Parasympathetic activity

Sympathetic and parasympathetic nerves innervate the penis. In the flaccid state, OC2-adrenergic receptors mediate tonic contraction of the arterial and corporal smooth muscles. This maintains high penile arterial resistance and a balance exists between blood flow into and out of the corpora. With sexual stimulation, nerve impulses from the brain travel down the spinal cord to the thoracolumbar ganglia.3 A decrease in sympathetic tone and an increase in parasympathetic activity then occurs, causing a net increase in blood flow into the erectile tissue. Erections may also occur as a result of a sacral nerve reflex arc while patients are sleeping (nocturnal erections). 

Acetylcholine-mediated parasympathetic activity leads to production of the non-adrenergic-non-cholinergic transmitter nitric oxide. By enhancing the activity of guanylate cyclase, nitric... 

At the onset of exercise, signals from the cerebral cortex are transmitted to the vasomotor center in the medulla of the brainstem. This central command inhibits parasympathetic activity and also initiates the mass sympathetic discharge associated with exercise. Sympathetic activity (including release of catecholamines from the adrenal medulla) increases proportionally with the intensity of exercise. 

Reserpine s strong inhibition of sympathetic activity allows increased parasympathetic activity to occur, which is responsible for side effects of nasal stuffiness, increased gastric acid secretion, diarrhea, and bradycardia. 

Being an anticholinergic, ipratropium interrupts the parasympathetic activities including the blocking of muscarinic receptors in the lung, resulting in an inhibition of bronchoconstriction and of mucus secretion. 

Autonomic ganglia. Ganglionic stimulation occurs in both the sympathetic and parasympathetic divisions of the autonomic nervous system. Parasympathetic activation results in increased production of gastric juice (smoking ban in peptic ulcer) and enhanced bowel motility ( laxative effect of the first morning cigarette defecation diarrhea in the novice). 

One exception to the generalization that the two systems work in opposition to each other is secretion by the salivary glands both sympathetic (noradrenergic) and parasympathetic (cholinergic) activation of these glands leads to an increase in the flow of saliva. However, the nature of the saliva produced by the two systems is qualitatively different. The saliva produced by activation of the sympathetic system is a sparse, thick, mucinous secretion, whereas that produced by parasympathetic activation is a profuse, watery secretion. 

Important considerations are as follows (1) The direct effect of norepinephrine on the heart is stimulatory. (2) The reflex initiated is inhibitory, that is, opposite to the direct effect. (3) The reflex varies with the level of sympathetic and parasympathetic activity just before the initiation of the reflex. (4) The distribution of sympathetic and parasympathetic nerves is not uniform in the heart. 

A common and troublesome side effect is postural hypotension. Sexual impotence does occur, and male patients may have difficulty ejaculating. Symptoms of unopposed parasympathetic activity include such gastrointestinal disturbances as diarrhea and increased gastric secretion. 

Peripheral nervous system side effects are the result of a reserpine-induced reduction of sympathetic function and unopposed parasympathetic activity symptoms include nasal congestion, postural hypotension, diarrhea, bradycardia, increased gastric secretion, and occasionally impotence. Because of the increased gastric secretion, reserpine is contraindicated for patients... 

At present five different muscarinic receptor subtypes are known that mediate the parasympathetic activity of the autonomic nervous system M-,-, M2-, M3-, M4-, and Ms-receptors [88, 116]. The odd-numbered muscarinic receptors are... 

PAM either activates or blocks autonomic ganglia, depending on dose and route and speed of administration. The changes In ganglionic function Induced by 2-PAM will be reflected In sympathetic and parasympathetic activity, which may cause changes In cardiovascular functions. These are discussed further In the next section. 

Probably through presynaptic inhibition of parasympathetic activity. 

Edrophonium Alcohol, binds briefly to active site of acetylcholinesterase (AChE) and prevents access of acetylcholine (ACh) Amplifies all actions of ACh increases parasympathetic activity and somatic neuromuscular transmission Diagnosis and acute treatment of myasthenia gravis Parenteral quaternary amine does not enter CNS Toxicity Parasympathomimetic excess Interactions Additive with parasympathomimetics... 

In discussing the physiological similarities and differences, it is for two reasons convenient to separate the peripheral from the central neurophysiology. The first reason is that there are dissociations between them such that the periphery can be sympathetically activated while the center is either sympathetically or parasympathetically activated. The second reason is that the central changes are, in all likelihood, much more important to phenomenology because it is there that conscious awareness is elaborated and because the state of the periphery may have little (waking) or no (REM sleep) impact upon central state. 

As a hydrogenated ketone of morphine, it shares common pharmacologic properties with other opioid analgesics.25 These include the expected changes in the CNS, including increased cerebrospinal fluid pressure, increased biliary pressure, and increased parasympathetic activity. It can also... 

Finally, activation of the sympathetic division tends to result in a more massive and diffuse reaction than does parasympathetic activation. Parasympathetic reactions tend to be fairly discrete and to affect only one organ or tissue. For instance, the parasympathetic fibers to the myocardium can be activated to slow down the heart without a concomitant emptying of the bowel through an excitatory effect on the lower gas-... 

Angiotensin II inhibitors lower blood pressure principally by decreasing peripheral vascular resistance. Cardiac output and heart rate are not significantly changed. Unlike direct vasodilators, these agents do not result in reflex sympathetic activation and can be used safely in persons with ischemic heart disease. The absence of reflex tachycardia may be due to downward resetting of the baroreceptors or to enhanced parasympathetic activity. 

The baroreflex system consists of mechanosensitive receptors in the aorta and carotid sinus that detect changes in blood pressure. The receptors give rise to afferent nerve fibers that relay impulses to the CNS. Within the CNS, the afferent signals are processed and ultimately transmitted to efferent sympathetic and parasympathetic fibers to the vasculature and heart. Increases in blood pressure will increase baro-receptors activity leading to an inhibition of sympathetic impulses to the blood vessels (thereby relaxing them) and to the heart (decreasing heart rate and contractility). In addition, parasympathetic activity to the heart is increased leading to a reduction in heart rate and possibly contractility. 

Due to the surgical procedure the connections of the autonomic nervous system of the isolated pouch are interrupted from those of the main stomach. Therefore, basal gastric acid secretion from the pouch, which based mainly on the parasympathetic activity, is reduced. 

The authors reviewed the biphasic effect of marijuana on the autonomic nervous system. At low to moderate doses it causes increased sympathetic activity, producing a tachycardia and increase in cardiac output blood pressure therefore increases. At high doses it causes increased parasympathetic activity, leading to bradycardia and hypotension. They thought that this patient most probably had adrenergic atrial flutter. 

Autonomic outputs. Hypoglycaemia and hypothermia both lead to snstained sympathetic responses. Subjects feel hungry and eat if possible, bnt they refine their other actions to suit the circumstances. Hypoglycaemia requires hepatic glycogenolysis and glnconeogenesis, while hypothermia requires increased heat prodnction and a redistribntion of blood flow. Sympathetic activity is controlled by the hypothalamns, which instrncts the adrenal medulla to secrete adrenalin. This is a rather blunt control, and so localised sympathetic responses (such as blood flow regulation) are mediated by individnal nerves. Parasympathetic activity can also respond to the hypothalamus, which controls the nnclens of the solitary tract. 

The time course of sympathetic activity is significantly slower than that of parasympathetic activity, taking 10 to 40 seconds to reach its maximum effect. In contrast, parasympathetically mediated responses are completed in approximately 1 to 2 seconds for normal visual environments. 

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