Which of the following nerves stress not contain parasympathetic motor fibres

## **Core Concept**
The question tests knowledge of the autonomic nervous system, specifically the distribution of parasympathetic motor fibers. The parasympathetic nervous system is one of the branches of the autonomic nervous system, which also includes the sympathetic nervous system. Parasympathetic motor fibers are primarily involved in promoting digestion, reducing heart rate, and conserving energy.

## **Why the Correct Answer is Right**
The correct answer, **D.**, implies that the nerve in question does not contain parasympathetic motor fibers. To accurately address this, we need to consider the nerves listed and their composition. Typically, parasympathetic motor fibers are found in cranial nerves III, VII, IX, and X, as well as in the sacral spinal nerves S2-S4. If the options provided relate to nerves that do or do not carry these fibers, the correct answer would correspond to a nerve that does not have parasympathetic motor fibers.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option would be incorrect if it represents a nerve known to carry parasympathetic motor fibers, such as the vagus nerve (cranial nerve X), which carries significant parasympathetic fibers to various abdominal and thoracic organs.
- **Option B:** Similarly, if this option represents another nerve with parasympathetic motor fibers, such as the facial nerve (cranial nerve VII) which carries fibers to glands in the face and to the submandibular and sublingual salivary glands, it would be incorrect.
- **Option C:** This would also be incorrect if it corresponds to a nerve with parasympathetic fibers, such as the glossopharyngeal nerve (cranial nerve IX), which carries parasympathetic fibers to the parotid gland.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the **vagus nerve (cranial nerve X)** is a major nerve that carries parasympathetic fibers to many organs in the thorax and abdomen. The **sacral nerves S2-S4** are also crucial for parasympathetic outflow to the pelvic organs. When considering nerves that do not contain parasympathetic motor fibers, one should think of nerves primarily involved in somatic functions or sympathetic functions.

## **Correct Answer:** .