Unit 1: Gross Anatomy of the Chest Part III: Muscles of Ventilation Reference & Reading: Egan's p.158-163

Muscles of Ventilation Primary Muscles Diaphragm Intercostal muscles Accessory Muscles Scalenes Sternocleomastoid Pectoralis Major Abdominals

Diaphragm Rises from costal margin Connects at central tendon Hemidiaphragms Separates thorax from abdomen

Diaphragm - Function Resting Position When muscle contracts, drops floor of thoracic cavity down Pulls air in

Intercostal Muscles Located between each rib pair External Intercostals Internal Intercostals External – rise from lower edge of each rib and into upper edge of rib below Internal - lie beneath external intercostals; lower edge of rib form anterior end

Intercostal Muscles - Function Active during quiet breathing Elevates ribs, ↑ thoracic volume - occurs closer to exhalation At increased lung volumes, ribs are lowered Stabilizes chest wall during large pressure changes Quiet Breathing – from www.gettyimages.com

Retractions Also called intercostal retractions There is increased amount of negative pressure generated Clinical sign of increased WOB; look at suprasternal notch Retractions on infant

Accessory Muscles - Inspiration Collection of chest wall muscles Help to increase thoracic space, by assisting the primary muscles: Includes: Scalene Sternocleomastoid Pectoralis Trapezius

Scalene Muscles 3 muscles Anterior Medial Posterior Arise from lower 5 cervical vertebrae & connect to 2nd rib anteriorly Function: Normal With increased WOB

Sternocledomastoids Rise from manubrium & medial end of clavicle Insert into the skull Function: Primary: supports head Increased WOB: raises sternum up & out

Pectoralis Muscles Rises from clavicle & anterior surface of sternum Function: Primary: hugging motion With increased WOB: pulls opposite of primary function

Trapezius Muscles Arise from the occipital bone in the skull & all thoracic vertebrae; insert into clavicle Function: Primary: shrug shoulders; raise or lower arms Increased WOB: Raises rib cage

Accessory Muscles - Exhalation Used to forcibly exhale (cough, sneeze, etc) Muscles used are the abdominal muscles Collectively compress abdominal contents to push diaphragm up Includes: External & internal obliques Transverse abdominals Rectus abdominus

Internal & External Oblique External Oblique: arise from lower 8 ribs Internal Oblique: Arise from iliac crest& inguinal ligament Fibrous aponeurosis Fibrous aponeurosis – fibrous sheath

Transverse Abdominis Arises from: Connects to a aponeurosis costal cartilages Iliac crest Part of inguinal ligament Connects to a aponeurosis

Rectus Abdominis Arises from pubic bones Inserts into costal cartilages 5 -7 Contraction ↓ distance from xiphoid to pubis