How Do the Face-Building Cells Get to the Right Place?
How do cranial travel from the neural folds to the right facial blocks, and why does taking the correct route matter?
💡 is delivery on a schedule: cells must reach the right place, in the right number, at the right time, or a stays hypoplastic and too small to fuse.
Prerequisite check
- The cells that build most of the face are cranial , which form at the crest of the neural folds where the folding meets.
- To leave home, undergo by an , switching from a stuck-together sheet cell to a free, crawling cell.
What you will learn
Goal: Describe how cranial migrate in organized streams from the neural folds into the and the pharyngeal arches, and explain why correct is required to fill the facial prominences on schedule.
- After , cranial travel in organized migratory streams, each with a destination, not at random.
- The front of the face is filled by cells that migrate into the and the first pharyngeal arch, which becomes the maxillary and mandibular processes.
- must deliver cells in the right place, right number, and right time so the prominences fill out enough to fuse later.
- When is disrupted, a can end up hypoplastic (under-grown) and too small to fuse with its neighbor.
Model: The streams map and a normal-versus-disrupted comparison
After they break free, cranial travel in three organized migratory streams. Picture the from the side with the brain at the front-top: the forebrain and midbrain crest fills the (the above the mouth), the first-arch stream fills the first pharyngeal arch (which becomes the maxillary and mandibular processes), and later streams fill the second and further arches. The cells that build Mateo's upper lip ride the front streams into the frontonasal process and the first arch, exactly the prominences that must fuse to make the lip.
When cannot migrate properly, the prominences they were supposed to fill end up too small, described as hypoplastic. Compare two embryos. In A (normal), cells delaminate, migrate in streams, and arrive in full numbers and on time, so the frontonasal and maxillary blocks fill out and can meet. In Embryo B ( disrupted), the cells are made but fewer reach the front of the face, or they arrive late, so the blocks are smaller and may not reach across to fuse.
Explore (work the model before reading on)
- Into which two destinations do the front migratory streams deliver cells that build the upper lip?
- What are the bulges below the mouth called, and which one becomes the maxillary and mandibular processes?
- What does it mean for a facial block to be hypoplastic?
- Using A versus Embryo B, explain why correct (right place, right number, right time) matters for whether two blocks can later fuse.
- Predict the effect on the face if cells were made and delaminated normally, but one front stream got partly blocked so fewer cells reached the .
Guided notes
Organized streams, not random
- The front of the face is filled by cells that migrate into the and the first ____ arch.
- That first arch becomes the maxillary and ____ processes.
Delivery on a schedule
- The cells must arrive in the right place, in the right number, and at the right ____.
- When is disrupted, a can end up ____ (under-grown).
- An under-grown block may be too small to ____ with its neighbor.
An honesty note
- We are NOT claiming Mateo had a defect; we are still building the ____.
- Many clefts involve the lip-closing step itself, not the ____ of cells.
Reading the Research
- Skim the title and abstract first to get the gist.
- Circle the one sentence that states the main claim.
- Box the evidence the authors give for that claim.
- Mark one sentence that confuses you, and move on.
Vetted readings for this lesson
Track your progress today
Check these off as you work through the lesson, then submit. This tells Mr. Mendoza how you're doing so he can help the class. It does not replace turning in your producible.
Use the code Mr. Mendoza gave you, not your name. Saved on this device.
- Read the Model and answered the Explore questions.
- Filled in the guided notes in my own words.
- Defined the new vocabulary with an example.
- Built the producible: On a side-view sketch of the early embryo, draw three arrows from the neural folds to the three destinations and label each. Circle the two destinations that supply the upper-lip prominences. Then finish a sentence with a real consequence: if the maxillary-bound stream were short by half, the maxillary process would be ____, which could leave a gap because it cannot ____.
- Wrote my Claim, Evidence, and Reasoning exit ticket.
Exit ticket (Claim, Evidence, Reasoning)
- Claim: Cranial reach the facial prominences by traveling in organized streams, not at random.
- Evidence: The front streams deliver cells into the ____ process and the first pharyngeal ____, which build the lip-forming blocks.
- Reasoning: Because the prominences only fuse if they fill out enough to meet, the cells must arrive in the right place, number, and time, or a block stays hypoplastic and a gap can remain.
| Criterion | Proficient | Developing | Beginning |
|---|---|---|---|
| Complete | Every required part of the artifact is present and filled in. | Most parts are present, but one is missing or left blank. | Several parts are missing. |
| Accurate | The science and data are correct and match the evidence. | Mostly correct, with a small factual slip. | Key science or data is wrong. |
| Scientific reasoning (CER) | States a claim, backs it with specific evidence, and explains the reasoning. | Has a claim and evidence, but the reasoning is thin or missing. | Gives an answer with no evidence or reasoning. |
| Professional communication | Clear, organized, and labeled the way a clinician or scientist would write it. | Readable but disorganized or missing labels. | Hard to follow. |
| Submitted | Turned in the right way (Schoology for routine work) and confirmed. | Turned in, but in the wrong place or unconfirmed. | Not turned in. |
- CompleteProficient: Nothing is left blank: the model fills every part of "On a side-view sketch of the early embryo, draw three arrows from the neural folds to the three destinations and label each. Circle the two destinations that supply the upper-lip prominences. Then finish a sentence with a real consequence: if the maxillary-bound stream were short by half, the maxillary process would be ____, which could leave a gap because it cannot ____.".
- AccurateProficient: Every number and claim matches the case evidence.
- Scientific reasoning (CER)Proficient: It names a claim, cites the specific evidence, and explains the reasoning, not just the answer.
- Professional communicationProficient: It is organized and labeled like a real chart note.
- SubmittedProficient: It would be turned in on Schoology and confirmed.
Where this leads: careers
What's next: The face-building cells ride organized streams into the and the first arch, filling the prominences. But the lip is still open: the blocks have arrived and grown, yet they sit next to one another as separate pieces. So the next question is: how and when do those separate blocks actually close to make a lip? We chase that next time.