Intermediate and Deep Muscle Layers of the Back

You might recall that way back in Lesson 1 we examined the superficial layer of muscles of the back and they consisted of the:

  • trapezius
  • latissimus dorsi
  • rhomboid major
  • rhomboid minor
  • levator scapulae

Once these muscles were reflected, the intermediate layer of muscles can be seen. This layer consists of two muscles that act on the ribs and are, therefore, related to the thorax in function.

Intermediate back muscles

  • serratus posterior superior
  • serratus posterior inferior
serratus posterior muscles

Deep Muscles of the Back

The deep muscles of the back (intrinsic muscles) are responsible for keeping the body in the erect position during the waking hours, whether sitting or standing. You can imagine the amount of work that is placed on these muscles and why one of the population's most annoying medical problems is a painful back. You can also imagine how much money is spent to correct back problems. A correct posture and careful use of the back in carrying or picking up heavy objects is all that is necessary to allay most of back problems. The erector spinae group of muscles are the strongest muscles in the back and take on most of the work. The deep back muscles are both extensors and rotators of the axial skeleton. They are supplied segmentally by dorsal rami of the spinal nerves. Because of this segmental innervation, multiple injections of anesthetic are needed to relax these muscles.

Deep Back Muscles

  • erector spinae
    • iliocostalis (1)
    • longissimus (2)
    • spinalis (3)
  • splenius
    • capitis
    • cervicis
erectorspinae muscle splenius muscle
  • semispinalis
    • cervicis
    • capitis
semispinalis capitis muscle
  • suboccipital
    • rectus capitis posterior major
    • rectus capitis posterior minor
    • inferior oblique
    • superior oblique
  • small deep muscles
    • interspinous
    • intertransverse
    • levator costalis (not shown)
    • rotators (not shown)
suboccipital muscles intertransvers & spinous muscles
Skeleton of the Back Spinal Cord & Coverings


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