Transection of the brain stem at the mid-pontine level with bilateral vagotomy causes ______
**Core Concept**
Transection of the brain stem at the mid-pontine level disrupts the normal respiratory control centers, leading to an alteration in breathing patterns. The mid-pontine level transection affects the pneumotaxic center, which is responsible for regulating the rate and depth of breathing.
**Why the Correct Answer is Right**
Transection at the mid-pontine level causes apneusis, a breathing pattern characterized by prolonged inspiratory efforts followed by brief expiratory pauses. This occurs due to the loss of the pneumotaxic center's inhibitory influence on the inspiratory area of the ventral respiratory group. The pneumotaxic center normally helps to regulate the inspiratory phase of breathing, and its loss leads to prolonged inspirations. Bilateral vagotomy further disrupts the normal respiratory pattern by eliminating the afferent input from the lungs.
**Why Each Wrong Option is Incorrect**
**Option A:** Ceasation of spontaneous respiration would be more likely with a transection at a higher level, such as the pontomedullary junction, which would disconnect the entire respiratory control system.
**Option B:** Continuation of regular breathing is not possible with a mid-pontine transection, as the pneumotaxic center is crucial for regulating the rate and depth of breathing.
**Option C:** Irregular but rhythmic respiration might occur with a lower brain stem lesion, such as a medullary lesion, which would affect the dorsal respiratory group.
**Clinical Pearl / High-Yield Fact**
The pneumotaxic center is located in the upper pons and plays a critical role in regulating the inspiratory phase of breathing. Lesions affecting this area can lead to abnormal breathing patterns, including apneusis.
**✓ Correct Answer: D. Apneusis**