Back Muscles: Attachments, Nerve Supply & Action

Posted by Rafiqul Islam
May 19, 2018
Posted in Back & Thorax

Back Muscles: The muscles of the back that work together to support the spine, help keep the body upright and allow twist and bend in many directions. The back muscles can be three types.
a. Superficial Back Muscles
b. Intermediate Back Muscles and
c. Deep Back Muscles

Superficial Back Muscles
Action – Movements of the shoulder.

Intermediate Back Muscles
Action – Movements of the thoracic cage.

Deep Back Muscles
Action – Movement of the vertebral column
The deep muscles develop in the back called intrinsic muscles.
The superficial and intermediate muscles do not develop in the back so-called extrinsic muscles.

Superficial Back Muscles

These muscles are situated underneath the skin and superficial fascia. They arise from the vertebral column and inserted into the bones of the shoulder such as
Clavicle
Scapula and
Humerus
All superficial muscles associated with movements of the upper limb.
Superficial muscles are given below-
Trapezius
Latissimus dorsi
Levator Scapulae
Rhomboids

Trapezius and latissimus dorsi lie in the very much superficially. Trapezius covering levator scapulae and the rhomboids.

Trapezius: The trapezius is a broad, flat and triangular muscle. The muscles on each side form a trapezoid shape. It is the most superficial of all the back muscles.
Origin:
Occipital protuberance
Ligamentum nuchae
The spine of 7th cervical vertebra
Spine of all thoracic vertebra
Insertion:
Upper fibers into posterior border of the lateral third of the clavicle
Middle fibers into the medial margin of the acromion and upper lip of the crest of the spine of the scapula
Lower fibers on the deltoid tubercle
Nerve supply:
Spinal part of the accessory nerve is motor
Branches from C3, C4 are proprioceptive
Action:
Upper fibers elevate the scapula
Middle fibers retract the scapula
Lower fibers pull the scapula inferiorly.

Latissimus dorsi: The latissimus dorsi originates from the lower part of the back, where it covers a wide area.
Origin:
Posterior one-third of the outer lip of iliac crest
Posterior layer of lumbar fascia
Spines of T7-T12 Vertebra
Lower four ribs
Inferior angle of the scapula
Insertion:
The bicipital groove of the humerus
Nerve supply:
Thoracodorsal nerve ( nerve to latissimus dorsi)
Action:
Adduction, extension and medial rotation of the shoulder

Levator scapulae: The levator scapulae is a small strap-like muscle. It begins in the neck and descends to attach to the scapula.
Origin: Transverse process of first four cervical vertebrae (C1 –C4 )
Insertion: Superior angle and upper part of medial border of scapula
Nerve supply: Dorsal scapular nerve
Action: Elevation of the scapula

Rhomboids: There are two muscles.
Rhomboideus minor
Rhomboideus major
Rhomboideus minor is situated above major.
Rhomboideus minor:
Origin:
The lower part of ligamentum nuchae
The spine of C7 and T1 vertebra
Insertion: Upper 1/3rd of medial border of scapula
Nerve supply: Dorsal scapular nerve
Action: Retraction rotation of the scapula
Rhomboideus major:
Origin: Spine of the T2-T5 vertebra
Insertion: Medial border of scapula between the spine of scapula and inferior angle.
Nerve supply: Dorsal scapular nerve
Action:
Retraction rotation of the scapula

Intermediate Back Muscles

Serratus posterior superior
Serratus posterior inferior

Serratus posterior superior: The serratus posterior superior is a thin muscle, situated at the upper and back part of the thorax, deep to the muscles of the rhomboid.
Origin: Spinous processes and supraspinous ligaments of C7-T2
Insertion: Posterior aspect of ribs 2-5
Function: Assists forced inspiration
Nerve Supply: Anterior primary rami (T2-5)

Serratus posterior inferior: The serratus posterior inferior is one of the back's two intermediate muscles.
Origin: The serratus posterior inferior originates from the spinal processes of vertebrae T11 to T12 and L1 to L2.
Insertion: Inserts into the lower borders of ribs 9-12.
Function: The function of the serratus posterior inferior muscle depresses thoracic ribs 9-12, assisting with forced exhaling.
Nerve Supply: Intercostal nerves.

Deep Back Muscles

The deep back muscles have three layers-
a.Superficial
b.Intermediate
c.Deep.

Superficial Deep Back Muscles:
Action: Movement of the head and neck

Splenius Capitis:
Origin:
ligamentam nuchae
Spinus process of C7 –T3/T4 vertebrae
Insertion:
Mastoid process
The occipital bone of the skull
Nerve supply: Posterior rami of spinal nerves C3 and C4.
Actions: Rotate head to the same side.

Splenius cervicis:
origin: Spinus process of T3-T6 vertebrae
insertion: Transverse processes of C1-C4
Nerve supply: Posterior rami of the lower cervical spinal nerves.
Action: Rotate head to the same side.

Intermediate Deep Back Muscles:
There are in three muscle.

Iliocostalis: The muscle is situated laterally within the erector spinae.The muscle is related to the ribs.The muscle divided into three parts.
-Lumborum
- Thoracis and
-Cervicis
Origin: Common tendinous origin
Insertion:
The costal angle of the ribs
Cervical transverse processes
Nerve supply: Posterior rami of the spinal nerves.
Action:
Unilaterally to laterally flex the vertebral column
Bilaterally to extend the vertebral column and head.

Longissimus: The muscle is located between the iliocostalis and spinalis.This muscle is the largest of the three columns.
The muscle has three parts:
-Thoracic
-Cervicis and
-Capitis.
Origin: tendinous origin
Insertion:
Lower ribs
Transverse processes of C2-T12
Mastoid process of the skull
Nerve supply: Posterior rami of the spinal nerves.
Action:
unilaterally to laterally flex the vertebral column.
bilaterally to extend the vertebral column and head.

Spinalis: The muscle is situated medially within the erector spinae.The muscle is the smallest of the three muscle columns.
The muscle has three part.
- Thoracic
- Cervicis and
- Capitis
Origin: Common tendinous origin
Insertion:
Spinous processes of C2, T1-T8
The occipital bone of the skull
Nerve supply: Posterior rami of the spinal nerves.
Action:
Unilaterally to laterally flex the vertebral column.
Bilaterally to extend the vertebral column and head.
These three muscles called erector spinae.

Most Deep Back Muscles: These muscles are situated underneath the erector spinae.They are a group of short muscles.
Related to transverse and spinous processes of the vertebral column.
The deep back muscles are:
Semispinalis: The muscle is the most superficial of the deep intrinsic muscles.The muscle has three parts.
- Thoracic
- Cervicis and
- Capitis.
Origin: Transverse processes of C4-T10
Insertion:
Spinous processes of C2-T4
The occipital bone of the skull
Nerve supply: Posterior rami of the spinal nerves.
Action: Extends and contralaterally rotates the head and vertebral column.

Multifidus: The muscle is situated underneath the semispinalis muscle. This muscle is best developed in the lumbar area.
Origin:
Sacrum
Posterior iliac spine
Common tendinous origin of the erector spinae
Mamillary processes of the lumbar vertebra
Transverse processes of T1-T3 and
Articular processes of C4-C7.
Insertion: Spinous processes of the vertebrae.
Nerve supply: Posterior rami of the spinal nerves.
Action: Stabilises the vertebral column.

Rotatores: The muscles are most prominent in the thoracic region
Origin: Vertebral transverse processes.
Insertion: Lamina and spinous processes of the immediately superior vertebrae.
Nerve supply: Posterior rami of the spinal nerves.
Action:
Stabilises the vertebral column
Proprioceptive function.

Quadratus Lumborum: The quadratus lumborum is the most posterior deep back muscles of the posterior abdominal wall. The quadratus lumborum is the deepest abdominal muscle and commonly referred to as a back muscle.Quadratus Lumborum
Origin: Posterior Iliac Crest
Insertion: Medial half of 12th rib and transverse processes of lumbar vertebrae.
Nerve Supply: Subcostal nerve (T12), Iliohypogastric and Ilioinguinal nerve (both from L1) & Branches from the ventral rami (L2 and L3)
Function: Quadratus Lumborum fixes the12th rib to stabilize diaphragm attachments during inspiration, Lateral flexes the vertebral column & Extends lumbar vertebrae