Transection at mid pons level results in?
**Core Concept**
The mid pons level is a critical region in the brainstem that plays a significant role in controlling various autonomic functions, including respiration, cardiovascular regulation, and temperature control. Transection at this level can lead to significant alterations in these functions.
**Why the Correct Answer is Right**
Transection at the mid pons level results in the loss of pontine respiratory centers, including the pneumotaxic center and the apneustic center. The pneumotaxic center helps regulate the rate of breathing, while the apneustic center prolongs inspiration. Without these centers, breathing becomes irregular and shallow, leading to ataxic breathing. Additionally, the mid pons level also contains the parasympathetic preganglionic neurons that regulate heart rate and blood pressure. The loss of these neurons results in unopposed sympathetic tone, leading to tachycardia and hypertension.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because transection at the mid pons level does not result in the loss of cranial nerve nuclei controlling facial expression, which are located in the lower pons.
**Option B:** This option is incorrect because transection at the mid pons level does not result in the loss of the lateral spinothalamic tract, which is responsible for transmitting pain and temperature sensations. This tract is located in the spinal cord.
**Option C:** This option is incorrect because transection at the mid pons level does not result in the loss of the medial longitudinal fasciculus, which is a bundle of nerve fibers that coordinates eye movements. This structure is located in the midbrain.
**Clinical Pearl / High-Yield Fact**
The mid pons level is a critical region for controlling autonomic functions, and transection at this level can lead to significant alterations in breathing patterns and cardiovascular regulation.
**Correct Answer: D. Ataxic breathing with tachycardia and hypertension.**