Human Anatomy: Deltoid and Scapula Muscles

Lecture Fourteen: The Muscular System – I

• Learning Objectives:
  • Review details of the muscular system.
  • Define range of motion (ROM) and how it's assessed in patients.
  • Define extrinsic and intrinsic back muscles.
  • Differentiate between layers of back muscles.
  • Identify origins, insertions, and actions/functions of back, neck, shoulder, and arm muscles.

Introduction to Muscles

• Muscles convert chemical energy (ATP) into mechanical energy (and heat).
• Anatomical terms beginning with "myo" or "mys" refer to muscles.
• Muscle fibers (myofibers) are elongated muscle cells (skeletal or smooth).
• Cardiac muscle cells are not elongated and interconnected.

Our Focus for This Unit (KINE 1101): Skeletal Muscle

• Skeletal muscle is consciously controlled (somatic nervous system).
• Skeletal muscle is rich with blood supply.
• Each muscle fiber has a nerve ending (motor unit) that tells the muscle to contract.

Range of Motion (ROM)

• Active ROM: Movement occurring around a joint or body part with muscle activation.
• Passive ROM: Movement occurring around a joint or body part without muscle activation (manually moved by a healthcare practitioner).
• Active-Assisted ROM: Muscles are activated, but the movement is assisted.

Extrinsic vs. Intrinsic Muscles of the Back

• Extrinsic Muscles:
  • Superficial muscles with primary function being upper limb movement.
• Intrinsic Muscles:
  • Muscles attached to vertebrae or ribs.
  • Primary function is movement and support of the vertebral column.
  • Innervation: Posterior rami of spinal nerves.

Intrinsic Muscles of the Back: Erector Spinae

• Three vertical columns of muscle (iliocostalis, longissimus, spinalis).
• Commonly referred to as "I Like Standing" muscles.
• Function:
  • Bilateral: Extension of the spine.
  • Unilateral: Lateral flexion of the spine (iliocostalis).

Muscles of the Neck: Splenius Capitis and Cervicis

• Capitis: Insertion onto the skull (mastoid process).
• Cervicis: Insertion onto transverse processes of cervical vertebrae.
• Function:
  • Bilateral: Extension of the spine.
  • Unilateral: Ipsilateral lateral flexion and rotation of the head and cervical spine.

Muscles of the Neck: Sternocleidomastoid

• Origins: Sternum & Clavicle
• Insertion: Mastoid Process
• Function:
  • Bilateral: Extension of head/neck; flexion of the neck (inferior cervical vertebrae/sternal head).
  • Unilateral: Contralateral rotation, ipsilateral lateral flexion.

Deep Muscles of the Neck: Anterior

• Includes accessory muscles of respiration (longus capitis, anterior scalene, middle scalene, posterior scalene).
  • Specific functions for each muscle described.

Extrinsic Muscles: First Layer (Superficial) – Trapezius and Latissimus Dorsi

• Trapezius:

  • Origin: Posterior skull and cervical and thoracic vertebrae
  • Insertion: Clavicle, acromion and spine of the scapula
  • Function(s): Fiber group dependent: elevation, retraction, and upward rotation of scapula (upper/middle fibers) and depression of scapula (lower fibers).

• Latissimus Dorsi:

  • Origin: Lower thoracic and lumbar vertebrae, sacrum & iliac crest
  • Insertion: Floor of the intertubercular groove of the humerus
  • Function(s): Extension, adduction, and medial rotation of the arm at the glenohumeral joint.

Extrinsic Muscles: Second Layer (Superficial) – Levator Scapulae and Rhomboids

• Levator Scapulae:
  • Origin: Cervical spine
  • Insertion: Superomedial border of the scapula
  • Function(s): Elevation of the scapula.
• Rhomboid Major & Minor:
  • Origin: Cervical and thoracic spine
  • Insertion: Medial border of the scapula
  • Function(s): Retraction (adduction) of scapula.

Extrinsic Muscles: Third Layer (Superficial) – Serratus Posterior Superior & Inferior

• Serratus Posterior Superior:
  • Origin: SPs of lower cervical to upper thoracic spine
  • Insertion: First 4 ribs
  • Function: Elevation of the ribs.
• Serratus Posterior Inferior:
  • Origin: SPs of lower thoracic vertebrae
  • Insertion: Ribs 9-12
  • Function: Depression of lower ribs.

Muscles of the Shoulder: Anterior

• Pectoralis Major:
  • Origin: Clavicular and sternal heads.
  • Insertion: Lateral lip of the intertubercular groove.
  • Function(s): Glenohumeral flexion, medial rotation, and adduction of the arm.
• Subclavius:
  • Origin: First rib (costal cartilage)
  • Insertion: Clavicle (inferior surface)
  • Function: Depression of the clavicle.
• Pectoralis Minor:
  • Origin: Ribs 3-5
  • Insertion: Coracoid process of the scapula
  • Function: Depression and downward rotation of scapula.
• Serratus Anterior:
  • Origin: Lateral borders of the ribs
  • Insertion: Anteromedial border of the scapula
  • Function: Protraction of the scapula.

Muscles of the Shoulder: Lateral

• Deltoid:
  • Origin: Clavicle, acromion, and spine of the scapula
  • Insertion: Deltoid tuberosity on the humerus
  • Function(s): Fiber group dependent: flexion, abduction, extension, and lateral/external rotation.
  • (See details for anterior, middle and posterior portions of this muscle)

Muscles of the Rotator Cuff

• Subscapularis:
  • Origin: Subscapular fossa
  • Insertion: Lesser tubercle of the humerus
  • Function: Medial (internal) rotation of the glenohumeral joint.
• Supraspinatus:
  • Origin: Supraspinous fossa
  • Insertion: Greater tubercle of the humerus
  • Function: Initiation of arm abduction (approximately 30 degrees).
• Infraspinatus:
  • Origin: Infraspinous fossa
  • Insertion: Greater tubercle of the humerus
  • Function: Lateral (external) rotation of the glenohumeral joint
• Teres Minor: Origin: Lateral scapular border (superior portion)
  • Insertion: Greater tubercle of the humerus
  • Function: Lateral (external) rotation of the glenohumeral joint.

Summary: The Rotator Cuff

• Known as the "SITS" muscles, where each muscle letter stands for its name
• Common function is to create a cuff around the glenohumeral joint to stabilize the joint.

Muscles of the Shoulder: Posterior (Teres Major)

• Teres Major:
  • Origin: Lateral scapular border (inferior)
  • Insertion: Medial lip of the intertubercular groove on the humerus
  • Function: Extension, adduction, and medial (internal) rotation of the arm at the glenohumeral joint.

Muscular Compartments of the Arm

• Anterior: Flexor compartment ("flexion of the forearm at the elbow") - biceps brachii (long and short heads), coracobrachialis, brachialis
• Posterior: Extensor compartment ("extension of the forearm at the elbow") - triceps brachii (medial, lateral, and long heads)

The Arm: Anterior Compartment – Biceps Brachii

• Origins: Long head - supraglenoid tubercle of scapula; Short head - coracoid process.
• Insertion: Radial tuberosity.
• Function: Primary = Supination of forearm; Flexion of elbow joint, accessory flexor of GH joint.

Supination vs. Pronation

• This describes the movements of the forearm relating to the radius, ulna, and biceps brachii muscles. Details included.

The Arm: Anterior Compartment – Coracobrachialis and Brachialis

• Coracobrachialis:
  • Origin: Coracoid process
  • Insertion: Anterior humerus (shaft)
  • Function: Flexion of the arm at the glenohumeral joint.
• Brachialis:
  • Origin: Anterior shaft of the humerus
  • Insertion: Ulnar tuberosity
  • Function: Flexion of the forearm at the elbow.

Exception to Arm Compartments – Brachioradialis

• Brachioradialis: Stretches across the elbow joint, from the lateral supracondylar ridge of the humerus to the styloid process of the radius.
• Function: Flexion of forearm at the elbow.
• Tested in neutral position.

The Arm: Posterior Compartment – Triceps Brachii

• Origins: Long head - infraglenoid tubercle of scapula; Lateral & Medial Heads - posterior shaft of humerus.
• Insertion: Olecranon of the ulna.
• Function: Extension of the elbow joint.

Test your knowledge on the functions, origins, and insertions of the deltoid and subscapularis muscles. Match the various deltoid fibers with their primary functions and learn about the muscles responsible for the elevation of the scapula. This quiz will enhance your understanding of upper body anatomy.