Transection at mid pons level results in:
Apneusis Apneusis is the best option. Read below? To understand the effect of transection at different levels of brainstem, let's first understand the neural mechanism regulating respiration. Two separate neural mechanisms regulate respiration. One is responsible for voluntary control and the other for automatic control. The voluntary system is located in the cerebral coex and sends impulses to the respiratory motor neurons the coicospinal tracts which bypass the pontomedullary centres and directly descend to the lower motor neurons supplying the muscles of respiration. This voluntary control is needed during willed respiration as found in activities like singing, whistling, blowing etc. Automatic control is exeed by the pontomedullary respiratory centres which enable smooth and unconscious execution of respiratory activities even when there is no voluntary effo. Medullary centres: (1) a dorsal respiratory group (DRG), located in the dorsal poion of the medulla, which mainly causes inspiration; (2) a ventral respiratory group (VRG), located in the ventrolateral pa of the medulla, which mainly causes forced expiration; It has been found that neither DRG nor VRG maintains the respiratory rhythm. Rhythmic respiration is initiated by a small group of pacemaker cells in the pre-Biitzinger complex (pre-BOTC) on either side of the medulla between the nucleus ambiguus and the lateral reticular nucleus. These neurons discharge rhythmically, and they produce rhythmic discharges in phrenic motor neurons. The medullary centres receive several inputs from the periphery, which may alter its activity. These are: a.Afferent impulses from carotid and aoic bodies i.e.the chemoreceptors carried by glossopharyngeal and vagus nerves respectively. Hypoxia, hypercapnia and acidosis stimulate respiration through them. Afferent impulses from the pulmonary stretch receptors, carried by the vagi. The stretch receptors are located in the walls of the brochi and bronchioles theoughout the lungs.They transmit signals through the vagi into the dorsal respiratory group of neurons when the lungs become overstretched.These signals affect inspiration in much the same way as signals from the pneumotaxic center; that is, when the lungs become overly inflated, the stretch receptors activate an appropriate feedback response that "switches off' the inspiratory ramp and thus stops fuher inspiration.This is called the Hering-Breuer inflation reflex. This reflex also increases the rate of respiration, as is true for signals from the pneumotaxic center. In human beings, the Hering-Breuer reflex probably is not activated until the tidal volume increases to more than three times normal (greater than about 1.5 liters per breath). Therefore, this reflex appears to be mainly a protective mechanism for preventing excess lung inflation rather than an impoant ingredient in normal control of ventilation. The depth of inspiration is increased after vagotomy. Pontine centres: Pneunzotaxic Center: It limits the duration of inspiration and increases the respiratory rate. A pneumotaxic center, located dorsally in the nucleus parabrachialis of the upper pons, transmits signals to the inspiratory area. The primary effect of this center is to control the "switch-off' point of the inspiratory ramp, thus controlling the duration of the filling phase of the lung cycle. When the pneumotaxic signal is strong, inspiration might last for as little as 0.5 second, thus filling the lungs only slightly; when the pneumotaxic signal is weak, inspiration might continue for 5 or more seconds, thus filling the lungs with a great excess of air. The function of the pneumotaxic center is primarily to limit inspiration. This has a secondary effect of increasing the rate of breathing, because limitation of inspiration also shoens expiration and the entire period of each respiration. A strong pneumotaxic signal can increase the rate of breathing to 30 to 40 breaths per minute, whereas a weak pneumotaxic signal may reduce the rate to only 3 to 5 breaths per minute. Apneustic centre: The actual existence of this centre is debated. It is supposed to excite the DRG and stimulate inspiration. The Pneumotaxic centre and vagi send inhibitory impulses to the apneustic centre and this shoens the inspiration. Now let's see the effects of transaction at different levels: A transection above the pons has no effect on respiration. B. A mid-pontine transection with the vagi cut eliminates the inhibitory influences of both pneumotaxic centre and the vagi on the apneustic centre. The uninhibited action of the aneustic centre results in apneusis. (apneusis is sustained, gasping inspiration followed by sho, inefficient expiration, which can continue to the point of asphyxia). When vagi are intact the respiration becomes slower and tidal volume greater. C. In transection at the pontomedullary junction respiration is maintained with slight irregularity. D. Transection below medulla causes stoppage of respiration completely. Also know: Ondine's curse Because voluntary and automatic control of respiration are separate, automatic control is sometimes disrupted without loss of voluntary control. The clinical condition that results has been called Ondine's curse. In German legend, Ondine was a water nymph who had an unfaithful moal lover. The king of the water nymphs punished the lover by casting a curse on him that took away all his automatic functions. In this state, he could stay alive only by staying awake and remembering to breathe. He eventually fell asleep from sheer exhaustion, and his respiration stopped. Patients with this intriguing condition generally have bulbar poliomyelitis or disease processes that compress the medulla.
Asphyxia
Hyperventilation
Rapid and shallow breathing
Apneusis