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The axons follow a cir- THE PARASYMPATHETIC NERVOUS SYSTEM cuitous course through the lesser petrosal nerve to reach the otic ganglion best 260mg extra super avana, where they synapse extra super avana 260mg lowest price. From the otic gan- The parasympathetic division is comprised of a cranial glion, the postsynaptic axons join the auriculotemporal portion, emanating from the brainstem, and a sacral por- branch of cranial nerve V and arrive at the parotid gland, tion, originating in the intermediate gray zone of the where they stimulate secretion of saliva. In contrast to the wide- Sensory axons that are important for autonomic func- spread activation pattern of the sympathetic division, the tion are also conveyed in cranial nerve IX. The carotid bod- neurons of the parasympathetic division are activated in a ies sense the concentrations of oxygen and carbon dioxide more localized fashion. There is also much less tendency in blood flowing in the carotid arteries and transmit that for divergence of the presynaptic influence to multiple chemosensory information to the medulla via glossopha- postsynaptic neurons—on average, one presynaptic ryngeal afferents. The carotid sinus, which is located in the parasympathetic neuron synapses with 15 to 20 postsy- proximal internal carotid artery, monitors blood pressure naptic neurons. An example of localized activation is seen and transmits this baroreceptor information to the tractus in the vagus nerve, where one portion of its outflow can solitarius in the medulla. It has ther close to the organ innervated or embedded within its been estimated that vagal output comprises up to 75% of walls. The organs of the gastrointestinal system demonstrate total parasympathetic activity. Because of this arrangement, pregan- travel in the vagus trunks to ganglia in the heart and lungs glionic axons are much longer than postganglionic axons. Sympathetic postsynaptic axons also intermingle with the parasympathetic presynaptic axons in these plexuses and Brainstem Parasympathetic Neurons Innervate travel together to the target tissues. Structures in the Head, Chest, and Abdomen The right vagus nerve supplies axons to the sinoatrial Four of the twelve cranial nerves—numbers III, VII, IX, and node of the heart, and the left vagus nerve supplies the atri- X—contain parasympathetic axons. Vagal activation slows the heart rate and nerves, which occupy areas of the tectum in the midbrain, reduces the force of contraction. The vagal efferents to the pons, and medulla, are the centers for the initiation and in- lung control smooth muscle that constricts bronchioles, tegration of autonomic reflexes for the organ systems they and also regulate the action of secretory cells. Parasympathetic and sympathetic activities are to the esophagus and stomach regulates motility and influ- coordinated by these nuclei. Acetylcholine plus vasoactive intestinal peptide (VIP) are the transmitters of the postsynaptic neurons. The oculomotor nerve originates from There is also vagal innervation to the kidneys, liver, nuclei in the tectum of the midbrain, where synaptic connec- spleen, and pancreas, but the role of these inputs is not yet tions with the axons of the optic nerves provide input for oc- fully established. The parasympathetic neurons are located in the Edinger-Westphal nucleus. The presynaptic axons travel in the superficial aspect of cranial nerve III to the ciliary gan- Sacral Spinal Cord Parasympathetic Neurons glion, located inside the orbit where the synapse occurs. The Innervate Structures in the Pelvis postganglionic axons enter the eyeball near the optic nerve and travel between the sclera and the choroid. These axons Preganglionic fibers of the sacral division originate in the supply the sphincter muscle of the iris; the ciliary muscle, intermediate gray matter of the sacral spinal cord, emerging which focuses the lens; and the choroidal blood vessels. These pregan- About 90% of the axons are destined for the ciliary muscle, glionic fibers synapse in ganglia in or near the pelvic or- while only about 3 to 4% innervate the iris sphincter. SPECIFIC ORGAN RESPONSES TO AUTONOMIC ACTIVITY CONTROL OF THE AUTONOMIC NERVOUS SYSTEM As noted earlier, most involuntary organs are dually inner- vated by the sympathetic and parasympathetic divisions, of- The autonomic nervous system utilizes a hierarchy of re- ten with opposing actions. A list of these organs and a sum- flexes to control the function of autonomic target organs. The type of receptor at the one neuron, to regional, requiring mediation by the spinal cord and associated autonomic ganglia, to the most com- plex, requiring action by the brainstem and cerebral cen- ters.
Basal nuclei are specialized masses of gray reticular activating system in arousing the (a) The neuroglia that surround an axon matter located within the white matter of cerebrum buy extra super avana 260mg lowest price. The diencephalon is a major autonomic outer periosteal layer and an inner 4 discount 260 mg extra super avana mastercard. The thalamus is an ovoid mass of gray a single layer surrounded by the vascular (a) Sensory (afferent) neurons are matter that functions as a relay center for epidural space. The hypothalamus is an aggregation of surrounding the subarachnoid space, multipolar. The epithalamus contains the pineal smooth muscle, cardiac muscle, gland and the vascular choroid plexus and glands. Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 398 Unit 5 Integration and Coordination Ventricles and Cerebrospinal Fluid 4. The blood-brain barrier determines which (b) The conus medullaris is the terminal (pp. The lateral (first and second), third, and the extracellular fluid of the brain. Ascending and descending spinal cord continuous with the central canal of the 1. Cerebrospinal fluid is continuously formed and two longitudinal grooves that decussate (cross over) in the spinal by the choroid plexuses from blood plasma partially divide it into right and left cord or in the medulla oblongata of and is returned to the blood at the halves. Beside each Match the following structures of the brain to (d) the vermis. The structure of the brain that is most basic functional units of the nervous system? List the six principal types of neuroglia (c) mesencephalon (c) the medulla oblongata. Why is it called an all-or-none sheaths in the peripheral nervous system are (a) They are located within the response? A collection of neuron cell bodies located (d) They indirectly exert an inhibitory 8. The corpora quadrigemina, red nucleus, major part of the autonomic nervous (b) a nerve. List the nuclei located (a) sensory neurons in the midbrain and state the function (b) somatic motor neurons (c) the mesencephalon. Describe the location and structure of the (d) autonomic motor neurons 12. Describe the formation of the neural crest CT scan, MS, DSR, and CVA stand for? Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 Chapter 11 Nervous Tissue and the Central Nervous System 399 14. What causes it and how complains of loss of sensation from the specific irritable tissue, such as a tumorous is it controlled? Electrical stimulation of the cerebellum or before a focal seizure, the sufferer these conditions differ? How would damage to these called an aura, that suggests the origin of Critical-Thinking Questions two regions of the brain affect skeletal the electrical burst. If an entire cerebral hemisphere is origin of a seizure that was preceded by of body structures are reported. A flash of brief case study of a patient who has suffered damage to the medulla oblongata, a much light. A seizure occurs when abnormal electrical nose may be detected from a spinal tap legs over the course of several days, which activity overwhelms the brain’s normal performed in the lumbar region. A focal seizure originates from a also loses urinary bladder control and Visit our Online Learning Center at http://www.
Beyond that range extra super avana 260 mg generic, the pH shift that [HPO4 ] a a given amount of acid or base produces may be large extra super avana 260mg cheap, so The effectiveness of a buffer—how well it reduces pH the buffer becomes relatively ineffective. A good buffer is present in high concentrations and has a pKa close to the desired pH. As a strong acid or strong base is progres- sively added to the solution (shown on the x-axis), the re- Acids are continuously produced in the body and threaten sulting pH is recorded (shown on the y-axis). Physiologically speaking, acids fall into two groups: (1) right to left as strong acid is added, H combines with the H2CO3 (carbonic acid), and (2) all other acids (noncar- bonic; also called “nonvolatile” or “fixed” acids). The dis- tinction between these groups occurs because H2CO3 is in equilibrium with the volatile gas CO2, which can leave the body via the lungs. The concentration of H2CO3 in arterial blood is, therefore, set by respiratory activity. By contrast, 9 HPO 2 noncarbonic acids in the body are not directly affected by 4 breathing. Metabolism Is a Constant Source 8 of Carbon Dioxide A normal adult produces about 300 L of CO2 daily from metabolism. CO2 from tissues enters the capillary blood, where it reacts with water to form H2CO3, which dissoci- ates instantly to yield H and HCO3 : CO2 H2O 7 H2CO3 H HCO3. Fortunately, H2CO3 produced from metabolic CO2 is only formed transiently in the transport of CO2 by the 6 blood and does not normally accumulate. Instead, it is con- verted to CO2 and water in the pulmonary capillaries and the CO2 is expired. In the lungs, the reactions reverse: H HCO3 H2CO3 H2O CO2 (12) 5 H PO As long as CO2 is expired as fast as it is produced, arte- 2 4 rial blood CO2 tension, H2CO3 concentration, and pH do not change. Amount of HCl added (mEq) Amount of NaOH added (mEq) Incomplete Carbohydrate and Fat Metabolism A titration curve for a phosphate buffer. A strong acid Normally, carbohydrates and fats are completely oxidized (HCl) (right to left) or strong base (NaOH) (left to right) was added and the resulting solution pH recorded (y-axis). Incomplete oxi- a given amount of acid or base is least) when the solution pH is dation of carbohydrates occurs when the tissues do not re- equal to the pKa of the buffer. In such states, glucose me- Food intake tabolism yields lactic acid (pKa 3. Incomplete fatty acid oxidation occurs in uncontrolled diabetes melli- tus, starvation, and alcoholism and produces ketone body Absorption acids (acetoacetic and -hydroxybutyric acids). At blood pH, they Cell metabolism buffering response response of food mostly dissociate into their anions and H , making the + + H H blood more acidic. Bound by Sulfate body buffer CO2 Phosphate bases Protein Metabolism Generates Strong Acids Chloride CO 2 The metabolism of dietary proteins is a major source of Extracellular H. The oxidation of proteins and amino acids produces New strong acids such as H SO , HCl, and H PO. The oxi- fluid HCO - 2 4 3 4 [HCO -] 3 3 dation of sulfur-containing amino acids (methionine, cys- teine, cystine) produces H2SO4, and the oxidation of cationic amino acids (arginine, lysine, and some histidine Extracellular residues) produces HCl. H3PO4 is produced by the oxi- fluid [HCO -] dation of phosphorus-containing proteins and phospho- 3 CO2 esters in nucleic acids. H+ Excreted (combined with urinary On a Mixed Diet, Net Acid Gain Threatens pH buffer bases) A diet containing both meat and vegetables results in a net Excreted production of acids, largely from protein oxidation. To Sulfate Sulfate some extent, acid-consuming metabolic reactions balance Phosphate Phosphate Chloride Chloride H production. When these are oxidized to CO2 and water, H ions are consumed (or, amounting to The maintenance of normal blood pH by FIGURE 25. The balance of acid- chemical buffers, the respiratory system, forming and acid-consuming metabolic reactions results in and the kidneys.
The receptor mediating all three effects appears to be the D2 (or D3) receptor purchase extra super avana 260 mg on-line. Thus initially neuroleptics may increase DA turnover and possibly even its action depending on the degree of postsynaptic block purchase extra super avana 260mg otc. This may also change as the block induces compensating increases in receptor number. LATENCY OF NEUROLEPTIC EFFECT There is no reason why DA receptor block should not occur as soon as the antagonist reaches the brain. We now have a situation in which the drugs that are most useful in schizophrenia are regarded as atypical. While the term was introduced to cover those neuroleptics that do not cause EPSs, it has become synonymous with clozapine which has additional advantages over other neuroleptics (e. Hopefully this distinction between the neuroleptics will become unnecessary as better compounds are developed and the older ones become obsolete. One possibility is that even with a potentially effective drug, the necessary readjust- ments in the neuronal circuitry to reverse or compensate for the disorder-induced malfunction just requires time. These neurons are usually not very active but DA antagonists increase their excitability through the mechanisms outlined above so that their firing rates rise, the pattern of discharge changes from single- to multiple-spike burst discharges and the proportion of neurons firing increases. These changes are also aided by the fact that the excitatory inputs to A9 and A10 neurons normally promote a dendritic release of DA which through inhibitory soma D2 autoreceptors will automatically counteract the excitation (Fig. Clearly when these autoreceptors are blocked by acute neuro- leptic administration in rats they cannot be activated by released DA, and the neurons fire much more frequently. It was found, however, that if neuroleptic administration was continued for two weeks then neuronal firing stopped. Also while the neurons could not be made to fire by the excitatory NT glutamate, the inhibitory NT GABA activated them by reducing the SCHIZOPHRENIA 361 Figure 17. In (a) the excitatory effect of glutamate released on to the DA neuron from the afferent input is counteracted by the inhibitory effect of DA, presumed to be released from dendrites, acting on D2 autoreceptors. In the absence of such inhibition due to the presence of a typical neuroleptic (b) the neuron will fire more frequently and eventually become depolarised. Atypical neuroleptics, like clozapine, will be less likely to produce the depolarisation of A9 neurons because they are generally weaker D2 antagonists and so will reduce the DA inhibition much less allowing it to counteract the excitatory input. Additionally some of them have antimuscarinic activity and will block the excitatory effect of ACh released from intrinsic neurons (see Fig. Thus it appears that due to their continuous intense activity the neurons eventually become permanently depolarised (confirmed by intra- cellular recording) and inactive (Fig. The induction of depolarisation block in DA neurons needs afferent input to the nuclei, since prior lesion of the striatum and nucleus 362 NEUROTRANSMITTERS, DRUGS AND BRAIN FUNCTION Figure 17. Iontophoretic application of GABA the inhibitory NT, at the currents indicated (nA) actually induced firing which is shown as an oscilloscope sweep in (b). The excitatory NT glutamate failed to stimulate the neuron but apomorphine, which normally has an inhibitory effect through D2 receptors, increased firing when given intraventricularly in increasing amounts from 2±5 to 160 mgkg71. These effects are consistent with the neurons being overstimulated and depolarised as a result of chronic neuroleptic dosing and so requiring to be hyperpolarised (inhibited) in order to become active. In a neuron from an untreated rat (c), GABA produces the expected inhibition and glutamate the rapid excitation, shown as an oscilloscope sweep in (d).