Muscles of Inspiration and Expiration

Study Notes

Muscles of Inspiration

The diaphragm is the primary muscle for inspiration, separating abdominal and thoracic cavities; contracts to pull the central tendon down and expand lungs vertically.
Accessory muscles of thorax include:
- External Intercostal Muscles
- Internal Intercostal Muscles
- Levatores Costarum
- Serratus Posterior Superior

External Intercostal Muscles

Located between ribs; elevate the rib cage.
Originates from lower surface of each rib (except the 12th) and inserts into the upper surface of the rib below.

Internal Intercostal Muscles

Also assists in inspiration by elevating ribs.
Originates from the superior surface of ribs 2-12 and inserts into the inferior surface of ribs 1-11.

Levatores Costarum

Comprises two portions—Brevis and Longus—both involved in rib cage elevation during inspiration.
Brevis originates from transverse processes of C7 through T11; inserts into tubercle of the rib below.
Longus originates from T7 to T11 and inserts into the rib above the origin.

Serratus Posterior Superior

Elevates ribs 2-5 specifically.
Originates from spinous processes of C7 and T1-T3, inserting into ribs 2-5.

Muscles of the Neck

Includes Sternocleidomastoid and Scalenes (anterior, middle, and posterior), providing neck stability and assisting in respiration.

Sternocleidomastoid

Elevates the sternum and rib cage.
Originates from mastoid process of the temporal bone and inserts into the sternal head and clavicle.

Scalenes

Elevates ribs 1-2; aids in neck stability and head rotation.
Originates from transverse processes of C2-C7 and inserts into ribs 1-2.

Muscles of the Upper Arm and Shoulder

Includes Pectoralis Major, Pectoralis Minor, and Serratus Anterior, which all aid in inspiration.

Pectoralis Major

A fan-shaped muscle elevating the sternum and expanding the rib cage.
Has two heads: sternal head and clavicular head; inserts into the greater tubercle of the humerus.

Pectoralis Minor

Lies under Pectoralis Major; elevates ribs 2-5 when the shoulder is fixed.
Originates from ribs 2-5 and inserts into the coracoid process of the scapula.

Serratus Anterior

Elevates ribs 1-9 when the shoulder is fixed.
Originates from ribs 1-9 and inserts into the scapula.

Back Muscles of Inspiration

Comprises Levator Scapulae, Rhomboideus Major, Rhomboideus Minor, and Trapezius, all aiding in inspiration.

Levator Scapulae

Supports the neck and elevates the scapula.
Originates from transverse processes of C1-C4 and inserts into the medial border of the scapula.

Rhomboideus Major and Minor

Both stabilize the shoulder girdle.
Major originates from spinous processes of T2-T5; Minor from C7-T1, both inserting into the scapula.

Trapezius

Large, superficial muscle of the upper back and neck; assists in inspiration.
Originates from spinous processes of C2 to T12 and inserts into the scapula and clavicle.

Muscles of Expiration

Includes Internal Intercostal (interosseous portion), Transversus Thoracis, Subcostals, Serratus Posterior Inferior, and Latissimus Dorsi.

Internal Intercostal (Interosseous Portion)

Depresses ribs 1-11 during expiration; originates from the superior margin of each rib.

Transversus Thoracis

Decreases thoracic cavity volume during expiration.
Originates from lower third of the sternum, inserting into the inner chondral surface of ribs 2-6.

Subcostals

Variable in number; course parallel to internal intercostals, facilitating expiration.

Description

Explore the key muscles involved in breathing with these flashcards. This quiz covers the diaphragm and accessory muscles, detailing their functions and anatomical significance. Understand the mechanics of respiration and the role each muscle plays in inspiration and expiration.