Splenius Capitis Muscle
The splenius capitis is one of the deep muscles of the back of the neck. It acts as an extensor of neck, lateral flexor and assists in rotation of the neck, and forms part of the floor of the posterior triangle of the neck. In this article we will discuss the gross and functional anatomy of the splenius capitis. In order to understand the context of the splenius capitis muscle, we have also discussed the posterior triangle of the neck, and some of the main contents. We will also discuss the clinical relevance of the structure, and provide a summary of key points at the end of the article. We will finally conclude with some review questions to test the reader’s understanding of the article content.
Posterior triangle of the neck
This is formed by the posterior border of sternocleidomastoid, the anterior border of trapezius and the superior margin of the clavicle as the base. The accessory nerve passes obliquely across this space, and innervates the sternocleidomastoid muscle, and passes through the muscle to innervate the trapezius. At the lower part of the triangle is where the supraclavicular, transverse cervical (cutaneous branches of the cervical plexus) and superior part of the brachial plexus can be found. A sequence of lymph node are also located running along the posterior border of sternocleidomastoid.
The origin of the name splenius capitis originates from the Greek word ‘Splenion’ meaning bandage, and the Latin word ‘caput’ meaning head. The muscle has a bandage like appearance and attaches to the mastoid process of the base of the skull. The muscle arises from the lower half of the nuchal ligament and spinous processes of the 7th cervical vertebra and first three thoracic vertebrae. The muscle fibers then run superiorly and laterally, in order to insert onto the mastoid process of the temporal bone. The mastoid process is a pyramidal shaped eminence on the base of the skull, and is a pneumatised bone due to the mastoid air cells. The muscle also inserts in part onto the external surface of the occipital bone, below the lateral section of the superior nuchal line. The muscle lies deep to the sternocleidomastoid in its superior portion, and deep to trapezius in its inferior portion. The muscle acts as a shaker of the head, it causes neck extension and lateral flexion. Other muscles that extend and rotate the head include the semispinalis capitis and semispinalis cervicis (also laterally flexes the head). The superior portion of trapezius also acts as a lateral flexor of the neck. The innervation to the muscle arises from the posterior rami of the 3rd and fourth cervical spinal nerves. The blood supply to the muscle arises from the muscular branches of occipital artery, a branch of the external carotid artery.