TBL12

Question 1

Vertebral column derived from?

Answer 1

somite-derived

Question 2

Scapula, clavicle, and bones of the upper extremities derived from?

Answer 2

parietal mesoderm

Question 3

What forms the cartilaginous replicas of embryonic bones?

Answer 3

chondrocytes and the noncalcified, avascular extracellular matrix

Question 4

What surrounds the chondrocytes + matrix

Answer 4

perichondrium; oxygen and nutrients diffuse from the perichondrial capillaries

Question 5

Bony collar

Answer 5

forms around the diaphysis and blocks diffusion from the perichondrial capillaries into the avascular space -> degradation of chondrocytes

Question 6

Periosteum

Answer 6

covers the bony collar and eventually the whole bone except at the joints

Question 7

What happens after the bony collar forms?

Answer 7

periosteal capillaries, osteoblasts, and macrophages invade the degrading replica to initiate endochondral ossification (i.e., replacement of the replica by bone); clusters of fused macrophages form osteoclasts that aggressively phagocytize the degrading cartilage -> primary ossification center

Question 8

Osteoblasts

Answer 8

produce thick, randomly organized collagen fibers that enclose the osteoblasts within lacunae (i.e., the osteoblasts become osteocytes); osteocytes induce the deposition of hydroxyapatite crystals on the thick collagen fibers, which subsequently align in parallel rows that separate the osteocyte-filled lacunae.

Question 9

Trabecular bone. Purpose of collagen and hydroxyapatite?

Answer 9

osteocytes and mineralized matrix organize into a meshwork of trabeculae; collagen fibers provide strength and the hydroxyapatite crystals provide hardness to the matrix. Osteoblasts that cover the surface of the trabeculae are essential for continued bone maturation

Question 10

What section of the bone becomes trabecular bone first?

Answer 10

trabecular bone occupies the diaphysis and cartilaginous epiphyses (not labeled) reside at both ends of the diaphysis

Question 11

How do epiphyseal growth plates form?

Answer 11

epiphyseal chondrocytes near the diaphysis proliferate to form cellular columns that align parallel with the long axis of the developing bone

Question 12

Growth plate organization

Answer 12

chondrocytes immediately adjacent to the diaphysis degenerate and concurrent growth of the trabecular bone replaces the eroded cells (i.e., progressive replacement of eroded chondrocytes with trabecular bone enables lengthening of the developing bone).

Question 13

Secondary ossification center

Answer 13

As trabecular bone at the periphery of the diaphysis is transformed into compact bone, formation of trabecular bone occurs in the epiphyses; trabecular bone at the periphery of the epiphyses is transformed into compact bone by age 10

Question 14

When do bones stop growing?

Answer 14

growth plates remain active throughout puberty and bony union of the diaphysis with the epiphyses occurs at skeletal maturity.

Question 15

Why is achondroplasia associated with skeletal dysplasia (e.g., dwarfism)?

Answer 15

mutation in FGFR3; normally has a negative regulatory effect on bone growth but mutation has receptor constitutely on -> shortened long bones

Question 16

Structure of mature bone

Answer 16

compact (aka dense) bone at the periphery and the trabecular bone in the center

Question 17

What initiates transfomration of trabecular bone into compact bone

Answer 17

primary osteons (i.e., oval profiles of trabecular bone at the periphery of the developing bone)

Question 18

Structure of primary osteons

Answer 18

capillaries are centrally positioned and osteoblasts on the surface of the trabeculae create the peripheral boundaries

Question 19

How do primary osteons become secondary osteons?

Answer 19

continued, inward deposition of bony matrix by the osteoblasts encloses the capillaries with concentric rows of lacunae separated by parallel, mineralized collagen fibers (i.e., primary osteons of trabecular bone become secondary osteons of compact bone)

Question 20

Structure of secondary osteons (or Haversian system)

Answer 20

capillaries reside in osteoblast-lined central (ignore Haversian) canals; the concentric dotted lines represent osteocyte-filled lacunae separated by bony matrix. Oriented parallel to the long axis of the bone.

Question 21

Canaliculi structure

Answer 21

tiny canals in the bony matrix that interconnect the concentric rows of lacunae and connect the innermost row to the central canal

Question 22

Canaliculi function

Answer 22

enable capillary filtrates to spread from the central canals into the lacunae to sustain the osteocytes; connect the lacunae to the surface of the trabeculae to enable filtrates from capillaries in the bone marrow to sustain the osteocytes

Question 23

Volkmann canals

Answer 23

join the central canals at right angles to enable continuity of the periosteal capillaries with the capillaries of the secondary osteons

Question 24

Intersitial lamellae

Answer 24

separates adjacent osteons; remnants of secondary osteons after bone remodeling that occurs throughout life to adapt bones to changing physical stresses (e.g., after weight gains or new physical training regimens)

Question 25

Effect of bone vascularity

Answer 25

ensures good regenerative potential for remodeling and deposition rates must match resorption rates to maintain skeletal integrity

Question 26

Central trabecular bone of mature bones is occupied with?

Answer 26

bone marrow

Question 27

Glenohumeral (shoulder joint) structure

Answer 27

the humerus articulates with the scapula

Question 28

Glenoid cavity of scapula accept % of the humeral head at the joint

Answer 28

a third

Question 29

Glenoid labrum

Answer 29

concentric rings of collagen fibers that attaches to the rim of the cavity to slightly but effectively deepen it

Question 30

tonus of the rotator cuff muscles

Answer 30

essential for holding the humeral head in the glenoid cavity

Question 31

Acromioclavicular (AC) joint structure

Answer 31

the lateral end of the clavicle articulates with the acromion

Question 32

AC joint function

Answer 32

enables the clavicle to act as a strut (rigid support) that suspends the scapula and allows it to slide along the posterior thoracic wall

Question 33

Coracoclavicular ligament (2)

Answer 33

prevents dislocation of the AC joint

Question 34

Coracoacromial arch

Answer 34

coracoid process, acromion, and coracoacromial ligament -> prevents superior displacement of the humeral head from the glenoid cavity.

Question 35

When does dislocation of the acromioclavicular joint occur and why is it described as a _shoulder separation_?

Answer 35

Occurs from a hard fall on the shoulder/outstretched upper limb, driven into the boards, severe blow to superolateral part of the back; "shoulder separation" because shoulder separates from the clavicle and falls because of the weight of the upper limbb

Question 36

Why do most dislocations of the humeral head occur in an inferior direction, and why are such dislocations commonly described clinically as anterior dislocations?

Answer 36

Coraco-acromial arch prevents upward dislocation; anterior dislocation because hard blow when glenohumeral joint is fully abduted tilts the head of the humerus inferiorly onto the inferior weak part of the joint capsule

Question 37

Intrinsic shoulder muscle attachements (generally)

Answer 37

attach to the scapula and clavicle proximally and to the humerus distally; thus, the muscles act on the glenohumeral joint (i.e., a muscle or its tendon must cross a joint to act upon it)

Question 38

Adduction vs abduction

Answer 38

abduction - move arm to 90 degrees

Question 39

Flexion vs extension

Answer 39

flexion - forward (arm), upward (wrist, elbow)

Question 40

Location of greater and less tubercules, intertubercular sulcus, surgical neck, deltoid tuberosity

Answer 40

know it

Question 41

Deltoid attachment

Answer 41

proximal attachment of the anterior, middle, and posterior parts of the deltoid begins at the lateral end of the clavicle and continues onto the scapular spine. Recognize all three parts attach to the deltoid tuberosity distally

Question 42

Deltoid function

Answer 42

simultaneous contraction of all three parts of the deltoid with assistance from the supraspinatus muscle (assessed below) abducts the upper limb to 90 degrees

Question 43

Teres major

Answer 43

which attaches to the inferior angle of the scapula proximally and to the medial surface of the humerus distally, medially rotates the arm

Question 44

Location of supraspinous and infraspinous fossae, superior and inferior angles

Answer 44

know it

Question 45

What attaches to the superior angle distally?

Answer 45

levator scapulae

Question 46

Supraspinatus muscle

Answer 46

attaches to supraspinous fossae proximally and to the greater tubercle of the humerus distally; induces the first 15 degrees of abduction

Question 47

Infraspinatus muscle

Answer 47

attaches to infraspinous fossae proximally and to the greater tubercle of the humerus distally; laterally rotates the arm

Question 48

Teres minor

Answer 48

attaches to the lateral border of the scapula proximally and to the greater tubercle of the humerus distally; thus, it assists the infraspinatus during lateral rotation of the arm

Question 49

Subacromial bursa

Answer 49

thin, fluid filled; cushions the tendon of the supraspinatus as it passes between the humeral head and coracoacromial arch to reach the greater tubercle

Question 50

Subscapularis

Answer 50

attaches to the anterior surface of the scapula proximally and to the lesser tubercle of the humerus distally, medially rotates the arm

Question 51

Suprascapular nerve

Answer 51

innervates the supraspinatus and infraspinatus

Question 52

Axillary nerve

Answer 52

innervates the teres minor and courses across the surgical neck on the posterior surface of the humerus to innervate the deltoid

Question 53

Subscapular nerve

Answer 53

innervates both the subscapularis and the teres major

Question 54

Why is the upper extremity pulled into medial rotation after an avulsion fracture of the greater tubercle?

Answer 54

muscles (especially the subscapularis) that remain attached to the humerus pull the limb into the medial rotation

Question 55

How is the axillary nerve commonly injured at the surgical neck of the humerus, and where does loss of sensation occur after the injury?

Answer 55

axillary nerve injuried by fracture at the surgical neck, dislocation of the glenohumeral joint, and by compression from the incorrect use of crutches; loss of sensation occurs over the lateral side of the proximal part of the arm, the area supplied by the superior lateral cutaneous nerve of the arm, the cutaneous branch of the axillary nerve

Question 56

How would you test for degenerative tendinitis of the rotator cuff?

Answer 56

patient is asked to lower the fully abducted limb slowly and smoothly. From approximately 90 degrees abduction, the limb will suddenly drop to the side in an uncontrolled manner if the rotator cuff is diseased and/or torn

Question 57

Location of supraglenoid and infraglenoid tubercles

Answer 57

know it

Question 58

Locataion of the radial groove and olecranon

Answer 58

know it

Question 59

Long head of triceps attachment

Answer 59

attaches to the infraglenoid tubercle proximally and to the olecranon of the ulna distally

Question 60

Lateral head attachment

Answer 60

attaches proximally to the posterior humerus above the radial groove and and to the olecranon of the ulna distally

Question 61

Medial head attachment

Answer 61

attaches proximally to the posterior humerus below the radial groove and to the olecranon of the ulna distally

Question 62

Triceps function

Answer 62

extends the forearm at the elbow joint (the joint will be studied later)

Question 63

Radial nerve

Answer 63

courses along the radial groove on the posterior surface of the humerus. Innervates the long and lateral heads of the triceps before entering the radial groove and the medial head is innervated after the nerve enters the groove.

Question 64

Why is forearm extension weakened but not lost after fracture along the radial groove of the humerus?

Answer 64

long and lateral heads of the triceps are innervated before entering the radial groove