Anatomy Quiz on Shoulder Muscles

Lecture Fourteen: The Muscular System – I

• This lecture covers the muscular system, specifically focusing on the skeletal muscles.
• The learning objectives are to review the muscular system's details, define range of motion (ROM) and how it's assessed, and define intrinsic/extrinsic back muscles.
• Students will also learn to differentiate between muscular layers in the back, and identify and describe origin, insertion, and function of major muscles of the back, neck, shoulder, and arm.
• Muscles use chemical energy (ATP) and convert it to mechanical energy (and heat).
• Anatomical terms starting with "myo" or "mys" relate to muscles.
• Muscle fibers (myofibers) are elongated muscle cells (skeletal or smooth).
• Cardiac muscle cells are not elongated and are interconnected.
• The focus of this unit is on skeletal muscles. These are consciously controlled (somatic nervous system) and rich with blood supply, with a nerve ending (motor unit) associated with each muscle fiber.

Range of Motion (ROM)

• ROM is the amount of movement around a joint or body part.
• Active ROM involves independent muscle activation.
• Passive ROM involves movement without muscle activation (e.g., a healthcare professional moving the body part).
• Active-assisted ROM involves muscle activation, but movement is assisted.

Extrinsic vs. Intrinsic Muscles of the Back

• Extrinsic back muscles primarily control upper limb movement. Superficial muscles are part of this category.
• Intrinsic back muscles attach to the vertebrae and ribs and control movements of the vertebral column (spinal support and movement).

Intrinsic Muscles of the Back (Erector Spinae)

• Erector spinae is a group of three vertical columns of muscle (iliocostalis, longissimus, spinalis).
• This group is involved in spinal extension. The iliocostalis is also responsible for lateral flexion of the spine

Muscles of the Neck (Splenius Capitis and Cervicis)

• These muscles insert onto the skull (mastoid process) or the cervical vertebrae.
• Their function includes bilateral extension of the spine and unilateral lateral flexion and rotation of the head and cervical spine.

Sternocleidomastoid Muscle

• Originates from the sternum and clavicle and inserts on the mastoid process.
• Functions include bilateral extension and flexion of the head/neck.

Deep Muscles of the Neck (Anterior & Accessory Muscles of Respiration)

• These muscles, like longus capitis, anterior scalene, and posterior scalene, are involved in head and neck flexion, aiding in respiration.

Extrinsic Muscles: First Layer (Superficial)

• Trapezius, originating on the posterior skull, cervical, and thoracic vertebrae and inserting on the clavicle, scapula, and acromion, is involved in scapula elevation, retraction, and rotation.
• Latissimus dorsi, extending from the lower thoracic and lumbar vertebrae, sacrum, and illic crest to humerus, functions in arm extension, adduction, and internal rotation. (Intertubercular Groove).

Extrinsic Muscles: Second Layer (Superficial)

• Levator scapulae and rhomboid major and minor, originating from the cervical and thoracic spine and inserting on the medial border of the scapula, have the function of elevation and retraction/adduction of the scapula respectively.

Extrinsic Muscles: Third Layer (Superficial)

• Serratus posterior superior and inferior, originating from spine (processes) and inserting on ribs, function in rib elevation (superior) and rib depression (inferior), which can contribute to respiration or breathing.

Muscles of the Shoulder (Anterior)

• Pectoralis major, p. 14, originates at clavicular and sternal heads and inserts at the intertubercular groove. This muscle's function is in the glenohumeral flexion, medial rotation, and adduction of the arm. .
• Subclavius, p.15, originates on the first rib and inserts to the clavicle. Its function is in depression of the clavicle.
• Pectoralis minor , p.15, originates on ribs 3-5 and inserts at the coracoid process of the scapula, and functions in scapula depression.
• Serratus anterior , p. 16, originates on ribs and inserts on the scapula, and functions in scapula protraction.

Muscles of the Shoulder (Lateral)

• Deltoid, p17, originates at the clavicle, acromion, and spine of the scapula and inserts into the deltoid tuberosity. Its function is in glenohumeral flexion, abduction, and external rotation, depending on the involved fiber group (anterior, middle, posterior fibers).

Muscles of the Rotator Cuff

• Subscapularis, p. 18, originates on subscapular fossa and inserts on lesser tubercle, medial rotation. Common function: Creates a cuff around the shoulder joint for stabilization.
• Supraspinatus, p. 19, originates on supraspinous fossa and inserts onto the greater tubercle. It initiates shoulder abduction.
• Infraspinatus, p. 20, originates on infraspinous fossa and inserts onto greater tubercle. Functions include external rotation.
• Teres minor, p. 20, originates from the lateral scapular border and inserts onto the greater tubercle. Its function includes external or lateral rotation of the shoulder.

Muscles of the Shoulder (Posterior)

• Teres major, p. 22, originates at the scapular border and inserts onto the intertubercular groove. Function involves extension, internal rotation, and adduction of the shoulder.

Muscular Compartments of the Arm

• Anterior compartment, p. 23, called the flexor compartment, has the function of forearm flexion at the elbow (e.g., biceps brachii, coracobrachialis, brachialis).
• Posterior compartment, p. 23, contains extensor compartment muscles for forearm extension at the elbow (e.g., triceps brachii).

The Arm: Anterior Compartment

• Biceps brachii, p. 24, originates from the scapula and has a long and short head. Its function involves supination of the forearm and flexion of the elbow.
• Coracobrachialis, p.26, originates on the coracoid process and inserts into the humerus, Functioning to flex the arm at the shoulder.
• Brachialis, p. 26, originates in the humerus and inserts at the ulnar tuberosity. Its function is to flex the forearm at the elbow.

Exception to Arm Compartments

• Brachioradialis, p. 27, stretches across the elbow, from the humerus to the radius, and functions in forearm flexion at the elbow.

The Arm: Posterior Compartment

• Triceps brachii, p. 28, originates from three diverse locations: infraglenoid, the scapula; lateral, medial, and posterior shaft of the humerus. Its function is to extend the forearm at the elbow.