Back of the Neck

INTRODUCTION

• The back of the neck extends from the external occipital protuberance and superior nuchal lines above to the spinous process of C7 and an imaginary line joining the acromia of both scapulae below.
• It contains the following important anatomical structures:
  1. Ligamentum nuchae.
  2. Extensor muscles of the neck.
  3. Suboccipital triangle.
  4. Arterial anastomoses around semispinalis capitis.
  5. Third part of the vertebral artery.

SURFACE LANDMARKS

1. External occipital protuberance: It is a palpable bony prominence at the upper end of the midline nuchal furrow. It marks the junction between the head and neck.

2. Nuchal furrow: It is a vertical depression extending along the midline of the posterior neck.

3. Superior nuchal lines: These are curved bony ridges extending laterally from the external occipital protuberance on either side of the occipital bone.

4. Spinous process of C7: It forms a prominent bony projection near the lower end of the nuchal furrow and is commonly called the vertebra prominens. Most other cervical spinous processes are less readily palpable because of their shorter size and overlying soft tissues. 5. Acromion: It is the lateral projection of the spine of the scapula and forms the bony prominence at the summit of the shoulder.

LAYERS OF THE BACK OF THE NECK

– The back of the neck consists of four principal layers:

1. Skin.
2. Superficial fascia.
3. Deep fascia.
4. Muscles.

Skin of Back of the Neck

– The skin is supplied mainly by cutaneous branches of the posterior (dorsal) rami of cervical spinal nerves, particularly C2–C5.

1. Greater Occipital Nerve (C2)

• It is the medial branch of the posterior ramus of the second cervical spinal nerve.
• Course: It passes inferior to the obliquus capitis inferior muscle, curves upwards, and ascends deep to semispinalis capitis.
• It pierces semispinalis capitis and the aponeurosis of trapezius to become superficial.
• Distribution: It supplies the posterior scalp as far as the vertex.
• It is one of the largest cutaneous branches of the posterior spinal nerve rami.

2. Third Occipital Nerve (C3)

• It arises from the medial branch of the posterior ramus of the third cervical spinal nerve.
• Course: It pierces semispinalis capitis and trapezius and ascends medial to the greater occipital nerve.
• Distribution: It supplies the upper posterior neck and adjoining occipital scalp.

3. Cutaneous Branches of C4 and C5

• They arise from the posterior rami of the corresponding cervical spinal nerves.
• They pierce the deep fascia near the midline and supply the skin of the lower posterior neck.

Superficial Fascia

• The superficial fascia of the posterior neck is thick and contains connective tissue, cutaneous nerves, and blood vessels.
• Cutaneous nerves: It contains the greater occipital nerve, third occipital nerve, and cutaneous branches of C4 and C5.
• Blood vessels: It contains branches of the occipital artery and accompanying veins.

Deep Fascia

– The deep fascia of the posterior neck includes:

1. Investing layer of deep cervical fascia: It encloses trapezius posteriorly.
2. Ligamentum nuchae: It forms a median fibrous structure between the muscles on the two sides of the neck.

Ligamentum nuchae

General Features

• The ligamentum nuchae is a median fibrous structure extending along the posterior aspect of the cervical vertebral column.
• Unlike a typical ligament connecting two adjacent bones, it forms a fascial attachment and separation between the posterior cervical muscles.
• It consists of two components:
  • Dorsal median raphe.
  • Median fascial septum.

1. Dorsal Median Raphe

• It extends from the external occipital protuberance to the spinous process of C7.
• It provides attachment to:
  • Trapezius.
  • Splenius capitis.
  • Rhomboid minor.

2. Median Fascial Septum

• It extends forwards from the dorsal median raphe towards the cervical vertebral column.
• Superior attachment: It is attached to the external occipital crest and posterior tubercle of the atlas.
• Anterior attachment: It reaches the spinous processes of the cervical vertebrae.
• It separates the posterior cervical muscles of the two sides.

Functional Significance

• In quadrupeds, the ligamentum nuchae is well developed and contains abundant elastic tissue that helps support the head against gravity.
• In humans, it is comparatively less developed and contains a smaller proportion of elastic fibres.
• It provides fascial support and attachment for posterior cervical muscles and helps maintain the stability of the neck.

Anatomical note: The ligamentum nuchae was traditionally described as a fibroelastic sheet. A more detailed anatomical description recognises its two components, the dorsal median raphe and median fascial septum.

MUSCLES OF BACK

– The muscles of the back are classified into two major groups:

1. Extrinsic (immigrant) muscles: These muscles connect the axial skeleton to the upper limb or act on the ribs.
2. Intrinsic (deep) muscles: These are the true muscles of the back, mainly responsible for movements and stabilisation of the vertebral column.

A. Extrinsic Muscles of Back

– These muscles are arranged into three layers.

1. First Layer (Superficial)

• Trapezius.
• Latissimus dorsi.

2. Second Layer

• Levator scapulae.
• Rhomboid minor.
• Rhomboid major.

3. Third Layer (Intermediate Extrinsic Muscles)

• Serratus posterior superior.
• Serratus posterior inferior.

B. Intrinsic (Deep) Muscles of Back

• These muscles develop within the back and are supplied mainly by the posterior (dorsal) rami of spinal nerves.
• They are arranged into four layers.

1. First Layer (Superficial Intrinsic Layer)

• Splenius capitis.
• Splenius cervicis.

2. Second Layer (Erector Spinae Group)

• Iliocostalis.
• Longissimus.
• Spinalis.

3. Third Layer (Transversospinalis Group)

• Semispinalis.
• Multifidus.
• Rotatores.

4. Fourth Layer (Deepest Layer)

• Levatores costarum.
• Interspinales.
• Intertransversarii.
• Suboccipital muscles.

SUBOCCIPITAL REGION

• The suboccipital region lies deep in the upper part of the posterior neck, immediately below the occipital bone.
• It contains the suboccipital muscles, suboccipital triangle, and associated neurovascular structures.

Boundaries

• Superiorly: Inferior nuchal line of the occipital bone.
• Inferiorly: Spinous process and laminae of the axis (C2).
• Laterally: Mastoid process and transverse processes of the atlas and axis.

Contents

1. Suboccipital muscles.
2. Suboccipital triangle and its contents.

Exposure of suboccipital triangle

– The suboccipital triangle is exposed by reflecting the following structures sequentially:

1. Skin.
2. Superficial fascia.
3. Greater and third occipital nerves and branches of the occipital artery.
4. Trapezius medially and sternocleidomastoid laterally.
5. Splenius capitis.
6. Semispinalis capitis and longissimus capitis.

Identification of Muscular Layers

First Layer

• Trapezius: It lies medially, with fibres directed downwards and laterally.
• Sternocleidomastoid: It lies laterally, with fibres ascending towards the mastoid process.

Second Layer

– Splenius capitis: Its fibres pass upwards and laterally towards the mastoid process and occipital bone.

Third Layer

• Semispinalis capitis: Its fibres ascend almost vertically towards the occipital bone.
• Longissimus capitis: Its fibres pass upwards and laterally towards the mastoid process.

Suboccipital Muscles

• The suboccipital muscles are four pairs of short, deep muscles connecting the occipital bone, atlas (C1), and axis (C2).
• They maintain the posture of the head and produce fine movements at the craniovertebral joints.

Muscles

1. Rectus capitis posterior major.
2. Rectus capitis posterior minor.
3. Obliquus capitis inferior.
4. Obliquus capitis superior.

Nerve Supply

– All four suboccipital muscles are supplied by the suboccipital nerve, the posterior (dorsal) ramus of C1 spinal nerve.

Actions

• Rectus capitis posterior major: It extends the head and assists in rotation towards the same side.
• Rectus capitis posterior minor: It extends and stabilises the head at the atlanto-occipital joint.
• Obliquus capitis superior: It extends and laterally flexes the head towards the same side.
• Obliquus capitis inferior: It rotates the atlas and head towards the same side at the atlanto-axial joint.

Note: These muscles play an important role in maintaining head posture and coordinating movements at the atlanto-occipital and atlanto-axial joints.

SUBOCCIPITAL TRIANGLE

• The suboccipital triangle is a triangular intermuscular space situated deep in the upper part of the posterior neck.
• It is an important anatomical landmark for identifying the third part of the vertebral artery and suboccipital nerve.

Boundaries

• Superomedially: Rectus capitis posterior major.
• Superolaterally: Obliquus capitis superior.
• Inferiorly: Obliquus capitis inferior.

Roof

1. Dense fibrous tissue.
2. Semispinalis capitis medially.
3. Longissimus capitis laterally.
4. Occasionally, splenius capitis.

Floor

1. Posterior arch of the atlas (C1).
2. Posterior atlanto-occipital membrane.

Contents

1. Suboccipital venous plexus.
2. Suboccipital nerve (posterior ramus of C1).
3. Third part of the vertebral artery.

Note: The greater occipital nerve (C2) passes inferior to the obliquus capitis inferior muscle and is closely related to the triangle, but is not a true content of its cavity.

SUBOCCIPITAL VENOUS PLEXUS

• The suboccipital venous plexus is a network of communicating veins situated within and around the suboccipital triangle.
• It communicates with:
  • Veins of the adjoining muscles.
  • Occipital veins.
  • Internal and external vertebral venous plexuses.
  • Condylar and mastoid emissary veins.
  • Deep cervical veins.

Venous plexus surrounding the vertebral artery.

Occipital Artery in the Suboccipital Region

Origin

– The occipital artery arises from the posterior aspect of the external carotid artery, usually opposite the origin of the facial artery.

Course

• It passes upwards and backwards along the lower border of the posterior belly of digastric.
• It runs deep to the mastoid region and sternocleidomastoid before crossing the upper part of the posterior triangle.
• It continues deep to splenius capitis and reaches the occipital region.
• It pierces the superficial muscular or fascial layers and ascends with the greater occipital nerve towards the scalp.
• The artery follows a tortuous course.

Branches

1. Muscular branches.
2. Meningeal branches.
3. Mastoid branches.
4. Descending branch.

Descending Branch

– It is the largest branch of the occipital artery and divides into superficial and deep branches.

Superficial Branch

• It supplies trapezius and adjoining muscles.
• It anastomoses with the ascending branch of the transverse cervical artery.

Deep Branch

• It passes between the deep posterior cervical muscles.
• It anastomoses with the deep cervical and vertebral arteries.

Third Part Of Vertebral Artery

• The third part of the vertebral artery (V3) enters the suboccipital triangle after emerging from the transverse foramen of the atlas.
• It curves backwards and medially around the lateral mass of the atlas.
• It runs in the groove on the superior surface of the posterior arch of the atlas.
• It subsequently pierces the posterior atlanto-occipital membrane and dura mater before entering the cranial cavity through the foramen magnum.

Important Relations

• The suboccipital nerve (C1) lies between the vertebral artery and posterior arch of the atlas.
• The artery is surrounded by a venous plexus.
• Its curved course accommodates movements of the head and atlas.

Suboccipital nerve

• The suboccipital nerve is the posterior (dorsal) ramus of the first cervical spinal nerve (C1).
• It is predominantly motor and supplies the deep suboccipital muscles.

Course

• It emerges posteriorly between the vertebral artery and posterior arch of the atlas.
• It enters the suboccipital triangle and divides into muscular branches.

Muscular Branches

1. Rectus capitis posterior major: It assists in extension and ipsilateral rotation of the head.
2. Rectus capitis posterior minor: It extends and stabilises the head.
3. Obliquus capitis superior: It extends and laterally flexes the head.
4. Obliquus capitis inferior: It rotates the atlas and head towards the same side.
5. Semispinalis capitis: It contributes to extension and rotation of the head.

Communications

• The branch supplying obliquus capitis inferior may communicate with the greater occipital nerve (C2).
• The suboccipital nerve usually has no cutaneous branch, although occasional cutaneous contributions have been reported.

Note: The anterior ramus of C1 contributes to the formation of the cervical plexus.