Anatomical Position, Attachments, Nerve Supply, and Functions of the Trapezius and Latissimus Dorsi Muscles

Nerve Supply and Innervation of the Trapezius Muscle

The trapezius muscle is a large, superficial muscle extending from the occipital bone to the lower thoracic vertebrae and laterally to the scapula. It plays a crucial role in movements of the shoulder and neck.

Anatomical Position

The trapezius muscle is located in the upper back and neck region. It spans from the base of the skull, along the cervical and thoracic vertebrae, and inserts onto the clavicle and scapula.

Attachments

• Origin: Occipital bone, ligamentum nuchae, and spinous processes of C7-T12 vertebrae.
• Insertion: Lateral third of the clavicle, acromion, and spine of the scapula.

Nerve Supply and Innervation

The trapezius muscle is uniquely innervated by the spinal accessory nerve (cranial nerve XI), which provides motor function. Additionally, sensory innervation is supplied by branches of the cervical plexus (C3 and C4).

Functions

• Upper fibers: Elevate the scapula (shrugging motion).
• Middle fibers: Retract the scapula.
• Lower fibers: Depress the scapula.
• Assists in head and neck movements.

Latissimus Dorsi Muscle

The latissimus dorsi is a broad, flat muscle covering the lower back. It is responsible for various movements of the upper limb.

Anatomical Position

Located in the lower back, the latissimus dorsi extends from the thoracic and lumbar vertebrae to the humerus.

Attachments

• Origin: Spinous processes of T7-L5, iliac crest, thoracolumbar fascia, and inferior angle of the scapula.
• Insertion: Intertubercular groove of the humerus.

Nerve Supply and Innervation

The latissimus dorsi is innervated by the thoracodorsal nerve (C6-C8), a branch of the brachial plexus.

Functions

• Extension, adduction, and medial rotation of the humerus.
• Assists in movements such as pulling and climbing.