Semispinalis Capitis – Functional Anatomy

Overview

Semispinalis capitis anatomy is significant for managing pain. It is a large muscle that extends the head, perpetuates forward head posture, and squeezes the greater occipital nerve.

Origin

• articular processes of C4-C7
• transverse processes of T1-T6

Insertion

• between the superior and inferior nuchal ridges of the occipital ridge

Function

• extension and some rotation of the head

Nerve

• greater occipital nerve, posterior ramus of C2
• spinal nerve C3

Attachment Details

The functional anatomy of semispinalis capitis is significant regarding upper cervical pain. It attaches to the occiput and then usually skips the first three cervical vertebrae. After that, it has variable attachments to the vertebrae from C4 through T7.

Anomalies, Etc.

Dissection studies vary in their report of attachments on the thoracic vertebrae. They show that they differ in which vertebrae are attached, and some slips attach to the transverse or spinous processes.

The greater occipital nerve (GON) is structurally vulnerable to tension in semispinalis capitis. This nerve branches off of the C2 dorsal ramus below the posterior arch of the atlas. Often, it has fibers from the C1 nerve root and occasionally from C3. The palpable tension of the C2 nerve root at its emergence is a reliable indicator of atlas displacement. It winds around the lower border of the obliquus capitis inferior. Then, it passes superficial to the suboccipital muscles. The nerve extends superiorly until it pierces semispinalis capitis and emerges deep to the trapezius. It passes through the attachment tendon on the superior nuchal line near the external occipital protuberance. It then passes under the galea aponeurosis.

The GON has variations in its path. Studies vary slightly but show that the GON pierces the semispinalis capitis about 90% of the time. However, it pierces the trapezius about 45% of the time. In rare instances, about 7% of the time, it pierces the obliquus capitis inferior.

Tension in semispinalis capitis entraps the greater occipital nerve, creating posterior head pain and paraesthesia.

Semispinalis Muscle Group

The semispinalis muscle group includes:

• Semispinalis Capitis
• Semispinalis Cervicis
• Semispinalis Thoracis

Capitis attaches to the cranium base, but the other two are interspinous muscles. These muscles are deep to the extrinsic back muscles and superficial to other interspinous muscles. They provide another layer of paraspinal erectors to support the cervical muscles on the thoracic column.

Often, these muscles are considered to be another, deeper layer of the erector spinae. Comparatively, they have similar attachments and perform a similar function to the erectors just superficial to them. Likewise, they are a longer version of the multifidi muscles, which are deep to this semispinalis group.

All of the semispinalis muscles have statistically significant variations in their structure.

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