Which of the following are inactive during normal respiration ?
Ans. is 'c' i.e., Ventral group of neurons Medullary respiratory centers The principal areas in the medulla oblongata concerned with regulation of respiration are : ? 1) Dorsal respiratory group (DRG) : - The dorsal respiratory group of neurons are mainly concerned with inspiration. They descend and terminate on spinal motor neurons innervating the primary muscles of inspiration, i.e., the diaphragm and the external intercostal muscles. 2) Ventral respiratory group (VRG) : - The ventral respiratory group of neurons is mainly concerned with forceful expiration but also shows some activity during inspiration. Therefore, these neurons contribute to both expiration and inspiration. These neurons are divided into : ? i) The rostral VRG neurons : - These neurons show activity primarily synchronous with inspiration and therefore be called inspiratory (I) neurons. They terminate on spinal motor neurons supplying the accessory muscles of inspiration, i.e., sternocleidomastoid, scalenes and anterior serrati. ii) The ventral VRG neurons : - These are mostly expiratory (E) neurons. But since the expiration is generally a passive process, E neurons are silent most of the time. However, these neurons show activity when expiration is forceful, as during exercise. These neurons terminate on spinal motor neurons supply the muscles of expiration, i.e., internal intercostal and abdominal muscles. 3) Pre-Botzinger complex : - These neurons are responsible for generation of respiratory rhythm, i.e., the pacemaker cells which regulate the rate of respiration are located in Pre-Botzinger complex. Pontine respiratory centers The impoant pontine areas concerned with respiration are : ? 1) Pneumotoxic center (nucleus parabrachialis medialis) : - It is located in upper pa of pons and transmits signals to the inspiratory area. The function of the pneumotaxic center is primarily to limit inspiration, i.e., the primary effect of this center is to control the "switch-off" point of the inspiratory ramp thus controlling the depth of inspiration, i.e., the duration of the filling phase of the lung cycle. Pneumotaxic center also inhibits apneustic center fuher inhibiting inspiration. Therefore strong stimulation of this center results in an early termination of inspiratory ramp and hence, inspiration is shoened and the tidal volume decreases. Conversely, in the absence of inputs from this center, inspiratory ramp continues much longer and hence inspiration is prolonged and the tidal volume increases. 2) Apneustic center : - This center located in the lower (caudal) pa of pons. The apneustic center excites inspiratory center (DRG) and produce a prolonged inspiratory drive which delays the onset of expiration. Thus, though the respiratory rhythm is established in the medulla, this rhythm is spoilt by a strong inspiratory drive orginating in the apneustic centers. However, two influences seems to keep the apneustic center in check : (i) Pneumotaxic center of upper pons and (ii) Influence from stretch receptors in lung vagus. Both of these influence inhibit inspiratory activity.
Pre-Botzinger complex
Dorsal group of neurons
Ventral VRG group of neurons
Pneumotaxic center