Muscles innervated by the lateral branches of the dorsal/posterior rami include:

Question

BlackTom AI · Accepted Answer

Lateral branches of the posterior (dorsal) rami supply the more lateral and superficial intrinsic back muscles and the overlying skin, whereas the medial branches supply the deep, medial intrinsic muscles adjacent to the spinous processes. Key knowledge points: dorsal rami split into medial and lateral branches segmentally; medial branches typically innervate transversospinalis group members (multifidus, rotatores, interspinales) and suboccipital muscles, while lateral branches supply the erector spinae group (especially iliocostalis and longissimus) and the more laterally placed splenius group.

Step-by-step reasoning:
1. Identify each muscle’s location and typical innervation pattern.
   - Iliocostalis: the most lateral column of the erector spinae group; by position and function it is supplied by lateral branches of the dorsal rami. 
   - Splenius cervicis: a superficial/lateral posterior neck muscle (part of splenius group) lying lateral to the midline; it receives fibers from the lateral branches of cervical dorsal rami.
   - Semispinalis capitis: although belonging to the transversospinalis family, semispinalis capitis is a large muscle that lies more laterally and dorsally in the upper neck and often receives contributions from the lateral branches of the cervical dorsal rami (practically, its innervation pattern includes lateral-branch supply to its bulk).
2. Therefore, all three named muscles (semispinalis capitis, splenius cervicis, iliocostalis) are consistent with lateral-branch supply.

Why the other options are incorrect (brief):
- Option 1 (semispinalis cervicis, splenius cervicis, intertransversarii): intertransversarii are deep segmental muscles often innervated by medial branches (or segmental ventral rami depending on region); semispinalis cervicis is more medial.
- Option 3 (interspinales, spinalis, iliocostalis): interspinales and spinalis are medial, so this set is mixed and not characteristic of lateral-branch supply.
- Option 4 (multifidus, rotatores, sub-occipital group): these are classic targets of the medial branches of the dorsal rami, not the lateral branches.

Conclusion: based on the distribution of medial versus lateral branches of the dorsal rami and the anatomical positions of the listed muscles, the correct choice is Semispinalis capitis, Splenius cervicis, Iliocostalis, which matches the provided answer.

Muscles innervated by the lateral branches of the dorsal/posterior rami include:单项选择题

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