Development of the Limbs

Question 1

Outline the stages of the gait cycle

Answer 1

Initial contact,

loading response,

mid stance,

terminal stance,

pre-swing,

initial swing,

mid swing,

terminal swing

Question 2

What are the 6 basic movements of the hand?

Answer 2

Cylindrical grip, spherical grip, hook, tip, palmar, lateral

Question 3

What is the name of a pivot point around which a lever turns?

Answer 3

Fulcrum

Question 4

What is another name for a joint regarding its mechanical nature?

Answer 4

Fulcrum

Question 5

What is another name for bones regarding their mechanical nature?

Answer 5

Lever

Question 6

What is the difference between and first, second and third class lever?

Answer 6

First = load and effort on either side of the fulcrum.

Second = load and effort on the same side, effort is furthest away.

Third = load and effort on the same side, load is furthest away

Question 7

What is cadence?

Answer 7

Stride rate

Question 8

When do the limb buds appear?

Answer 8

Ends of 4th week, lower limb ~2 days behind upper limb

Question 9

What is a limb bid comprised of?

Answer 9

Core of proliferating mesenchymal cells with an ectoderm covering

Question 10

Why are the limbs one of the last structures to develop?

Answer 10

Priority is given to essential anatomy

Question 11

What are the 3 spatial axes in limb development?

Answer 11

1. Shoulder to fingertips = Proximal – distal axis
2. Palmar surface to dorsal surface = Dorsal – ventral axis
3. Side – to – side = Anterior – posterior axis

Question 12

Describe the role of the apical ectodermal ridge (AER)

Answer 12

Proximal-distal axis = orchestrated limb devel = tell immediate cell to remain undiff, proximal mesenchyme then begins to diff, final stage is the appearance of paddles

Question 13

Outline the role of the zone of polarising activity ZPA

Answer 13

Anterior – posterior axis

signalling centre located at the posterior base of the limb bud = produce morphogen, further away is lower in conc = conc determines where diff occurs

Question 14

What are digital rays?

Answer 14

Mesenchymal condensations within plates (hand and foot) forming cartilaginous condensations

Question 15

How are interdigital spaces achieved?

Answer 15

AER breaks up, maintained only above digital rays of hand/foot plates, apoptosis occurs between AER

Question 16

Name the disorder where fusion of the digest occurs

Answer 16

Syndactyly: fusion of connective tissue and/or bone

Question 17

What is polydactyly?

Answer 17

Recessive trait, extra digits

Question 18

What is the difference between amelia and meromelia?

Answer 18

A: complete absence of limb

M: partial absence of limb

Question 19

What 3 ways can morphogenesis be altered?

Answer 19

Malformation = intrinsic error (genetic).

Deformation = amniotic constriction bands.

Disruption = external agent e.g. thalidomide (affects APR)

Question 20

How do muscles develop?

Answer 20

Myogenic precursors migrate into limbs, form 2 common muscle masses around the newly formed skeletal elements – individual muscles then split from common masses

Question 21

During development which directions do the upper and lower limbs rotate in?

Answer 21

Upper = thumb lateral.

Lower = big toe medial