Video: Deep muscles of the back

Sigh! Isn’t this ballet dancer just beautiful? When we’re dancing, I’m pretty sure, we all like to think we have the posture and pose of a ballet dancer, but in reality, we’re not all so blessed. I bet you’re thinking ballet dancers must have some pretty strong back muscles to support that beautiful arched spine and, to be honest, you’d be pretty right. But the muscles you can see in this image are only part of the picture. What we’re interested in today is what’s beneath this top layer of muscle as we uncover the deep muscles of the back.

As you might have guessed, there’s more to the muscles of the back than meets the eye. The layer of muscle that we can see on the backs of our friends and family around us is the layer known as the superficial or extrinsic back muscles. These include all the muscles you see popping during back day at the gym, but beneath that layer is a group of deep layer muscles known as the deep or intrinsic muscles of the back.

Like many things in anatomy, deep muscles of the back can sometimes be split into a series of groups in an effort to help us learn and memorize them. However, being the big, diverse and wonderful world of humans that we are, different schools of anatomy approach this division differently. One way of approaching the division of the intrinsic back muscles is through dividing the muscles into two longitudinal tracts – a medial tract, which involves the muscles that are closest to the vertebrae and, a lateral tract, which involves the muscles that are a little more lateral.

The other way of approaching the division of deep back muscles is by dividing them into layers. This division gives us four layers – a superficial layer, an intermediate layer, a deep layer, and, finally, the deepest layer. The division of the intrinsic back muscles into tracts is usually found in some European textbooks while the division of the intrinsic back muscles into layers is usually found in English language textbooks.

In this tutorial, we’re going to be using the division into layers as it’s more commonly used in popular textbooks, but don’t worry, if you’re feeling like learning the intrinsic back muscles via tracts, the attachments, innervation, and functions remain the same, you can just regroup them in your notes as we work through the muscles.

So as we have a lot to cover, let’s begin with the superficial layer.

So we mentioned earlier that the superficial layer of the intrinsic back muscles is made up of the spinotransverse group of muscles, which itself is made up of two muscles – the splenii muscles which are the splenius capitis and the splenius cervicis. We’re going to begin by looking at the splenius capitis.

The splenius capitis muscle has its origin on the spinous processes of the C7 to T3 vertebrae as well as the nuchal ligament. It inserts on the lateral part of the superior nuchal line which is found on the occipital bone and the mastoid process which is found on the temporal bone. It receives innervation from the lateral branches of the posterior rami of the spinal nerves C1 to C6. In terms of its functions, the bilateral contraction of this muscle extends the cervical spine and head while the unilateral contraction flexes and rotates the head to the same side.

The splenius cervicis muscle has its origins on the spinous processes of the third to sixth thoracic vertebrae and inserts on the transverse processes of the cervical vertebrae C1 to C3. Like the splenius capitis, it is also innervated by the lateral branches of the posterior rami of the spinal nerves C1 to C6. And again, like the splenius capitis, bilateral contraction results in the extension of the cervical spine and the head while unilateral contraction of this muscle also flexes and rotates the head to the same side.

Okay, so that’s it for the superficial layer of the deep back muscles. Let’s move on to the intermediate layer.

The intermediate layer of the intrinsic muscles of the back consists of a major muscle group called the erector spinae muscle. And just to confuse us a little, the erector spinae muscle can be divided into three muscles which form columns within the muscle. The lateral column is made up of the iliocostalis muscle, the intermediate column is made up of the longissimus muscle, and the medial column is made up of the spinalis muscle. And just to make things even more complicated, each of these muscles can be further broken down into smaller muscles that are associated with the region of the vertebrae that they’re connected to – for example, cervical, thoracic, and lumbar, but we’ll discuss each of these divisions as we go along. But don’t worry, there’s nothing we can’t handle, let’s proceed gently with the lateral column and have a look at the iliocostalis muscle.

The iliocostalis muscle, our lateral column, can be divided into three parts. The cervical part of the muscle is known as the iliocostalis cervicis. It has its origins on the angle of the third to sixth ribs and inserts on the transverse processes of the fourth to sixth cervical vertebrae. The thoracic part of the muscle, known as the iliocostalis thoracis, has its origins on the angle of the seventh to twelfth ribs and inserts on the angles of the first to sixth ribs. And the lumbar part of this muscle is known as iliocostalis lumborum. It has its origins on the lateral crest of the sacrum, the medial end of the iliac crest, and the thoracolumbar fascia. It inserts on the angle of the sixth to twelfth ribs, the deep layer of the thoracolumbar fascia, and on the transverse processes of the vertebrae L1 to L4.

Although this muscle can be broken into three parts based on their origins and insertions, the entire muscle is generally innervated by the lateral branches of the posterior rami of spinal nerves C4 to C8. While the bilateral contraction of the entire iliocostalis muscle extends to the spine, unilateral contraction results in the bending of the spine laterally to the same or ipsilateral side.

The next muscle in the erector spinae is the longissimus muscle. The longissimus muscle is situated medial to the iliocostalis muscle. Like the iliocostalis, the longissimus muscle has three parts. The most superior part of the muscle – the longissimus capitis – has its origins on the transverse processes of the fourth cervical vertebra to the fifth thoracic vertebra. It inserts superiorly on the mastoid process of the temporal bone.

The middle part of this muscle – the longissimus cervicis – has its origins on the transverse processes of the first to sixth thoracic vertebrae and inserts superiorly on the transverse processes of the second to sixth cervical vertebrae. And the most inferior part of this muscle which is the thoracic part is known as the longissimus thoracis. It has its origins on the medial end of the iliac crest, the lateral crest of the sacrum, and the spinous and transverse processes of vertebrae L1 to L5. It inserts on the transverse processes of the vertebrae of T1 to T12 and the angles of the fifth to twelfth ribs.

The longissimus muscle receives innervation from the lateral branches of the posterior rami of spinal nerves C1 to L5. The bilateral contraction of the entire longissimus muscle extends the spine while unilateral contraction bends the spine laterally to the same side. The most superior part of this muscle – the longissimus capitis – extends the head and neck when it contracts bilaterally and laterally flexes and rotates the head to the same side upon unilateral contraction.

The last muscle of the erector spinae is the spinalis muscle, and there are three parts to this muscle. The superior part of this muscle is the spinalis capitis, which has its origins on the spinous processes of C7 – T1 vertebrae and inserts on the occipital bone at the midline.

The middle part of the muscle is the spinalis crevices and has its origins on the spinous processes of vertebrae C7 to T1 as well as the nuchal ligament. It inserts superiorly on the spinous processes of vertebrae C2 to C4. In general, this part of the spinalis muscle is not well-developed and is quite variable in its attachments.

The inferior part of this muscle – the spinalis thoracis – has its origins on the spinous processes of vertebrae T11 to L2 and inserts superiorly on the spinous processes of the second to eighth thoracic vertebrae.

Like the other members of the erector spinae, the spinalis muscle receives innervation from the lateral branches of the posterior rami found along the length of the muscle. The bilateral contraction of the spinalis muscle extends the cervical and thoracic spine while unilateral contraction bends the cervical and thoracic spine laterally to the same side.

And that’s it, for the intermediate layer. We’re certainly making progress, so let’s move on now to the deep layer.

The penultimate group of muscles we want to look at in this tutorial is the deep layer, which itself consists of the transversospinal group and is comprised of the semispinalis, the multifidus, and the rotatores. And, of course, let’s begin with the semispinalis muscle.

The semispinalis is the most superficial of the transversospinal muscle group and, like many of the long back muscles, is made up of three parts. The capital, or most superior part of the muscle, is known as semispinalis capitis. It has its origins on the articular processes of the vertebrae C4 to C7 and the transverse processes of vertebrae T1 to T6. The semispinalis capitis inserts between the superior and inferior nuchal lines of the occipital bone.

The cervical part of the muscle is appropriately known as the semispinalis cervicis. It has its origins on the transverse processes of vertebrae T1 to T6 and inserts on the spinous processes of vertebrae C2 to C5. And the thoracic part of the semispinalis is known as the semispinalis thoracis. It has its origins on the transverse processes of vertebrae T6 to T12 and it inserts on the spinous processes of vertebrae C6 to T4.

The semispinalis capitis is innervated by the descending branches of the greater occipital nerve, which is a branch of the posterior ramus of spinal nerve C2 as well as branches of spinal nerve C3. The semispinalis cervicis and thoracis portions, on the other hand, are innervated by the medial branches of the posterior rami of spinal nerves.

In terms of the functions of the semispinalis, bilateral contraction results in the extension of the head, cervical, and thoracic spine while unilateral contraction results in the lateral flexion of the head, cervical, and thoracic spine on the same side with rotation of the head, cervical and thoracic spine on the opposite side.

Next stop is the multifidus, which is made up of triangular bundles of muscle that pass superiorly and medially to the spinous processes of their adjacent superior vertebrae, as you can see in this image. And, once again, we can divide our muscle into three parts. The multifidus cervicis, which originates in the superior articular processes of cervical vertebrae; the multifidus thoracis, which originates in the transverse process of the thoracic vertebrae or mammillary processes of the second to fifth lumbar vertebrae below the vertebra of origin; and the multifidus lumborum, which originates from the posterior aspect of the sacrum, the posterior superior iliac spine of the ilium, and the sacroiliac ligament. The multifidus lumborum is the thickest part of the multifidus muscle.

And as we mentioned earlier, the multifidus inserts on the lateral aspect and tips of the spinous processes of the vertebrae two to four levels superior to their origin, otherwise known as vertebrae C2 to L5. The multifidus is innervated by the medial branches of the posterior rami of the spinal nerves. And when it comes to function, bilateral contraction results in the extension of the spine while unilateral contraction results in the lateral flexion of the spine on the same side and rotation of the spine on the contralateral side.

The last and the deepest part of the transversospinal muscle group are the rotatores muscles. These muscles are most developed in the thoracic region and arise from the transverse process of one vertebra while inserting into the spinous process of one or two vertebrae superior to it, as you can see in the image. And it has only two parts – the rotatores brevis, which originates from the transverse processes of the thoracic vertebrae T2 to T12 and insert onto the laminae of the spinous processes of the vertebra one level above their origin, and the rotatores longi, which originates from the transverse processes of the thoracic vertebrae and insert onto the laminae or the spinous processes of the vertebra two levels above their origin.

Like the multifidus, the rotatores are innervated by the medial branches of the posterior rami of the spinal nerves and, functionally, bilateral contraction of these muscles results in the extension of the thoracic spine while unilateral contraction results in the rotation of the thoracic spine of the opposite or contralateral side which makes sense given their name, rotatores.

Okay, so we’re now at the last layer of our deep back muscles. And these final muscles that we’re going to look at today are said to belong to the deepest layer. So let’s check them out!

The muscles that can be found in the deepest layer include the interspinales, the intertransversarii, and the levatores costarum. Let’s begin with the interspinales.

The interspinales are a series of small muscles which true to their name connect the spinous processes of the vertebrae to one another as you can see in this image. And, once again, like many of our other muscles, this muscle has three parts. The interspinales cervicis which originates from the superior aspect of the spinous processes of the C3 to T1 vertebrae and insert onto the inferior aspect of the spinous processes of vertebrae C2 to C7. The interspinales thoracis which are generally quite variable and not well developed originate from the superior aspect of the spinous processes of the vertebrae T2, T11, and T12 and inserts onto the inferior aspect of the spinous processes of vertebrae T1, T10, and T11.

The interspinales lumborum originates from the superior aspects of the spinous processes of the vertebrae L2 to L5 and inserts onto the inferior aspect of the spinous processes of vertebrae L1 to L4. The interspinales are innervated by the posterior rami of the spinal nerves and in terms of function, the interspinales is involved in extension of the cervical and lumbar spine.

The intertransversarii muscle, like its name suggests, connects the transverse processes of adjacent vertebrae, which you can see in the image. This muscle has two parts – the intertransversarii cervicis muscles and the intertransversarii lumborum muscles. They’re also known as the intertransverse muscles, so the cervical intertransverse muscle and the lumbar intertransverse muscle respectively.

The intertransversarii muscles originate from the transverse processes of the cervical and lumbar vertebrae and insert into the transverse processes of adjacent vertebrae. These muscles are innervated by the posterior and anterior rami of the spinal nerves. In terms of their function, these muscles assist in the lateral flexion of the spine as well as stabilizing it.

Our final muscle of the deep muscles of the back are the levatores costarum muscles. The levatores costarum originates from the transverse processes of vertebrae C7 to T11 and insert onto the superior border or the external surface of the rib, one level below the origin, and they’re innervated by the posterior rami of the spinal nerves T1 to T12. As for their function, these muscles assist in the elevation of the ribs as well as the thoracic spine.

And that’s it, for the deep muscles of the back. You’ve been a superchamp for keeping out with it all. Since this has been such a long tutorial, I am going to try and keep our clinical section as short as humanly possible. So the most common clinical scenario you’ll see relating to the deep muscles of the back is back strain.

Back strain usually presents as a non-radiating, dull, aching sensation around the lumbar spine. It’s most often caused by overstretching of the muscles of the back which then results in microscopic tears of the muscle fibers or the ligaments. The muscles that are usually involved are those found in the erector spinae – that is, the iliocostalis, the longissimus, and the spinalis, which are the muscles that produce movements of the lumbar intervertebral joints.

It often occurs in people who use forceful, repeated back movements usually while rotating their spine. So your weightlifter who doesn’t balance her weight properly is prone to back strain, but so is your granddad who bends over using his back instead of his legs.

Back strain can be acute or chronic – acute meaning pain less than a month and chronic meaning longer than two months. If severe, it can result in muscle spasms presenting with cramps, pain, and a lack of function of the muscle injured. Both back strain and muscle spasms can be treated with massage, physical therapy, and rest. Treatment using medications such as nonsteroidal anti-inflammatories, pain relievers, and muscle relaxants are also recommended. But, of course, prevention is better than cure.

Back pain can be minimized by keeping the back straight and using the muscles of the legs and buttocks when bending to pick something heavy up. Athletes who lift weights or older persons with weaker muscles can also use a back stabilizing brace to help protect the spine.

So that’s it for clinical notes. Let’s quickly summarize what we talked about today.

So, first, we discussed how intrinsic muscles of the back are sometimes broken down in different ways. The first way is through tracts – a medial and a lateral tract. The second way is through layers. According to this system, there’s a superficial, intermediate, deep, and deepest layer.

The superficial layer includes the spinotransverse group which contains the two parts of the splenius muscle – the splenius capitis and the splenius cervicis. The intermediate layer includes the erector spinae which contains the sacrospinal group which itself includes the iliocostalis and its three parts – the iliocostalis cervicis, the iliocostalis thoracis, and the iliocostalis lumborum; the longissimus muscle and its three parts – the longissimus capitis, the longissimus cervicis, and the longissimus thoracis; and the erector spinae also contains the spinalis muscle which has three parts – the spinalis wapitis, the spinalis cervicis and the spinalis thoracis.

The deep layer includes the transversospinal group which if you recall includes the semispinalis which has three parts – the semispinalis capitis, the semispinalis cervicis, and the semispinalis thoracis; the multifidus which again has three parts – the multifidus cervicis, the multifidus thoracis, and the multifidus lumborum; and the rotatores which has two parts – the rotatores brevis and the rotatores longi.

And finally, the deepest layer includes the interspinales which has three parts – the interspinales cervicis, the interspinales thoracis, and the interspinales lumborum; the intertransversarii which has two parts – an intertransversarii cervicis and an intertransversarii lumborum; and the levatores costarum.

In our clinical notes, we talked about back strain which is caused by overstretching of the back muscles treated with medication and massage, and prevented by using the legs and buttocks when bending or wearing a back brace.

And that’s it! If you want to learn more about the human body and anatomy, don’t forget to check out our website for more helpful articles and atlas, quizzes, and videos. In the meantime, thanks for watching, and happy studying!