The muscles of the back can be divided into three groups – superficial, intermediate, and deep or intrinsic. The deep muscles are separated from the superficial and intermediate muscles, in that they develop in the back itself. As a result, the deep muscles are referred to as intrinsic, whereas the superficial and intermediate muscles are considered extrinsic. In this article, we will focus on the anatomy, attachments, innervation, and functions of the muscles found in the intermediate back muscles group – the serratus posterior superior and serratus posterior inferior.
The serratus posterior superior is a thin, rectangular shaped muscle that lies deep to the rhomboid muscles in the upper back. It originates from the lower part of the ligamentum nuchae, and from the cervical and thoracic spines (usually C7 – T3). Its fibres pass in an inferolateral direction, attaching to ribs 2 – 5. The primary roles of the serratus posterior superior are elevating the ribs 2 – 5 and respiratory function. The muscle is innervated by the intercostal nerves.
The serratus posterior inferior is a broad and strong muscle that lies underneath the latissimus dorsi. It originates from the thoracic and lumbar spines (usually T11 – L3) and passes in a superolateral direction, attaching to ribs 9 – 12. Its primary functions are depressing the ribs 9 – 12 and aiding in respiration. The serratus posterior inferior is innervated by the intercostal nerves.
The embryology and development of the serratus posterior superior and serratus posterior inferior muscles are complex and multi-faceted. While the primary role of these muscles is movement of the rib cage and respiration, they do also play a role in other bodily functions. The ligamentum nuchae and the cervical and thoracic spines are also important for the innervation of the serratus posterior superior and inferior muscles, respectively.
The intrinsic and extrinsic muscles of the back play an important role in human anatomy, and the intermediate back muscles are no exception. The serratus posterior superior and serratus posterior inferior are essential for respiration and lift of the rib cage, and are innervated by the intercostal nerves. It is essential to recognize and understand the anatomy, attachments, innervation, and functions of these muscles in order to better understand the complex system of human anatomy.
