Back Muscles

Original Editor - Lucinda hampton

Top Contributors - Lucinda hampton and Kim Jackson  

Introduction

A well muscled back

There are three major groups of back muscles:

1. Superficial: attached to the shoulder girdle
2. Intermediate: attached to the posterior thorax
3. Deep: attached to the vertebral column, also known as the intrinsic muscle group

These groups serve to allow: flexion/extension, rotation, and side bending of the back; movement of the limbs; locomotor function; and assistance in the respiratory effort.

Additional terminology

1. The superficial and intermediate muscle groups (or extrinsic muscles) are also called immigrant muscles, since they actually represent muscles of the upper limb that have migrated to the back during fetal development.
2. The deep/intrinsic back muscles, are also called true back muscles. They are located deep to the extrinsic muscles, being separated from them by the thoracolumbar fascia.

Generalized back pain is a common presenting symptom for patients, the etiology of the pain commonly traces to a strain of the skeletal muscle.

Superficial Group

A Trapezius D Latissimus Dorsi E Levator Scapulae F Rhomboid Major

The first category is the superficial back muscles. These muscles are located posteriorly on the back, whose function is to move the scapula.. The superficial muscles include:

• Trapezius
• Latissimus dorsi
• Levator scapulae
• Rhomboids

Each of the muscles in this group are fairly large and superficial and correctly locating any one of them by palpation is easily accomplished.

Intermediate Muscles

Serratus posterior inferior

The intermediate group contains two muscles:

• Serratus posterior superior
• Serratus posterior inferior

These muscles run from the vertebral column to the ribcage, and assist with elevating and depressing the ribs.

Both serratus posterior superior and inferior are thought to have a role as accessory muscles for respiration.

Deep/Intrinsic Muscles

The deep muscles of the back are well-developed, and collectively extend from the sacrum to the base of the skull. They are associated with the movements of the vertebral column, and the control of posture.

The muscles themselves are covered by deep fascia, which plays a key role in their organisation.

The deep muscles of the back can be further subdivided into their own superficial, intermediate and deep layers.

The superficial muscles are also known as the spinotransversales.

There are two muscles in this group

1. Splenius capitis
2. Splenius cervicis.

They are both associated with movements of the head and neck. They are located on the posterolateral aspect of the neck, covering the deeper neck muscles.

Erector Spinae.

Erector spinae group

The erector spinae (ES) group (medially to laterally) consist of:

1. Iliocostalis
2. Longissimus
3. Spinalis

The muscle group is bilateral on either side of the vertebral column and when both sides are engaged function as the primary extensor of the back. Unilaterally they assist with lateral bending and rotation of the spine.

The Deep Intrinsic Muscles - Transversospinales

Transversospinales group and segmental muscles

They are a group of short muscles (deep to ES), associated with the transverse and spinous processes of the vertebral column. Transversospinalis group consist of (from superficial to deep):

1. Semispinalis
2. Multifidus
3. Rotatores

Like the erector spinae group, the transversospinalis group is located bilaterally on the vertebral column between the transverse processes and the spinous processes. These muscles assist in bending the back posteriorly when contracted bilaterally. When unilateral contraction occurs, they are responsible for assisting with lateral bending and rotation.

Nerves

Ventral and Dorsal Rami Formation

Nervous supply to the intrinsic/deep back primarily arises from dorsal rami of the spinal nerves, providing sensation the skin of the back, and the intrinsic muscles of the back.

This innervation is in contrast to the extrinsic muscles of the back, which are innervated by ventral rami.

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