Appendicular System Development

Question 1

The first week of gestation includes:

Answer 1

1. Fertilization of the egg by sperm
2. Cleavage (series of mitotic division)
3. Implantation (zygote implants into uterine wall)
4. Formation of the blastocyst

Question 2

The second week of gestation includes:

Answer 2

Reorganization of the blastocyst into a bilaminar embryonic germ disk

Question 3

What is the first step in the third week of gestation?

Answer 3

Primitive streak formation

Question 4

What marks the beginning of gastrulation?

Answer 4

Primitive streak formation

Question 5

Describe the second step of the third week of gestation.
What is formed at this time?

Answer 5

Epiblast cells proliferate into hypoblast, displacing hypoblastic cells.
Newly arrived epiblast cells form the endoderm.

Question 6

Describe the third step of the third week of gestation.
What is formed at this time?

Answer 6

Epiblast cells proliferate into the space between the epiblast and endoderm.
These cells form the mesoderm.

Question 7

When does gastrulation occur?

Answer 7

Week 3
Around day 15, ending by day 18

Question 8

gastrulation

What do the remaining epiblast form?

Answer 8

Ectoderm

Question 9

week 2 of gestation

The bilaminar embryonic germ disk into what two sections of cells?

Answer 9

Epiblast and hypoblast

Question 10

week 3 of gestation

What are the four steps of gastrulation?

Answer 10

1. Primitive streak formation
2. Endoderm formation
3. Mesoderm formation
4. Ectoderm formation

Question 11

How are the notochordal process and prechordal plate formed?

Answer 11

Newly formed mesoderm cells migrate through the primitive streak and knot, condensing along the midline

Question 12

When newly formed mesoderm cells migrate through the primitive streak and knot, and condense along the midline, what is formed?

Answer 12

The notochordal process and prechordal plate

Question 13

What does the notochordal process become?

Answer 13

The notochord

Question 14

When the notochordal process becomes the notochord, overlying ectoderm is stimulated into…

Answer 14

neural tissue

Question 15

When is the development of somites initiated?

Answer 15

When the notochordal process becomes the notochord

Question 16

When are the fates of certain cells in the nervous system specified?

Answer 16

When the notochordal process becomes the notochord

Question 17

When the notochord and prechordal plate approximate each other, inductive changes occur that trigger the formation of the…

Answer 17

neural plate in the ectoderm

Question 18

The neural plate in the ectoderm overlies the…

Answer 18

notochord

Question 19

What does the neural plate give rise to?

Answer 19

Most of the central nervous system

Question 20

What is neuralation?

Answer 20

The process that forms the neural tube from the neural plate

Question 21

What are the three types of mesoderm?

Answer 21

1. Paraxial
2. Intermediate
3. Lateral plate

Question 21

What are the three parts of the somite?

Answer 21

1. Dermatome
2. Sclerotome
3. Myotome

Question 22

The limb bud has a core of…

Answer 22

lateral plate mesoderm

Question 23

The limb bud is surrounded by…

Answer 23

ectoderm

Question 24

Growth of the limb bud occurs via...

Answer 24

mitosis of mesodermal cells

Question 25

Growth of the limb bud induces formation of the...

Answer 25

apical ectodermal ridge

Question 26

The apical ectodermal ridge induces the underlying mesoderm to...

Answer 26

increase mitosis, growing the limb bud

Question 27

The apical ectodermal ridge forms a progressive zone that...

Answer 27

controls and organizes the proximodistal development of the limb

Question 28

When does differentiation of the limb bud occur?

Answer 28

between weeks 5 and 8

Question 29

As the apical ectodermal ridge degenerates, what happens?

Answer 29

It defines regions where cell death occurs to form the digits

Question 30

What are some dysmorphologies resulting from AER dysfunction?

Answer 30

Syndactyly (webbing) Polydactyly Amelia (lack or incomplete formation of AER) Combinations

Question 31

The limb bud consists of... that interacts with the AER to direct the overall shape of the future limb

Answer 31

lateral plate mesoderm

Question 32

Describe differential growth

Answer 32

The dorsal half grows faster than the ventral half, causing the limbs to occupy a position along the ventral body wall

Question 33

What cells migrate into a developing limb bud?

Answer 33

Lateral plate mesoderm Myoblasts Neural crest cells Lower motor neuron axonal sprouts

Question 34

# limb bud growth The lateral plate mesoderm gives rise to what?

Answer 34

The connective tissues, bones, and some blood vessels

Question 35

# limb bud growth Where do myoblasts migrate from? What do they form?

Answer 35

They migrate from the somite and form limb muscles

Question 36

#limb bud growth Neural crest cells migrate and form...

Answer 36

pigment cells

Question 37

#limb bud growth Where do lower motor neuron axonal sprouts from ventral horn cells migrate from?

Answer 37

The neural tube, following migrating mass of muscle tissue

Question 38

What kind of cells migrate from the myotome into the limb bud to form musculature?

Answer 38

Myogenic cells

Question 39

After myogenic cells form limb musculature, what happens to remaining cells in the myotome?

Answer 39

Remaining myogenic cells form hypomeres (hypaxial mm.) and epimeres (epaxial mm.)

Question 40

What do myogenic cells mature into when they reach the limb bud?

Answer 40

Myoblasts

Question 41

Describe the masses of myoblasts in the upper limb.

Answer 41

Ventral mass: flexors and pronators Dorsal mass: extensors and supinators

Question 42

Describe the masses of myoblasts in the upper limb.

Answer 42

Ventral mass: flexors and adductors Dorsal mass: extensors and abductors

Question 43

What somite levels are associated with upper limb?

Answer 43

C4-T2

Question 44

What somite levels are associated with lower limb?

Answer 44

L1-S2

Question 45

Limb rotation results in:

Answer 45

Dermatomal patterning of limbs

Question 46

What are the two acceptable dermatomal maps?

Answer 46

Foerster (1933) and Garrett (1948)