Musculoskeletal Embryology II

Question 1

Limb buds appear at week ___ of developments.

Answer 1

4

Question 2

Limb bud tissues are derived form ____ and ____

Answer 2

mesoderm; ectoderm

Question 3

Initially, the limb bud mesenchyme consists of cells from the somatic layer of the ___ mesoderm. These cells will form the skeleton, connective tissue and some blood vessels

Answer 3

lateral

Question 4

The mesenchyme is covered by ectoderm that thickens at the distal border of the limb bud forming the ____ _____ ridge. The ridge exerts inductive influence on other tissues, promotes differentiation and initiated development of the limbs in a ____ axis.

Answer 4

apical ectodermal; proximodistal

Question 5

At the posterior margin of the limb bud the mesenchyme forms a zone of polarizing activity that influences the _____-____ axis formation of the limb

Answer 5

anterior-posterior

Question 6

Condensation of mesenchyme form digital rays- finger buds in the ___ week and digital rays - toe b7uds in the ___ week

Answer 6

6; 7

Question 7

At the tip of each digital ray, a part of AER develops into mesenchymal ___ of the bones in the digits

Answer 7

primordia

Question 8

In the ____ week, apoptosis breaks down the tissues in the interdigital regions, resulting in the formation of digits

Answer 8

7

Question 9

Blocking of cellular and molecular events during apoptosis may cause webbing of the fingers or toes, known as ____

Answer 9

syndactyly

Question 10

The upper limbs develop opposite the ___ ___ segments and the lower limb buds opposite the ___ and ___ ___ segments

Answer 10

caudal cervical; lumbar, upper sacral

Question 11

The prefixal border of the upper limb bud will form the ___ while the post axial border forms the ___ ___

Answer 11

thumb; little finger

Question 12

The prefixal border of the limb bud will form the ___ toe while the post axial border forms the ___ toe

Answer 12

big toe; little toe

Question 13

Initially, the planter surface of the foot faces ___

Answer 13

medially

Question 14

The upper limbs rotate ___ through 90 degrees on their longitudinal axes, thus the future elbows come to point distally

Answer 14

laterally

Question 15

The lower limbs rotate ____ through almost 90 degrees; thus the future knees come to face ventrally

Answer 15

medially

Question 16

Rotation places the big toe and little finger ____ and the thumb and little toe ____

Answer 16

medially; laterally

Question 17

The axis of the foot assumes a right angle with the axis of the rest of the limb, so when standing, the sole of the foot is in contact with the ground. This orientation adapts the lower limb for what?

Answer 17

bipedal standing and weight bearing

Question 18

The skeletal elements are the first major tissue of the limb to show signs of differentiation. true or false?

Answer 18

true

Question 19

Limb bones are developed by ____ bone formation

Answer 19

endochondral

Question 20

Mesenchymal models of bones (chondrificaiton centers) are formed in week ___

Answer 20

5

Question 21

Chondrificaiton centers form in the mesenchyme and in week ___, limb skeleton is cartilaginous

Answer 21

6

Question 22

In week 7, ____ begins in the center of cartilaginous models of long bones

Answer 22

osteogenesis

Question 23

In week 12, all long bones have ___ ____ centers in the shaft

Answer 23

primary ossification

Question 24

At birth, the diaphyses of long bones are ____, but their two ends are still _____

Answer 24

ossified; cartilaginous

Question 25

The upper segment is formed by the ____, in the intermediate segment, the preaxial bone is the ____ and the post axial bone is the ___. Terminal segments are formed by the ____

Answer 25

humerus; radius; ulna; carpals

Question 26

The upper segment of the lower limb is built around the ___, which defines the axis of the limb. In the intermediate segment, the preaxial bone is the ____ and the post axial bone is the ____. In the terminal segment, primordial are established for ___

Answer 26

femur; tibia; fibula; tarsals

Question 27

Up to the age of ___ - ___ years, the ilium, ischium, and pubis are united by hyaline cartilage which ossifies later

Answer 27

15-16

Question 28

During the sixth week, joints begin to develop with the appearance of ___ mesenchyme and by the end of the eight week, they resemble adult joints

Answer 28

interzonal

Question 29

This type of joint has little to no movement, the interzonal mesenchyme between developing bones differentiates into dense fibrous tissue

Answer 29

fibrous joint

Question 30

In regards to the synovial joint, describe how the internal mesenchyme differentiates peripherally, centrally, and in the lining

Answer 30

peripherally: forms capsule and other ligaments centrally: disappears and space becomes joint cavity lining: forms synovial membrane (secretes synovial fluid)

Question 31

True or false? early joint development is dependent on muscular activity

Answer 31

false; independent note: later in life, muscular activity is required to maintain the integrity of joints

Question 32

As long bones form, myogenic precursor cells from the somites migrate into the limb bud and later differentiate into ____

Answer 32

myoblasts

Question 33

The myoblasts fuse to form ___ and ___ cells

Answer 33

myotubes; muscle

Question 34

The extensor muscles in the upper limb lie on ____ and ____ aspects of the limb, while the extensor muscles of the lower limb lie on the ____ aspect of the limb

Answer 34

lateral, posterior; anterior

Question 35

True or false? the formation of new muscle fibers ceases at birth

Answer 35

true

Question 36

In week ___, motor nerve fibers arising from the spinal cord form a ventral nerve root and sensory nerve fibers from neural crest cells form the dorsal nerve root

Answer 36

5

Question 37

The dorsal and ventral nerve root join to form a spinal ____ which then divides into dorsal and ventral ___ ___

Answer 37

nerve; primary rami

Question 38

____ ____ cells, the precursors of schwann cells enter the limb bud and surround the motor and sensory fibers with myeline sheaths and neurolemma

Answer 38

neural crest

Question 39

The primordial vascular pattern in limbs consists of a ___ ___ artery

Answer 39

primary axial

Question 40

In the arm, the primary axial artery becomes the ___ artery

Answer 40

brachial

Question 41

In the thigh, the primary axial artery is the ___ artery of the thigh, while in the leg it becomes the ___ ___ and ___ ___ arteries

Answer 41

deep; anterior tibial, posterior tibial

Question 42

The critical period for limb defects during development is between days ___-___

Answer 42

24-36

Question 43

The rate of limb malformations

Answer 43

2 per thousand

Question 44

Polydactyly

Answer 44

extra toe, usually on lateral side. this is an autosomal dominant trait often found in closed communities (amish)

Question 45

Syndactyly

Answer 45

webbing of digits, often between second and third toes. This is the most common limb anomaly. Two types: cutaneous (failure of webs to degenerate) and osseous (notches fail to appear)

Question 46

clubfoot

Answer 46

deformity of foot involving the talus. Sole of foot is turned medially and the foot is inverted. Occurs mostly in males

Question 47

cleft foot

Answer 47

absence of one or more central digits resulting from failure of development of one or more digital rays

Question 48

congenital dislocation of hip

Answer 48

occurs after birth and more common in females. may involve an abnormal development of acetabulum of the hip bone and femur. common in breech deliveries

Question 49

amelia

Answer 49

absence of limb. teratogen induced limb defect, caused by using thalidomide as drug