This is the best information I have seen so far in what the Vagus nerve has to do with the respiratory system.... even speaking to a pulmonary specialist yesterday...he could not answer my questions, and admitted needing to get the text books out to research it on hiw own.
Thank you much, Connie > From: "C Creel" <[email protected]> > Reply-To: [email protected] > Date: Fri, 4 Oct 2002 09:51:02 -0400 > To: <[email protected]> > Subject: CS>Re: Respiratory System and Vagus Nerve > Resent-From: [email protected] > Resent-Date: Fri, 4 Oct 2002 12:28:21 -0700 > > This gives a brief overview of the role of the vagal nerve in the control > of proper respiration. > > > Mechanical Receptors and their Effects on Respiratory Control: > > Mechanical receptors located throughout the respiratory system also > contribute to the integrated control of ventilation. There are three basic > receptor classes to be considered: > > 1) Pulmonary Stretch Receptors > > 2) Irritant Receptors > > 3) C-fibers (small unmyelinated fibers) > > Pulmonary stretch receptors: > > Pulmonary stretch receptors are thought to lie within the airway smooth > muscle and are sensitive to transmural pressure gradients. These afferent > impulses travel in the vagus nerve (CN X) from the airways to the > respiratory control centers in the brainstem. The maintenance of transmural > pulmonary pressure or the release of it account for both the Hering-Breuer > reflex and the deflation reflex. > > The inflation reflex (Hering-Breuer reflex) is the inhibition of inspiration > in response to an increase in transmural pulmonary pressure. It was once > thought to be an important respiratory control reflex in humans; however, we > now know that bilateral vagal blockade (temporary or permanent) does not > markedly change the respiratory rate or tidal volumes of awake humans. The > reflex can be elicited in anesthetized patients with the use of large tidal > volumes, but it is relatively unimportant in eupnic breathing. Furthermore, > patients who have undergone bilateral lung transplants have a normal rate > and depth of breathing--these lungs are completely denervated! > > The deflation reflex is an increase in subsequent inspiration by a decrease > in the transmural pulmonary pressure. It too can be demonstrated in man, but > is probably not important in normal breathing. For newborns, both inflation > and deflation reflexes may play a more important role in respiratory > regulation. > > Irritant receptors: > > Such receptors are thought to lie between the airway epithelial cells, and > their afferent traffic is also carried in CN X. These receptors respond to a > variety of respiratory irritants such as small particles, chemicals, smoke, > and cold. > > Juxtapulmonary Capillary Receptors: > > Juxtapulmonary capillary receptors ("J" Receptors) are located in close > proximity to capillaries in the pulmonary interstitium. These C-fiber > afferent impulses are carried in the vagus nerve and are activated when > there is pulmonary parenchymal damage, edema formation (as in left > ventricular failure), or the release of certain chemical mediators. These > receptors have classically been thought to be responsible for the dyspnea > (shortness of breath) experienced by patients with congestive heart failure > (and subsequent pulmonary interstitial edema). > > Upper Airway Receptors: > > In addition to the receptors mentioned above, there are also receptors > located in the upper respiratory tract: nose, pharynx and larynx. These give > rise to reflex arcs that result in coughing or sneezing, bronchoconstriction > and tachypnea. > > Gamma system of muscle control: > > Many skeletal muscles contain muscle spindles which help to regulate the > tension output of the muscle. Muscle spindles have been identified (in very > small numbers) in the diaphragm, but are probably most importantly found in > intercostal muscle fibers. This feedback system helps to deliver the > appropriate amount of tension necessary for a certain mechanical load. As > the load changes, for example by a sudden increase in airway resistance or a > change in chest wall compliance, the inspiratory muscle output from the > anterior horn of the spinal cord is augmented (increased). > > The major components of this feedback control system are the tension > generating muscle fibers (extrafusal m. fibers), the muscle fibers which > contain a nuclear bag structure and an annulospiral ending (intrafusal m. > fibers), a gamma efferent motor neuron fiber to the intrafusal m. fiber, an > alpha motorneuron fiber to the extrafusal m. fiber, and an afferent spindle > fiber. The major regulation occurs when there is tension on the nuclear bag. > This induces firing of the annulospiral ending which sends afferent nerve > traffic, through the dorsal root, to augment the output of the anterior horn > cells. Although this system is more complicated than presented here, the > basic plan is as follows. > > The a-motorneurons are excited by descending UMNs that originate in > brainstem structures previously described, and this serves to initiate > contraction of the effector muscles (e.g., intercostal muscles). If the > tension generated is sufficient to shorten the muscle, then both the > intrafusal and extrafusal muscles shorten together, the nuclear bag is not > stretched, and there is no discharge from the annulospiral endings. If, > however, the tensions generated is insufficient to produce shortening of the > muscle, the intrafusal muscle fibers develop tension and stretching of the > nuclear bag causes discharge from the annulospiral endings. This afferent > signal is conveyed to the spinal cord via the dorsal root, and anterior horn > cell activity is increased (increased a-motorneuron output) to match the > amount of tension generated with mechanical load. In this way, the muscles > can balance their tensions output with the mechanical load. > > > > -- > The silver-list is a moderated forum for discussion of colloidal silver. > > Instructions for unsubscribing may be found at: http://silverlist.org > > To post, address your message to: [email protected] > > Silver-list archive: http://escribe.com/health/thesilverlist/index.html > > List maintainer: Mike Devour <[email protected]> > >
