What portion of the body do the pectoral muscles cover?
The pectoral muscles cover the anterolateral wall.
Where do the sternocostal and clavicular heads of the pectoralis major attach to proximally and distally?
The attachments of the sternocostal and clavicular heads of the pectoralis major are as follows:
Proximal: Sternum, superior six costal cartilages, and clavicle.
Distal: Anteromedial aspect of the proximal humerus.
What does simultaneous contraction of the sternocostal and clavicular heads of the pectoralis major result in? What are the innervations of these two heads?
The simultaneous contraction of the sternocostal and clavicular head results in adduction and medial rotation of the upper limb.
The innervations of these two heads are the Lateral and Medial Pectoral Nerves (C5-C8, T1)
For the Pectoralis Minor:
1) Where is it found?
2) What innervates it?
3) What is its proximal attachment?
4) What is its distal attachment?
5) What is its function?
The Pectoralis Minor:
1) is found beneath the pectoralis major
2) is innervated by the medial pectoral nerve (C8, T1)
3) is proximally attached to the 3rd and 5th ribs near their costal cartilages
4) is distally attached to the medial border and superior surface of the coracoid process of the scapula
5) stabilizes the scapula by drawing it inferiorly and anteriorly against the thoracic wall
For the Serratus Anterior:
1) Where does it attach proximally?
2) Where does it attach distally?
3) What innervates it?
4) What is its function?
The Serratus Anterior:
1) attaches proximally to the lateral portions of the first 8 ribs
2) attaches distally to the medial border of the scapula
3) is innervated by the long thoracic nerve
4) protracts the scapula when stretching to reach for something
What muscle stabilizes the scapula during protraction and what muscle retracts the scapula from the protracted position?
The pectoralis minor stabilizes the scapula during protration and the trapezius subsequently retracts the scapula from the protracted position.
Which muscles abduct the upper limb to 90 degrees? What muscle allows for abduction above 90 degrees?
The supraspinatus and deltoid muscles abduct the upper limb up to 90 degrees, and the serratus anterior works synergystically with these muscles to further abduct the upper limb beyond 90 degrees.
Why is the long thoracic nerve vulnerable to injury and how are abduction and rotation at the glenohumeral joint hindered after its injury? How does the winged scapula deformation occur?
The thoracic nerve is vulnerable to injury because it is located on the superficial aspect of the serratus anterior which lies directly beneath the limbs when they are normally at your side. When the limbs are raised this leaves the thoracic nerve unshielded from injury as commonly seen in a knife fight.
Since the thoracic nerve innervates the serratus anterior, if this nerve is damaged the serratus anterior no longer has muscle tone necessary to keep the scapula pulled tightly against the posterior thoracic wall (winged scapula).
Also, a damaged serratus anterior will not rotate the glenoid cavity superiorly, is is needed for full abduction of the upper limb.
From which myoblasts do the pectoral muscles derive from?
The pectora muscles are derived from the myoblasts of the parietal layer of lateral plate mesoderm.
What is the Poland Sequence?
The Poland Sequence is a rare serious defect resulting in the absence of the pectoralis minor and some of the pectoralis major (usually the sternal head).
Typical characteristics are absence or displacement of nipple and areola, along with syndactyly (fused fingers) and brachydactyly (short fingers) on the affected side.
What essentially are mammary glands and how are nipples formed?
Mammary glands are essentially highly specialized apocrine sweat glands.
At 6 weeks, the embryo develops two ridge-like thickenings of epidermis called mammary (milk) lines. These lines each start on one side of the ventral side of the body beginning at the axilla (armpit) and travelling down the ventral side of the body ending at the inguinal (groin) area, [see below]. Most of this ridge quickly disappears on both sides except for one very small portion in the pectoral region, which forms the primitive nipple.
What can be found within the breasts?
Inside the breasts, the functional substance (parenchyma of mammary gland, which is 15-25 rudimentary lactiferous ducts) can be found which open up onto the surface of the nipple.
Nipple Image Key
BV = Blood Vessel
De = Dermis
EP = Stratified Squamous Epithelium
SM = Smooth muscle
* = Lactiferous Duct
What is the effect of ovarian hormones on lacteriferous ducts in the breasts, and what are the names of these hormones?
Estrogen and Progesterone induce budding of multiple, small terminal ducts from the distal end of each lactiferous duct. They also induce white fat accumulation between these newly budding ducts.
What happens to the distal ends of the terminal lacteriferous ducts during pregnancy, and what is responsible for this occurance?
During pregnancy, the ovarian hormones (estrogen/progesterone) and prolactin (from the pituitary gland) do two things:
1) stimulate secretory acini formation at the distal ends of terminal lacteriferous ducts.
2) induce milk secretion into the lumens of acini during lactation.
Image of Lactating Mammary Gland (Key)
Du = Ducts
* * = acini filled with milk
* = empty acini
What happens to the breasts after breast-feeding?
The terminal lactiferous ducts regress but remaining lactiferous ducts can transform into fluid-filled cysts.
What anchors the breasts to the dermis, and what proportion of the breasts lie on the underlying muscles (which muscles)?
The breasts are firmly attached to the overlying dermis by suspensory ligaments.
Two-thirds of each breast lies on the pectoralis major muscle and one-third lies on the serratus anterior muscle.
Where does lymph from the lateral quadrants of the breast drain into? Where does lymph from the medial quadrants drain into?
Lymph from the lateral quadrants drains into the pectoral lymph nodes which is a consituent group of the axillary nodes.
Lymph from the medial quadrants drains into the parasternal lymph nodes.
Both axillary and parasternal lymph nodes ultimately drain into the supraclavicular lymph nodes.
Where do breast carcinomas typically arise and what is the most common site for metastasis?
Breast carcinomas typically arise in the epithelial cells of the lactiferous ducts in the mammary gland lobules.
The most common site for metastasis is the axillary lymph nodes since most of the lymph of the breasts drains here. (Metastatic cancerous cells travel through the lymph vessels)
What is fascia, how is it named and whichfascia sheaths the neurovascular contents of the axilla?
Fascia is a tough sheet of dense connective tissue that is
named according to the muscle beneath it.
The pectoral fascia leaves the lateral border of the pectoralis major to become the axillary fascia.
Which muscles form the following boundaries of the axilla:
1) posterior boundary
2) medial boundary
3) anterior boundary
The following muscles form the posterior, medial, and anterior boundaries, respectively:
1) the subscapularis
2) the serratus anterior
3) pectoralis major
What is the purpose of the axilla?
The axilla is a passageway for nerves and blood vessels from the root of the neck to the upper extremities.
Which vessel connects the axillary artery with the aorta?
The subclavian artery recieves blood from the aorta and is continous with the axillary artery at the lateral border of the first rib.
Where does the axillary artery end and what does it become at the point?
The axillary artery ends at the inferior border of the teres major where it continues as the brachial artery.
What is unique about the subscapular artery?
The subscapular artery is the branch of the axillary artery with the largest diameter and shortest length.
What are the two terminal branches of the subscapular artery?
The two branches of the subscapular artery are:
1) the circumflex scapular artery
2) the thoracodorsal arteries
What muscle does the thoracodorsal artery supply?
The thoracodorsal artery supplies the latissimus dorsi.
What is characteristic about the circumflex scapular artery?
The circumflex scapular artery curves around the lateral border of the scapula and anastomoses (reconnects) with the suprascapular artery.
Which arteries supply the deltoid, and where do these arteries arise from?
The deltoid is supplied by the posterior circumflex humeral artery and the anterior circumflex humeral artery which both anastomose (reconnect) after separately branching off from the axillary artery.
Where can the axillary artery be ligated without stopping blood flow into the upper limb?
The axillary artery can be ligated between the 1st rib and the subscapular artery because the direction of the blood flow becomes reversed following ligation and enables blood to still reach the third part of the axillary artery.
There are venous tributaries that correspond to the branches of the axillary artery, where do these tributaries flow into?
Venous tributaries enter into the axillary vein either directly or via the cephalic vein. The axillary vein then becomes the subclavian vein at the lateral border of the first rib.
Name the five groups of axillary lymph nodes and where do they all mainly drain into?
The five groups of axillary lymph nodes are:
1) Humeral (lateral) lymph nodes
2) Central lymph nodes
3) Apical lymph nodes
4) Subscapular lymph nodes
5) Pectoral (anterior) lymph nodes
All of these drain mainly into the supraclavicular nodes.
Where do the lymph vessels from the supraclavicular lymph nodes drain into?
The lymph vessels from the supraclavicular lymph nodes drain into veins in the root of the neck.
What accompanies veins of the upper limb and what is their purpose?
Lymph vessels accompany veins of the upper limn and their purpose is to drain lymph ino the axillary lymph nodes.
Compare these two lymph nodes:
1) The Subscapular Lymph Node
2) The Humeral Lymph Node
1) The Subscapular Lymph Node:
- 6-7 nodes
- located along posterior axillary fold
- receives lymph from the posterior aspect of the thoracic wall and scapular region.
2) The Humeral Lymph Node:
- 4-6 nodes
- located along the lateral wall of the axilla
- receives nearly all the lymph from the upper limb except lymph from the cephalic vein (goes to axillary and infraclavicular nodes)
What is the drainage order for the axillary lymph nodes?
The pectoral, humeral, and subscapular lymph nodes -->
Central lymph nodes -->
Apical lymph nodes -->
Which two nerves are at risk during surgical removal of pathologic axillary nodes? Why can removal result in lymphedema?
During surgey, the long thoracic nerve (innervates serratus anterior) and the thoracodorsal nerve (innervates latissimus dorsi) are at risk of being cut.
Removal of pathologic axillary nodes may cause lymphatic drainage of the upper limb to become impeded which leads to lymphedema (swelling as a result of accumulated lymph).
What constitutes the roots of the brachial plexus and what do these roots form?
The anterior rami of spinal nerves C5-T1 constitute the roots of the brachial plexus.
These roots join to form the superior, middle, and inferior trunks that create anterior and posterior divisions under the clavicle.
Starting with the roots of the brachial plexus at the spinal cord, describe the path of these nerves.
The 5 roots of the brachial plexus (C5-T1)
3 trunks (superior, middle, inferior)
3 trunks each branch into an anterior and posterior division
all divisions converge into the lateral, posterior, and medial cords -->
the three cords become the peripheral nerves (axillary, radial, median, musculocutaneous, and ulnar).
Where do the three cords of the brachial plexus reside and how are they named?
The three cords of the brachial plexus reside in the axilla and they are named according to their relative placement around the axillary artery.
Which roots of the brachial plexus generates:
a) the dorsal scapular nerve
b) the long thoracic nerve
c) the suprascapular nerve
What do these nerves innervate, respectively?
a) the dorsal scapular nerve is formed from the C5 root and innervates the rhomboid muscles (occasionally the levator scapulae)
b) the long thoracic nerve is formed from roots C5, C6, C7 and it innervates the serratus anterior
c) the suprascapular nerve is formed from the superior trunk which recieves nerve fibers from roots C4, C5, C6 and it innervates the supra/infra-spinatus muscles and glenohumeral joint.
How does avulsion of the brachial plexus roots C5 and C6 typically occur in adults and newborns?
Avulsion (forcible detachment from the normal point of insertion) of the brachial plexus roots C5 and C6 typically results from an excessive increase in the angle between the neck and shoulder, for example:
- a person thrown from a motorcycle or horse landing on his shoulder in such a way that his shoulder stops but head and trunk continue to move.
- during excessive stretching of the neck of a baby during delivery.
What forms the end of the humerus and what surrounds this end?
The end of the humerus is made up of the capitulum and trochlea. It is surrounded by the lateral/medial epicondyle, the radial/coronoid fossa, and the olecranon fossa (posterior side)
Identify structures A through F in the image below.
What are the two structures (A and B in image below) that form the trochlear notch of the proximal ulna?
The trochlear notch articulates with what part of the humerus?
The radial head articulates with what part of the humerus?
The trochlear notch articulates with the trochlea of the humerus.
The radial head articulates with the capitulum of the humerus.
What is the purpose of the coronoid fossa and what is the purpose of the olecranon fossa?
The coronoid fossa receives the coronoid process of the ulna during flexion of the forearm.
The olecranon fossa receives the olecranon of the ulna during extension of the forearm.
What is responsible for strengthening the joint capsule of the elbow on its lateral and medial sides, respectively?
The radial collateral ligament strengthens the joint capsule of the elbow on its lateral side, while the ulnar collateral ligament strengthens it on its medial side.
Identify structures A through G in the image below.
Identify structures A through D in the image below.
What is the function of the anular ligament of the radius?
The anular ligament encircles and holds the head of the radius in the radial notch of the ulna.
How does posterior dislocation of the elbow joint typically occur and why is the distal humerus driven anteriorly? Which nerve may be damaged?
Posterior dislocation of the elbow joint typically occurs:
a) when children fall on their hands with their elbows flexed
b) from hyperextension at this joint
c) from a blow that drives the ulna posterior or posterolateral
The anterior part of the fibrous layer of the joint capsule is relatively weak so the distal end of the humerus is usually driven right through it. This dislocation often injures the ulnar nerve.
What is the most common cause of subluxation of the radial head in preschool children? Which ligament is commonly damaged and how is the injury treated?
The most common cause of subluxation (incomplete dislocation) of the radial head in preschool children is a sudden lift by the upper limb (see image).
The anular ligament is commonly pinched
treatment is supination of the child's forearm while the elbow is flexed.
What happens to the blood within a bone after it fractures?
A coagulation of blood from torn blood vessels creates a hematoma (clot) within the fracture.
What are the intrinsic events associated with fracture repair?
The intrinsic events associated with fracture repair begins with an acute inflammatory response which recruits macrophages to the site and causes proliferation of osteoprogenitor cells in the periosteum and endosteum.
What role do the periosteal capillaries have in fracture repair?
After a bone fracture, angiogenic capillaries sprout from the periosteal capillaries and selectively induce osteoprogenitor cell differentiation. Cells closest to these capillaries differentiate into osteoblasts and cells further from theses capillaries differentiate into chondroblasts (via an oxygen gradient that decreases further from the capillaries).
What forms between the bony fragments of the fracture and what happens to this structure further in the repair process?
Hyaline cartilage forms an external callus around the ends of the bony fragments and an internal callus between these bony fragments.
Macrophage-derived osteoclasts gradually replace this cartilaginous callus with trabecular bone as they degrade it.
What are the characteristic responsibilites of the internal callus and external callus, respectively?
The internal callus has the responsibility of restoring the damaged marrow cavity
The external callus has the responsibility of completing the fracture repair with the transformation of trabecular bone into compact bone (similar to endochondral ossification).
How might mesenchymal stem cell technology be beneficial for the reconstruction of fractured bones?
Mesenchymal stem cells can be harvested from the umbilical cord, bone marrow, and other sites to be cultured and differentiated into osteoblasts. These osteoblasts can be used in fabrication of tissue-engineered bone for reconstruction of bone defects.
What muscle fasciae are continuous with the brachial fascia inferiorly and what does the brachial fascia do?
The deltoid, pectoral, and axillary fasciae are continuous with the brachial fascia and the function of the brachial fascia is to enclose the arm like a "snug sleeve".
What guides the long head of the biceps brachii to its proximal attachment, and what is this attachment?
The intertubercular sulcus guides the biceps brachii to its proximal attachment on the supraglenoid tubercle of the scapula.
Cite the proximal and distal attachments for both heads of the biceps brachii.
proximal attachment - coracoid process of the scapula
distal attachment - radial tuberosity (common)
proximal attachment - supraglenoid tubercle of the scapula
distal attachment - radial tuberosity (common)
What do the biceps flex?
I think you got this.
Where is the tendon of the long head of the biceps commonly ruptured and what deformity results?
The tendon of the long head of the biceps is commonly torn from its attachment to the supraglenoid tubercle of the scapula.
This is usually a result of forceful flexion against excessive resistance or more commonly as a result of prolonged tendinitis that weakens it.
This rupture results in the Popeye Deformity (see below).
Where does the coracobrachialis attach proximally and distally, and what is its function?
Proximal Attachment - coracoid process
Distal Attachment - middle third portion of the humerus
Function - works synergistically with the anterior part of the deltoid to flex the arm at the shoulder joint while walking.
Which spinal cord segments are tested by the biceps tendon reflex?
The C5 and C6 spinal cord segments are tested by the biceps tendon reflex.
Which cord generates the lateral root of the median nerve?
The lateral cord generates the lateral root of the median nerve.
Which nerves are formed by the bifurcation of the posterior cord? which nerves arise from the posterior cord before it bifurcates?
The axillary and radial nerves are formed from the bifurcation of the posterior cord.
The thoracodorsal and subscapular nerves arise from the posterior cord before it bifurcates.
What is the main spinal segmental origin of the axillary nerve and what are its muscular and cutaneous innervations?
The spinal segmental origin of the axillary is C5, C6.
It innervates all the muscles of posterior compartments of arm and forearm, skin of posterior arm, inferolateral arm, posterior forearm, and dorsum of hand lateral to axial line of digit 4.
Would flexion and supination of the forearm be lost after injury to the musculocutaneous nerve? Where would sensation be lost?
Flexion and supination of the forearm would be greatly weakened but would not be lost following an injury to the musculocutaneous nerve. In this injury, the brachioradialis and supinator would be able to produce weak flexion and supination, respectively.
Loss of sensation may occur on the lateral surface of the forearm.
How is an affected upper limb positioned after the onset of Erb-Duchenne palsy?
An upper limb affected with Erb-Duchenne palsy usually appears with an adducted shoulder, medially rotated arm, and extended elbow.
What happens to the axillary artery at the inferior border of the teres major muscle?
The axillary artery becomes the brachial artery at the inferior border of the teres major muscle.
What is the name of the first and largest branch of the brachial artery? What does this artery usually travel alongside?
The deep artery of the arm (aka profunda brachii) is the first and largest branch of the brachial artery. It usually travels alongside the radial nerve in the radial groove.
What arteries does the brachial artery bifurcate into when it reaches the distal arm?
At the distal portion of the arm, the brachial artery bifurcates into the radial and ulnar arteries.
What is the role of collateral circulation in regards to the brachial artery and its branches?
Collateral circulation allows blood to reach the forearm when flexion of the elbow compromises flow through the terminal part of the brachial artery.
Why is laceration or occlusion of the brachial artery proximal to the profunda brachii artery a surgical emergency?
Laceration or occlusion of the brachial artery is a surgical emergency because paralysis of muscles results from ischemia of the elbow and forearm within a few hours.
Muscles and nerves can only tolerate up to 6 hours of ischemia, anything after this causes the deposition of scar tissue and permanent muscle shortening.
Why can the brachial artery be blocked at any level distal to the deep artery of the arm without stopping blood flow to the forearm and hand?
There are anastomoses (reconnection of two or more streams) around the elbow which provides functional collateral circulation.