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Deep muscles of the back
Deep muscles of the back
The prosection is in the prone position:
Let’s begin with muscles that extend the spine and head. These are worth knowing about since back pain and muscle spasm are so common.
Splenius Muscles
Splenius translates to “bandage”—indeed these muscles look like bandages applied to the posterior head and neck.
■Identify the splenius capitis and splenius cervicis muscles.
■The splenius muscles arise together from the nuchal ligament and C-7 to T-6 vertebral spinous processes.
■The splenius capitis inserts on the skull.
■The splenius cervicis inserts on cervical transverse processes.
■The splenius muscles extend the head and neck.
Erector Spinae Muscles
This is a thick longitudinal column of muscles that fills the concavity of the vertebral column between the spinous processes and transverse processes. The erector spinae span the entire back—from skull to sacrum. The erector spinae have three parts:
■Spinalis. The smallest and most medial column of the erector spinae—runs from “spine to spine.” It arises below from spinous processes in the lumbar and thoracic region and inserts above into spinous processes of upper thoracic vertebrae.
■Longissimus. Intermediate column. It arises from the iliac crest and posterior sacrum. It inserts above into the posterior ribs, transverse processes of cervical vertebrae, and to the skull. The longissimus is the “longest” column of the erector spinae, thus its name.
■Iliocostalis. Lateral column of the erector spinae. As its name implies—it spans from hip bones to ribs. It arises with the longissimus from the iliac crest and posterior sacrum. It inserts above on the angles of all the ribs and to the transverse processes of the cervical vertebrae.
Functions of the erector spinae:
■Returns the head and spine to the erect position after it has been flexed.
■Supports the spine and keeps it from drifting forward. Consider this: most the weight in our body is anterior to the spine, especially if a person is carrying extra weight in their midsection. The erector spinae has continuous tone, to prevent forward drift.
■The erector spinae controls flexion of the head and spine. The erector spinae contracts during BOTH flexion and extension of the head and spine. As the head and spine move forward during flexion, the erector spinae contracts to allow for smooth flexion to occur, and not a forward “lurch” of the head and spine which would happen due to gravity pulling forward, since most of the weight of the head and trunk is anterior to the spine. Kind of like “paying out rope” to a climber that is rappelling down a mountainside.
■Innervation of splenius muscles and erector spinae—Since these muscles are dorsal to the vertebral column, they are innervated segmentally by dorsal rami of spinal nerves.
These deep muscles of the back are the only muscles that we will encounter in our anatomy course that are innervated by dorsal rami of spinal nerves.
Superficial Muscles of the Back and Posterior Shoulder Muscles
Superficial muscles of the back & shoulder
These muscles move the scapula and upper limb.
On the superficial side of the dissection, identify the following muscles:
■Trapezius
■Trace out its upper portion (descending fibers), middle portion (transverse fibers), and inferior portion (ascending fibers). What are the functions of these parts of the muscle?
■Latissimus dorsi
■Posterior part of the deltoid muscle
■Triceps brachii—this muscle is in the posterior arm—we will see it again
■The long head and lateral head of the triceps should be visible.
On the deep side of the dissection, identify the following muscles:
■Rhomboid muscles (major and minor)
■Levator scapulae
■Supraspinatus
■Infraspinatus
■Teres minor
■Teres major
Question
Muscles of the back have at least one attachment to the vertebral column. The deep back muscles (splenius & erector spinae muscles) were covered at the start. There are 5 superficial muscles of the back covered in this section - can you name them?
We will encounter the muscles of this section again as we move into studying the shoulder. As we do, continue to work on learning the attachments, actions, and innervations of these muscles.