Semispinalis

Original Editor - Lucinda hampton

Top Contributors - Lucinda hampton, Chioma Clara Okeakpu and Kim Jackson  

Introduction

Semispinalis muscle

The muscles of the back are divided into three groups. The intrinsic or deep muscles which fuse with the vertebral column, the superficial muscles, which help with shoulder and neck movements and the intermediate muscles, which help with the movement of the thoracic cage. Only the intrinsic muscles are considered true back muscles. The Semispinalis muscles belong to the intinsic/ deep muscles of the back . Other deep muscles of the back include the multifidus, and rotatores which makes them three deep muscles of the back collectively called the Transversospinales muscle group . These muscles are well-developed, and collectively extend from the sacrum to the base of the skull. They stabilize the vertebral column and play a role in proprioception and balance. They help with the movements of the vertebral column and maintain posture. Among this muscle group, semispinalis forms the most superficial layer and largest muscle mass in the posterior aspect of the neck. It has the longest fascicles of transversospinalis group, spanning six segments.

Origin & Insertion

As the muscles of the back develop, they extend caudally. The origins and insertions are described as though the fibers run caudocranially. In this manner, origins are inferior to their insertions. Semispinalis originates from the thoracic and cervical transverse processes and inserts at the occipital bone and spinous processes in thoracic and cervical regions 4 to 6 segments above the origin.

Nerve

The intrinsic or true back muscles are innervated by the posterior, or dorsal, primary rami of the spinal nerves while the extrinsic back muscles are innervated by the ventral rami of the spinal nerves therefore the transversospinalis group of muscles are innervated by the dorsal primary rami of C1-L5.

Arterial Supply

Although arterial supply varies from person to person , all muscle groups of the back are supplied by deep cervical, posterior intercostal, subcostal, or lumbar arteries.

Location & Anatomical Relations

Semispinalis muscles are long flat skeletal muscles found along the upper back and posterior neck regions and are the most superficial of the transversospinal muscles. The muscle is divided into three parts which are the semispinalis capitis, semispinalis cervicis, and the semispinalis thoracis.

1. Semispinalis capitis muscle- This is the superior portion which lies superficial to the semispinalis cervicis muscle and deep to the splenius capitis and cervicis and trapezius.
2. Semispinalis cervicis muscle - fascicles which cover the cervical and thoracic multifidus muscles. It is the middle portion.
3. Semispinalis thoracis muscle - thin, fleshy fascicles with long tendons at either end. Covers the thoracic multifidus muscle and is regarded as the inferior portion.
   • origin: T6-T10 transverse processes
   • insertion: C6-T4 spinous processes

Deep Intrinsic Back Muscles

Deep Muscles of the back

Functions

1. Rotation of the head ,neck and trunk to the opposite side during unilateral contraction
2. Extension and hyperextension of the cervical spine during bilateral contraction.
3. Lateral head flexion during unilateral contraction.

Clinical Relevance

Cervical intermediate muscles

The semispinalis capitis is the largest muscle in the posterior neck. The semispinalis cervicis and capitis lie deep to the upper trapezius.

• Muscle pain that emanates from this region is often misdiagnosed as a trapezius injury, when it is a semispinalis problem.

• The greater occipital nerve (innervates the posterior scalp) pierces through the semispinalis capitis (as well as the upper trapezius). Occipital neuralgia may on occasion be produced by entrapment of the greater occipital nerve in the perforation site of the semispinalis capitis.
• See Introduction to Cervicogenic Headaches