Back Muscles - Intrinsic Superficial & Intermediate

Intrinsic Back Muscles: Superficial & Intermediate Layers The muscles of the back can be broadly separated into intrinsic and extrinsic groups, based on their embryological origins and functional roles. The intrinsic muscles can be further divided into deep, intermediate, and superficial layers: The intermediate intrinsic muscles are collectively referred to as the erector spinae. The superficial intrinsic back muscles comprise the two splenius muscles; we'll show these in our main diagram. The intrinsic muscles are enclosed in the deep fascia of the back, which runs from the nuchal ligament to the sacrum; these muscles are responsible for movements of the vertebral column. The deepest muscles are collectively referred to as the transversospinalis muscles, and we'll discuss them in detail, separately. Note the nuchal ligament, which is an important attachment site in this tutorial: the nuchal ligament (aka, ligamentum nuchae), which is thick, strong ligament that extends inferiorly from the external occipital protuberance of the skull over the spinous processes of the cervical vertebrae; at C7, it thins out and continues as the supraspinous ligament. These muscles are thick and flat, and cover the back and sides of the neck; it's helpful to remember that "splenius" comes from the Latin word "splenion," which means bandage – these muscles travel superolaterally from the midline and wrap around the neck like a bandage. Splenius cervicis Arises from the spinous processes of thoracic vertebrae 3-6 and inserts on the transverse processes of cervical vertebrae 1-3. When contracted bilaterally, splenius cervicis extends the neck; unilateral contraction turns the head to the same side. Cervicis" refers to the neck; splenius cervicis acts on the neck. Splenius capitis Then, superior to splenius cervicis, show that splenius capitis arises from the nuchal ligament and the spinous processes of C7-T4 and extends to insert on the mastoid process of the skull and below the nuchal line. When contracted bilaterally, splenius capitis extends the neck and the head (thanks to its insertion on the skull); unilateral contraction turns the head to the same side. "Capitis" refers to the head; splenius capitis acts on both the head and neck. The erector spinae comprise three groups of overlapping, multipart muscles that arise from a common tendon that spans the low back; together, produce back extension when contracted bilaterally, and lateral flexion when contracted unilaterally. Includes: Spinalis, Longissimus, and Iliocostalis. The cervical portion arises from the nuchal ligament and the spinous process of C7 and inserts on the spinous process of C2. The thoracic portion arises from the spinous processes of T11 and T12 and inserts on the spinous processes of T2-T8. The name "spinalis" helps us remember that these muscles insert on the spinous processes of the vertebrae. Arises from the tendon that attaches to the posterior iliac crest, sacrum, and spinous processes of the lumbar vertebrae; it inserts on the lower ribs, transverse processes of the cervical and thoracic vertebrae, and the mastoid process. Notice that longissimus runs from the low back to the skull; its name means "the longest one" – it's the longest of the erector spinae. Arises from the common tendon and inserts on the lower ribs and transverse processes of cervical vertebrae. Its name gives us its origin (ilo = ilium) and its insertion (costalis = ribs). If we can remember that spinalis lies closest to the spine, the mnemonic "I like spaghetti" can help us remember the order of the erector spinae from lateral to medial: Iliocostsalis (i), longissimus (like), spaghetti (spinalis). These muscles comprise many short segments of muscle fibers. The erector spinae muscles are prone to injury as a result of improper heavy lifting. When contracted bilaterally, the erector spinae muscles extend the back; Unilateral contraction produces lateral flexion of the back (moves the shoulder towards the lateral hip of the same side). The erector spinae muscles can be further subdivided according to vertical region: For example, the portion of iliocostalis that lies within the lumbar region is referred to as iliocostalis lumborum; the portion of spinalis that lies with the thoracic region is referred to as spinalis thoracis, and so on.