Development of the Limbs Flashcards
What is the sagittal plane
Sagittal plane divides left and right
What is the transverse plane
Transverse plane divides upper from lower
What is the front/coronal plane
frontal/coronal divides front from back
What is the difference between the axial skeleton and the appendicular skeleton?
Axial skeleton are the limbs whilst appendicular is what’s left over.
What is supine/prone
Supine is face up prone is face down.
How many levels of asymmetry does a limb have?
The hand/arm/leg/foot has three levels of asymmetry.
Generally in terms of development what is the main different between the arms and the legs?
The difference in rotation of legs to arms.
How do the two pairs of limb buds appear and what are they formed from?
Originates from lateral plate mesoderm and somites. Limb buds form appearing ventro-laterally, lower buds after the upper buds. These limb buds appear ventrally to the neural tube and are formed from a core of mesenchymal cells covered in ectoderm.
How does elongation of the limb occur?
Elongation of the limb takes place by proliferation of undifferentiated mesenchyme core.
What is the AER and what is it’s purpose?
Thickened ectoderm ridge at the apex called the AER. The AER prevents differentiation of nearby mesenchymal cells by diffusion of signals. Hence differentiation happens from proximal to distal. AER ridge marks the boundary between dorsal and ventral.
What is the zone of polarising activity?
Zone of polarising activity – posterior base of the AER helps maintain the AER and causes posterior/anterior or dorsal/ventral differentiation.
How are the hand and fingers formed and what structure controls this?
Once appropriate length reached the end flares to form a paddle. Differentiation occurs and condensation of mesenchyme forming cartilaginous models of the bones, then apoptosis models the hand and fingers. AER cotnrols this and regresses apart form at the finger tips.
How does the bone and musculature appear?
Ossification then forms the bones and the musculature appears from migration of myogenic precursor cells bringing nerve innervation with them.
Define: Polydactyly Syndactyly Amelia Meromelia
Which limbs are more likely to suffer defects?
The upper limb is much more likely to be affected than the lower limb but still most are very rare.
Extra digits which is called Polydactyly and fusion of digits via bone or just connective tissue (webbing) which is called Syndactyly.
Amelia is a complete absebce of limb(s) and
Meromelia which is partial absence of one or more limb structures (happened as a cosequence of thalidomide).
