74.Following a positive α-fetoprotein test a child is born with anen-
cephaly. The development of this open neural tube defect (NTD) is caused
by failure of primary neurulation. The mechanism for tube formation as
occurs during development of the neural tube could best be explained by
which of the following?
a. Contraction of microfilament bundles associated with the zonula adherens
b. Increased condensation of the transmembrane linkers of the desmosomes
c. Expansion of the sealing strands in the zonulae occludentes
d. Condensation of the gap junctions
e. Contraction of tonofilaments associated with desmosomes
154 Anatomy, Histology, and Cell Biology