Question

Which of the following nerves is the pretrematic branch associated with the first pharyngeal (mandibular) arch?

• A. Facial nerve
• B. Recurrent laryngeal nerve
• C. External laryngeal nerve
• D. Chorda tympani

Hint:

Pretrematic nerve = branch of the next arch nerve supplying the previous archFor the first arch, the pretrematic branch is chorda tympani (from facial nerve).

Answer 1

The Correct Option is D

To determine which nerve is the pretrematic branch associated with the first pharyngeal (mandibular) arch, we need to understand some basic embryological concepts related to cranial nerve development.

The first pharyngeal (mandibular) arch in vertebrate embryology is associated with the mandibular nerve, which is a branch of the trigeminal nerve (Cranial Nerve V). Generally, the pretrematic branch of a nerve is the branch that innervates structures derived from a particular embryonic arch.

The chorda tympani is a branch of the facial nerve (Cranial Nerve VII), but it is considered to be the pretrematic branch associated with the first pharyngeal arch. Here is why:

• Chorda Tympani: The chorda tympani branches off the facial nerve, yet it serves sensory (taste) and secretomotor functions for the anterior two-thirds of the tongue, which is derived from the first pharyngeal arch. Hence, it is considered a pretrematic nerve for the first arch.
• Facial Nerve: While the chorda tympani is a branch of this nerve, the facial nerve itself does not innervate first arch derivatives primarily.
• Recurrent Laryngeal Nerve: This is a branch of the vagus nerve (Cranial Nerve X) and is associated with the fourth and sixth pharyngeal arches.
• External Laryngeal Nerve: This nerve is a branch of the superior laryngeal nerve (part of the vagus nerve) and does not associate with the first arch.

Therefore, the correct answer is the Chorda Tympani.

In conclusion, even though the chorda tympani is a branch of the facial nerve, it specifically fulfills the role of the pretrematic nerve for the first pharyngeal arch by its function and embryological development.