Muscles that Move the Shoulder and Upper Limb

Overview: Scapula and Humerus Musculature

The shoulder and upper limb are moved by a complex group of muscles, many of which are unique compared to those found in the lower limb. This complexity is due to the anatomy and functional requirements of the upper limb, which is not as firmly attached to the axial skeleton as the leg.

• Brachial plexus: The upper limb is innervated by five terminal branches of the brachial plexus, which do not follow a simple quadrant system as in the leg. Instead, muscle actions help organize the region.

• Attachment: The upper limb's loose attachment to the skeleton requires additional muscles for stabilization and movement.

• Muscle structure: Several large, fan-shaped muscles support the scapula, which are not present in the lower limb.

Movements of the Scapula

Types of Scapular Movements

The scapula can perform a variety of movements depending on which muscles are activated. These movements are essential for positioning the upper limb and facilitating shoulder joint mobility.

• Stabilization: Contraction of specific muscles stabilizes the scapula against the thoracic wall.

• Movement: Sequential contraction of different muscles causes the scapula to move in various directions.

Main movements of the scapula include:

• Elevation: Lifting the scapula upwards (e.g., shrugging shoulders).

• Depression: Lowering the scapula downwards.

• Protraction: Moving the scapula forward along the rib cage.

• Retraction: Pulling the scapula backward toward the spine.

• Superior (Upward) Rotation: Rotating the glenoid cavity upward.

• Inferior (Downward) Rotation: Rotating the glenoid cavity downward.

Muscles that Move the Scapula

Trapezius

The trapezius is a large, superficial muscle that plays a key role in scapular movement and stabilization.

• Origin: Occipital bone, spines of cervical and thoracic vertebrae.

• Insertion: Acromion, spine of scapula, lateral third of clavicle.

• Innervation: Cranial Nerve XI (Spinal Accessory Nerve).

• Functions:

  • Extends the neck.

  • Elevates, depresses, and retracts the scapula.

  • Superior rotation of the scapula, moving the glenoid cavity upward and anterior.

Example: Shrugging the shoulders involves elevation of the scapula by the trapezius.

Additional info:

• Other muscles involved in scapular movement include the levator scapulae, rhomboids, serratus anterior, and pectoralis minor. Each contributes to specific movements such as elevation, retraction, protraction, and rotation.