Embryology Of The Limbs

Question 1

What are the six basic movements of the hand

Answer 1

1) cylindrical grasp
2) hook/snap
3) spherical grasp
4) tip to tip
5) palmer
6) lateral

Question 2

What is an example of a first class lever in the body

Answer 2

Extension and Flexion of head

Question 3

What is a first class lever

Answer 3

Where the opposing forces are on either side of fulcrum

Question 4

What is a second class lever

Answer 4

Where effort is at one end and the fulcrum at the other with load in the middle

Question 5

What is an example of a second class lever

Answer 5

Plantar Flexion of foot

Question 6

What is a third class lever

Answer 6

Where the effort is in the middle with fulcrum and load at the ends

Question 7

What is an example of a third class lever

Answer 7

Flexion of Elbow

Question 8

What are the two main parts of your stride (gait cycle)

Answer 8

Stance and swing

Question 9

What are the 5 sections in ‘stance’

Answer 9

1) initial contact
2) loading response
3) mid stance
4) terminal stance
5) pre swing

Question 10

What are the 3 sections of ‘swing’

Answer 10

1) Initial swing
2) mid swing
3) terminal swing

Question 11

When do limb buds first appear in the growth of the embryo

Answer 11

End of the 4th week

Question 12

Which set of limbs lag behind the other by ~2 days

Answer 12

The lower limbs lag behind the upper limbs

Question 13

Why do the limbs develop late

Answer 13

All energy is put into developing the most important systems first such as the CVS

Question 14

What is the Limb bud composed of

Answer 14

Core proliferating mesenchymal cells with ectoderm covering

Question 15

What is the mesenchymal core made of

Answer 15

Mesenchyme and flexible mesoderm

Question 16

How does the limb bud elongate

Answer 16

Through proliferation of mesenchymal core

Question 17

What is the Apical Ectodermal Ridge

Answer 17

A thickened section of ectoderm at the apex of the limb bud

Question 18

What structure governs the asymmetry in the posterior-Anterior axis

Answer 18

Zone of polarising activity (ZPA)

Question 19

What structure governs the asymmetry in the dorsal - ventral axis

Answer 19

Differences in the ectoderm

Question 20

What structure governs the asymmetry in the proximal - dorsal axis

Answer 20

Apical Ectodermal Ridge (AER)

Question 21

What is the function of the Apical Ectodermal Ridge

Answer 21

Secrete molecules that tell underlying mesenchyme to stay undifferentiated

Question 22

What happens to the proximal mesenchyme as the limb bud elongates

Answer 22

Cells begin to differentiate into constituent tissues

Question 23

How does the zone of polarising activity cause Anterior - posterior axis

Answer 23

It is a signalling centre in the posterior base of limb bud

Question 24

How do the Hand and foot plates appear

Answer 24

AER breaks up (only maintained over tips of digits)

Interdigital spaces are sculpted by apoptosis

Question 25

What is syndactyly

Answer 25

Fusion of digits (either connective tissue or bones)

Question 26

What is polydactyly

Answer 26

Extra digits (autosomal recessive trait)

Question 27

What is Amelia

Answer 27

Complete absence of limb

Question 28

What is meromelia

Answer 28

Partial absence of one or more limb structures

Question 29

What is phocomelia

Answer 29

Where a hand or foot is attached straight to a joint (eg hand on elbow or shoulder)

Question 30

What are three causes of morphogenesis

Answer 30

1) malformation
2) deformation (constriction bands)
3) disruption (thalidomide - disrupted AER)

Question 31

As limbs extend they rotate, in what direction does the upper limb rotate

Answer 31

Laterally

Question 32

As limbs extend they rotate, in what direction does the lower limb rotate

Answer 32

Medially (hence big toe is medial to foot)

Question 33

What are digital rays in hand and foot plates

Answer 33

Mesenchyme condensations within plates

Question 34

By what process do the digits form

Answer 34

Apoptosis