Intrinsic Postvertebral Muscles

Okay, I should probably stop soon and focus on cramming for those embryo slides, since that's what the test is going to be focused on. But oh well.

Vertebral Ligaments

First, I'm going to touch on the vertebral ligaments. I've touched on the annulus fibrosus, the outer layers of which join the endplates of adjacent vertebrae together. Here's a list of some others:

• Anterior longitudinal ligament- runs all the way up the anterior side of the vertebral bodies. Multisegmental (i.e. crosses many segments).
• Posterior longitudinal ligament- runs all the way up the posterior side of the vertebral bodies. Multisegmental.
• Ligamentum flavum- joins the laminae of adjacent vertebrae. "Flavum" means "yellow," and it refers to the yellow-looking elastic tissue that makes up this ligament. The elasticity means that it doesn't buckle into the spinal cord, which is pretty important.
• Intertransverse ligament- connects the transverse processes of adjacent vertebrae.
• Capsular ligament of zygapophysial joints- surrounds the joints I guess?
• Interspinous ligament- joins the spinous processes of adjacent vertebrae.
• Supraspinous ligament- runs along the tips of the vertebrae. Multisegmental.

Unisegmental

The three unisegmental muscles are, as their name suggests, muscles that only run between one segment. The intertransverse muscle pretty much runs along with the intertransverse ligament and the interspinous muscle pretty much runs along with the interspinous ligament. The third unisegmental muscle, the levatores costarum, lifts the ribs.

Transversospinales

Transversospinales are muscles that run from a transverse process UP to a spinous process of a vertebra above it. There are three main types.

Rotatores muscles, found only in the thoracic region, run from a transverse process to the spinous process of a vertebra 1 or 2 segments above the first. Their fibres are almost horizontal. As their name suggests, they are good at rotating things.

Multifidus muscles are found everywhere in the vertebral column, but are less important in the thorax. They cross 3 or 4 segments.

Finally, semispinalis muscles, found only in the upper back, cross 5 or 6 segments.

Erector spinae

The erector spinae muscles run longitudinally up the spine. They all begin inferiorly as the sacrospinalis tendon, and each fibre runs 6 segments before "passing the baton" to another fibre which runs up another 6 segments. Spinalis muscles attach to the spinous processes, longissimus muscles attach to the transverse processes and iliocostalis muscles attach to the ribs (costalis = ribs).

Before I move on, I'm just going to quickly mention a few more points. All of the muscles that I have spoken about so far are known as the intrinsic postvertebral muscles. They are all derived from the epimere, and therefore their nerve supply is from the dorsal rami.

There is one more muscle that is derived from the epimere. It's not part of the erector spinae, but I don't know where else to put it so I'm going to put it here. It's called the splenius. The splenius, in contrast to the transversospinales, is a spinotransverse muscle. That means that it runs from the spinous process of a vertebra UP to the transverse processes. They arise from the upper thoracic and cervical spinous processes. The splenius cervicis, which is the lower part, inserts on the transverse processes of C1 to C4. The splenius capitus, which is the upper part, goes up to the nuchal line of the skull.

Other muscles derived from hypomere

Aside from the above muscles derived from the epimere, there are several muscles derived from the hypomere. Some of the deeper ones include the serratus posterior superior and serratus posterior inferior. These go from the upper 4 or lower 4 thoracic spinous processes to the upper 4 or lower 4 ribs, respectively. Of course, there are many other muscles involved, like the obliques and stuff, but I won't go into those now.

The thoracolumbar fascia

The thoracolumbar fascia is a sheet of connective tissue that encloses the intrinsic postvertebral muscles in the thoracic and lumbar regions (hence "thoraco" and "lumbar"). In the thorax, the fascia is thin and stretchy to accommodate breathing, but in the lumbar region it's tougher (in order to provide stability) and has three layers. The posterior layer attaches to the spinous processes, the middle layer attaches to the transverse processes and the anterior layer attaches to the vertebral bodies. The three layers all meet laterally to the vertebrae, and then continue on to form the transversus abdominus, which is one of the muscles of the abdominal wall. The muscles I have talked about so far (well, aside from the serratus posterior) are enclosed within the middle and posterior layers. Between the anterior and middle layers lie two more muscles: the anterior one is the psoas, whereas the posterior one is the quadratus lumborum.

Aaaaand now I should take a break from stressing about muscles! (Now I'm just going to stress about something else instead... bugger.)