THE UPPER TRUNK

THE LIST OF TOPICS

Deep Back; suboccipital triangle

Thorax and lungs

Heart and mediastinum

Superior and posterior mediastinum

Vertebral column

The vertebrae are held together by the (Clemente 343-352; Grant p. 304; Netter 3e 146, 4e 158):

• ligaments
• intervertebral discs
• and synovial joints between the articular processes.

Movement between 2 vertebrae is slight but movement of the vertebral column as a whole is over quite a range (Grant p. 292-293).

The thoracic vertebra (Clemente 347; Grant p. 300-301; Netter 3e 147, 4e 154):

The body of the vertebra is the weight-bearing part and contains red bone marrow, drained by basivertebral veins (Clemente 361; Grant p. 309; Netter 3e 166, 4e 173).

The neural arch and the processes exist:

• for the protection of the spinal cord (Clemente 360; Grant p. 304-305; Netter 3e 163, 4e 170)
• for attachment of muscles
• for articulation with ribs (long transverse processes)
• and for regulation of movements.

Superior and inferior articular facets form synovial joints with the adjoining articular facets (Clemente 348; Grant p. 291, 300; Netter 3e 147, 4e 154).

The spinous process is downturned so as to overlap the inferior one.

The cervical vertebra (Clemente 342-344; Grant p. 294-295; Netter 3e 16, 4e 18-19):

• has a smaller body which carries less weight and overlaps the lower vertebra anteriorly (Clemente 343, Grant p. 295; Netter 3e 16, 4e 19).
• has a bifid spinous process

The transverse process has (Clemente 342; Grant p. 294; Netter 3e 16, 4e 18):

• anterior and posterior tubercles
• and a transverse foramen.

All vertebrae have costal elements (Grant p. 290), but in the cervical, lumbar and sacral regions, they are incorporated into the vertebrae. Thus, in the cervical vertebrae, the posterior tubercle is the true transverse process and the anterior tubercle is the costal element.

C7 costal element may form a cervical rib. C7 is the vertebra prominens (but is usually less prominent than T1).

C1 (Atlas) and C2 (Axis) are atypical (Clemente 342; Grant p. 297; Netter 3e 15, 4e 17).

The dens of C2 protrudes through the ring of the atlas (Clemente 343; Grant p. 297; Netter 3e 15, 4e 17) and is held in place by a transverse ligament (Clemente 344; Grant p. 299; Netter 3e 18, 4e 22).

The upper articular facets of C1 are concave (for the occipital condyles - "YES" joint) and the lower articular facets of C1 are flatter ("NO" joint; Clemente 342; Grant p. 299; Netter 3e 15, 4e 17).

The lumbar vertebrae (Clemente 350-351; Grant p. 302-303; Netter 3e 148-149, 4e 155-156)

• are the most massive vertebrae, with increasing body size inferiorly.
• The lumbar spines are massive and project posteriorly. Since they do not overlap, lumbar pucture may be performed at this level.

The sacrum

• is formed by 5 sacral vertebrae fused into one (Grant p. 313; Netter 3e 150, 4e 157).
• has 4 intervertebral foramina modified into anterior and posterior sacral foramina, transmitting anterior and posterior primary rami of sacral nerves (Clemente 353; Grant p. 313; Netter 3e 150, 4e 157).
• The lower opening of the sacral canal may be used for introduction of anesthetic into the vertebral canal.
• Auricular surfaces are found at the sides for articulation with the ilium (Clemente 353; Grant p. 313; Netter 3e 150, 4e 157).

The intervertebral joints are symphyses between the vertebral bodies (Clemente 352, Grant p. 304-305; Netter 3e 148, 4e 158).

• A layer of hyaline cartilage and fibrocartilage (anulus fibrosus) forms the intervertebral disc (Clemente 352; Grant p. 305; Netter 3e 148, 4e 155).
• The intervertebral disc has a high water content. The nucleus pulposus is rich in glycosaminoglycans.
• The intervertebral discs are compressed by the weight of the body resulting in differences in height between the beginning and end of the day.

Pathological problems associated with the intervertebral disc (Grant p. 308; Netter 3e 156, 4e 152):

• Herniated disc.
• Schmorls's node: the upward herniation erodes the body of the adjacent vertebra.

Ligaments of the vertebrae: 2 ligaments per component of the vertebra, i.e., paired components are each joined by one ligament and unpaired components are joined by 2.

• The vertebral spines are joined by supraspinous and interspinous ligaments (Clemente 351; Grant p. 308; Netter 3e 152, 4e 158).
• The vertebral bodies are joined by the anterior and posterior longitudinal ligaments (Clemente 348-349, 351; Grant p. 306-307; Netter 3e 151-152, 4e 158).
• The paired articular processes are joined by the capsular ligaments of the synovial (zygapophyseal) joints (Clemente 350; Grant p. 304; Netter 3e 151, 4e 158).
• The transverse processes are joined by the intertransverse ligaments.
• The laminae are joined by the ligamenta flava (Clemente 349; Grant p. 306; Netter 3e 151, 4e 158).

There is no ligament between the pedicles because of the intervertebral foramina and the emergence of spinal nerves.

Flexures (curvatures) of the vertebral column (Clemente 346; Grant p. 287; Netter 3e 146, 4e 153):

• Cervical flexure (support of head)
• Thoracic flexure (original fetal curve)
• Lumbar flexure (support of trunk for standing and walking).

Movements of the vertebral column are anterior flexion, extension, lateral flexion (Grant p. 307) and rotation.

Rotation is free in the thoracic region because the superior articular facets face postero-laterally. But in the lumbar region, it is almost nonexistent because the superior articular facets face almost medially (Clemente 347, 350; Grant p. 303; Netter 3e 147-148, 4e 154-155).

On a flexed trunk, the spines of most vertebrae are palpable except for the first 6 because of the anterior cervical flexure. So C7, T1, etc..are palpable vertebral spines.

Bony landmarks:

• The scapula lies between T2-T7.
• The supracristal plane runs between the 2 highest point of the iliac crest through L4.
• The posterior superior iliac spines lie at the level of S2.

The spinal cord ends in the adult at L1 and the subarachnoid space at S2 (Clemente 356-357; Grant p. 344; Netter 3e 154, 4e 160-161).

A lumbar puncture is performed at the level of L3-4.

The needle passes (Clemente 351, 360; Grant p. 308; Netter 3e 151, 4e 163):

• through/along the supra- and interspinous ligaments,
• through/along the ligamenta flava,
• and finally the dura and arachnoid into the subarachnoid space.

MUSCLE LAYERS OF THE BACK are organized into 3 layers.

• A superficial group (see lecture notes on the Superficial Back)
• An intermediate group
• A deep group

The intermediate group

• is formed by the serratus posterior superior and inferior (Clemente 332; Grant p. 322; Netter 3e 167, 4e 174-175).
• has respiratory functions. They elongate the thoracic cavity and are thus muscles of inspiration.
• are innervated by the ventral rami of intercostal nerves.

The deep group are intrinsic muscles of the back. When acting jointly, they extend the vertebral joints (they prevent/regulate flexion at these joints). Unilaterally, they laterally bend and rotate the spinal column.

The splenius capitis and cervicis (Clemente 332; Grant p. 323; Netter 3e 167-168, 4e 174)

• attach from the inferior 1/2 of the ligamentum nuchae and spines of T1-5.
• Splenius capitis attaches to the superior nuchal line and mastoid process (along with the sternocleidomastoid).
• Splenius cervicis attaches to the transverse processes of C1-4 (along with levator scapulae).

The thoracolumbar fascia (Clemente 332; Grant p. 321; Netter 3e 167, 4e 174)

• The lumbar portion is the dorsal aponeurosis of the transversus abdominis muscle.
  • The superficial layer attaches to the lumbar spines.
  • The deep layer attaches to the tips of the lumbar transverse processes.
• The thoracic portion attaches from the vertebral spines to the angle the ribs, over the deep dorsal muscles.

The erector spinae:

• fill the grooves between the spines of the vertebrae (Clemente 327; Grant p. 324; Netter 3e 172, 179), the transverse processes and the ribs (they form the edible part of the porkchop!).
• start from the sacral region, enlarge and are powerful in the lumbar region (Clemente 331; Grant p. 323; Netter 3e 168,  4e 175-176).
• splits into columns of separate muscles attaching to spines, transverse processes and ribs in the thoracic region (Clemente 332; Grant p. 323; Netter 3e 168, 4e 175).
• The longest bundle is most superficial and the shortest is deep, in contact with the bone.

Longitudinal muscles

The erector spinae are also called sacrospinalis.

They attach from the pelvis to the skull.

They split near rib 12 into:

• The iliocostalis attaches to the angles of the ribs and C4-6 transverse processes.
• The longissimus (thoracis, cervicis and capitis) attach into the lumbar accessory and transverse processes, thoracic transverse processes and parts of T2-12. Bundles arising from T1-4 attach to C2-6.
• The spinalis is found only in thoracic regions.

Oblique muscles: The transversospinalis group is deep to the erector spinae, run from transverse processes to spines and are disposed in 3 layers (Clemente 335, 337; Grant p. 325, 328; Netter 3e 169, 4e 176):

• Semispinalis
• Multifidus
• Rotatores

Semispinalis (Clemente 335; Grant p. 328; Netter 3e 168, 4e 176)

• forms the superficial layer.
• has a more vertical course (from near the tips of transverse processes to the tips of spinous processes)

The semispinalis capitis attaches from the transverse processes of T1-5 and the articular processes of C4-7 to the occipital bone (Clemente 333; Grant p. 328; Netter 3e 168, 4e 175).

The large uppermost muscle is the semispinalis capitis which forms the ridges on either side of the posterior midline of the neck, covered by trapezius. It is innervated by the dorsal primary rami of all cervical nerves.

Multifidus (Clemente 335; Grant p. 328; Netter 3e 169,  4e 176)

• attach from the dorsal sacrum between the spinous and transverse crests from all transverse processes (up to C4) and from adjacent ligaments and fascia of erector spinae,
• to the inferior border of C2-L5 spinous processes.

Rotatores (Clemente 335; Grant p. 329; Netter 3e 169, 4e 176)

• originate from the inferior transverse process,
• attach to the superior spinous process or lamina.

Interspinales (Clemente 335; Grant p. 328; Netter 3e 169, 4e 176) and intertransversarii.

• are well developed in cervical and lumbar regions but absent from thoracic regions.
• Interspinales unite bifid tubercles of adjacent cervical spinous processes and adjacent border of lumbar spines.
• Intertransversarii (anterior and posterior) unite adjacent anterior tubercles and adjacent posterior tubercles of cervical transverse processes.

SPINAL CORD AND MENINGES

• At birth, the spinal cord is at L3.
• In the adult, at L1 (Clemente 356; Grant p. 344; Netter 3e 154, 4e 160-161).

The upper cervical nerves pass horizontally from cord to intervertebral foramina but the nerve roots become more oblique inferiorly. They become vertical at L1 forming the cauda equina which is composed of anterior and posterior nerve roots (Clemente 358; Grant p. 334; Netter 3e 154, 4e 161).

The true end of the spinal cord is the conus medullaris, which is attached by the filum terminale to provide vertical stability to the spinal cord (Clemente 359; Grant p. 334; Netter 3e 153-154,4e 161).

The denticulate ligaments are formed by reflections of pia mater and are responsible for the lateral stability of the spinal cord (Clemente 358; Grant p. 335; Netter 3e 162, 4e 169).

The subarachnoid space ends at S2 (Clemente 357; Grant p. 337; Netter 3e 154, 4e 161). The filum terminale pierces the dura and runs to the posterior aspect of coccyx as the coccygeal ligament.

The dura mater is prolonged along spinal nerves for a short distance.

DORSAL RAMI OF SPINAL NERVES (Clemente 361; Grant p. 20, 338; Netter 173)

• are typical except for the first 2 and the last 3.
• typically originate lateral to the spinal ganglion and pass dorsally on the side of the superior articular process (dorsal sacral rami use dorsal sacral foramina).
• supply skin and deep muscles of the back medial to the angles of the ribs (Clemente 329; Grant p. 20; Netter 3e 173, 4e 177).
• innervate the articular facets of vertebrae which are synovial joints and may, in time,be affected by arthritis.

Some cutaneous branches travel further:

• C2 (greater occipital nerve) to scalp (Clemente 338; Grant p. 330; Netter 3e 170, 4e 178).
• T2 (intercostobrachial nerve;
• L1, 2, 3 to the gluteal region.

Each dorsal ramus divides into medial and lateral branches (except C1, S4, S5 and Co1) and either one ends as a cutaneous branch (except for C1, C6, C7, C8, L4 and L5).

VENOUS PLEXUS (Clemente plate 433 fig. 689; Grant p. 309; Netter 166)

The vertebral column has a dense plexus of thin-walled valveless veins surrounding the spinal dura mater.

The plexus communicates superiorly with the occipital and basilar sinuses of the cranium (Clemente plate 489; Grant p. 639; Netter 97, 98).

The vertebral venous plexus (Clemente 361; Grant p. 309; Netter 3e 166, 4e 173):

• is divided into anterior and posterior longitudinal channels.
• receives a vein from the spinal cord and a basivertebral vein from the body of a vertebra at each segment.
• is drained by intervertebral veins passing through the intervertebral (sacral) foramina to the vertebral, intercostal, lumbar and lateral sacral veins.

There is also an anterior external vertebral plexus formed by veins from the body of the vertebrae and a posterior external vertebral plexus formed by veins passing through the ligamenta flava (Clemente 359, 361; Grant p. 305; Netter 3e 166, 4e 173).

updated 9/16/2009

The suboccipital triangle

The apex of the posterior triangle of the neck is formed by the posterior border of the sternocleidomastoid and the anterior border of the trapezius (Clemente 338; Grant p. 332; Netter 3e 167, 4e 178).

Under the trapezius is the semispinalis capitis (Clemente 338; Grant p. 330; Netter 3e 167, 4e 178) which is attached to the skull between the superior and inferior nuchal lines (Clemente 516; Grant p. 332; Netter 3e 8, 167, 4e 8).

The occipital artery emerges from under cover of the splenius capitis and breaks into branches to supply the back of scalp.

2 nerves emerge through the semispinalis capitis and supply the skin of scalp:

1) The greater occipital nerve (dorsal primary ramus of C2)

2) The third occipital nerve (dorsal primary ramus of C3).

The suboccipital triangle is deep to C3.

BONY LANDMARKS:

• The superior and inferior nuchal lines on the occipital bone.
• C1 (atlas) has a posterior tubercle (It has no spine to allow for head extension in looking up), and long transverse processes (for use as levers in rotation of the head and C1 on the dens; Clemente 342; Grant p. 297; Netter 3e 15, 4e 17).
• The spine of the axis.

Muscles (Clemente 339-341; Grant p. 330-331; Netter 3e 168-169, 178):

• Rectus capitis posterior (RCP) major attaches from the spine of the axis to below the inferior nuchal line, lateral to RCP minor.
• RCP minor attaches from the posterior tubercle of the Atlas to below the inferior nuchal line, bilaterally.
• Obliquus superior attaches from the transverse process of the Atlas to the area between the nuchal lines lateral to semispinalis.
• Obliquus inferior attaches from the spine of the Axis to the transverse process of the Atlas.

The vertebral artery

• runs through the transverse foramina of the upper 6 cervical vertebrae (Clemente 490; Grant p. 333; Netter 3e 17, 4e 21).
• emerges onto the upper surface of the Atlas, passes posteriorly, closely related to the articular facet to reach a deep groove on the superior aspect of the posterior arch of the atlas (Clemente 339; Grant p. 332; Netter 3e 171, 178)
• passes into the foramen magnum to meet with the opposite vertebral artery and to form the basilar artery.

*If the vertebral artery is affected by atheroma (atherosclerosis), movements of head and neck may affect movement of blood through it and cause faintness or unconsciousness.

C1 nerve

• emerges from the spinal cord
• lies in the groove between artery and bone.
• the dorsal primary ramus (named the suboccipital nerve) enters the suboccipital triangle and innervates the muscles (Clemente 339; Grant p. 330-331; Netter 3e 171, 4e 178).
• the ventral primary ramus runs forward, lateral to the superior articular facet and joins the hypoglossal nerve (cranial nerve XII; Grant p. 839; Netter 3e 67, 122, 4e 128).

C2 emerges between the Atlas and the Axis (Clemente 640; Grant p. 330-331; Netter 171) and travels superiorly over the suboccipital triangle to form the greater occipital nerve.

C3 emerges between axis and C3 vertebra.

updated 9/16/2009

Thorax

The thorax

• is flattened anteroposteriorly in the adult.
• is covered by upper limb muscles (Clemente 102; Grant p. 3; Netter 3e 176, 4e 188-189).

The thoracic spinal nerves supply thoracic as well as the abdominal wall (Clemente 176; Grant p. 101-104; Netter 3e 249, 4e 188).

The ribs enclose and protect some of the abdominal viscera (Clemente plates 188-189; Grant p. 96-97; Netter 260).

The 12 thoracic vertebrae (Clemente 109; Grant p. 300-301; Netter 3e 147, 4e 268) have the following landmarks:

• The body or centrum is flattened, on the left side, from T6 down due to the impression of the descending aorta.
• The pedicle
• The transverse processes
• The spinous processes
• The articular processes (synovial joints)
• The laminae, which are removed during a laminectomy to gain access to the spinal cord.
• The vertebral foramen forms the vertebral canal with the vertebral foramina from other vertebrae.
• The intervertebral foramina formed by vertebral notches are the exit points for the spinal nerves.

The 12 pairs of ribs (Clemente 103-109; Grant p. 10-11; Netter 3e 178-179, 4e 185-187)

• rib + cartilage = costa
  • Ossification begins around 9th prenatal week and spreads in both directions.
  • Epiphyses capping the head and tubercle fuse by year 24.
• Ribs 1-7 are classified as vertebrosternal.
• Ribs 8-10 are classified as vertebrochondral.
• Ribs 11 and 12 are classified as vertebral (floating).

The different parts of the ribs have the following articulations:

• The head articulates with the sides of bodies of 2 vertebrae (at the same and superior levels; Clemente 347-349; Grant p. 14-15; Netter 3e 180, 4e 187), except for rib 1, 11, and 12. It is attached to the intervertebral disc by an intraarticular ligament, but not ribs 1, 11, and 12.
• The neck
• The articulating tubercle attaches to the transverse process of vertebra at the same level (rib 6 is attached to T6); this is a synovial joint called the costotransverse joint.

Costotransverse joints (Clemente 347-348; Grant p. 15, 17; Netter 3e 180, 4e 187)

• The superior joints (ribs1-7) permit mostly rotation of the rib and the inferior ones (ribs 8-10) permit mostly gliding movement for the articulated rib.
• Attachments are by medial (neck) and lateral (tubercle) costotransverse ligaments. The superior costotransverse ligament descends from the superior transverse process to the crest of inferior rib.

The rib has the following landmarks (Clemente 106; Grant p. 13-14; Netter 3e 179, 4e 186):

• The crest for attachments of the superior costotransverse ligaments.
• The angle
• The body
• The costal groove

The costovertebral articulation is formed by the joint of the head and the joint of the tubercle of the rib (Clemente 347; Grant p. 15; Netter 3e 180, 4e 187).

The sternocostal articulation: the joint cavity is divided into 2 by an intraarticular ligament and closed ventrally by ligaments radiating from the perichondrium to the sternum (Clemente 104, 107; Grant p. 12; Netter 3e 179, 4e 186).

Interchondral joints exist between the costal cartilages of ribs 7, 8, and 9 (Clemente 104; Grant p. 12; Netter 3e 179, 4e 186)

The sternum contains red bone marrow and is thus used for sternal punctures in diagnosing blood diseases.

The manubrium (Clemente 104-105; Grant p. 12; Netter 3e 179, 4e 185)

• has the jugular (suprasternal) notch.
• articulates with the clavicle at the sternoclavicular joint (the only bony attachment point of the upper limb to the trunk), rib 1 and half of rib 2.
• forms the attachment points for the pectoralis major, sternocleidomastoid, sternohyoid and sternothyroid muscles.

The sternal angle (of Louis) or manubriosternal joint is a cartilaginous joint and is at the same level as: (Clemente 130; Grant p. 26, 27, 29; Netter 3e 178, 192, 4e 233)

• the 2nd rib and T4, 5 vertebrae
• the carina of trachea.
• the aorta crossing from right to left.

The second intercostal space is used for listening to aortic (right) and pulmonary (left) valves (Clemente 129; Grant p. 44, Netter 213).

The body of the sternum (Clemente 104; Grant p. 10: Netter 3e 179, 4e 186)

• develops from bilateral sternal bars. If they fail to fuse, a sternal foramen (Grant p. 16) or bifid xiphisternum results.
  • 4 fused sternebrae (ossify during the 3rd trimester of uterine life).
• articulates with half of the head of rib 2 and the heads of ribs 3-7.
• contains red bone marrow.
• forms the attachment site for the pectoralis major anteriorly (Clemente plate 11; Grant p. 4; Netter 3e 182, 4e 188), and transversus thoracis posteriorly (Clemente 110; Grant p. 21, 23; Netter 3e 184, 4e 191).

The xiphoid process (Clemente 105, 8; Grant p. 348; Netter 3e 157, 4e 185-186, 164)

is at the level of the 6th thoracic dermatome on the anterior surface of the body.

The thoracic inlet is located superiorly and is the site of entrance of the viscera and vessels from the head, neck and upper limb into the thorax (Clemente 113; Grant p. 25; Netter 3e 190, 4e 198).

The thoracic outlet is closed by the diaphragm, pierced by the inferior vena cava (T8), aorta (T12) and esophagus (T10), and innervated by the phrenic nerves (C3, 4, 5; Clemente 156-157, 163; Grant p. 25, 73; Netter 3e 188, 229, 4e 194232-233).

• Paraplegic (2-limb paralysis)
• Quadriplegic (4-limb paralysis)
• Pentaplegic (involvement of the diaphragm due to a lesion affecting C3, 4, 5).

Muscles of the thoracic wall (Clemente 110; Grant p. 17-18, 21-24; Netter 3e 182-185, 4e 188-189, 191-192)

• The external intercostal muscles project inferiorly in a posterior to anterior direction. They are replaced in the front by the external intercostal membrane. They are most active in INSPIRATION
• The internal intercostal muscles project superiorly in a posterior to anterior direction (perpendicular to fibers of external intercostals). They are replaced in the back by the internal intercostal membrane. They are most active in EXPIRATION.
• The innermost intercostal muscles include the transversus thoracis. The transversus thoracis arises from the back of the sternum and the xiphoid process and inserts onto costochondral junctions from ribs 3-6. Innermost intercostal muscles can bridge more than one intercostal space.

The primary role of the intercostal muscles is to act together to stiffen the chest wall, preventing paradoxical motion during descent of the diaphragm in inspiration.

Intercostal spaces

Intercostal vein, artery and nerve form a neurovascular bundle lying between internal intercostals and innermost intercostals (Clemente 158-159; Grant p. 17-20; Netter 3e 184-187, 4e 192).

Intercostal nerves are mixed nerves containing both motor and sensory fibers (Clemente 163; Grant p. 20; Netter 3e 187, 4e 192).

• Posterior (dorsal) rami innervate back muscles between the angle of the ribs and the spinous processes of the vertebrae, with cutaneous branches innervating the overlying skin.
• Anterior (ventral) rami innervate intercostal musculature, periosteum of the ribs and skin of the thorax (dermatome).
• T7, 8, 9 , 10 and 11 innervate the abdominal wall (Clemente 176; Grant p. 100-101; Netter 3e 249, 4e 257).
• T12 (the subcostal nerve) and L1 innervate the region above the pubis.

Intercostal arteries and veins

• Intercostal vessels bifurcate in intercostal spaces and have branches running in the intercostal groove as well as collateral branches above the body of the subjacent rib (Clemente 158; Grant p. 17-18; Netter 3e 187, 4e 192).
• The posterior intercostal arteries in the first 2 intercostal spaces arise from the costocervical trunk, branching from the subclavian artery (Clemente 158; Grant p. 75; Netter 3e 29, 4e 33).
• Other posterior intercostal arteries are branches of the thoracic aorta.
• The posterior intercostal veins drain into right azygos and left hemiazygos system. The superior veins also drain into the brachiocephalic veins (Clemente 159; Grant p. 76; Netter 3e 226-227, 4e 238).
• Anterior intercostal arteries and veins arise from the internal thoracic vessels (Clemente 111; Grant p. 22-23; Netter 3e 183-184, 4e 191) and anastomose with the posterior vessels in the intercostal spaces around the midclavicular line (Grant p. 20, Netter 3e 187, 4e 192). They also supply the skin over the sternum by perforating branches.

The internal thoracic artery:

• is a branch of the subclavian artery.
• runs between the transversus thoracis and the sternum.
• terminates inferiorly by dividing around the xiphisternal joint into the superior epigastric artery (which enters the rectus sheath inferiorly; Clemente 111; Grant p. 103; Netter 3e 176, 4e 192-193) and the musculophrenic artery (which follows the attachment of the diaphragm to the ribs).
• also sends branches to the thymus, bronchi and pericardium.

The parasternal lymph nodes (Clemente 7; Grant p. 9; Netter 3e 177, 4e 184) drain this anterior region and also the medial aspect of the breast. Examination is required if a tumor is found in the medial 1/2 of the breast.

updated 9/16/2009

Lungs

The thoracic cavity contains:

• right and left pleural cavities (Clemente 113; Grant p. 26; Netter 3e 192-193, 4e 198).
• right and left lungs.
• the mass of the mediastinum in the middle (Clemente 130; Grant p. 29; Netter 3e 198, 4e 212).

The mediastinum contains (Clemente 126-127, 130; Grant p. 48-49; Netter 3e 190, 4e 211-212, 230-232):

• the heart
• the pericardium and associated great vessels.
• the trachea and the structures traversing the thorax such as the esophagus, the vagus nerves, the phrenic nerves and the thoracic duct.

A change in the pressure in one pleural cavity may deflect the mediastinum to the opposite side. This can be checked by the position of the trachea at the root of the neck.

The lungs and heart are contained within separate pleural and pericardial cavities and are separated from the abdomen by the diaphragm (Clemente 113; Grant p. 25, 28; Netter 3e 190, 4e 212-213).

An imaginary line joining the manubriosternal joint and T4-T5 subdivides the mediastinum into superior and inferior parts (Clemente 130; Grant p. 29; Netter 3e 227, 4e 230-231, 233).

The visceral pleura

• is a layer of simple squamous epithelium over surface of lung.
• is not innervated and thus is insensitive to pain
• provides a moistened and lubricated surface for lung movement.

Adhesions with the parietal pleura may result from infections, inflammatory reactions and lung immobility.

The parietal pleura (Clemente 114-116; Grant p. 28, 30-31; Netter 3e 192-193, 4e 196-197)

• is attached to the costal, diaphragmatic and mediastinal surfaces by the endothoracic fascia.
• projects into the root of the neck as the cupula. This area is vulnerable to wounds and needles and its perforation will result in equalization of external and pleural pressures, i.e. a pneumothorax. The pressure in the pleural cavity is slightly below atmospheric pressure but is referred to as "negative pressure".
• is innervated by free sensory nerve endings of the intercostal and phrenic nerves. Pain may be referred to dermatomes served by specific thoracic intercostal and phrenic nerves. Severe pain caused possibly by adhesions is called pleurisy.

Visceral and parietal pleurae are continuous at the root of the lungs, where pulmonary artery and vein, and bronchus penetrate the lung (Clemente 120; Grant p. 28, 34-35; Netter 3e 195, 4e 199). The pulmonary ligament found inferior to the root of the lungs is a segment of reflected pleura which forms a sleeve.

The parietal pleura:

• on the costal surface, is continuous with the mediastinal pleura anterior to the vertebral column (vertebral reflection).
• is continuous with the mediastinal pleura posterior to the sternum (sternal reflection).
• and is continuous with the diaphragmatic pleura near the thoracic wall (costal reflection).

The parietal pleurae (Clemente 114-116; Grant p. 30-31; Netter 3e 192-193, 4e 196-197):

• touch at the level of ribs 2-4.
• are separated between ribs 4-6 due to the heart indentation.

The base of the parietal pleurae is found:

• at the level of the 8th costal cartilage in the midclavicular line .
• at the level of the 10th costal cartilage in the midaxillary line.
• at the level of rib 12 dorsally.

The pleural cavity contains pleural fluid.

Pleural recesses

• Costodiaphragmatic recesses: sampling of pleural fluids between ribs 8-10 is possible without lung penetration. This is the costophrenic angle of radiologists. The costal and diaphragmatic pleurae are in contact during expiration.
• Sternocostal recesses
• Costomediastinal recesses over the heart and pericardium.

The lungs (Clemente 118-121; Grant p. 32, 34-35; Netter 3e 195, 4e 199-201)

• have rounded posterior borders shaped by the ribs and sharp anterior borders fitting between the heart and the chest.
• have concave bases. The dome of the diaphragm is higher on the right (T8) than on the left (T8/T9), due to the underlying mass of the liver, so the right lung is shorter.

The base of the lungs (Clemente 114-116; Grant p. 30-31; Netter 3e 192-193, 4e 196-197)

• is found:
• at the level of the 6th costal cartilage in the mid-clavicular line.
• at the level of the 8th costal cartilage in the mid-axillary line.
• at the level of rib 10 dorsally.
• Due to the position of the heart, the base of the right lung is broader than that of the left lung (Clemente 201; Grant p. 28; Netter 3e 190, 4e 120-121).

The lungs have the following landmarks (Clemente 118, 120; Grant p. 32, 34-35, Netter 3e 195, 4e 199):

• The apex forms the cupula.
• The costal surface
• The medial surface has vertebral and mediastinal parts.
  • The vertebral part is posterior and round with the costal surface, occupying the thoracic gutters.
  • The mediastinal part of the medial surface lies anterior to the vertebral column. It contains the root or hilus of the lung. The cardiac impression is anterior to the hilus and larger on the left than on the right.

The hilus (root of the lung) is the point of entry of vessels, nerves, and bronchi.

• The uppermost structure in the hilus is the pulmonary artery (Artery Above).
• The most posterior structure is the bronchus (Bronchus Behind).

Relationships to the hilus:

• The phrenic nerve is the only structure traversing the thorax which passes anterior to the hilus (Clemente 126-127; Grant p. 80-81; Netter 3e 226-227, 4e 230-231).
• On the right side, the azygos arch passes from posterior to anterior above the right hilus, to reach the superior vena cava.
• On the left side, the arch of the aorta passes from anterior to posterior above the left hilus.

THE RIGHT LUNG (Clemente 118, 120; Grant p. 32, 34; Netter 3e 193, 4e 199-201).

• The right lung has 3 lobes demarcated by the oblique fissure (between superior and inferior lobes). The oblique fissure is in line with rib 6 and the medial border of the scapula (when the arm is raised).
• Examination of the superior lobe is done on the anterior chest wall, whereas examination of the inferior lobe is done posteriorly below the scapula (Clemente 115-116; Grant p. 30; Netter 3e 188, 4e 197).
• The superior lobe of the right lung is further divided from the middle lobe by a horizontal fissure (in line with rib 4, from the midaxillary line to the attachment of rib 4 to the sternum).

THE LEFT LUNG

• has a superior and inferior lobe divided by an oblique fissure. It also has a large cardiac notch found on the mediastinal surface. The lingula which is an anterior projection of the superior lobe overlies the anterior aspect of the heart.
• Examination of the superior lobe is done anteriorly and of the posterior lobe posteriorly, below the level of rib 6.

THE BRONCHIAL TREE (Clemente 117, 122-125; Grant p. 36-40; Netter 3e 190, 191, 4e 202-205)

• It is formed by the branching of the trachea at the level of T4/5.
• The primary bronchus is in the mediastinum and it enters the hilus of the lung. The primary bronchus divides into secondary or lobar bronchi (3 - upper, middle, lower - for the right lung and 2 - upper and lingular, lower - for the left lung). The lobar bronchi divide into the tertiary or segmental bronchi which supply bronchopulmonary segments of the lung. The tertiary bronchus is joined by a tertiary division of the pulmonary artery (Clemente 124; Grant p. 33, 41; Netter 3e 201, 4e 205).

Bronchopulmonary segments (Clemente 117, 119, 121; Grant p. 36-38; Netter 3e 196-197, 4e 200-201, 203)

• A bronchopulmonary segment can be resected with less physiological loss than a lobectomy or pneumonectomy and thus the pattern of bronchopulmonary segments is important.
• The right lung has 10 bronchopulmonary segments and the left lung has 8.

Body positions for lung drainage

• To drain the base of the lung, the patient must have the head down.
• To drain the upper lobe, the patient must be sitting down.

Aspiration of foreign bodies

• Objects aspirated into the trachea from a vertical position tend to be found in the right lung (the posterior basal segment is most likely) because the right bronchus is almost in line with the trachea.
• With patient lying on the right side, the object would be in the bronchopulmonary segments of the right posterior or middle lobes.
• With patient lying on the left side, it would be in the superior or inferior bronchopulmonary segments of the lingula.
• With the patient lying supine, it would be in the superior bronchopulmonary segment of the lower lobe.

The upper respiratory tract insures the patency of the airways, via bony and cartilaginous structures.

2 PULMONARY ARTERIES

• are derived from the bifurcated pulmonary trunk (Clemente 206; Grant p. 41; Netter 3e 202, 4e 124).
• lie anterior to the bronchi as they enter the hilus.

The right pulmonary artery:

• is crossed over by the azygos vein whereas the left one is crossed over by the arch of the aorta at T5 (Clemente 126-127; Grant p. 66-68; Netter 3e 226-227, 4e 230-231).
• divide into lobar branches
• and then tertiary branches which have a close relationship with the tertiary bronchi in the bronchopulmonary segments (Grant p. 33; Netter 3e 197, 201, 4e 205).
• bring deoxygenated blood which will be oxygenated at the level of the terminal alveolar ducts and the bronchial sacs. Oxygenated blood is returned to the heart by pulmonary veins.

4 PULMONARY VEINS (Clemente 126-127; Grant p. 41; Netter 3e 202, 4e 206)

• 2 lower pulmonary veins from the veins of the inferior lobe of each lung, return to the left atrium of the heart.
• The upper right pulmonary vein comes from the superior and middle lobe of the right lung.
• The upper left pulmonary vein comes from the superior lobe of the left lung.
• The pulmonary veins also drain oxygenated blood supplied to the lungs by the bronchial arteries.

BRONCHIAL ARTERIES (Clemente 157, 158; Grant p. 75; Netter 3e 203, 4e 207) arise from the descending aorta or 3rd intercostal branch and supply oxygenated blood to the lung tissue.

Lymphatics (Clemente 134; Grant p. 43; Netter 3e 204, 4e 208)

• are extensive and follow the vascular tree.
• At the hilus of the lung, they are filtered by the pulmonary lymph nodes and then enter the right lymphatic duct, on the right side. The latter join with the intersection of the right subclavian and right internal jugular veins (Clemente 168-169).
• On the left side, lymph vessels enter the thoracic duct which returns lymph at the intersection between the left subclavian and the left internal jugular veins.

Nerves (Clemente 166-167; Grant p. 42; Netter 3e 205-206, 4e 210)

• The bronchopulmonary plexus supplies both para- and sympathetic nerves to the bronchial and vascular trees.
• Parasympathetic fibers are preganglionic vagal and secretomotor to glands in the bronchial mucosa.
• Sympathetic fibers are postganglionic fibers and vasomotor to arterial system.

*Bronchodilatation can be achieved by epinephrine which mimics the sympathetic nervous system.

updated 9/16/2009

Heart and Mediastinum

The pericardium is a fibrous sac lining a serous sac invaginated by the heart and great vessels during development (Clemente 112; Grant p. 25; Netter 3e 208, 211, 4e 211-212).

• The visceral pericardium (epicardium) lines the surface of the heart.
• The parietal pericardium lines the inner surface of the fibrous sac.
• The pericardial cavity contains fluid. Increased amount of fluid results in cardiac tamponnade, requiring opening of the fibrous sac.
• The pericardium is continuous with the connective tissue of the central tendon of the diaphragm inferiorly and that of the great vessels superiorly (Clemente 135; Grant p. 51; Netter 3e 211, 4e 212). It defines the mediastinum (Clemente 130; Grant p. 25, 29; Netter 3e 207, 4e 230-231, 233).

THE HEART

has 4 chambers

• left and right atria
• left and right ventricles

Atria and ventricles are separated by the coronary (atrioventricular) sulcus (Clemente 132-133; Grant p. 46; Netter 3e 210, 4e 214).

The ventricles are separated from each other by the anterior and posterior interventricular sulci (Clemente 132-133; Grant p. 46-49; Netter 3e 210, 4e 212, 214).

The base of the heart

• is posterosuperior;
• is most stationary during heartbeats;
• is formed by the left atrium and the 4 pulmonary veins (Clemente 133; Grant p. 47; Netter 3e 210, 4e 214);
• The visceral pericardium is continuous with the parietal pericardium at this point and forms the oblique pericardial sinus (Clemente 135; Grant p. 51; Netter 3e 211, 4e 215).

The apex of the heart

• is most moveable
• is located in the left 5th intercostal space (Clemente 129; Grant p. 45; Netter 3e 192, 4e 213).

Surfaces of the heart are:

• anterior (right sternocostal)
• left sternocostal
• inferior diaphragmatic.

• The anterior interventricular sulcus is on the left sternocostal surface.
• The posterior interventricular sulcus is on the diaphragmatic surface.
• Coronary vessels are found in the coronary sulcus and their branches are found in the anterior and posterior interventricular sulci (Clemente 139; Grant p. 46-52; Netter 3e 212, 4e 216-217).

SURFACE ANATOMY (Clemente 109; Grant p. 28, fig. 1.23; Netter 3e 184, 4e 198)

• The right subclavian vein, under the right clavicle, joins with right internal jugular vein at the sternoclavicular joint, forming the right brachiocephalic vein (Clemente 113; Grant p. 48; Netter 3e 207-208, 4e ).
• The left brachiocephalic vein joins with the right posterior to the right side of the sternum, superior to the sternal angle.
• The Superior Vena Cava (SVC) descends posterior to the right of the sternum to rib 3 costal cartilage where it enters the right atrium.
• The Inferior Vena Cava (IVC) pierces the diaphragm at T8 (at the level of the xiphisternal joint) and enters the right atrium at the level of rib 6 costal cartilage (Clemente 135; Grant p. 51; Netter 3e 228, 4e 206).
• The right ventricle forms most of the anterior (sternocostal) surface of the heart, posterior to the inferior portion of sternum and the costal cartilages of ribs 4 and 5 (Clemente 134; Grant p. 49; Netter 3e 208, 4e 212-213).
• The apex of the heart is the tip of left ventricle, related to the left 5th intercostal space, 10 cm from the sternal midline.
• The left margin of the heart extends in an oblique line from the left 5th to the 2nd intercostal spaces (Clemente 129; Grant p. 45; Netter 3e 192, 4e 213).
• The left ventricle is found along the inferior left margin of the heart on an oblique line .
• The tip of the left auricle is on the left margin posterior to rib 3.

*The ascending aorta and pulmonary artery were embryonically a single vessel forming the truncus arteriosus. They eventually become divided to form the outlet vessels for the right and left ventricles (Clemente 151; Grant p. 46, 49; Netter 3e 210, 4e 229).

Pulmonary trunk

• is in the 2nd intercostal space.
• overlaps posteriorly with the descending aorta.
• pierces pericardium and divides into the right and left pulmonary arteries (Clemente 132-133; Grant p. 46; Netter 3e 211, 4e 214-215).

Pulmonary arteries (Clemente 134-135; Grant p. 66; Netter 3e 208, 4e 215)

• The right pulmonary artery is longer and runs behind the ascending aorta to enter the lung.
• The left pulmonary artery enters the left lung by running anterior to the descending aorta.
• The pulmonary arteries in the middle mediastinum lie between the bronchi anteriorly and the pulmonary veins posteriorly.
• Between the left proximal pulmonary artery and the aortic arch is the ligamentum arteriosum. The ligamentum arteriosum is the vestigial ductus arteriosus which bypassed the collapsed lungs to provide blood to the rest of the fetus.

The ascending aorta

• is continuous with the arch of aorta at the sternal angle (Clemente 129; Grant p. 45; Netter 3e 208, 4e 233).
• crosses posteriorly and to the left over the hilus of the left lung, forming the aortic knuckle on radiographs (Clemente 128; Grant p. 27; Netter 3e 209, 4e 213).

AORTIC AND PULMONARY SEMILUNAR VALVES

• Both pulmonary trunk and ascending aorta have a semilunar valve (Clemente 136, 143, 145; Grant p. 60-61; Netter 3e 218-219, 4e 222-224) to prevent reflux into the ventricles during systole and diastole (ventricular contraction and relaxation).
• The semilunar valves are formed by 3 cusps (valvules). A nodule is present in the middle of the free edge and the portion below the free edge is the lunule (Clemente 143-145; Grant p. 61; Netter 3e 219, 4e 223).
• During diastole, the closing of the valves can be heard over the right 2nd intercostal space for the aorta and over the left 2nd intercostal space for the pulmonary trunk (Clemente 129; Grant p. 44; Netter 4e 213).
• Each valve has 3 sinuses to prevent the valvules from sticking to the vessel walls.
• The aortic valve has right (with the ostium for the right coronary artery), posterior (noncoronary) and left (with the ostium for the left coronary artery) sinuses associated with the cusps (Clemente 145; Grant p. 61; Netter 3e 219, 4e 223).
• The pulmonary valve has right, left and anterior cusps.

BLOOD SUPPLY OF THE HEART

Coronary refers to arterial vessels whereas cardiac refers to venous vessels.

Right and left coronary arteries arise from right and left coronary sinuses of the aortic valve (Clemente 145; Grant p. 52; Netter 3e 214-215, 4e 223).

The left coronary artery (Clemente 136-140; Grant p. 54; Netter 3e 215, 4e 216-217, 219)

• passes anterior between the pulmonary trunk and the tip of the auricle of the left atrium. It divides on the anterior aspect of the heart into the anterior interventricular branch (1) and the circumflex branch (2).
• (1) descends in the anterior interventricular sulcus to the inferior margin of the heart and continues into the posterior interventricular sulcus on the diaphragmatic surface. It supplies the anterior aspects of the right and left ventricles and the anterior 1/2 of the interventricular septum.
• (2) runs to the left in the atrioventricular sulcus between the left atrium and ventricle. It gives off a marginal branch for the lateral margin of the left ventricle and continues onto the posterior aspect of the heart. It forms an anastomosis with the arteries (derived from the right coronary artery) in the posterior interventricular sulcus.

The right coronary artery (Clemente 136-141; Grant p. 52, 54-55; Netter 3e 214, 4e 216-218)

• runs in the coronary sulcus between the right atrium and right ventricle.
• gives off a nodal artery which passes onto the posterior aspect of the right atrium and supplies the area of the sinoatrial (SA) node.
• then gives off a marginal branch (smaller than the left one) to supply the right ventricle.
• terminates in the posterior interventricular sulcus as the posterior interventricular artery, supplying mainly the posterior aspect of the right and left ventricles as well as the posterior 1/2 of the interventricular septum.

The cardiac veins (Clemente 136-137; Grant p. 53; Netter 3e 212-213, 4e 216-217)

• accompany coronary arteries and their branches.
• lie superficial to the arteries in the sulci.
• Most of the veins drain into the coronary sinus.

The coronary sinus

• is derived from the sinus venosus (the primitive receiving chamber of the developing heart).
• lies in the coronary sulcus between the left margin of the heart and the posterior interventricular sulcus. It drains into the right atrium by an opening to the left of the entrance of the inferior vena cava.

The great cardiac vein

• forms in the anterior interventricular sulcus
• joins the coronary sinus near the left margin of the heart.

The middle cardiac vein

• occupies the posterior interventricular sulcus
• enters the coronary sinus near the entrance to the right atrium.

The small cardiac vein

• follows the right marginal branch of the right coronary artery
• joins the coronary sinus near the junction with the middle cardiac vein.

The oblique vein drains from the left atrium into the coronary sinus along with posterior ventricular veins draining the diaphragmatic surface of the left ventricle.

The anterior cardiac veins

• drain the anterior surface of the right ventricle.
• open directly into the right atrium.

Venae cordis minimae or thebesian veins

• are tiny veins draining the heart wall.
• open directly into the chambers.

Chambers of the heart

Right atrium (Clemente 142; Grant p. 56; Netter 3e 216, 4e 220)

• forms the right margin of the heart with the right auricle projecting superiorly and anteriorly over the base of the ascending aorta. The superior vena cava drains into the superior margin. The inferior vena cava and coronary sinus drain via the posterior surface (Clemente 137; Grant p. 50; Netter 3e 210, 4e 214).
• contains a roughened area with musculi pectinati, derived from the embryonic atrium which is now represented by the auricle (Clemente 142; Grant p. 56; Netter 3e 216, 4e 220). These merge with the crista terminalis. The crista terminalis extends from the superior vena cava to the inferior vena cava and on the exterior side, it is marked by the sulcus terminalis. The sinuatrial node is located in the floor of the sulcus terminalis near the superior vena cava (Clemente 225; Grant p. 64; Netter 3e 221, 4e 149).
• The smooth area of the right atrium is derived from the sinus venarum cavarum (primitive receiving chamber of the developing heart).
• The inferior vena cava opening contains a fenestrated, non-functional valve in the adult.
• The coronary sinus also contains a valve and its opening is located between the inferior vena cava and the tricuspid.
• The fossa ovalis is a depression on the interatrial wall superior to the opening of the inferior vena cava and used to be the opening in the developing prenatal heart shunting blood from right atrium to left atrium, bypassing the pulmonary system.
• Superior to the fossa ovalis is the annulus which is the inferior border of the rigid superior part of the interatrial wall; thus the mobile inferior wall opens when the pressure is higher in the right atrium and closes when the left atrial pressure is higher, sealing the foramen ovale.
• The right atrioventricular or tricuspid valve is located anteriorly and closes during ventricular contraction.

The left atrium (Clemente 144; Grant p. 58; Netter 3e 58, 4e 221)

• forms 2/3 of base of heart. The auricle is visible anteriorly from the left side of the pulmonary trunk.
• lies superior to the coronary sulcus.

The right and left superior and inferior pulmonary veins drain into the left atrium and the portion of the atrium derived from these vessels is smooth. The auricle contains musculi pectinati capable of contraction.

The left atrioventricular (or bicuspid or mitral valve) is located anteriorly.

The ventricles (Clemente 143-145, 147-149; Grant p. 57, 59; Netter 3e 216-217, 4e 220-224)

• Right and left ventricles lie anterior to their atria.
• The right ventricle forms most of the anterior sternocostal part of the heart and the inferior margin posterior to sternum.
• The left ventricle forms the left margin of the heart and most of the diaphragmatic base.

The right ventricle works against pulmonary pressure (4/25 mm Hg) whereas the left ventricle works against systemic pressure (80/120 mm Hg).

The left ventricular wall is about 5 times thicker than the right one (Clemente 143-145; Grant p. 64; Netter 3e 220, 4e 224) and the thickness of the interventricular septum approximates that of the left. The interventricular wall is fleshy except for its superior part where the membrane is continuous with the membranous spiral septum which divided the primitive truncus arteriosus into the pulmonary trunk and the ascending aorta.

Ventricular walls are lined with trabeculae carnae. Some form papillary muscles arising from the anterior and posterior walls (Clemente 147; Grant p. 57-59, 63; Netter 3e 219-220, 4e 220-224). The right ventricle also has septal papillary muscles. The apex of a papillary muscle is attached to the cusp of an atrioventricular valve by the chordae tendinae.

In each ventricle, the portions below the pulmonary trunk and the ascending aorta are called the conus arteriosus (infundibulum; Clemente 143; Grant p. 62; Netter 3e 216, 4e 220) and the aortic vestibule, respectively. They are noncontractile.

In the atrioventricular valves, the chordae tendinae from each papillary muscle control the contiguous margins of 2 cusps (Clemente 142-145; Grant p. 63; Netter 3e 219, 4e 223), preventing eversion during ventricular contraction.

On the chest, an oblique line from the 3rd intercostal to the 6th intercostal spaces will have all 4 valves of the heart lined up: Pulmonary, Aortic, Mitral, and Tricuspid.

Listen for heart sounds at the left 2nd intercostal space (pulmonary), right 2nd intercostal space (aortic), left 5th intercostal space (mitral) and right 5th intercostal space (tricuspid; Clemente 129-131; Grant p. 44; Netter 4e 213).

CONDUCTION SYSTEM OF THE HEART (Clemente 148-149; Grant p. 64; Netter 3e 221, 4e 225)

The sinoatrial (SA) node

• is the pacemaker
• is vascularized by the nodal branch of the right coronary artery (Clemente 138-139; Grant p. 52; Netter 3e 214, 4e 218).
• is innervated by fibers from the vagus (parasympathetic) and the sympathetic chain of ganglia.

The atrioventricular (AV) node is located in the wall of the right atrium anterior to the mouth of the coronary sinus.

The atrioventricular bundle (of His) connects atria to ventricle in the interventricular septum and divides into right and left bundle branches (crura).

The rigth crus is visible in the right ventricle as the septomarginal trabecula (moderator band) running to the anterior papillary muscle.

The heart innervation:

• The SYMPATHETIC innerviation is via 1-3 cervical cardiac branches, 2-3 cervicothoracic branches from the stellate (cervicothoracic) ganglion, and 2-4 thoracic branches from the upper 4 thoracic levels. They are cardiac accelerators.
• The VAGUS innervation (Clemente 635; Grant p. 42, 65; Netter 3e 223, 4e 227) is via a single cervical branch, 1-2 cervicothoracic cardiac branches from the main nerve at the thoracic inlet (Grant p. 65) or from the right recurrent laryngeal branch), and 2-4 thoracic cardiac branches from the thoracic part of the vagus nerve (or left recurrent branch). They are inhibitory to the cardiac rate.

All the branches fuse into a cardiac plexus which courses around the right pulmonary artery to the posterior aspect of the atria. They distribute to the SA and AV nodes and to the coronary plexuses.

Visceral afferent (sensory) fibers are chemosensitive to ischemic byproducts (lactic acid) and pain from ischemic heart muscle. They enter the spinal cord at level of T1 and thus angina pectoralis may manifest itself as referred pain on the T1 dermatome of the left arm (Grant p. 346, 348; Netter 3e 157, 4e 227)

updated 9/16/2009

Mediastinum (Clemente 130; Grant p. 25-29; Netter 3e 192-194, 4e 211-212)

• divides the thoracic cavity
• contains all the thoracic viscera, except for the lungs.
• extends:

• from the posterior aspect of the sternum anteriorly to the thoracic vertebrae posteriorly (Clemente 126-127; Grant p. 25, 29; Netter 3e 194, 226-227, 4e 230-231)
• from the thoracic inlet superiorly to the diaphragm inferiorly.

A line through the sternal angle and the intervertebral disc T4/5 subdivides the mediastinum into the superior and inferior mediastinum (Clemente 130; Grant p. 29, Netter 213). The inferior mediastinum is further divided into the anterior, middle and posterior mediastinum.

• The anterior mediastinum contains fatty and thymic tissues.
• The middle mediastinum contains the heart and great vessels.
• The posterior mediastinum contains viscera traversing the thorax and going to abdomen.

CONTENTS OF THE SUPERIOR MEDIASTINUM

• The thymus gland
• The great veins
• The vagus and phrenic nerves
• Tje retrosternal structures

The thymus (Clemente 112-113; Grant p. 66; Netter 207)

• is derived from the 3rd pharyngeal pouch similarly to the inferior parathyroid glands.
• lies posterior to the manubrium sterni.
• The costomediastinal recesses are on either side, and the left brachiocephalic vein and aortic arch lie posteriorly.

The left brachiocephalic vein (Clemente plates 101, 119; Grant p. 26, 48, 67; Netter 194)

• is formed by the left jugular and the left subclavian veins, posterior to the left sternoclavicular joint.
• joins with the right brachiocephalic vein and they form the superior vena cava at the level of the 1st right intercostal space.
• The left brachiocephalic vein passes anterior and superior to the 3 great branches of the aortic arch.

The right brachiocephalic vein

• is formed by the union of the right internal jugular and right subclavian veins posterior to the right sternoclavicular joint.
• forms the superior vena cava with its left counterpart.
• The superior vena cava enters the right atrium at the level of the 3rd right costal cartilage (Clemente 129; Grant p. 26; Netter 3e 208, 4e 213). It receives the arch of the azygos system on its posterior surface (Clemente 126; Grant p. 80; Netter 3e 226, 4e 230) and the right phrenic nerve runs with it.

Both vagus and phrenic nerves descend posterior to the brachiocephalic veins bilaterally in the superior mediastinum. The phrenic nerve passes anterior to the root of the lung whereas the vagus nerve passes posterior to the root of the lung (Clemente plates 115, 117; Grant p. 80-81; Netter 226-227).

Prevertebral structures

The esophagus lies posterior to the trachea (Clemente 155; Grant p. 67; Netter 3e 226, 4e 232-233)

The trachea

• begins below the larynx (below the cricoid cartilage) at the level of C6 (Clemente 586-587; Grant p. 750; Netter 3e 229, 4e 233).
• Half is in the neck and half is in the superior mediastinum.
• bifurcates at the level of T4/5, at the carina.
• lies in the median plane and inferiorly it is displaced to the right by the aortic arch.
• Its right relationships are the brachiocephalic artery, the right vagus (Clemente 126, 155; Grant p. 68; Netter 3e 228, 4e 230, 232), and the azygos arch.
• To the left are the left common carotid and left subclavian arteries, left vagus, and left recurrent laryngeal nerve between the trachea and the mediastinal pleura (Clemente 127, 155; Grant p. 68-69; Netter 3e 228, 4e 231).
• The lymph nodes are found in the 3 bifurcation angles of the trachea (Clemente 156; Grant p. 68; Netter 3e 204, 4e 208, 239). They drain into the right lymphatic duct and the thoracic duct (Clemente 168-169; Grant p. 76; Netter 3e 204, 4e 208).

The cardiac plexus

• contains sympathetic and vagal fibers located anterior to the bifurcation of the trachea, inferior to the bifurcation of the pulmonary trunk and the arch of the aorta.
• has extensions as the right and left pulmonary plexus (Clemente 130; Grant p. 68; Netter 3e 205, 222, 4e 209, 226) cervical, cervicothoracic and thoracic cardiac branches; anterior and posterior vagal and sympathetic nerves at the hilus) and the plexus of the thoracic aorta.

Preganglionic sympathetic nerves (Clemente 165; Grant p. 346; Netter 3e 223, 4e 210, 227)

• originate at T1-T4 lateral horn of spinal cord.
• enter the paravertebral sympathetic chain of ganglia via the white rami communicantes
• may synapse in the upper ganglia or as high up as the cervical ganglia.
• Postganglionic fibers produce tachycardia and vasodilation of the coronary arteries.

Separate visceral afferent fibers carry visceral reflexes and visceral pain sensation to the spinal cord.

• The cell bodies are in the dorsal root ganglion and fibers enter the spinal cord at the level of T1-T2.
• Thus pain due to myocardial ischemia can be referred to T1 and T2 dermatomes of left arm and chest.

Preganglionic vagal fibers

• arise from cell bodies in the brainstem
• reach the heart via the right and left vagus nerves.
• The ganglia are confined to the atria and the interatrial septum near the roots of the great vessels.
• Efferent vagal fibers produce bradycardia.
• Afferent vagal fibers from the heart, aorta and great vessels are for chemo- and baroreception. The cell bodies are in the inferior ganglion of the vagus nerve.

Intermediate structures

The aortic arch and its 3 great branches (Clemente 161; Grant p. 68-69; Netter 3e 228, 4e 232).

• The inferior aspect of the aortic arch lies on a line from the sternal angle through the T4/5 intervertebral disc.
• The ascending aorta is posterior to the right margin of the sternum. It arches over the right pulmonary artery and left bronchus, curves to the left (Clemente 127; Grant p. 67; Netter 3e 202, 4e 231-232) and becomes the descending aorta to the left of the T5 vertebral body.
• The aortic arch lies anterior to the end of the trachea, left recurrent laryngeal nerve (Clemente 127, 155, 158; Grant p. 67; Netter 3e 228, 4e 231-233), superior portion of the esophagus and the thoracic duct.
• The left vagus, left phrenic nerves, and left superior intercostal vein cross it anteriorly.

Branches of the aorta (Clemente 161; Grant p. 70; Netter 3e 228, 4e 232)

• All the branches arise from the superior aspect of the aortic arch.
• They are the brachiocephalic trunk, the left common carotid and the left subclavian arteries.
• The left brachiocephalic vein crosses them anteriorly (Clemente 159; Grant p. 67; Netter 3e 202, 4e 212).

The brachiocephalic trunk (Clemente 155; Grant p. 26; Netter 3e 192, 4e 212)

• arises posterior to the manubrium
• divides posterior to the right sternoclavicular joint into the right subclavian and the right common carotid arteries.

The left common carotid courses into the head in the carotid sheath

The left subclavian artery arches over the apex of the left lung, posterior to rib 1 costal cartilage and enters the axilla.

The inferior aspect of the aortic arch contains the ligamentum arteriosum (Clemente 136; Grant p. 49; Netter 3e 202, 4e 212, 231), vestige of the ductus arteriosus.

• The ductus arteriosus shunted blood from the pulmonary system in prenatal life.
• With expansion of the lungs and a decrease in resistance in the pulmonary arterial system postnatally, it closes.

The ligamentum arteriosum is intimately associated with the course of the left recurrent laryngeal nerve.

The vagus nerves

• descend in the neck on the post. aspect of the common carotid arteries in the carotid sheath (Clemente 479; Grant p. 48; Netter 3e 222, 4e 71).
• enter the thoracic inlet posterior to rib 1.
• pass anterior to the arterial system (subclavian artery on the right side and aortic arch on the left side (Clemente 126-127; Grant p. 67; Netter 3e 222, 4e 230-231).
• The 2 vagi then course posterior to the roots of the lung giving out branches to the cardiac and pulmonary plexuses.

The left recurrent laryngeal nerve (Clemente 127, 158; Grant p. 67; Netter 3e 228, 4e 231, 232)

• branches from the left vagus,
• passes below the ligamentum arteriosum and the arch of the aorta,
• ascends between the trachea and the esophagus into the root of the neck.

The right recurrent laryngeal nerve (Clemente 126, 158; Grant p. 67; Netter 3e 228, 4e 230, 232)

• arises from the right vagus anterior to the rigth subclavian artery,
• courses around the artery
• ascends in the neck.
• Both recurrent nerves provide vagal innervation to the trachea and esophagus before innervating the larynx.

The phrenic nerves (Clemente 126, 127; Grant p. 67; Netter 3e 218, 219, 4e 230-231)

• arise from anterior rami of C3,4,and 5.
• enter the thoracic inlet, coursing medially.
• The left phrenic nerve crosses the left vagus anteriorly (Grant p. 42, 67).
• descend anterior to the root of the lungs, between the lateral wall of the fibrous pericardium and the mediastinal pleura.
• The right phrenic nerve is associated with the superior vena cava in its upper course and pierces the diaphragm with the inferior vena cava (Clemente 126; Grant p. 80; Netter 3e 226, 4e 230).
• The left phrenic nerve pierces the diaphragm at the margin of the fibrous pericardial attachment to the central tendon (Clemente 127; Grant p. 81; Netter 3e 227, 4e 231).

POSTERIOR MEDIASTINUM

Descending aorta

• from the left side of the body of T5, descends on the left of the vertebral column posterior to the root of the left lung (Clemente 156; Grant p. 81; Netter 3e 228, 4e 231).
• is in the midline at T8
• passes through the aortic hiatus at T11/12 (Clemente 155; Grant p. 74; Netter 3e 229, 4e 233).
• The greater splanchnic nerve from the sympathetic trunk joins the descending aorta and enters the abdomen with it (Clemente 158; Grant p. 81; Netter 3e 236, 4e 240).

The visceral branches of the descending aorta are (Clemente 156, 158; Grant p. 75; Netter 3e 233, 4e 207, 237):

• 1-3 bronchial arteries
• 1-3 esophageal arteries
• branches to pericardium and diaphragm.

The parietal (thoracic) branches are:

• the right and left posterior intercostal arteries from the 3rd intercostal space to the subcostal arteries below rib 12.
• The right posterior intercostal arteries from T3-T8 cross the vertebral column anteriorly. They anastomose with the anterior intercostal arteries of the internal thoracic artery at the midclavicular line.
• The 1st and 2nd intercostal spaces are supplied from the costocervical trunk of the subclavian arteries.

The thoracic duct (Clemente 159; Grant p. 76-77; Netter 235)

• begins at the cisterna chyli, posterior to the abdominal aorta, inferior to the diaphragm (Clemente 159; Grant p. 83; Netter 3e 305, 4e 266).
• enters the thorax posterior to the descending aorta.
• stays on the right of the vertebral column.
• At T8, the thoracic duct lies posterior to the esophagus and ascends to T5.
• It then crosses the vertebral column and enters the root of the neck on the left side, terminating at the junction between the left subclavian and left internal jugular veins.
• It drains all the lymph of the body except for the right thorax, right upper limb and right side of the head and neck.
• These remaining areas drain into the right lymphatic duct which joins the junction of the right internal jugular and right subclavian veins.

The azygos and hemiazygos venous systems (Clemente 159; Grant p. 78-79; Netter 3e 234, 4e 238)

• drain the posterior thoracic wall from the 3rd intercostal space to the subcostal veins.
• The posterior intercostal veins on the left side drain into the hemiazygos veins. They join with the azygos sytem in the mid-thorax by passing anterior to the vertebral column .
• The azygos system ascends on the right side of the vertebral column and arches over the right bronchus to enter the posterior aspect of the superior vena cava at the level of the costal cartilage of rib 3 (Clemente 126; Grant p. 80; Netter 3e 234, 4e 230).
• The right superior intercostal vein joins the azygos after draining the 2nd, 3rd, 4th right intercostal spaces.
• The left superior intercostal vein joins the left brachiocephalic vein by crossing the anterior aspect of the aortic arch.
• The highest posterior intercostal veins drain the 1st intercostal space and join the brachiocephalic veins.
• The anterior intercostal veins drain into the internal thoracic veins (Clemente 111; Grant p. 23; Netter 3e 184, 4e 191).

Esophagus

• extends from the posterior aspect of the pharynx at the level of C6 (Clemente 155; Grant p. 788; Netter 3e 229, 4e 233) to the stomach, below the left dome of the diaphragm.
• pierces the diaphragm at the level of the rib 7 costal cartilage at the level of T10.
• is constricted in 4 regions:
  • C6 (upper esophageal sphincter-voluntary),
  • T2/3 (crossing of aortic arch),
  • T4/5 (crossing of left primary bronchus),
  • T10 (diaphragm).
• Obstructions may occur at these levels. These levels are respectively 15 cm, 22 cm, 27 cm and 40 cm from the incisor teeth.
• lies anterior to the vertebral bodies of C7-T8
• swings to the left in the lower thorax, in front of the descending aorta to pass through the left dome at T10.
• is anterior to the thoracic duct, right posterior intercostal arteries (T3-T7), azygos and hemiazygos systems in the midthoracic region.
• The trachea is anterior to the esophagus from C7 to T4 (Clemente 155; Grant p. 74; Netter 3e 229, 4e 233). Then the esophagus lies posterior to the base of the heart (left atrium; Clemente 156; Grant p. 65; Netter 3e 229, 4e 233).

The superior esophageal sphincter is the cricopharyngeus (a voluntary muscle; (Grant p. 787; Netter 3e 229, 4e 233).

The inferior esophageal cardiac sphincter is under the control of vagal (opener) and sympathetic fibers (closer).

The recurrent laryngeal nerves

In the cervical region, both recurrent laryngeal nerves lie between the trachea and the esophagus (Clemente plate 554; Grant p. 788-789; Netter 228).

The vagus nerves

• inferior to the root of the lung, the left vagus lies anterior to the esophagus (Clemente 127; Grant p. 81; Netter 3e 228, 4e 231) and the right vagus lies posterior.
• Their branches form the anterior and posterior esophageal plexuses (Clemente 126-127, 167; Grant p. 80-81; Netter 3e 236, 4e 232) which form single nerves to pierce the diaphragm at the esophageal hiatus.
• Below the diaphragm they are renamed the anterior and posterior gastric nerves.
• Vagal branches induce peristalsis in the esophagus and are secretomotor to mucous glands.

Sympathetic nerves are vasomotor to blood vessels.

updated 9/16/2009

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