Deep Back Muscles: Anatomy

• Deep muscles of the back are also known as intrinsic back muscles or erector spinae.
• There are three groups of back muscles: extrinsic and intrinsic, as well as deep muscles.

Intrinsic Back Muscles

• Responsible for maintaining posture and facilitating movements of the vertebral column.
• Innervated by the dorsal rami of spinal nerves.
• Enclosed by deep fascia.
• Organized into three layers: superficial, intermediate, and deep.
• The intermediate layer consists of the erector spinae/sacrospinalis muscles; the deep layer consists of transversospinal muscles.

Superficial Layer

• Includes splenius capitis and splenius cervicis muscles.
• Acting alone, these muscles laterally bend and rotate the head to the same side.
• Acting together, they extend the neck.

Intermediate Layer

• Arranged in three groups from lateral to medial.
• These groups include:
  • Iliocostalis muscles (lumborum, thoracis, and cervicis).
  • Longissimus muscles (thoracis, cervicis, and capitis).
  • Spinalis muscles (thoracis, cervicis, and capitis).
• Acting alone, these muscles laterally bend the vertebral column.
• Acting together, they extend the vertebral column and the head.

Deep Layer

• Arranged in three groups from superficial to deep.
• These groups include:
  • Semispinalis muscles (capitis, cervicis, and thoracis).
  • Multifidius muscles.
  • Rotatores muscles.
• These muscles function in extending the head and vertebral column and rotating the column to the opposite side.
• Interspinal, intertransverse, and levatores costarum muscles are minor muscles in the deep layer.

Deep Muscles of the Neck

• There are two groups of muscles at the root of the neck known as prevertebral muscles.
• Prevertebral muscles lie posterior to the prevertebral fascia.
• These groups are the anterior and lateral vertebral muscles.
• The anterior vertebral muscles are the longus capitis, longus colli, rectus capitis anterior, and rectus capitis lateralis.
• Splenius capitis, levator scapulae, and the anterior, middle and posterior scalene muscles are the lateral vertebral muscles
  • Splenius capitis is considered a muscle of the back
  • Levator scapulae is considered a muscle of the upper limb.

Longus Capitis Muscle

• Innervated by the ventral rami of C1-C3 spinal nerves.
• Flexes the head (anterior bending of the head relative to atlanto-occipital joints).

Longus Colli Muscle

• Innervated by the ventral rami of C2-C6 spinal nerves.
• Flexes the neck.
• Facilitates anterior bending of the cervical vertebrae C2-C7.
• Acting unilaterally, rotates the head to the opposite side (rotation occurs at the atlanto-axial joint).

Rectus Capitis Anterior

• Innervated by branches from C1 and C2 spinal nerves.
• Flexes the head.

Rectus Capitis Lateralis

• Innervated by branches from C1 and C2 spinal nerves.
• Flexes the head.
• Helps to stabilize the atlanto-occipital joint.

Anterior Scalene Muscle

• Innervated by C4-C6 spinal nerves.
• Elevates the first rib.
• Flexes and laterally rotates the neck.

Middle Scalene Muscle

• Innervated by the ventral rami of the C3-C8 spinal nerves.
• Elevates the first rib during forced inspiration.
• Bends the neck laterally.

Posterior Scalene Muscle

• Innervated by the ventral rami of the C7 and C8 spinal nerves.
• Elevates the second rib during forced inspiration.
• Bends the neck laterally.

Scalene Muscles

• During inspiration, these muscles help increase the volume of the thorax by elevating the 1st and 2nd ribs.
• Classified as accessory muscles of respiration.
• Two critical structures pass between the anterior and middle scalene muscles: the subclavian artery and the trunks of the brachial plexus.
• The phrenic nerve also passes between these muscles, though it can pierce the anterior scalene muscle.

Suboccipital Region

• Located on the upper part of the posterior aspect of the neck.
• Extends between the occipital bone and the first two cervical vertebrae.

Muscles of the Suboccipital Region

• Rectus capitis posterior major muscle: Extends from the spinous process of the axis to the lateral part of the inferior nuchal line.
• Rectus capitis posterior minor muscle: Extends from the posterior tubercle of the atlas to the lateral part of the inferior nuchal line.
• Inferior oblique muscle of the head (obliquus capitis inferior muscle): Extends from the spinous process of the axis to the transverse process of the atlas.
• Superior oblique muscle of the head (obliquus capitis superior muscle): Extends from the transverse process of the atlas to the upper part of the inferior nuchal line.
• These muscles are innervated by the suboccipital nerve (dorsal ramus of the C1 spinal nerve).
• Primary function is extending or rotating the head.

Suboccipital Triangle Borders

• Superomedial: rectus capitis posterior major.
• Superolateral: obliquus capitis superior muscle.
• Inferolateral: obliquus capitis inferior muscle.
• Floor: posterior atlanto-occipital membrane.
• Roof: semispinalis capitis muscle.

Suboccipital Triangle Contents

• Vertebral artery.
• Suboccipital nerve.