EC

Dissection 2.1 - Superficial Thorax

Dissection guide

Articulated Skeleton

  • Costal groove: inferior border ribs 2-12

  • Costal margin: inferior border of rib cage

  • Sternum sections (superior → inferior)

    • Suprasternal notch → Manubrim → Sternalchondral ligamen → Body of sternum → Xiphoid process

Anterior Thoracic Wall

  • Cephalic vein: located between deltoid and pectoralis major (in deltopectoral groove)

  • Layer 1: Pectoralis major

    • 3 bony attachments: ribs, sternum, clavicle

    • Innervated by lateral pectoral n. (superior to medial pectoral n.)

  • Layer 2: Pectoralis minor

    • Deep to pectoralis major

    • Innervated by medial pectoral n. (nerve pierces muscle and then enters pectoralis major)

  • Layer 3: External intercostal muscles

    • Fibers slant inferiorly and medially

      • Collagen fibers have same orientation

    • Medial part → External intercostal membrane (thin stretched out external intercostal m.)

  • Layer 4: Internal intercostal muscle

    • Lateral to sternum

    • Fibers slant inferiorly and laterally (perpendicular to external intercostal m.)

  • Intercostal VAN located in costal groove

    • Ventral rami of first 11 thoracic spinal n. → 11 intercostal n.

    • Ventral ramus T12 → Subcostal n.

Dermatomes

  • Cutaneous n. that innervate a region of skin

    • All SS cell bodies located in DRG of spinal n.

  • Clinically relevant for herpes zoster

Skinning the Neck

  • Layer 1: Platysma (embedded in superficial fascia)

    • SM innervated by cervical branch of CN VII

    • Other structures in the area include tributaries of anterior jugular v. and cutaneous branches of cervical plexus

    • Attaches onto the clavicle

  • Layer 2: SCM (not covered in this dissection)

    • Attaches onto the clavicle

Clavicle Removal

  • Clavicle is superficial to structures of the neck and thorax

  • Sternoclavicular joint: Joint between sternum and clavicle


Bolded terms

Acromion process

  • Flat, expanded projection at the outer end of the spine of the scapula (shoulder) and articulates with clavicle

Body of the sternum

  • Part of sternum between manubrium and xiphoid process

    • Manubrium is superior to the body (manubirosternal joint aka sternal angle in between, contain intraarticular sternochondral ligament)

    • Xiphoid process is inferior to the body

Cephalic vein

  • Located between deltoid and pectoralis major

  • Cephalic v. → Axillary v. → Subclavian v. → Brachiocephalic v. → Superior vena cava → Right atrium

Clavicle

  • Bone located superficial to structures of the neck and thorax but deep to muscles of the thorax

  • Attachment for SCM and platysma at superior border

Corpus (body) of the mandible

  • Section of mandible between mental protuberance and ramus

Costal cartilage

  • Hyaline cartilage that connects the ribs to the sternum

Costal groove

  • Groove located on the inferior border of ribs 2 to 12

  • Formed by pulsations of the intercostal artery

  • Holds the intercostal VAN

Costal margins

  • Inferior border of the ribcage

Costochondral joint

  • Short bar of costal cartilage located between the anterior end of the first rib

  • Articulates with the manubrium of the sternum (sternochostal joint)

Dermatome

  • Strip of skin innervated by dorsal and ventral cutaneous nerves from a single spinal nerve

External intercostal membrane

  • The most medial part of external intercostal muscle that is a semi-transparent membrane (under which we can see internal intercostal muscles)

External intercostal muscle

  • Seen lateral to the costochondral joint

  • Muscle fibers point inferior-medially

  • Elevate the ribs and expand the chest cavity

First rib

  • Most superior rib

Genu/symphysis of the mandible

  • The point of fusion where the two halves of the lower jaw (mandible) join together during development, forming a single bone

  • Located in midline - near chin

Gonial angle

  • Inferior angle of mandible (between body and rami)

Intercostal artery

  • Runs in intercostal groove

  • Subclavian a. → Costocervical trunk → Intercostal a.

Intercostal nerve

  • Runs in intercostal groove

  • Arises from ventral rami of 1st 11 thoracic spinal nerves

Intercostal vein

  • Runs in intercostal groove

Internal intercostal muscle

  • Located just lateral to the sternum and deep to external intercostal membrane

  • Fibers run inferiorly and laterally

  • Pulling the ribs downward and inward, effectively reducing the thoracic cavity volume and pushing air out of the lungs

Lateral pectoral nerve

  • Supplies innervation to pectoralis major (located medially)

  • Branch of lateral cord of brachial plexus

Manubrium

  • Superior portion of sternum

Medial pectoral nerve

  • Supplies innervation to pectoralis minor (located laterally - pierces into pectoralis minor and enters pectoralis major)

  • Branch of medial cord of the brachial plexus

Pectoralis major

  • Superficial muscle in thorax

  • Innervated by medial and lateral pectoral nerves

Pectoralis minor

  • Deep to pectoralis minor

  • Innervated by medial pectoral nerve

Platysma

  • Thin muscle embedded in the superficial fascia deep to the skin

  • Innervated by CN VII

Ribs

Second rib

Sternocostal joint

  • Joint between manubrium of the sternum and the costal cartilage which joins the anterior ends of the 1st rib

Sternum

Subcostal nerve

  • The ventral ramus of T12 that lies below the 12th rib

Suprasternal/jugular notch

  • Notch at the superior margin of the manubrium

Trapezius muscle

  • Large diamond shape muscle that spans the back

Ventral rami

  • Carry all 3 fiber types to the ventral side of the body (SM, SS, VS)

Xiphoid process

  • Inferior portion of the sternum