Which cranial nerve innervates the geniohyoid muscle?

Question

BlackTom AI · Accepted Answer

The geniohyoid is innervated by fibers of the first cervical spinal nerve (C1) that travel with the hypoglossal nerve (CN XII), so the supplying cranial nerve is considered CN XII.

1. Relevant knowledge points and concepts
- The geniohyoid is a suprahyoid muscle that runs from the genial tubercle of the mandible to the hyoid bone; it elevates and protracts the hyoid and shortens the floor of the mouth.
- Motor supply to some neck muscles can come from cervical spinal nerves that "hitchhike" along cranial nerves. For geniohyoid, C1 fibers travel with CN XII.
- Distinguish this from other suprahyoid muscles: mylohyoid and anterior belly of digastric (mylohyoid nerve, V3), posterior digastric and stylohyoid (facial nerve, VII).

2. Step-by-step reasoning
- Motor fibers originate from the ventral ramus of the first cervical spinal nerve (C1).
- These C1 fibers join the hypoglossal nerve shortly after it exits the skull (they run in company with CN XII).
- The C1 fibers then leave the hypoglossal nerve as a branch to supply the geniohyoid.
- Because the motor fibers travel with CN XII, the geniohyoid is classically described as being innervated by the hypoglossal nerve.

3. (No numerical calculations required.)

4. Why the correct answer is correct
- Anatomical dissections and standard neuroanatomy texts show that geniohyoid motor innervation is provided by C1 fibers conveyed via the hypoglossal nerve; clinically, lesions that interrupt CN XII course can affect geniohyoid function because those C1 fibers run with it.

5. Why the other options are incorrect
- Facial nerve (CN VII): innervates posterior digastric and stylohyoid, not geniohyoid.
- Spinal accessory (CN XI): supplies sternocleidomastoid and trapezius, not suprahyoid muscles.
- Trigeminal (CN V): the mandibular division (V3) via the mylohyoid nerve supplies mylohyoid and anterior digastric, not geniohyoid.

6. Conclusion
Therefore, the correct cranial nerve is the hypoglossal nerve (CN XII), which matches the provided answer.

Which cranial nerve innervates the geniohyoid muscle?单项选择题

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