Muscles and nerves of the back

Dr.Mohammed Mahmoud Mosaed

Cutaneous innervation and blood supply of the back

• Cutaneous innervation • The sensory nerve supply to the skin of the back is

from the posterior rami of the spinal nerves. The first and eighth cervical nerves do not supply the skin, and the posterior rami of the upper three lumbar nerves run downward to supply the skin over the buttock.

• The blood supply to the skin is from the posterior branches of the posterior intercostal arteries and the lumbar arteries.

• The veins correspond to the arteries and drain into the azygos veins and the inferior vena cava.

• The lymph drainage of the skin of the back above the level of the iliac crests is upward into the posterior group of axillary lymph nodes.

MUSCLES OF BACK ACT ON THE UPPER LIMBS

• First Layer: • Trapezius • Latissimus dorsi.

• Second Layer: • Levator scapulae, • Rhomboid minor • Rhomboid major.

Trapezius• Origin: Medial third of superior nuchal line of occipital bone.• External occipital protuberance. Ligamentum nuchae.• Spine of the seventh cervical vertebra. Spines of all thoracic vertebrae• Insertion:• Upper fibers into the posterior aspect of the lateral third of the clavicle.• Middle fibers into the medial border of the acromion process of the

scapula.• Lower fibers into the spine of the scapula.• Nerve Supply:• Motor fibers from the spinal part of accessory nerve.• Proprioceptive sensory fibers from the third and fourth cervical nerves.• Action:• Upper fibers: elevates the scapula.• Middle fibers: retracts the scapula.• Lower fibers: depresses the scapula.• With serratus anterior: rotates the scapula upward (for abduction of the

arm more than 90°.

Latissimus dorsiOrigin:• Spines of the lower 6 thoracic vertebrae.• Lower 3 or 4 ribs.• Lumbar fascia and posterior part of iliac crest.• Inferior angle of the scapula.Insertion: Floor of the bicipital groove of the

humerus.Nerve Supply: Thoracodorsal nerve.Action: Adduction, extension and medial rotation of the arm

Levator scapulaeOrigin: The transverse processes of the upper

four cervical vertebrae.Insertion: Dorsal lip of the medial border of the

scapula above the level of its spine.Nerve Supply: From the ventral rami of the 3rd

and 4th cervical nerves and form dorsal scapular nerve (C5).

Action: Elevation of the scapula.

Rhomboid major and minor• Rhomboid major• Origin: From 2nd to 5th spines of the thoracic vertebrae

and their supraspinous ligaments.• Insertion: Dorsal lip of the medial border of the scapula

below the level of its spine.• Nerve Supply: Dorsal scapular nerve (C5).• Action: Raises medial border of scapula upward and

medially • Rhomboid minor• Origin: 1. Lower part of ligamentum nuchae.• 2. Spine of seventh cervical vertebra.• 3. Spine of first thoracic vertebra.• Insertion: Dorsal lip of the medial border of the scapula opposite the root of its spine.• Nerve Supply: Dorsal scapular nerve (C5).• Action: Raises medial border of scapula upward and medially

Spinal Part of the Accessory Nerve (Cranial Nerve XI)

• The spinal part of the accessory nerve runs downward in the posterior triangle of the neck on the levator scapulae muscle.

• The accessory nerve runs beneath the anterior border of the trapezius muscle at the junction of its middle and lower thirds and, together with the cervical nerves, supplies the trapezius muscle.