Which of the following is the odd one out in terms of motor innervation by ventral/anterior rami?

Question

BlackTom AI · Accepted Answer

Splenius group is innervated by dorsal (posterior) rami, not ventral (anterior) rami, so it is the odd one out.

1) Relevant knowledge points and concepts
- Spinal nerves split into dorsal (posterior) and ventral (anterior) rami after leaving the intervertebral foramen.
- Dorsal rami supply intrinsic (deep) back muscles and skin over the back.
- Ventral rami supply limb muscles, anterolateral trunk muscles, and many neck muscles (including prevertebral and scalene groups) via cervical and brachial plexuses or thoracoabdominal nerves.

2) Step-by-step reasoning
- Determine typical motor innervation for each option.
  - Anterior abdominal wall muscles (e.g., rectus abdominis, external oblique): innervated by thoracoabdominal nerves (continuations of ventral rami T7–T11 and subcostal T12) → ventral rami.
  - Scalene group (anterior, middle, posterior scalene): innervated by cervical ventral rami (C3–C8 branches) → ventral rami.
  - Prevertebral group (longus colli, longus capitis): innervated predominantly by branches from cervical ventral rami (direct anterior rami contributions) → ventral rami.
  - Splenius group (splenius capitis and splenius cervicis): innervated by dorsal rami of middle cervical nerves (posterior rami of cervical spinal nerves) → dorsal rami.

3) Intermediate steps (explicit mapping)
- Anterior abdominal wall: thoracoabdominal nerves = ventral rami T7–T11, T12.
- Scalenes: cervical ventral rami (e.g., C4–C6 contributions depending on source).
- Prevertebrals: ventral rami fibers to longus colli/capitis.
- Splenius: dorsal rami (posterior primary rami) of cervical nerves.

4) Why the correct answer is correct
Because splenius muscles receive motor supply from dorsal rami, while the other three groups are supplied by ventral/anterior rami. This difference in the branch of the spinal nerve makes splenius the odd one out.

5) Why the other options are incorrect
Each of the other listed groups (anterior abdominal wall, scalene, prevertebral) is supplied by ventral/anterior rami, so they share the same type of innervation and are not the odd one out.

6) Conclusion
Therefore the correct odd one out is Splenius Group, which matches the provided answer.

Which of the following is the odd one out in terms of motor innervation by ventral/anterior rami?单项选择题

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