If the spinal cord is severed where it joins the brain stem, what would happen to breathing?

Options

A. Inspiration occurs while expiration stops
B. Expiration occurs while inspiration stops
C. The length of inspiration increases abruptly
D. Both inspiration and expiration cease

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the consequences of severing the spinal cord at the point where it joins the brain stem, specifically regarding the process of breathing.

2. **Role of the Spinal Cord and Brain Stem**: The spinal cord is a crucial part of the central nervous system that connects the brain to the rest of the body. The brain stem, which includes the medulla and pons, is responsible for regulating vital functions, including breathing.

3. **Breathing Process**: Breathing consists of two main phases:
- **Inspiration**: The process of taking air into the lungs.
- **Expiration**: The process of expelling air from the lungs.
These processes are regulated by signals from the brain.

4. **Regulation of Breathing**: The medulla oblongata (part of the brain stem) contains the respiratory rhythm center, which controls the rate and depth of breathing. The pons also plays a role in regulating breathing patterns.

5. **Effect of Severing the Spinal Cord**: If the spinal cord is severed at the junction with the brain stem, the communication between the brain and the body is disrupted. This means that the brain cannot send signals to the muscles involved in breathing.

6. **Conclusion**: Without the connection between the brain and the respiratory muscles, both inspiration and expiration will cease. Therefore, the correct answer is that both processes of breathing will stop.

### Final Answer:
If the spinal cord is severed where it joins the brain stem, both inspiration and expiration will cease.