Muscles of back - active recall summary

Which nerve innervates the 4 muscles of the deep neck (rectus capitis posterior minor, rectus capitis posterior major, obliquus capitis inferior, obliquus capitis superior)?

Suboccipital nerve (C1)

What are the contents of the suboccipital triangle?

Vertebral artery and suboccipital nerve (C1)

Explain the *layering* (according to depth) of the back muscles

Dividing the layers of the back according to depth: Extrinsic muscles: 1. Superficial layer: latissimus dorsi, rhomboids, levator scapulae, trapezius, 2. Intermediate layer: serratus posterior superior and inferior 3. Deep layer - Intrinsic muscles: 1. Superficial layer: splenius 2. Intermediate layer: erector spinae (sacrospinalis) 3. Deep layer: transversospinales 4. Minor deep layer.

Explain the meaning of "transversospinales"

Each of the three transversospinales muscles (semispinalis, multifudus, rotatores) originate from the vertebral transverse processes and insert superomedially onto the vertebral spinous processes.

What is the chief extensor of the vertebral column?

Erector spinae (sacrospinalis)

How does the location of erector spinae affect its action?

Erector spinae is located posterior to the line of gravity through the body. Therefore, its *eccentric contractions* help maintain the spine in extension for posture, preventing it from flexing rapidly. *The erector spinae is the muscle that holds us upright.*

[*Mnemonic*] for deep layer of intrinsic back muscles (transversospinales)?

From superior to deep: 1. *S*emispinales (*S*uperior) 2. *M*ultifidus (*M*iddle) 3. *R*otatores (*R*oot = deep)

Which muscles of the minor deep layer of the intrinsic muscles of back are only found in the cervical and lumbar regions?

Interspinales and intertransversarii

What is the suboccipital artery's course in the suboccipital triangle?

Courses through *foramen of transverse process* and into suboccipital triangle via *groove for vertebral artery* of C1 and then into the brain.

What are the functions of the minor deep layer of intrinsic back muscles?

Intertransversarii and interspinalis: proprioception Levator costarum: side flexion, assists in respiration by elevating ribs.

What is the surface anatomy of the semispinalis muscle?

Semispinalis capitis is responsible for the longitudinal bulge felt on either side of the nuchal ligament proximal to the superior nuchal lines.

What are the functions of the intermediate layer of the extrinsic muscles of the back?

Serratus posterior superior and inferior: respiration and proprioception

Which structures form the floor and roof of the suboccipital triangle?

*Floor*: posterior atlanto-occipital membrane, posterior arch of atlas. *Roof*: semispinalis capitis

List the muscles that constitute the borders of the suboccipital triangle and their attachments

*Medial border*: rectus capitis posterior major (origin: spinous process of C2, insertion: inferior nuchal line of occipital bone). Rectus capitis posterior minor is medial to the major and does not form the medial border (origin: posterior tubercle of C1, insertion: inferior nuchal line). *Superolateral border*: obliquus capitis superior (origin: transverse process of C1, insertion: occipital bone between superior and inferior nuchal lines) *Inferior border*: obliquus capitis inferior (origin: spinous process of C2, insertion: transverse process of C1). *Does not insert onto occipital bone*.

What are the actions of the 4 muscles of the deep neck (rectus capitis posterior minor, rectus capitis posterior major, obliquus capitis inferior, obliquus capitis superior)?

1. Extension of head on atlas: rectus capitis posterior major and minor, obliquus capitis superior. 2. Rotation of atlas on axis (atlantoaxial joint): obliquus capitis inferior. 3. Lateral flexion of head on atlas: obliquus capitis superior.

5 features of rotatores (layer, fibre direction, span, characteristic, insertion)

1. Intrinsic back muscles --> deep layer --> deepest layer. 2. Superomedial fibre direction. 3. Span 1-2 segments. 4. *Thickest in the thoracic region*. 5. Attach to the *root* of the spinous process of adjacent superior vertebra.

5 features of multifidus (layer, fibre direction, course, characteristic, insertion)

1. Intrinsic back muscles --> deep layer --> middle layer. 2. Superomedial, oblique fibre direction. 3. Short triangular bundles that span 2-4 segments. 4. Thickest in the lumbar region. 5. Attach to the entire length of the spinous process of adjacent superior vertebra.

4 features of semispinalis

1. Intrinsic back muscles --> deep layer --> superficial layer 2. Superomedial fibre direction. 3. Small muscular bundles that pass to the occipital bone/thoracic/cervical spinous processes superiorly. 4. Arises from half the vertebral column (*semi*spinalis). 5. Divided regionally into thoracis, cervicis and capitis. 6.

7 features of erector spinae (layer, location, function, divisions, origin, regional divisions, fibre direction)

1. Intrinsic back muscles --> intermediate layer. 2. Located in *groove* between veretebral spinous process and angle of ribs. 3. Chief extensors of the back. 4. Divided into 3 muscle columns: iliocostalis (lateral column), longissimus (middle column), spinalis (medial column). 5. All 3 originate from a broad tendon in the sacral and inferior back region. 6. All 3 are divided regionally into 3 parts according to superior verterbal attachment: iliocostalis (lumborum, thoracic, cervicis); longissimus and spinalis (thoracis, cervicis, capitis). 7. Superior fibre directions.

Where on the spinous processes do the transversospinales (deep layer, intrinsic) muscles insert? How does the site of insertion correspond to the muscle's layer? [*Reference point*]

1. Semispinalis capitis: tip of spinous process. 2. *M*ultifudus: whole length of *M*iddle of spinous process. 3. *R*otatores: *R*oot of spinous process. Spinous process insertions correspond to muscle layer: semispinalis = superficial (tip of SP), multifudus = middle (length of SP) , rotatores = deep (root of SP)

How many segments does each of the transversospinales (deep layer) muscles span and what are the depths of the layers?

1. Semispinalis: 5 segments. (supeficial) 2. Multifidus: 3 segments. (middle) 3. Rotatores: 1 segments. (deepest)

What is the common origin of the three erector spinae muscles? What are its attachments?

A broad common extensor tendon that attaches to: 1. Posterior part of iliac crest. 2. Posterior surface of sacrum. 3. Sacral and inferior lumbar spinous processes. 4. Supraspinous ligament. 5. Sacro-iliac ligaments.

What is the supraspinous ligament and what is its course?

A ligament that connects the tips of the spinous process. Course: - Superiorly: continuous with the nuchal ligament at C7. - Inferiorly: runs to sacrum, blends with thoracolumbar fascia.

What are the fibre directions and attachments of minor deep layer of intrinsic back muscles?

Intertransversarii: inferiorly from superior transverse process to inferior transverse process. Interspinalis: inferiorly from superior spinous process to inferior spinous process. Levator costarum: inferolaterally from tips of transverse processes to area of rib between tubercle and angle.

mnemonic for erector spinae?

Lateral to medial: *I* *L*ove *S*tanding *I*liocostas *L*ongissimus *S*pinalis

Borders of suboccipital triangle

Medial: rectus capitis major Lateral: obliquus capitis superior Inferior: obliquus capitis inferior

Which muscle of the deep neck *does not insert onto the cranium*?

Obliquus capitis inferior. (origin: spinous process of C2, insertion: transverse process of C1).

[*Reference point*] Layers and thicknesses of transversospinales muscles

Superficial layer: semispinalis (thoracis, cervicis, capitis) Middle layer: multifidus Deepest layer: rotatores Multifidus is thickest in the lumbar region Rotatores is thickest in the thoracic region

The suboccipital triangle is deep to which muscles? Which of these is considered the *roof* of the suboccipital triangle.

Superficial to deep: trapezius, splenius, semispinalis capitis. *Roof*: semispinalis capitis.

How are the fibres arranged in the erector spinae muscle columns? What does this arrangement provide?

The *long fibres* of the erector spinae muscles define the 3 columns of isolated muscles: iliocostalis, longissimus and spinalis. This provides energy saving because each column can act independently. The short fibres of all columns overlap with each other. This provides: 1. Stability, 2. Localised action, 3. Segmental neurovasculature supply.

Why is the function of the intertransversarii and interspinalis so important?

The intertransversarii and interspinalis muscles are responsible for proprioception. This is important because of the large number of intervertebral joints.

List the divisions of each group of intrinsic back muscles

The intrinsic muscles of the back are divided into 3 groups according to *layers*: 1. Superficial: splenius 2. Intermediate: erector spinae which is divided into 3 columns: iliocostas, longissimus, spinalis 3. Deep (transversospinales): semispinalis, multifudus, rotatores 4. Minor deep layer: interspinalis, intertransversarii, levator costarum. Each layer of splenius, erector spinae and semispinalis is subdivided according to the *vertebral level* of the muscle's superior attachment. 1. Splenius: capitis, cervicis 2. Erector spinae: Iliocostalis: cervicis, thoracis, lumborum; Longissimus & spinalis: capitis, cervicis, lumborum. 3. Semispinalis: capitis, cervicis, thoracis

Describe the differences in nerve supply of the extrinsic and intrinsic muscles of the back?

The intrinsic muscles of the back are supplied by the posterior rami of the spinal nerves. The extrinsic muscles of the back are supplied by the anterior rami of the spinal nerves.

The thoracic and lumbar parts of the erector spinae and transversospinales are enclosed in what?

The middle and posterior layers of the thoracolumbar fascia

Where are the transversospinales muscles located in general?

The space between the transverse and spinous processes (therefore "transversospinales")