extremities back pain with radicolopathy headache F generic lotensin 5 mg without prescription. Trigeminal neuralgia probably arises from transmission of nerve impulses in areas of demyelination. In the chronic phase, anticonvulsants such as carbamaze- pine and gabapentin are used. Less common is the painful tetanic posturing of an arm or leg, usually on one side of the body. Treatment consists of carbamazepine, clonazepam, tizanidine, and baclofen. Lightning-like extremity pain can be treated with carbamazepine, gabapentin, and phenytoin. Lhermitte’s sign responds to the above medications and also to tricyclic antidepressant medications. Headache has been reported to be causally related to demye- linating lesions. When associated with a relapse, treatment with steroids may cause resolution of headache. Optic neuritis is due to inflammation and demyelination occurring in and around pain-sensitive meninges surrounding the optic nerve. Gabapentin—useful in dysesthetic and paroxysmal pain; better SE profile than phenytoin 3. Accentuation of DTR and clonus occurs, with exaggeration of flexor reflexes C. Spasms and stiffness are common in the quadriceps, hamstrings, and gastrocnemious muscles D.