Questions: The dorsal respiratory group is located dorsally at the root of cranial nerve IX extends from the brain stem is located in the pons ends at the pons-medullary junction

The answer is the first one: the original text in the question states that the dorsal respiratory group is located dorsally at the root of cranial nerve IX.

Explanation for each option:

1. The dorsal respiratory group is located dorsally at the root of cranial nerve IX: This is correct. The dorsal respiratory group (DRG) is indeed located in the medulla oblongata, specifically in the dorsomedial region at the root of cranial nerve IX (the glossopharyngeal nerve).

2. Extends from the brain stem: This statement is somewhat vague. While the DRG is part of the brainstem, it does not "extend" from it; rather, it is a specific group of neurons within the brainstem.

3. Is located in the pons: This is incorrect. The DRG is located in the medulla oblongata, not the pons. The pons contains other respiratory centers, such as the pneumotaxic center.

4. Ends at the pons-medullary junction: This is also incorrect. The DRG is situated within the medulla oblongata and does not extend to the pons-medullary junction.

Summary: The dorsal respiratory group is located dorsally at the root of cranial nerve IX. This group of neurons plays a crucial role in the regulation of breathing by integrating sensory information and influencing the activity of the respiratory muscles.