Limb Development Flashcards
What happens during first week of conception?
1.) Egg is fertilized by sperm.
2.) Cleavage (mitotic cell division)
3.) implantation
4.) formation of blastocyst
Second week of embryonic development?
Reorganization of blastocyst into bilaminar embryonic germ disk.
What is the 1st step of the third week of development?
Primitive streak formation
2nd step of third week of development?
Proliferation of epiblast cells into hypoblast to displace hypoblast cells so newly arrived epiblast cells form endoderm.
3rd step of third week of development?
Proliferation of epiblast cells into space between epiblast and endoderm to form mesoderm.
Where does ectoderm come from?
Remaining epiblast.
Summarize gastrulation.
1.) form primitive streak.
2.) form endoderm.
3.) form mesoderm.
4.) form ectoderm.
How are notochordal process and prechordal plate formed?
Newly formed mesodermal cells migrate through primitive streak and knot and condense along midline.
What forms neural plate in ectoderm that overlies notochord?
When notochord and prechordal plate approximate each other and inductive changes occur that trigger formation
Neural plate gives rise to what?
Most of CNS
Neurulation?
Process that forms neural tube from neural plate
Function of notochord?
Stimulate conversion of overlying ectoderm into neural tissue, specifies fate of certain cells within nervous system, and initiates development of somites.
Name three types of mesoderm.
1.) parasail
2.) intermediate
3.) lateral plate
Name three parts of somite.
1.) dermatome.
2.) sclerotome.
3.) myotome.
What is the limb bud?
The core of lateral plate of mesoderm surrounded by ectoderm.
How does growth occur in limb bud?
Via mitosis of mesodermal cells and induces formation of apical ectodermal ridge to direct overall shape of future limb. Consists of lateral plate mesoderm. Differential growth occurs so that dorsal half grows faster
What develops first, upper or lower limb bud?
Upper limb bud
When does limb bud development initiate?
34th day embryonic development
What does apical ectodermal ridge do?
Induce underlying mesoderm to increase mitosis, growing limb bud. Forms in progressive zone that controls and organizes the proximodistal development of the limb.
Day 33
Upper limb regions distinguishable and lower limb bud is organizing
Day 37
Upper limb’s carpals and finger rays seen in hand, and lower limb regions distinguishable
Day 38
Upper limb’s digits begin to form via apoptosis and lower limb’s tarsals and digits begin forming
Day 44
Upper limb’s elbow is prominent and fingers are formed and lower limb’s toe rays are visible in foot
Day 47
Upper limb has horizontal flexion and rotation, and lower limb’s digits begin apoptosis
Day 52
Upper limb’s elbows and wrists flex and finger pads are developed, lower limb’s digits are formed and rotation begins.
Day 56
Limb buds done developing!
How are fingers and toes formed?
As AER degenerates, it defines regions where cell death occurs to form digits
What happens due to the fact that the dorsal half grows faster than ventral half during limb bud development?
The limbs occupy a position along the ventral body wall.
Name the cells that migrate to developing limb bud?
1.) lateral plate mesoderm
2.) myoblasts
3.) neural crest cells
4.) lower motor neuron axonal sprouts
Lateral plate mesoderm gives rise to what?
CT, bones, some BVs
Myoblasts?
Migrate from somite and form limb muscles.
Neural crest cells?
Migrate and form pigment cells.
Lower motor neuron axonal sprouts?
Come from ventral horn cells and migrate from neural tube, following migrating mass of muscle tissue.
Describe development of limb muscles.
1.) myogenic cells migrate from myotome into limb bud and mature into myoblasts and coalesce into two masses.
2.) remaining myogenic cells in myotome form hypomeres and epimeres and dorsal and ventral masses, axonal sprouts from ventral horn cells grow into respective masses
Ventral mass of upper limb?
Flexors and pronators.
Dorsal mass of upper limb?
Extensors and supinators.
Lower limb ventral mass?
Flexors and adductors.
Dorsal mass of lower limb?
Extensors and abductors.
What results in patterning of dermatomes?
Rotation and differential growth of limbs
What are the two acceptable dermatome maps?
Forester and Garrett
Do dermatomes overlap?
Yes, extensively, so that loss of inner action to the skin from damage to a single nerve may only involve a small part of dermatome.
C3 and C4 dermatome.
Base of neck and laterally over shoulder.
C5 dermatome
Lateral aspect of arm
C6 dermatome
Lateral aspect of forearm and thumb
C7 dermatome
Middle and ring fingers and middle of posterior surface of forearm
C8 dermatome
Little finger, medial aspect of hand and forearm
T1 dermatome
Medial aspect of middle of forearm to axilla.
T2 dermatome
Skin of axilla, perhaps some of arm
