What is correct about spinal nerves

Options

A. These are all mixed nerves
B. Some are sensory and others are motor nerves
C. all vertebrates have only 12 pairs of spinal nerves
D. Both (1) and (3)

Answer

### Step-by-Step Solution:

1. **Understanding Spinal Nerves**: Spinal nerves are part of the peripheral nervous system and emerge from the spinal cord. Each spinal nerve is formed by the combination of motor and sensory fibers.

2. **Identifying the Nature of Spinal Nerves**: The first statement claims that spinal nerves are mixed nerves. This is correct because spinal nerves contain both sensory (afferent) and motor (efferent) fibers. They transmit signals to and from the spinal cord.

3. **Evaluating Other Statements**:
- The second statement suggests that some spinal nerves are purely sensory while others are purely motor. This is incorrect. All spinal nerves are mixed; they do not exist as purely sensory or purely motor.
- The third statement claims that all vertebrates have only 12 pairs of spinal nerves. This is also incorrect. The number of spinal nerve pairs varies among vertebrates. For example, humans have 31 pairs of spinal nerves.

4. **Conclusion**: Based on the evaluation of the statements, the correct answer is that spinal nerves are mixed nerves, which aligns with the first statement.

### Final Answer:
The correct statement about spinal nerves is: **They are mixed nerves.**

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