Limb Development

Question 1

What happens during first week of conception?

Answer 1

1.) Egg is fertilized by sperm.
2.) Cleavage (mitotic cell division)
3.) implantation
4.) formation of blastocyst

Question 2

Second week of embryonic development?

Answer 2

Reorganization of blastocyst into bilaminar embryonic germ disk.

Question 3

What is the 1st step of the third week of development?

Answer 3

Primitive streak formation

Question 4

2nd step of third week of development?

Answer 4

Proliferation of epiblast cells into hypoblast to displace hypoblast cells so newly arrived epiblast cells form endoderm.

Question 5

3rd step of third week of development?

Answer 5

Proliferation of epiblast cells into space between epiblast and endoderm to form mesoderm.

Question 6

Where does ectoderm come from?

Answer 6

Remaining epiblast.

Question 7

Summarize gastrulation.

Answer 7

1.) form primitive streak.
2.) form endoderm.
3.) form mesoderm.
4.) form ectoderm.

Question 8

How are notochordal process and prechordal plate formed?

Answer 8

Newly formed mesodermal cells migrate through primitive streak and knot and condense along midline.

Question 9

What forms neural plate in ectoderm that overlies notochord?

Answer 9

When notochord and prechordal plate approximate each other and inductive changes occur that trigger formation

Question 10

Neural plate gives rise to what?

Answer 10

Most of CNS

Question 11

Neurulation?

Answer 11

Process that forms neural tube from neural plate

Question 12

Function of notochord?

Answer 12

Stimulate conversion of overlying ectoderm into neural tissue, specifies fate of certain cells within nervous system, and initiates development of somites.

Question 13

Name three types of mesoderm.

Answer 13

1.) parasail
2.) intermediate
3.) lateral plate

Question 14

Name three parts of somite.

Answer 14

1.) dermatome.
2.) sclerotome.
3.) myotome.

Question 15

What is the limb bud?

Answer 15

The core of lateral plate of mesoderm surrounded by ectoderm.

Question 16

How does growth occur in limb bud?

Answer 16

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

Question 17

What develops first, upper or lower limb bud?

Answer 17

Upper limb bud

Question 18

When does limb bud development initiate?

Answer 18

34th day embryonic development

Question 19

What does apical ectodermal ridge do?

Answer 19

Induce underlying mesoderm to increase mitosis, growing limb bud. Forms in progressive zone that controls and organizes the proximodistal development of the limb.

Question 20

Day 33

Answer 20

Upper limb regions distinguishable and lower limb bud is organizing

Question 21

Day 37

Answer 21

Upper limb’s carpals and finger rays seen in hand, and lower limb regions distinguishable

Question 22

Day 38

Answer 22

Upper limb’s digits begin to form via apoptosis and lower limb’s tarsals and digits begin forming

Question 23

Day 44

Answer 23

Upper limb’s elbow is prominent and fingers are formed and lower limb’s toe rays are visible in foot

Question 24

Day 47

Answer 24

Upper limb has horizontal flexion and rotation, and lower limb’s digits begin apoptosis

Question 25

Day 52

Answer 25

Upper limb’s elbows and wrists flex and finger pads are developed, lower limb’s digits are formed and rotation begins.

Question 26

Day 56

Answer 26

Limb buds done developing!

Question 27

How are fingers and toes formed?

Answer 27

As AER degenerates, it defines regions where cell death occurs to form digits

Question 28

What happens due to the fact that the dorsal half grows faster than ventral half during limb bud development?

Answer 28

The limbs occupy a position along the ventral body wall.

Question 29

Name the cells that migrate to developing limb bud?

Answer 29

1.) lateral plate mesoderm
2.) myoblasts
3.) neural crest cells
4.) lower motor neuron axonal sprouts

Question 30

Lateral plate mesoderm gives rise to what?

Answer 30

CT, bones, some BVs

Question 31

Myoblasts?

Answer 31

Migrate from somite and form limb muscles.

Question 32

Neural crest cells?

Answer 32

Migrate and form pigment cells.

Question 33

Lower motor neuron axonal sprouts?

Answer 33

Come from ventral horn cells and migrate from neural tube, following migrating mass of muscle tissue.

Question 34

Describe development of limb muscles.

Answer 34

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

Question 35

Ventral mass of upper limb?

Answer 35

Flexors and pronators.

Question 36

Dorsal mass of upper limb?

Answer 36

Extensors and supinators.

Question 37

Lower limb ventral mass?

Answer 37

Flexors and adductors.

Question 38

Dorsal mass of lower limb?

Answer 38

Extensors and abductors.

Question 39

What results in patterning of dermatomes?

Answer 39

Rotation and differential growth of limbs

Question 40

What are the two acceptable dermatome maps?

Answer 40

Forester and Garrett

Question 41

Do dermatomes overlap?

Answer 41

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.

Question 42

C3 and C4 dermatome.

Answer 42

Base of neck and laterally over shoulder.

Question 43

C5 dermatome

Answer 43

Lateral aspect of arm

Question 44

C6 dermatome

Answer 44

Lateral aspect of forearm and thumb

Question 45

C7 dermatome

Answer 45

Middle and ring fingers and middle of posterior surface of forearm

Question 46

C8 dermatome

Answer 46

Little finger, medial aspect of hand and forearm

Question 47

T1 dermatome

Answer 47

Medial aspect of middle of forearm to axilla.

Question 48

T2 dermatome

Answer 48

Skin of axilla, perhaps some of arm