By S. Ateras. Vanguard University.
Central chemoreceptors detect changes only in arterial of breathing is minimized despite changes in activity cheap haldol 10 mg mastercard medications elavil side effects, the PCO2; peripheral chemoreceptors detect changes in arterial environment generic 1.5 mg haldol otc treatment 5 shaving lotion, and lung function. The hypoxia-induced stimulation of ventilation is not great brainstem and can be modified by ventilatory reflexes. Sleep is induced by the withdrawal of a wakefulness stimu- gal nerve endings that are sensitive to lung stretch. The autonomic nerves and vagal sensory nerves maintain sults in a general depression of breathing. Mechanical or chemical irritation of the airways and lungs increases breathing. GENERATION OF THE BREATHING PATTERN study extensively the subtleties of such a complex system in humans, much of what is known about the control of The control of breathing is critical for understanding of breathing has been obtained from the study of other respiratory responses to activity, changes in the environ- species. Breathing is an automatic process The control of upper and lower airway muscles that af- that occurs without any conscious effort while we are fect airway tone is integrated with control of the muscles awake, asleep, or under anesthesia. During quiet breathing, in- the heartbeat in terms of an automatic rhythm. However, spiration is brought about by a progressive increase in acti- there is no single pacemaker that sets the basic rhythm of vation of inspiratory muscles, most importantly the di- breathing and no single muscle devoted solely to the task aphragm (Fig. Breathing depends on the cyclic with time causes the lungs to fill at a nearly constant rate excitation of many muscles that can influence the volume until tidal volume has been reached. Control of that excitation is the result of is associated with a rapid decrease in excitation of inspira- multiple neuronal interactions involving all levels of the tory muscles, after which expiration occurs passively by nervous system. Furthermore, the muscles used for breath- elastic recoil of the lungs and chest wall. For ex- inspiratory muscles resumes during the first part of expira- ample, talking while walking requires that some muscles tion, slowing the initial rate of expiration. As more ventila- simultaneously attend to the tasks of posturing, walking, tion is required—for example, during exercise—other in- phonation, and breathing. Because it is impossible to spiratory muscles (external intercostals, cervical muscles) 363 364 PART V RESPIRATORY PHYSIOLOGY Diaphragm electromyogram Diaphragm electrical activity per unit time Inspiration Expiration Inspiration Expiration Pleural pressure FIGURE 22. During inspiration, the number of active muscle medulla oblongata and a cross section in the region of the fourth fibers, and the frequency at which each fires, increases progres- ventricle. C1, first cervical nerve; X, vagus nerve; IX, glossopha- sively, leading to a mirror-image fall in pleural pressure as the di- ryngeal nerve. In addition, expiration becomes an active complex, but the exact anatomic and functional description process through the use, most notably, of the muscles of remains uncertain. The neural basis of these breathing pat- does not arise from a single pacemaker or by reciprocal in- terns depends on the generation and subsequent tailoring hibition of two pools of cells, one having inspiratory- and of cyclic changes in the activity of cells primarily located in the other expiratory-related activity. An integrator-based theoretical model, as Oblongata Control the Basic Breathing Rhythm described below, is suitable for a first understanding of res- The central pattern for the basic breathing rhythm has piratory pattern generation. Cells in the medulla oblongata associated Onset of Inspiration with breathing have been identified by noting the correla- tion between their activity and mechanical events of the Many different signals (e. Two different groups of cells have been loskeletal movements, pain, chemosensor activity, and hy- found, and their anatomic locations are shown in Figure pothalamic temperature) provide a background ventilatory 22. Inspiration begins by the abrupt re- dorsal location in the region of the nucleus tractus solitarii, lease from inhibition of a group of cells, central inspiratory predominantly contains cells that are active during inspira- activity (CIA) integrator neurons, located within the tion. The ventral respiratory group (VRG) is a column of medullary reticular formation, that integrate this back- cells in the general region of the nucleus ambiguus that ex- ground drive (see Fig. Integration results in a pro- tends caudally nearly to the bulbospinal border and cra- gressive rise in the output of the integrator neurons, which, nially nearly to the bulbopontine junction. The VRG con- in turn, excites a similar rise in activity of inspiratory pre- tains both inspiration- and expiration-related neurons. The rate of ris- groups contain cells projecting ultimately to the bul- ing activity of inspiratory neurons and, therefore, the rate bospinal motor neuron pools. The DRG and VRG are bi- of inspiration itself, can be influenced by changing the laterally paired, but cross-communication enables them to characteristics of the CIA integrator. Inspiration is ended respond in synchrony; as a consequence, respiratory move- by abruptly switching off the rising excitation of inspira- ments are symmetric. The CIA integrator is reset before the begin- The neural networks forming the central pattern gener- ning of each inspiration, so that activity of the inspiratory ator for breathing are contained within the DRG/VRG neurons begins each breath from a low level. CHAPTER 22 The Control of Ventilation 365 may serve to integrate many different autonomic functions Pontine respiratory in addition to breathing. This effect is greatest early in off-switch Chemoreceptors neurons expiration and recedes as lung volume falls.
These project to different regions of the brain but the differences in their functional influences are buy haldol 10mg low cost treatments, as yet haldol 5mg overnight delivery medications similar to gabapentin, poorly understood. Most studies have in fact investigated the DRN, which innervates forebrain areas, but it does seem that other serotonergic nuclei in the medulla show a similar pattern of responses. Moreover, unlike DRN neurons, those in the NRO and NRP continue to fire, albeit at a reduced frequency, during REM sleep. The implications of these differences in the regulation of the sleep cycle are unclear. However, environmental stimuli that provoke behavioural orientation induce a marked phasic increase in serotonergic neuronal activity (see Chapter 9) suggesting that they do have some role in the response to stimuli requiring attention. A link between 5-HT release and increased waking is supported by evidence from in vivo microdialysis of cats and rats. This has confirmed that the extracellular concen- tration of 5-HT in all brain regions studied to date is lower during both SWS and REM sleep than in the awake state (see Portas, Bjorvatn and Ursin 2000). Interestingly, if behaviour is maintained at a constant level, the activity of 5-HT neurons does not show circadian variation although 5-HT turnover in the brain areas to which they project 492 NEUROTRANSMITTERS, DRUGS AND BRAIN FUNCTION Figure 22. Neurons that release 5-HT are clustered in two groups of nuclei in the pons and upper brainstem. The reasons for this apparent dissociation between firing rate and transmitter release are not clear but it does suggest that neuronal firing rate is not necessarily a reliable indicator of transmitter release in the terminal field. In so doing, they are responsible for gating motor output and coordinating this with homeostatic and sensory function (Jacobs and Azmitia 1992; Jacobs and Fornal 1999). This would be consistent with evidence that, like the noradrenergic system, increases in the firing rate of neurons in the DRN precede an increase in arousal. The frequency of discharge would code the state of arousal and prime target cells for forthcoming changes in the response to sensory inputs. Apart from the problem of trying to associate the effects of 5-HT with specific nuclei, there is also no clear picture of which 5-HT receptors mediate any of these changes in sleep and waking. This is not least because of the large number of receptor subtypes, the limited receptor selectivity of most test drugs, species differences in the response, as well as time- and dose-related differences in the response to any given agent. Nevertheless, it is evident that activation of many different receptor subtypes affect the sleep±waking cycle. For instance, recent evidence suggests that activation of 5-HT1A, 5-HT1B, 5-HT2A/C and 5-HT7 receptors in the SCN all affect circadian rhythms. Activation of 5-HT1B (presynaptic) receptors in the retinohypothalamic tract is thought to attenuate 5-HT release and so blunt light inputs to the SCN and reduce its phototic regulation. In contrast, postsynaptic 5-HT7 receptors, 5-HT2C, and possibly postsynaptic 5-HT1A receptors, are thought to have an important role in phototic entrainment and to mediate phase-shifts in circadian rhythms (reviewed by Barnes and Sharp 1999). In addition to these effects on circadian rhythms, it is clear that 5-HT receptors affect sleep more directly. A detailed review of this subject is to be found in Portas, Bjorvatn and Ursin (2000) but key findings are summarised here. Postsynaptic : 5-HT3 : Postsynaptic : The actions of 5-HT1A receptor agonists in rats depend on their route of administration (Bjorvatn and Ursin 1998). When they are given systemically they cause a transient increase in waking time and a reduction in SWS and REM sleep which is followed by a delayed increase in SWS. This latter response is possibly mediated by activation of inhibitory postsynaptic 5-HT1A receptors in the nucleus basalis (Table 22. Certainly, local infusion of 5-HT1A agonists into this area increases SWS. Another contributory factor is suggested by the reduction in waking and increase in SWS following intrathecal infusion of 8-OH-DPAT. This is thought to reflect inhibition of primary sensory afferents, by activation of presynaptic 5-HT1A receptors, an action which would be conducive with induction of sleep. However, infusion of low concentrations of the 5-HT1A agonist, 8-OH- DPAT, into the DRN to activate autoreceptors induces a type of REM sleep which is explained by a reduction in the firing rate of 5-HT neurons. In turn, this is presumed to result in disinhibition of mesopontine cholinergic neurons in the PPT and LTD nuclei which are responsible for REM sleep. Such a scheme is supported by evidence that local infusion of a 5-HT1A agonist into these areas reduces REM sleep, presumably by inhibition of mesopontine cholinergic neurons by postsynaptic 5-HT1A receptors.
Synovial fluid is similar to interstitial fluid (fluid between nied by the formation of a bunion at the medial base of the proximal phalanx of the hallux buy discount haldol 5 mg on-line symptoms 10dpo. It is rich in hyaluronic acid and albumin purchase haldol 10 mg with amex medicine hollywood undead, and also callus that develops in response to pressure and rubbing of a shoe. The bones that articulate in a synovial joint are capped with a smooth layer of hyaline cartilage Kinds of Synovial Joints called the articular cartilage. Articular cartilage is only about 2 Synovial joints are classified into six main categories on the basis mm thick. Because articular cartilage lacks blood vessels, it has of their structure and the motion they permit. The six categories to be nourished by the movement of synovial fluid during joint are gliding, hinge, pivot, condyloid, saddle, and ball-and-socket. Composed of dense regular connective tissue, ligaments are flexible cords that connect from bone to bone as they help bind Gliding synovial joints. Ligaments may be located within the joint cavity Gliding joints allow only side-to-side and back-and-forth move- or on the outside of the joint capsule. The articulating surfaces are nearly flat, or one the knee joint,where they cushion and guide the articulating may be slightly concave and the other slightly convex (fig. A few other synovial joints,such as the temporomandibu- The intercarpal and intertarsal joints, the sternoclavicular joint, lar joint (see fig. Many people are concerned about the cracking sounds they hear as joints move, or the popping sounds that result from Hinge “popping” or “cracking” the knuckles by forcefully pulling on the fin- Hinge joints are monaxial—like the hinge of a door, they permit gers. When a synovial joint is pulled upon, its volume is suddenly expanded and the pressure of movement in only one plane. In this type of articulation, the sur- the joint fluid is lowered, causing a partial vacuum within the joint. As face of one bone is always concave, and the other convex the joint fluid is displaced and hits against the articular cartilage, air (fig. Hinge joints are the most common type of synovial bubbles burst and a popping or cracking sound is heard. Examples include the knee, the humeroulnar articulation displaced water in a sealed vacuum tube makes this sound as it hits against the glass wall. Popping your knuckles does not cause arthri- within the elbow, and the joints between the phalanges. Pivot The articular cartilage that caps the articular surface of each bone and the synovial fluid that circulates through the joint The movement at a pivot joint is limited to rotation about a cen- during movement are protective features of synovial joints. In this type of articulation, the articular surface on one serve to minimize friction and cushion the articulating bones. Should trauma or disease render either of them nonfunctional, the two articu- bone is conical or rounded and fits into a depression on another lating bones will come in contact. Examples are the proximal articulation of the type of arthritis will develop within the joint. These closed sacs are com- monly located between muscles, or in areas where a tendon Condyloid passes over a bone. They function to cushion certain muscles and A condyloid articulation is structured so that an oval,convex ar- assist the movement of tendons or muscles over bony or ligamen- ticular surface of one bone fits into a concave depression on an- tous surfaces. This permits angular movement in two surrounds and lubricates the tendons of certain muscles, particu- directions,as in up-and-down and side-to-side motions. The radiocarpal joint of the wrist and the metacarpophalangeal joints are examples. Improperly fitted shoes or inappropriate shoes can cause joint related problems. People who perpetually wear high-heeled shoes often have backaches and leg aches because their posture Saddle has to counteract the forward tilt of their bodies when standing or walking. Their knees are excessively flexed, and their spine is thrust Each articular process of a saddle joint has a concave surface in forward at the lumbar curvature in order to maintain balance. This articulation fitted shoes, especially those with pointed toes, may result in the de- is a modified condyloid joint that allows a wide range of move- velopment of hallux valgus—a lateral deviation of the hallux (great toe) ment. One is at the articulation of the trapezium of the carpus with the first metacarpal bone (fig.