Which letter is labelling a muscle or group of muscles innervated by medial branches of dorsal (posterior) rami?

Question

BlackTom AI · Accepted Answer

Medial branches of the dorsal (posterior) rami supply the deep intrinsic (paraspinal) muscles that lie closest to the spinous processes — principally the transversospinalis group (semispinalis, multifidus, rotatores) and the short intersegmental muscles (interspinales, intertransversarii). Lateral branches supply the more lateral erector spinae (longissimus, iliocostalis) and overlying skin.

1) Relevant knowledge points and concepts
- Dorsal rami of spinal nerves divide into medial and lateral branches.
- Medial branches innervate the deep, medial intrinsic back muscles (transversospinales and interspinal muscles).
- Lateral branches innervate the more superficial/lateral erector spinae and lateral skin.

2) Step-by-step reasoning
- Identify which labeled region corresponds to muscles immediately adjacent to the midline spinous processes (these are the ones medial branches supply).
- On the dissection image, label A is located in the upper midline/paramedian neck area over the deep column of short, segmented muscles (semispinalis and other transversospinales fibers).
- Labels B, D and E are placed more laterally over the long vertical muscle bundles (erector spinae group) or over scapular/shoulder muscles, which are typically supplied by lateral branches or by other nerves (e.g., accessory nerve for trapezius, dorsal scapular for levator scapulae).

3) Intermediate identification/calculations
- No numeric calculation required; anatomical mapping: medial branch → deep medial muscle column (A); lateral branch → lateral column (B/D/E).

4) Why the correct answer is correct
- A sits over the deep, medial intrinsic back muscles (transversospinalis group) — the classic targets of medial branches of the dorsal rami. Therefore A correctly labels muscles innervated by medial branches.

5) Briefly why other options are incorrect
- B marks more lateral, long vertical fibers of erector spinae (longissimus/iliocostalis) innervated predominantly by lateral branches.
- C is over shoulder/neck superficial muscles (e.g., trapezius/levator scapulae) innervated by other nerves (accessory or dorsal scapular).
- D/E are lateral back or shoulder region muscles (latissimus/serratus/other superficial muscles) not primarily supplied by medial dorsal rami.

6) Conclusion
This anatomical distribution confirms that the muscle/group labeled A is innervated by the medial branches of the dorsal rami. Final answer: A.

Which letter is labelling a muscle or group of muscles innervated by medial branches of dorsal (posterior) rami?Single choice

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