Paraxial mesoderm means mesoderm surrounding the axis, aka the neural tube. They eventually form a pair of somites on either side. Somites then differentiate into:
In this case, the patient is lacking spinous processes on top of having spina bifida. Maybe you were thinking spina bifida = neuropore defect, but what does this have to do with sclerotomes? This is what I found:
"Failure of closure of the caudal neuropore during embryogenesis will lead to spina bifida. This condition is always marked by a local lack of osteogenesis, or bone growth. The reason is that the correct differentiation and placement of underlying tissues (the spinal chord and spinal nerves and associated tissues) induce the osteogenesis, even small flaws in the underlying tissues can lead to a problem in the formation of the spine (vertebrae)." Source
So I'm guessing that when the question asks for "cause of the defect" they are talking about the vertebrae, not exactly the cause of spina bifida, which would be failure of neuropores to fuse. If that was an answer choice then def pick that, but the lack of vertebrae is due to lack of sclerotome fusion (because spina bifida could not induce it properly).
These sclerotome cells differentiate into chondroblasts that form the cartilaginous precursors of the axial skeleton and bones of the cranial base (form netter embrio)
submitted by โlsmarshall(465)
Patient has Spina bifida occulta which is a neural tube defect (failure of fusion of the neuropores). Sclerotomes are the part of each somite in a vertebrate embryo giving rise to bone or other skeletal tissue. Since a part of this patient's spina bifida included "abscense of spinous process" then a sclerotome was involved. Knowing that neural tube defects are an issue with fusion should be enough to get to the right answer.
If the notochord failed to develop then the entire CNS would not develop as the notochord induces formation of neural plate.
If the neural tube failed to develop then the whole CNS would not have developed.
Yolk sac is irrelevant to this patient.
When neural crest cell it has different outcomes in different tissues. Failure of neural crest to migrate in heart can cause Transposition of great vessels, Tetralogy of Fallot, or Persistent truncus arteriosus. Failure of neural crests to migrate in GI can cause Hirschsprung disease (congenital megacolon). Treacher Collins Syndrome can occur when neural crest cells fail to migrate into 1st pharyngeal arch. Neural tube defects has nothing to do with failure of neural crest migration though.