Flashcards in MSK 1 - Development Of Limbs Deck (21):
What are the three different types of grasp with the hand?
Cylindrical, hook/snap, spherical
What are the three different types of precision grip with the hand?
Tip, palmar, lateral
When do the limb buds develop?
Towards the end of the 4th week
Which develops first - the upper or lower limb?
Lower limb development lags around two days behind the upper limb
What are the limb buds composed of?
Core of proliferating mesenchymal cells with an ectoderm covering
How does elongation of the limb bud occur?
Through proliferation of mesenchymal core. There is a thickened ectoderm at the apex of the limb bud.
What are the three spatial axes in limb development?
- proximal-distal axis (shoulder to fingertips)
- dorsal-ventral axis (palmar surface to dorsal surface)
- anterior-posterior axis (side to side)
What does the 'zone of polarising activity' (ZPA) control?
Specification of anterior-posterior axis
What does the 'apical ectodermal ridge' (AER) control?
Specification of apical-ectodermal ridge
What controls the specification of the dorsal-ventral axis?
What does AER stimulate?
- Induces immediately underlying mesenchyme, which begins to differentiate.
- causes appearance of 'paddles' which form digits.
- AER regresses after this.
Where is the ZPA found? What does it do?
It is a signalling centre located at the posterior base of the limb bud, where it controls patterning and maintains AER, generating asymmetry in the limbs
How do hand and foot plates form fingers and toes?
- mesenchyme condensations within plates lead to cartilaginous models of the digital bones
- apoptosis of tissue between digits leads to interdigital spaces.
What is syndactyly?
Fusion of digits, may be just connective tissue or may also affect bones
What is polydactyly?
Extra digits, a recessive genetic trait
What is 'amelia'?
Complete absence of a limb
What is 'meromelia'?
Partial absence of one or more limb structures
Give some examples of the underlying problem in behind a limb defect
- malformation (intrinsic error in coordination of morphogenesis)
- deformation (constriction bands)
- disruption via an external agent eg thalidomide
What are the TORCH infections?
These can be passed from mother to child and cause congenital anomalies
How do muscles form within the limb bud?
- myogenic precursors migrate into limbs from somites (body segments)
- coalesce into two common muscle masses around skeletal elements
- individual muscles split from common masses