Session 3 - Development of the Limbs

Question 1

What appears at fourth week of development?

Answer 1

Limb buds

Question 2

What are the limb buds in embryonic development made up of?

Answer 2

Core of proliferating mesenchymal cells with an ectoderm covering

Question 3

What are A and B?

Answer 3

A - Anterior B - Posterior

Question 4

What are C and D?

Answer 4

C - Dorsal D - Ventral

Question 5

What are E and F?

Answer 5

E - Distal F - Proximal

Question 6

Give two examples of a dorsal location on the body

Answer 6

Back of the hand and top of the foot

Question 7

Give two examples of a ventral position on a foetus

Answer 7

Palm of the hand and sole of the foot

Question 8

What is the proximo-distl axis?

Answer 8

Base of the limb to the tips of the digits

Question 9

What is the antero-posterior axis

Answer 9

From 1st digit to 5th

Question 10

Where do limb buds first appear?

Answer 10

On the ventro-lateral body wall

Question 11

What order to limb buds appear in?

Answer 11

Upper limb first, lower limb second

Question 12

In which direction do limb buds at first extend?

Answer 12

Ventrally at first

Question 13

What does limb development begin with?

Answer 13

Activation of mesenchyme within lateral mesoderm

Question 14

Where are limb buds derived from?

Answer 14

The somatic layer of lateral plate mesoderm

Question 15

What does somatic mesoderm contribute to?

Answer 15

Limb skeleton

Question 16

What do somites contribute to?

Answer 16

Musculature

Question 17

What is mesenchyme?

Answer 17

Flexible mesoderm

Question 18

How does limb bud elongate?

Answer 18

Through proliferation of mesenchyme core

Question 19

Give a feature of the apex of a limb bud

Answer 19

Thickened ectoderm

Question 20

Give the three degrees of asymmetry of limb development

Answer 20

Top and bottom (Shoulder to fingertips) Front and back (No hairy palms) Side to side (Left and right hands mirror images)

Question 21

What is the AER?

Answer 21

The apical ectodermal ridge

Question 22

What is the AER critical for?

Answer 22

Limb bud outgrowth

Question 23

What does the AER facillitate?

Answer 23

Limb development, proximal to distal

Question 24

What is the final appearance of the AER before it regressed?

Answer 24

Appearance of paddles

Question 25

What is the arrow pointing to?

Answer 25

The Apical Ectodermal Ridge

Question 26

What are the anatomical effects of the AER?

Answer 26

Causes differentiation of underlying tissue, before finally inducing development of the digits within the hand/foot plates

Question 27

What is the ZPA?

Answer 27

Zone of polarising activity

Question 28

What are the three functions of the zone of polarising activity?

Answer 28

Generation of assymetry in the limbs Asignalling centra located at the posterior base of the limb bud Controls both patterning and maintains the AER

Question 29

What does the AER mark the boundary between?

Answer 29

The dorsal and ventral ectoderm

Question 30

Label A, B and C

Answer 30

A - Dorsal ectoderm B - Ventral ectoderm C - AER

Question 31

What does AER mark the boundary between?

Question 32

What do preaxial and postaxial refer to?

Answer 32

Preaxial - Medial - Thumb and Big to Postaxial - Lateral - Little finger and little toe

Question 33

What controls anterior/posterior development?

Answer 33

ZPA

Question 34

What controls proximal - distal development?

Answer 34

AER

Question 35

What controls dorsal/ventral development?

Answer 35

Ectoderm

Question 36

What occurs in hand and foot plates to convert them from buds to appendages?

Answer 36

_Digital rays_ Mesenchyme condensations within plates Cartaliginous models of the digital bone _Apoptosis_ Of the tissues between the digits

Question 37

What is syndactyly?

Answer 37

Fusion of digits, may involve just CT or bones may be fused

Question 38

Polydactyly

Answer 38

Extra digits, genetic recessive trait

Question 39

What happens to lateral plate mesoderm? What is Amelia?

Answer 39

Condenses and diffentiates, undergoes endochondral ossification. Amelia - Complete abcense of a limb

Question 40

How do long bones extend? What is Meromelia?

Answer 40

Secondar ossification centres appear in epiphyses. Bone growth maintained by cartilage forming regions (epiphyseal growth plates) Partial abcesnse of one or more limb structures

Question 41

How is musculature formed?

Answer 41

Myogenic precursors migratre into limbs from somites. Form two muscles msses - Vental (flexors) and dorsal (extensors)

Question 42

What is the difference in comparments between upper and lower limb?

Answer 42

U limb - flexor anterior L limb - flexor posterior

Question 43

How do the reveresed compartments formed in upper limbs and legs?

Answer 43

Both limbs extend ventrally However * Upper limb: rotates laterally * Lower limb: rotates medially

Question 44

Why do limbs have the innervation they do?

Answer 44

Upper limb bud appears opposite the caudal cervical spinal segments

Question 45

Why is innervation vital to limb development?

Answer 45

Without it development stalls

Question 46

Describe formation of brachial plexus

Answer 46

Anterior divisions for anterior compartments - Regroup to form lateral and medial cords. Posterior compartments supplied by posterior divisions

Question 47

Why do nails have different innervation to rest of dorsal surface of hand?

Answer 47

Nails develop from nail fields on the tips of the fingers

Question 48

What is a dermatome?

Answer 48

A single strip f skin supplied by a single spinal nerve?

Question 49

What is a myotome?

Answer 49

Myotome is a muscle/group of muscles supplied by a single spinal nerve

Question 50

What occurs in hand and foot plates to convert them from buds to appendages?

Answer 50

_Digital rays_ Mesenchyme condensations within plates Cartaliginous models of the digital bone _Apoptosis_ Of the tissues between the digits