Nuchal region

Extrinsic layer

The extrinsic or superficial layer of the nuchal region consists of the descending part of the trapezius. It is located directly underneath the subcutaneous layer. As a whole, the trapezius muscle consists of three parts: descending, transverse and ascending. The descending (superior) part originates from the medial third of superior nuchal line, external occipital protuberance and nuchal ligament. Close to these points of origin, the muscle forms part of the nape of the neck. The transverse and descending parts of the trapezius originate from the spinous processes and supraspinous processes of C7 and all twelve thoracic vertebrae.

Distally, the muscle inserts into the clavicle, acromion and the spine of the scapula. Additionally, it is enclosed within the investing layer of the deep cervical fascia, sometimes called the nuchal fascia of the trapezius muscle.

Intrinsic layer

This layer is located at a deeper level and the muscles, collectively, act to maintain posture and control the movements of the vertebral column. In the nuchal region, these muscles are enclosed within the prevertebral layer of the deep cervical fascia which attaches medially to the nuchal ligament, the spinous processes of the vertebrae and the supraspinous ligament. Laterally, the fascia attaches to the transverse processes of the cervical vertebrae. The intrinsic layer is subdivided into several layers, as given below:

a) Superficial layer - Splenius

b) Intermediate layer- Erector spinae, consisting of spinalis, longissimus and iliocostalis

c) Deep layer - Transversospinalis

• Semispinalis group
• Multifidus group
• Rotatores group

a) In the nuchal region, the superficial intrinsic layer consists of the splenius muscles. They lie on both the lateral and posterior aspects of the neck. There are two splenius muscles: splenius cervicis and splenius capitis.

Splenius cervicis originate from the transverse processes of C1-C3 and inserts into the spinous processes of T3-T6 vertebrae. Splenius capitis originate from the mastoid process and from a surface just below the lateral third of the superior nuchal line. They insert into the spinous processes of C7, T1 to T3 or sometimes T4 and the associated supraspinous ligaments.

b) The intermediate layer consists of the erector spinae muscles and lie along the vertebral column, on either side. Their role is to extend the vertebral column. These band like muscles consist of three types: the iliocostalis found laterally, the longissimus found intermedially and the spinalis found medially, closest to the vertebral column.

Regionally, each set of erector spinae is further subdivided into three parts: cervicis, thoracis and lumborum. All the erector spinae muscles originate from a broad tendon located in the area of the sacrum. Their points of insertions vary but all three of them extend up to the nuchal region. The iliocostalis runs up to the transverse process of C4-C7 in the nuchal region. The iliocostalis cervicis runs between the posterior tubercles of C4-C6 and the ribs in the thoracic region. The longissimus fibers extend superiorly to the transverse processes of cervical vertebrae and past them, until the mastoid process.

The longissimus capitis originates from the articular and transverse processes of C4-C7 (nuchal region) and from the transverse processes of T1-T4. In turn, it inserts into the mastoid process of the temporal bone. The longissimus cervicis connects the posterior tubercles of the C2-C6 transverse processes with the transverse processes of T1-T6 in the thoracic region. The spinalis cervicis extend from the spinous processes of the axis and C3-C4 and inserts into the lower part of the nuchal ligament and the spine of C7.

c) The deep layer consists of muscles occupying the space between the transverse and spinous processes of the vertebrae. Collectively, this muscle group is known as the transversospinalis muscle group.

The semispinalis is the most superficial group of this layer and it is also divided regionally into capitis, cervicis and thoracis. Semispinalis capitis covers semispinalis cervicis. They originate from the area between the superior and inferior nuchal lines and insert into the superior articular processes of C4-C7 within the nuchal region and further down in the thoracic vertebrae. The semispinalis cervicis arises from the spinous processes of C2-C5 and insert into the transverse processes of the thoracic vertebrae.

The middle layer of the deep muscles is the multifidus. In the nuchal region, they originate from the spinous processes of cervical vertebrae and insert into the superior articular processes of a different vertebrae located between two and five positions below.

The deepest muscles of the transversospinalis group are the rotatores. These originate from the transverse processes of the vertebrae and insert into the spinous processes or the junction between the lamina and the transverse processes. The rotatores brevis insert into the spinous process of the vertebra immediately adjacent while the rotatores longus insert into the spinous process of a vertebrae located two segments away. The rotatores are not obviously present in the cervical and lumbar region, where they may be represented by the deeper fascicles of the multifidus.

There is also a minor layer of deep muscles in this region called the interspinales and intertransversarii (anterior and posterior). The interspinales are located between the spinous processes of adjacent cervical vertebrae. The intertransversarii extend between the transverse processes of adjacent vertebrae. Together, this minor muscle group aids in stabilizing and extending the vertebral column.

Subcutaneous layer

This layer of fatty tissue contains the terminal branches of the superficial and deep cervical arteries together with the occipital artery. The blood from this region drains to the posterior external jugular vein, which is sandwiched between the trapezius and the splenius muscles. In turn, the posterior external jugular vein drains into the external jugular vein. The superficial cervical lymph nodes are responsible for the lymphatic drainage, with the help of the occipital and the mastoidian ones.

The greater occipital nerve, lesser occipital nerve and the cutaneous branches of the posterior rami of C2-C4 are present in this layer. The largest cutaneous nerve of this region is the greater occipital nerve coming from the posterior primary ramus of C2. It exits superficially to the trapezius by piercing it close to the external occipital protuberance and travelling upwards towards the occipital region. The lesser occipital nerve, a branch of the cervical plexus, runs upwards towards the occipital region and through the nuchal region. The third occipital nerve is also situated in this area and it usually arises from medial branch of posterior primary ramus of C3.

Muscular layer

The trapezius is innervated by the spinal accessory nerve (CN XI) and the C3-C4 spinal nerves, which are present in the nuchal region. The latter also supply the skin of this region.

With the exception of the rotatores, all the intrinsic back muscles receive their blood supply from the branches of the occipital, deep cervical and vertebral arteries. The rotatores receive blood from the dorsal branches of the segmental arteries. The occipital artery originates from the external carotid artery. It ascends towards the level of the transverse process of the atlas and mastoid process and it passes backwards in a horizontal fashion, being sandwiched between the intermediate and deep muscle groups of the intrinsic layer, supplying those.

The deep cervical artery originates from the costocervical trunk. It runs up the back of the neck between the semispinalis capitis and semispinalis cervicis until the level of the axis, supplying the surrounding muscles. Therefore, it is mainly located within the deep layer of the intrinsic muscles.

The vertebral arteries branch of the subclavian arteries ascending through the nuchal region through the transverse foramina of C2-C6. After reaching the level of C2, it gives a transverse branch travelling through the deepest muscles of the intrinsic layer and also through the suboccipital triangles.

The muscles are drained by the posterior external carotid vein together with the vertebral veins. They receive blood from the occipital vein, from the internal and external venous plexuses and from the deep cervical veins.All of these muscles in the nuchal region are innervated by the posterior rami of cervical spinal nerves. Specific ones include suboccipital, greater occipital and lesser occipital nerves. The suboccipital nerve travels between the cranium and C1 vertebra towards the suboccipital triangles, supplying the muscles present there. The posterior rami of nerves C3-C7 pass segmentally to muscles, providing muscular innervation for the intrinsic muscle layer in addition to the cutaneous innervation.