Musculoskeletal Embryology II Flashcards
Limb buds appear at week ___ of developments.
4
Limb bud tissues are derived form ____ and ____
mesoderm; ectoderm
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
lateral
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.
apical ectodermal; proximodistal
At the posterior margin of the limb bud the mesenchyme forms a zone of polarizing activity that influences the _____-____ axis formation of the limb
anterior-posterior
Condensation of mesenchyme form digital rays- finger buds in the ___ week and digital rays - toe b7uds in the ___ week
6; 7
At the tip of each digital ray, a part of AER develops into mesenchymal ___ of the bones in the digits
primordia
In the ____ week, apoptosis breaks down the tissues in the interdigital regions, resulting in the formation of digits
7
Blocking of cellular and molecular events during apoptosis may cause webbing of the fingers or toes, known as ____
syndactyly
The upper limbs develop opposite the ___ ___ segments and the lower limb buds opposite the ___ and ___ ___ segments
caudal cervical; lumbar, upper sacral
The prefixal border of the upper limb bud will form the ___ while the post axial border forms the ___ ___
thumb; little finger
The prefixal border of the limb bud will form the ___ toe while the post axial border forms the ___ toe
big toe; little toe
Initially, the planter surface of the foot faces ___
medially
The upper limbs rotate ___ through 90 degrees on their longitudinal axes, thus the future elbows come to point distally
laterally
The lower limbs rotate ____ through almost 90 degrees; thus the future knees come to face ventrally
medially
Rotation places the big toe and little finger ____ and the thumb and little toe ____
medially; laterally
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?
bipedal standing and weight bearing
The skeletal elements are the first major tissue of the limb to show signs of differentiation. true or false?
true
Limb bones are developed by ____ bone formation
endochondral
Mesenchymal models of bones (chondrificaiton centers) are formed in week ___
5
Chondrificaiton centers form in the mesenchyme and in week ___, limb skeleton is cartilaginous
6
In week 7, ____ begins in the center of cartilaginous models of long bones
osteogenesis
In week 12, all long bones have ___ ____ centers in the shaft
primary ossification
At birth, the diaphyses of long bones are ____, but their two ends are still _____
ossified; cartilaginous
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 ____
humerus; radius; ulna; carpals
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 ___
femur; tibia; fibula; tarsals
Up to the age of ___ - ___ years, the ilium, ischium, and pubis are united by hyaline cartilage which ossifies later
15-16
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
interzonal
This type of joint has little to no movement, the interzonal mesenchyme between developing bones differentiates into dense fibrous tissue
fibrous joint
In regards to the synovial joint, describe how the internal mesenchyme differentiates peripherally, centrally, and in the lining
peripherally: forms capsule and other ligaments
centrally: disappears and space becomes joint cavity
lining: forms synovial membrane (secretes synovial fluid)
True or false? early joint development is dependent on muscular activity
false; independent
note: later in life, muscular activity is required to maintain the integrity of joints
As long bones form, myogenic precursor cells from the somites migrate into the limb bud and later differentiate into ____
myoblasts
The myoblasts fuse to form ___ and ___ cells
myotubes; muscle
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
lateral, posterior; anterior
True or false? the formation of new muscle fibers ceases at birth
true
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
5
The dorsal and ventral nerve root join to form a spinal ____ which then divides into dorsal and ventral ___ ___
nerve; primary rami
____ ____ cells, the precursors of schwann cells enter the limb bud and surround the motor and sensory fibers with myeline sheaths and neurolemma
neural crest
The primordial vascular pattern in limbs consists of a ___ ___ artery
primary axial
In the arm, the primary axial artery becomes the ___ artery
brachial
In the thigh, the primary axial artery is the ___ artery of the thigh, while in the leg it becomes the ___ ___ and ___ ___ arteries
deep; anterior tibial, posterior tibial
The critical period for limb defects during development is between days ___-___
24-36
The rate of limb malformations
2 per thousand
Polydactyly
extra toe, usually on lateral side. this is an autosomal dominant trait often found in closed communities (amish)
Syndactyly
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)
clubfoot
deformity of foot involving the talus. Sole of foot is turned medially and the foot is inverted. Occurs mostly in males
cleft foot
absence of one or more central digits resulting from failure of development of one or more digital rays
congenital dislocation of hip
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
amelia
absence of limb. teratogen induced limb defect, caused by using thalidomide as drug
