Back, Spine, and Spinal Cord Anatomy

03:13 Let's now discuss the Seven Secondary Back Muscles.

03:16 They are called secondary because their ventral aspect is covered and there innervated by the ventral branches of the brachial plexus.

03:23 Can you name the seven muscles? They include the trapezius.

03:28 They include the latissimus dorsi.

03:31 And the scapular muscle triad consisting of the levator scapula, rhomboid minor, and rhomboid major.

03:39 Deep to the muscle triad we find the serratus posterior superior and the serratus posterior inferior.

03:46 Now, let's get specific.

03:47 The trapezius muscle is innervated by the 11th cranial nerve.

03:51 the spinal accessory nerve, and for this reason it's called a cranial nerve muscle.

03:56 It's descending or superior portion originates from the External Occipital Protuberance between the highest and superior nuchal lines.

04:03 As well as from all the spinous processes of the cervical spine along the nuchal, supraspinous, and interspinous ligaments.

04:12 The descending portion extends laterally to the clavicle and acromion.

04:19 The transverse portion originates on the spinous processes of the lower cervical and upper thoracic spine and extends the middle of the scapular spine.

04:28 The ascending portion originates from the spinous process of the entire lower thoracic spine and inserts on the medial surface of the scapular spine.

04:36 The function of this muscle includes head and cervical spine, the dorsiflexion, and lateral flexion.

04:46 While the superior component rotates the head towards the opposite side.

04:52 It also helps hold the scapula against the body wall.

04:55 If the accessory nerve is injured, the scapula protrudes producing lateral scapular winging.

05:01 Specifically, the medial scapular margin and the inferior angle protrude.

05:06 Furthermore, because of the descending and transverse attachment points, the scapula can be rotated.

05:15 Let's take a look on the left.

05:17 The pars descendens extend to the clavicle and acromion laterally.

05:22 The pars ascendens insert on the medial scapular spine.

05:27 If the pars descendens now contract, then imagining my hand is the scapula, the scapula can be rotated with the inferior angle moving ventrolaterally.

05:39 This is necessary when lifting the arm above the horizontal position.

05:44 Why? Because the greater tuberosity of the humerus would be obstructed by the acromion.

05:51 By rotating the scapular angle ventrolaterally and therefore moving the acromion the arm can be further elevated above 90 degrees.

06:01 Now, we move on to the latissimus dorsi.

06:03 Lattice being wide, and dorsi on the back.

06:07 Innervation is via the thoracodorsal nerve of the brachial plexus.

06:12 The muscle originates from the superficial thoracolumbar fascia, and the spinous processes of T7 through T12.

06:20 That thoracolumbar fascia envelops the primary back muscles.

06:24 It has the superficial lamina, here at my thumb, and transitions into the deep lamina.

06:30 It ends laterally at the transverse process.

06:34 The latissimus dorsi courses away from the superficial lamina.

06:38 Furthermore, a portion of the muscle originates from the sacral Os and the lumbar spine is processes.

06:43 Other fibers arise from the posterior iliac crest as well as ribs 9 through 12.

06:51 From the inferior angle, the muscle travels mediately to the humerus and inserts onto the lesser tuberosity.

06:57 It's important to remember that the lesser tuberosity is more anterior, while the greater tuberosity is more lateral.

07:05 The muscle inserts at the elongation of this lesser tuberosity called the humeral crest.

07:12 Because it passes medially to the humerus, it assists with internal rotation.

07:16 It also pulls posteriorly causing extension as well as adduction of the humerus.

07:22 A helpful learning aid is to think of this as the apron knotter.

07:25 So when you think about tying an apron, you have internal rotation, extension and adduction of the humerus.

07:31 It's also sometimes called the pull up muscle.

07:34 As you can see here, when I lengthen it by bringing my arm up, then the tendon can now optimally pull the arm back into place.

07:41 If I fix both arms and space, it can rotate the trunk to the side and swivel back again.

07:49 This is important for paraplegics that have an injury to the thoracic spinal cord.

07:54 Because this muscle has innervation from spinal cord segments C6, C7, and C8.

07:59 This means they can use their latissimus to bring their trunk out of the wheelchair.

08:03 Historically, the latissimus dorsi was sometimes even transplanted to the heart allowing it to contract in an emergency.

08:09 Though this procedure is obviously not used anymore.

08:13 Let's now discuss the muscle triad that lies deep to the trapezius.

08:17 The first of these muscles is the levator scapula.

08:20 It originates from the transverse processes of C1 through C4, and extends distally, inserting on the medial and inferior borders of the scapula.

08:34 Next, we have the rhomboid minor.

08:36 It's smaller than the rhomboid major.

08:38 Normally being about the size of two fingers side by side.

08:42 The muscle originates from C7 and T1 spinous processes and courses laterally to insert on the medial scapula.

08:48 Usually around the level of the scapular spine.

08:51 The rhomboid major is double the size of the minor and originates from the T2 through T5 spinous processes.

08:57 The muscle inserts along the medial scapula usually inferior to the level of the scapular spine.

09:01 All these muscles pull the scapula upwards and medially, helping to fix the scapula to the trunk.

09:11 The levator scapula is also used in coordination with the trapezius when loads are placed on the shoulder.

09:18 This can lead to muscle tension with continued use.

09:20 For example, using a computer mouse can create tension because your levator and trapezius are tension to maintain that position.

09:27 These three muscles, the levator and the rhomboids are innervated by the dorsal scapular nerve, the brachial plexus.

09:33 When the nerve is injured, the scapula will not wing spontaneously so a provocative test must be used.

09:38 This is accomplished by bringing the arms forward and pressing against a wall.

09:42 If the nerve is injured, the medial scapular border will protrude when compared to the normal side.

09:52 Next, we have the serratus posterior muscle, which lies deep to the muscle triad we just discussed.

09:57 It originates from the spinous processes of C7 through T3 and inserts on the posterior lateral aspects of ribs 2 through 5.

10:04 It travels underneath the scapula and can be visualized here.

10:07 It forms a muscle plate as a joined with the serratus posterior inferior.

10:11 They form a circle.

10:12 This is the top and that's the bottom.

10:15 The superior muscle originates from C7 to T2 while the inferior muscle originates from T11 to L2.

10:21 They then insert onto the lower three ribs.

10:24 The innervation because of the proximity to the ribs is done by the intercostal nerves.

10:29 These nerves are ventral rami of the thoracic spinal nerves.

10:33 Though these muscles can perform slight rib elevation, they have minimal inspiratory function.

10:39 When we say they have inspiratory function, we're describing their antagonism to the pars costalis of the diaphragm.

10:47 So if the diaphragm wants to pull the ribs inwards during contraction, the serratus posterior inferior muscle can contract antagonistically and oppose the action.

10:58 So those were the Seven Secondary Back Muscles.

11:00 Looking at the cadaver, let's again discuss the secondary back muscles and start with the most superficial, the trapezius.

11:05 It's innervated by the 11th cranial nerve, the spinal accessory nerve, a brachial nerve, hence a brachial arch muscle.

11:13 The origin, the pars descendens, the descending portion is the external occipital protuberance between the nuchal lines, as well as the spinous processes of the C-spine and ligamentum septum.

11:25 The pars descendens attaches laterally to the clavicle and to the acromion.

11:32 The function of the protuberance is dorsiflexion, lateral flexion, and turning of the face to the opposite side.

11:42 Because the pars descendens is most lateral it can function with the pars ascendens which is more medial.

11:50 With contraction of the pars descendens the scapula can rotate causing the inferior scapula to move ventrolaterally.

12:00 This is important for raising the arm beyond the horizontal as we saw earlier on the skeleton.

12:06 The transverse part originates from the spinous processes and travels laterally.

12:10 It inserts on the medial scapula at the level of the scapular spine.

12:13 The pars ascendens extends from the spinous processes of the lower thoracic vertebrae to the medial scapular border.

12:22 The trapezius thereby fixes the scapula to the trunk.

12:26 If the spinal accessory nerve fails, for example, a tumor in the area of the jugular foramen at the base of the skull scapular winging will occur.

12:37 That's the medial border of the scapula and the inferior scapular angle protruding outward like a wing.

12:42 hence called lateral scapular winging.

12:44 Now onto the latissimus dorsi.

12:46 The latissimus dorsi, lattice (wide), wide on the dorsum or back is innervated by the thoracodorsal nerve with the brachial plexus.

12:57 A split from it above is the teres major muscle.

13:00 They are originally related during development, so it's also innervated by the thoracodorsal nerve.

13:07 The latissimus dorsi originates from the superficial lamina and cervical fascia.

13:12 The connective tissue sac that surrounds the erector spinae muscles.

13:17 It also originates from the sacral os and iliac crest.

13:23 It courses below the trapezius on the lower three ribs and inferior angle of the scapula.

13:28 The latissimus dorsi internally rotates the humerus because of its attachment on the humeral crest beneath the lesser tuberosity.

13:38 Remember our learning aid, the apron knotter muscle.

13:43 That is it does internal rotation, extension, and adduction of the humerus.

13:50 So tying an apron knot behind your back.

13:52 If you stretch your arm forward, like when doing a pull up, it has a particularly strong advantage.

13:56 That's why it's often called the chin-up muscle.

13:59 Furthermore, if you fix your arm sideways, it can pull the ribs outward so to speak.

14:05 It's sometimes called the cough muscle.

14:06 And in asthmatics it can become hypertrophied.

14:10 A paraplegic generally has an injury with a thoracic spine below the level of the C8 nerve.

14:17 The patient can use this muscle to transfer because of its innervation.

14:21 By fixing their arms, they can rotate their trunk into or out of a wheelchair.

14:26 Here we see the muscle triad, the levator scapulae, rhomboid minor, and the rhomboid major muscles.

14:35 All three are located on the dorsal side of the scapula and thus are innervated by the dorsal scapular nerve arising from the brachial plexus.

14:44 The levator has its origin on the C1 through C4 transverse processes.

14:50 The transverse process has an anterior and posterior tubercles.

14:54 And because we are at the back they originate from the posterior tubercles.

14:58 Insertion is to the superior and medial scapula.

15:04 The rhomboid minor originates from the C7 to T1 spinous processes.

15:11 The rhomboid major originates from the spinous processes of T1 through T4 and inserts onto the medial scapula inferior to the scapular spine.

15:20 The rhomboid minor also inserts onto the scapula but above the scapular spine.

15:27 Here we see the right and left very thin serratus posterior superior muscles.

15:33 You start to form the beginning of a circle here because it originally formed a muscular plate with the inferior.

15:41 Here you see this serratus posterior inferior muscle.

15:44 And here on the right side you see a small remnant of the serratus posterior inferior muscle.

15:51 The origin is up here at the C6 through T1 spinous processes.

15:56 They insert on the ribs normally three through five.

15:59 And their function is to primarily assist aspiration by pulling the ribs apart.

16:03 Because of the weak contraction strength it has a minimal effect.

16:07 Innervation is from the intercostal nerves which are the ventral rami of the thoracic spinal nerves.

16:14 Down here, the origin of the serratus posterior inferior muscle is shared with the latissimus.

16:21 It arises from the superficial lamina in the thoracolumbar fascia, which is the connective tissue envelope that encases the erector spinae muscles.

16:30 It pulls the ribs inward, which is antagonistic to the diaphragm.

16:34 It prevents the rib expansion when the diaphragm contracts by pulling the ribs inward as you see here.

16:40 The erector spinae muscle is the same as the erector tunica muscle, because the truncus is the trunk, and spinea is the spine.

16:47 It makes the spine erect and can cause extension of the spine so to speak.

16:51 It lies in a connective tissue fascial sac, the thoracolumbar fascia.

16:56 It's called the thoracolumbar because it's particularly strong in the thoracolumbar region.

17:01 It has a superficial lamina that starts at the spinous process and runs to the deep lamina or profunda, which then transitions to the transverse process.

17:12 So this thoracolumbar fascial sac is especially strong but thins out superiorly as it extends to the occiput.

17:21 This muscle has two portions.

17:23 One tract lies deep and medial between the spinous processes and transverse processes.

17:30 This is called the medial tract.

17:32 More lateral and superficial with longer muscle fibers, we find the lateral tract of this muscle.

17:40 The lateral tract is innervated by the lateral branches of the spinal nerves.

17:44 In the medial tract is innervated by the medial branches of the dorsal rami.

17:50 Overall, in addition to extension, because they pull laterally here, they also assist with lateral flexion.

17:58 Furthermore, the vertebrae can rotate relative to one another.

18:01 The ribs are mainly pulled down during exploration.

18:05 Some muscles can be inspirational, but they shouldn't be memorized individually for testing purposes.

18:15 And ultimately the back muscles stabilize.

18:19 As antagonist the anterior abdominal muscles, the entire trunk, so that muscular balance is ensured.

18:26 In addition, the individual spinal muscles are arranged like sails wrapping around the trunk.

18:31 This also helps stabilize the spine as a whole.

18:35 The lateral tract is made up of systems similar to the medial tract.

18:40 Each tract has two main systems but the lateral does have a third system.

18:45 The lateral tract here consists of fibers that run medial to lateral from the spinotransversales system Expands from the spinous process to the transverse process all the way up to the occiput.

18:57 This is the splenius capitis muscle, and the splenius cervicus muscle.

19:02 They traveled distally as we can see here laterally.

19:07 Here you can see the sacral spinal system.

19:09 It consists of the more lateral, more superficial iliocostalis muscle because it runs from the sacral os, to the iliac bone, and into the ribs.

19:20 Here on the medial side we see the longissimus muscle.

19:25 In addition, there are the so called musculi levatores costarum, in the thoracic area.

19:30 The longissimus overlays the ribs and attaches one rib to the next.

19:36 If we now look at the medial tract, let's go upstairs again.

19:40 Now, it works the other way around.

19:42 Not as before, but rather transversospinalis.

19:45 That is the transverse spinal system.

19:47 It consists of three muscle tears.

19:51 Superficial such as the semispinalis.

19:55 The central or multifidus, and very deep rotators or rotator muscles.

20:03 And from top to bottom, the muscles get subsequently shorter.

20:07 You skip about six vertebrae, then three vertebrae, then just one.

20:11 So superficial semispinalis, central multifidus with the rotators below in order of depth.

20:19 In addition, the second system for the medial side is the supraspinous or interspinous system.

20:25 A spinal interspinous system.

20:28 It runs laterally along the spinous processes and long layers and skips several vertebrae.

20:34 Overall, all these muscles in their various track systems are partially related.

20:40 Some of them have been artificially isolated.

20:42 You've been given their names, origins, and attachments.

20:46 You'll learn these at the very end.

20:47 How do you continue to learn now? You learn further that each of these muscles mentioned always occurs in three levels.

20:53 For example, we have an iliocostalis lumborum, thoracis, and cervicis.

20:59 Then the longissimus, one higher thorachis, cervicis, and capitis.

21:03 Up here we have only one splenius capitis and one splenius cervicis.

21:08 then the semispinalis, the central multifidus, and the rotators.

21:11 There we have the semispinalis capitis, a semispinalis cervicis, and a semispinalis thoracis.

21:18 And then with the spinal muscles, we have a musculus splenius cervicis, thoracis, and lumborum.

21:23 So you see there are three levels indicated for some -- iliocostalis lumborum, thoracis, and cervicis longissimus thoracis, cervicis, capitis.

21:33 But for splenius capitis and cervicis there are only two.

21:36 Then semispinalis capitis, cervicis, thoracis.

21:40 In spinalis cervicis, thoracis, lumborum.

21:46 Here we see again, thoracolumbar fascia, the lamina superficialis, and the muscles of the erector spinae The thoracolumbar fascia is particularly strong in that the thoracolumbar region.

21:58 Then thins out towards the top and of course is no longer present here.

22:02 It runs up to the occiput and forms a complete fascial sac in which the erector spinae muscles encased.

22:09 Here, the latissimus dorsi originates from the superficial lamina of the thoracolumbar fascia.

22:15 If you reflect it, because it belongs to the secondary back muscles, you can still see this serratus posterior inferior, which is another secondary back muscle.

22:25 If you then take that away, then you can see that thin sheets here.

22:30 This is the thoracolumbar fascia.

22:35 Beneath that we can see the entire muscle groups, the individual tracks of the erector spinae.

22:42 Let's take a closer look.

22:46 Here's the lateral tract that runs along the lateral surface.

22:50 You can see it here and appreciate that these are very long systems, very lateral and superficial.

22:56 It's innervated by the lateral branches of the dorsal rami.

23:00 Now if we go deeper and take them away, you can see partially here at the bottom, the medial tract running between the spinous and transverse processes.

23:09 And remember, it's applied by the medial branches of the dorsal rami.

23:18 Each of these tracks has two main systems though the lateral one has the third it's not very important.

23:28 Let's start up above under the trapezius muscle.

23:30 The one we see here is bordered by the splenius capitis and cervicis muscle.

23:36 Here you can see from the lateral tract we know belongs to the spinotransversal system because it moves from the spinous process to the transverse process.

23:45 Then as we go down, we have what's called the sacrospinal system and it's bordered by the long iliocostalis.

23:54 Because here it runs from the sacral os, and iliac bone to the ribs.

24:01 A little further medial we had the longissimus muscle.

24:05 That's not prepared here for you to see.

24:08 Further down in the area of the ribs, we can see the levator castoreum longi and brevis.

24:18 If we look at the medial track now one can see that conversely, because it's medial, it is not spinotransversal but rather it travels in the transversal spinal system.

24:32 It consists of three layers which are shown here.

24:36 We can again see the medial tract is different from the lateral system which runs medial to transverse (ie) it goes final transversely.

24:44 But instead, this is the transversal spinal system.

24:49 And that's what's shown here.

24:52 Remember, we have three levels.

24:54 And the further up I get the muscles cover about six vertebrae.

24:58 Then in the middle, they cover three, and further down, which has not prepared here, they span only single vertebral levels.

25:05 And remember from before, we have the superficial semispinalis, the central multifidus, and the deep rotators.

25:16 The semispenalis arises here. We can see that.

25:24 The semispenalis capitis comes under the splenius.

25:26 It forms the roof of the deep neck triangle, where the two rectus muscles and the two oblique muscles are the sides.

25:39 Then we have the semispinalis capitis, cervicis, and thoracis.

25:43 They appear in three levels.

25:44 Then the central multifidus, which can now also be seen running deep here.

25:49 Next we have the multifidus cervicis.

25:52 And then there's thoracis.

25:54 We can't see it here in the lumbar region, but it's particularly strong.

26:02 It's a very important stabilizer of both the lumbar and cervical spine.

26:07 We have each of our spinal lordosis regions in these areas.

26:11 Strong multifidus muscles can be trained if you have spinal problems.

26:16 The rotators are very deep.

26:18 They are rotatores laborum, thoracis, and cervicis and they move from one vertebrae to the next.

26:23 Of course there's rotation in the spine, it's highest at the top and decreases further down.

26:28 This is due to orientation of the spinal joints.

26:31 Superiorly, the joint surfaces are angled near 45, 45 degree angle, so rotation is very easy.

26:36 Moving distally they're closer to a 60, 40 degree angle.

26:40 And down here in the lumbar region they are 90, 45 degree angle so rotation is very limited.

26:45 More rotation can occur when the person bends forward, which causes the vertebrae to gap apart, allowing for 5 to 15 degrees of rotation to take place.

26:55 In addition to this transversal spinal system with the superficialis and semispinalis there are the central multifidus and deep rotatores.

27:04 Lateral to the spine is processes.

27:06 The musculus spinalis and interspinales muscles run along the spine.

27:10 There is also a cervicis, thoracis, and lumborum which are closely related to the semispinal system.

27:18 Back to the top under the trapezius muscle lies the splenius capitis muscle.

27:23 It belongs to the lateral tract the so called spinotransversal system.

27:29 Because it runs from the spinous process towards the transverse process and head.

27:33 If we fold it away, we see the musculus semispinalis capitis beneath, which belongs to the medial track, which is basically the reverse of the lateral.

27:41 What I mean is the medially running transversal spinal system because it moves from the transverse process towards the spinous process.

27:49 When we fold it away, we see the four muscles of the deep triangle of the neck.

27:53 We have four muscles on the right and accordingly four muscles on the left.

27:57 Which muscles are these? There are two diagonally oriented muscles on each side.

28:02 Erectus major and erectus minor.

28:04 There are also two vertically oriented muscles on each side, an inferior oblique and a superior oblique.

28:09 All these muscles are at the back of the head.

28:11 Therefore they're called the capitis posterior.

28:14 The only one who has the wrong name is the one at the bottom because it doesn't start at the caput.

28:18 Now in detail the rectus capitis posterior major muscle is long.

28:22 Therefore it has its origin from C2 behind the spinous process axis.

28:28 The rectus capitis posterior minor muscle is small and short.

28:32 That's why it backfires.

28:34 At the atlas we have no spines process, but only a posterior tubercle.

28:39 Both muscles insert here.

28:41 To the Linea Nuchae inferior, a bit higher or lower, it doesn't really matter.

28:45 Then here we have the oblique capitis posterior inferior muscle.

28:50 It extends laterally from the axis spinous process to the transverse process of the atlas.

28:57 From there it runs up the Linea Nuchae superior.

29:01 Please note the course of the musculus obliquus capitis posterior superior muscle.

29:06 The fact that it runs from the front below to the rear above, well, when it contracts help it turn the head to the opposite side.

29:15 When the sternocleidomastoid and trapezius do this, this muscle supports their action.

29:21 About the function of the muscles.

29:23 All of these muscles are behind the flex x axis, so they do extension.

29:28 The dorsal extension is called retraction in the upper first joint.

29:35 Thus between the atlas and the occiput and the second joint between the atlas and axis.

29:39 These are the two superior head joints, the atlanto-occipital articulation, and below, we have the three partial joints functionally forming a swivel joint called the atlantoaxial joint.

29:52 These muscles can also do lateral flexion because they're on the side of the flex x axis.

29:56 So lateral flexion occurs in the upper head joints.

30:00 Then what else can you do? They can rotate.

30:03 But only the obliquus capitis inferior and the two larger rotator muscles because only they cross over the atlas axis joint in which the rotation takes place.

30:13 In the deep neck triangle of the back we see the vertebral arteries and the posterior atlanto-occipital membrane.

30:19 The vertebral artery runs through it.

30:21 And in the opposite side here we can see the sub occipital nerve, which is the dorsal rami of the first spinal nerve.

30:27 It innervates the four muscles of the deep neck triangle.