Getting Above the Tongue: Palatal Shelf Elevation
How do two downward-pointing shelves move to a position above the tongue, and what can stop them?
💡 Elevation needs two things at once: the shelf must remodel from the inside AND the space above the tongue must open up, and blocking either one leaves the shelves vertical and the .
Prerequisite check
- The roof of the mouth behind the lip is the secondary ; it begins as two palatal shelves that bud from the maxillary processes at about human week 6.
- The shelves first grow vertically (downward), one on each side of the tongue, and are made mostly of neural-crest-derived .
What you will learn
Goal: Explain how the vertical palatal shelves rotate to a position above the tongue, and identify one mechanical and one cause of failed elevation.
- Elevation is the step where each vertical rotates to above the tongue at about human week 8.
- Elevation depends on internal remodeling of the shelf, including the water-holding matrix molecule , plus external room as the tongue descends and the head grows wider.
- A cause of failed elevation is a shelf that cannot remodel; a mechanical cause is something blocking the path.
- In a small jaw holds the tongue up, mechanically blocking elevation, and about 85 percent of these babies have a even when palate genes are normal.
Model: Before and after, and the small-jaw natural experiment
Compare two stages. Before (about human week 7, mouse about E12.5), the shelves are vertical, hanging down on each side of the tongue, with the tongue high and filling the space. After (human week 8, mouse about E13.5 to E14), the shelves are , lying flat above the tongue and nearly meeting in the ; the tongue has dropped down and forward, and the head has grown wider and taller. Between these snapshots each shelf has rotated roughly 90 degrees, a fast change called elevation.
Now a natural experiment. Sometimes a baby is born with a much smaller-than-normal lower jaw. The tongue then sits higher and farther back, and in about 85 percent of these babies the is . The reason is mechanical: the high tongue physically blocks the shelves from flipping up, so they cannot elevate in time and never meet. This pattern is the (small jaw, tongue back, cleft palate). Importantly, the palate genes can be perfectly fine; the shelves are blocked by a neighbor, the tongue, so the cleft is a consequence of something else.
Explore (work the model before reading on)
- What position are the shelves in BEFORE elevation, and AFTER?
- What two changes happen to the surroundings between the before and after snapshots (think tongue and head)?
- In , what is physically in the way of the shelves flipping up?
- In Pierre Robin the genes can be normal but the palate still clefts. What does that tell you about whether a always means a broken palate gene?
- Mateo has an and a normal-sized jaw on exam, with no other body differences noted. Does the small-jaw story fit Mateo? Argue yes or no with evidence, and say what ruling it out tells you.
Guided notes
The rotation
- Elevation is a fast remodeling of the shelf's inside; a key matrix molecule is ____, which holds water and swells the .
- At the same time, the ____ (tongue) descends and the head grows wider, opening room above the tongue.
Two kinds of failure
- A ____ reason: the shelf itself cannot remodel properly (matrix or problems).
- A ____ reason: something blocks the path, classically a small jaw holding the tongue up ().
Crossing one possibility off for Mateo
- In Pierre Robin a ____ holds the tongue up, and about 85 percent of these babies have a .
- If Mateo's jaw and tongue are normal, we can ____ the mechanical (Pierre Robin) explanation and keep looking at other steps.
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.
Vocabulary (the same words your classes use)
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: Add the "Act 2: Elevation" entry to Mateo's developmental chart: describe the position change, name one tissue cause and one mechanical cause of failed elevation, then make a call about the small-jaw (Pierre Robin) route for Mateo given his normal jaw and otherwise normal exam, and note what your decision rules out.
- Wrote my Claim, Evidence, and Reasoning exit ticket.
Exit ticket (Claim, Evidence, Reasoning)
- Claim: For the palatal shelves to elevate, two things must happen: ____ and ____.
- Evidence: In , a ____ holds the tongue up, and about ____ percent of these babies have a .
- Reasoning: This matters for Mateo because if his jaw and tongue are normal, we can ____ the mechanical (Pierre Robin) explanation and keep looking at other steps.
| 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 "Add the "Act 2: Elevation" entry to Mateo's developmental chart: describe the position change, name one tissue cause and one mechanical cause of failed elevation, then make a call about the small-jaw (Pierre Robin) route for Mateo given his normal jaw and otherwise normal exam, and note what your decision rules out.".
- 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 shelves remodel and rise above the tongue once the tongue drops and the head widens. But now the two shelves sit almost edge to edge at the , still separate. What actually lets two separate edges of become one continuous roof? We chase that next time.