MUSCLES OF RESPIRATION Muscles of the Thorax Diaphragm – dome shaped
O: entire internal circumference of lower thorax; ziphoid cartilage anteriorly, cartilages and bony portion of 6 or 7 lower ribs laterally, upper lumbar vertebrae posteriorly
C: muscle fibers fan centrally (up and in)
I: central tendons ( umbrella shaped)
A: chief muscle of respiration; elevates ribs and draws down upon the central tendon; increases vertical dimensions of thorax
N: phrenic nerve from cervical nerves 3, 4, and 5 External Intercostals
O: outer lip of lower border of each rib
C: oblique (diagonally)
I: outer lip of upper border of the rib below
A: elevates ribs in inhalation
N: intercostals nerves from the thoracic nerves 1-11 Internal Intercostals
O: inner border and inner surface of the rib and costal cartilage
C: oblique; almost at right angles to external intercostals
I: upper border and inner surface of the rib and cartilage below
A: elevates and may also lower ribs
N: Intercostal from thoracic nerves 1-11 Transverse Thoracic
O: body and zyphoid process of sternum
C: some fibers vertical, some upward obliquely, and some nearly horizontally (fan)
I: costal cartilages and bony ends of ribs 2-6
A: depresses ribs
N: intercostal from thoracic nerves 2-6 Serratus Posterior Superior
O: spines of the cervical vertebrae
C: down and slightly lateral
I: upper borders of ribs 2-5
A: assists in elevation of the ribs in inhalation
N: upper thoracic spinal nerves

Serratus Posterior Inferior
O: spines of lower thoracic and upper lumbar vertebrae
C: rise and fan out (upward and obliquely)
I: the inferior borders of lower four ribs, 9-12
A: depresses lower lungs in expiration
N: lower thoracic spinal nerves Muscles of the Chest Wall
Pectoralis Major
O: ventral end of clavicle, sternum, costal cartilages 2-6
C: converges laterally
I: head of the humerus bone
A: elevates ribs, rotation of arm
N: lower cervical and first thoracic Pectoralis Minor
O: bony ends of ribs 2-5
C: fan up and laterally
I: coracoid process of scapula
A: shoulder extensor; elevated ribs
N: C-7 to 8 Muscles of the Neck
Sternocleidomastoid – neck muscle; clavicular breathing
O: 2 heads: sternal head has its origin on the anterior surface of the manubrium of sternum; the clavicular head has its origin on the superior surface of the sternal end of the clavicle
C: upward, with fibers from the two heads uniting
I: mastoid process of the temporal bone; few fibers in the occipital bone
A: draw head toward shoulders and rotate it with unilateral contraction: tilt head toward thorax with bilateral contractions; may raise sternum and clavicle to assist in inhalation
N: accessory nerve (CNXI) Scalene
O: connected variously to cervical vertebrae 3 to 7 at transverse processes
C: downward and slightly laterally
I: upper surface of ribs 1 and 2 or outer surface of rib 2
A: elevates first 2 ribs
N: C-4-8 Muscles of Torso (Accessory Respiratory Muscles)
Trapezius
O: occipital bone, spinous processes of eleventh cervical and thoracic vertebrae and corresponding supraspinous ligaments
C: converge laterally
I: lateral third of posterior surface of clavicle, medial slide of acromion, and upper border of the spine of the scapula
A: draws head to one side or backward, rotates scapula, raises shoulder
N: accessory and cervical plexus Lattisimus Dorsi (broadest muscle of back)
O: spinous processes of lower five or six thoracic and lumbar vertebrae, median ridge of sacrum, and outer lip of iliac crest
C: up and lateral, converging
I: upper humerus (arm)
A: adducts arm, rotates it medially, and extends it; may influence the lower three or four ribs
N: thoracodorsal Rhomboids (major and minor)
O: spinous process of 7th cervical through the 5th thoracic vertebrae
C: obliquely down and lateral
I: vertical border scapula
A: draw scapula toward vertebral column and to adduct the arm
N: dorsal nerve of scapula Levator scapulae
O: transverse process of cervical vertebrae 1-4
C: vertically downward
I: vertebral border of the scapula
A: elevate and steady scapula
N: dorsal nerve of scapula Muscles of the Abdomen
External Oblique
O: external surfaces and lower borders of ribs 5-12
C: down and medially
I: anterior half of iliac crest and abdominal aponeurosis
A: depresses thorax and compresses the abdominal viscera in forced exhalation
N: lower intercostals

Internal Oblique
O: lateral half of the inguinal ligament and from the anterior two-thirds of the iliac crest
C: medially and superiorly
I: abdominal aponeurosis
A: compress viscera, used forced expiration
N: lower intercostals Transverse Abdominus
O: broad origin—inner surface of ribs 6-12; interdigiates with fibers from diaphragm and transverse thoracic
C: horizontal
I: deepest layer of abdominal aponeurosis
A: compress as in forced expiration
N: lower intercostals Rectus Abdominus
O: tendons from the crest of the pubis
C: vertical
I: cartilages of 5, 6, 7 ribs and xiphoid process
A: compress abdominal wall; used in forced expiration
N: lower intercostals