Question

1. The role of Hensen's node in a chicken versus the dorsal lip in the frog.

a. Hensen's Node_______________

b. Dorsal Lip___________________

2. During the late stages of neurulation part of the neural tubes cells leave and migrate through what structure to become the peripheral nervous system (a.)? What is the germ layer from which this structure arises (b.)?

a.

b.

Answer 1

1.

a. Hensen's node:

At the anterior end of the primitive streak is a regional thickening of cells called the primitive knot or Hensen's node. The center of this node contains a funnel-shaped depression through which cells can pass into the blastocoel. Hensen's node is the functional equivalent of the dorsal lip of the amphibian blastopore (i.e., the organizer) and the fish embryonic shield. Cells migrating through Hensen's node pass down into the blastocoel and migrate anteriorly, forming foregut, head mesoderm, and notochord; cells passing through the lateral portions of the primitive streak give rise to the majority of endodermal and mesodermal tissues

b. Dorsal lip:

Dorsal lip of the blastopore in frog is a key player in the future development of tissue. Tissue rolls over the dorsal lip of the blastopore as it moves into the embryo. This process is called involution. The new cavity is called the archenteron (primitive gut) and will eventually become the digestive tract. The blastopore will become the anus in the frog, because the frog is a deuterostome.

2.

a. Part of the neural tube cells called Neural crest cells migrate through embryo and will give rise to several cell populations, including cells of the peripheral nervous system.

b. Neural crest is derived from the ectoderm.