Okay so this tutorial is on the back muscles. If you want to learn a bit more in detail about the back muscles, look at my individual tutorials on the extrinsic muscles of the back, and the intermediate and deep muscles of the back. I talk about innervation, insertion and all that kind of stuff in a bit more detail than I'm going to do here.

 

I'm just going to work from superficial to deep and point out some of the major muscles that you should know about.

 

Extrinsic Muscles

This muscle here is the trapezius, you probably all know this one, and this muscle elevates and depresses the scapula, and it can also retract the scapula.  that's the trapezius.

 

You've got the latissimus dorsi, which is Latin for "the broadest muscle of the back", and this is the biggest back muscle obviously. And this muscle inserts onto the humerus, it adducts, extends and internally rotates the humerus.

 

Just working our way deeper, just underneath the trapezius, you've got the rhomboids. The rhomboid major and the rhomboid minor. And these muscles attach to the scapula and they function to keep the scapula pressed against the thoracic wall, and when the trapezius is contracted they can retract the scapula.

 

Here you've got the levator scapulae, and this muscle as you can see it attaches to the top of the scapula and it elevates the scapula when it's contract, so that's the levator scapulae - these two muscles here.

 

Intermediate Muscles

Those muscles which I've just covered are the extrinsic muscles of the back, now we're going to be working our way deeper into the intermediate muscle layer, and here you've got the serratus posterior superior, and the serratus posterior inferior.

 

You can see these muscles they attach to the ribs and the superior one elevates the ribs and the inferior one depresses the ribs.  these are the intermediate muscles involved in respiratory function.

 

Deep Muscles

Now we've got the deep muscles of the back, the intrinsic muscles, which are responsible for the movement of the spine and the head. So you've got these spinotransversales muscles which move the head and neck; you've got the splenius capitis and the splenius cervicis - two spinotransversales muscles. This muscle here is the splenius capitis, and as you can see it inserts onto the skull.

 

What this muscle does, if both muscles are contracted, it draws the head backwards and extends the neck. If just one of the muscles is contracted, then it will rotate the head around to that side. So that's the splenius capitis. For some reason on this model, the splenius cervicis isn't shown, but this originates a little bit lower down and inserts onto the transverse process of the first vertebra.

 

Erector Spinae Muscles

So I'll get rid of those. So next we've got those muscles which move the vertebral column. You've got the erector spinae muscles and the transversospinales muscles. The erector spinae muscles are more superficial, so I'll begin with those. You've got three groups, so laterally you've got the iliocostalis - this one here. In the middle you've got the longissimus, and most medially you've got the spinalis.

 

An acronym...not an acronym - a mnemonic for remembering this is "I long for spinach" - "I" iliocostalis, "Long" longissimus, "Spinach" spinalis.

 

Laterally to medial, those are the erector spinae muscles, and these are the primary extensors of the vertebral column and head, and they're the largest group of intrinsic back muscles.

 

Transversospinales Muscles

Deep to the erector spinae muscles, you've got the transversospinales muscles.  you've got three transversospinales muscles. The semispinalis which is the most superficial. You've got the multifidus here. And then most deep you've got the rotares muscles.

 

That covers very briefly the muscles of the back, if you want to look in more depth at those, take a look the individual tutorials I've done on those various groups. But hopefully that's useful and just shows how which muscles are deep which muscles are superficial.

The major muscles of the back, from superficial to deep are divided in three groups: extrinsic, intermediate and intrinsic muscles. The general action of the back muscles allows movement in the head, shoulders, arms, and the spine they are also involved in movement of the ribs which allows for respiratory function. These groups are:

  • Extrinsic muscles (superficial)
    • Trapezius - actions: Elevates and depresses the scapula; Retract scapula.
    • Latissimus dorsi - Biggest muscle of the back. Inserts on to the humerus. Actions: Adducts, extends and internally rotates the humerus.
      • Rhomboids- Both attach to the scapula. Actions: keep scapula pressed against the thoracic wall; also can retract the scapula.
        • Rhomboid major
        • Rhomboid minor
      • Levator scapulae - attaches to the top of the scapula. Action: Elevates scapula
  • Intermediate Muscles- Attached to ribs; involved in respiratory function.
    • Serratus posterior superior: elevates ribs
    • Serratus posterior inferior: depresses ribs
  • Intrinsic Muscles (deep)
    • Spinotransversales:
      • Splenius capitus: contraction of both muscles extends the neck; contraction of one rotates head.
      • Splenius cervicus
    • Erector spinae: three groups (“I long for spinach”), lateral to medial:
      • illiocostalis: lateral
      • longissimus: in the middle
      • spinalis: medial
    • Transversospinales: three groups, from superficial to deep:
      • semispinalis
      • multifidus
      • rotares