science

Paraxial mesoderm

Paraxial mesoderm is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Paraxial mesoderm rather than just read about it. In short: Paraxial mesoderm, also known as presomitic or somitic mesoderm, is the area of mesoderm in the neurulating embryo that flanks and forms simultaneously with the neural tube. The cells of this region give rise to somites, blocks of tissue running along both sides of the neural tube, which form muscle and the tissues of the back, including connective tissue and the dermis.

Key takeaways

Paraxial mesoderm belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Paraxial mesoderm to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Paraxial mesoderm from memory before moving on to harder problems.

Reference excerpt

Paraxial mesoderm, also known as presomitic or somitic mesoderm, is the area of mesoderm in the neurulating embryo that flanks and forms simultaneously with the neural tube. The cells of this region give rise to somites, blocks of tissue running along both sides of the neural tube, which form muscle and the tissues of the back, including connective tissue and the dermis.

Formation and somitogenesis

The paraxial and other regions of the mesoderm are thought to be specified by bone morphogenetic proteins (BMPs) along an axis spanning from the center to the sides of the body. Members of the fibroblast growth factor family also play an important role, as does the Wnt pathway. In particular, Noggin, a downstream target of the Wnt pathway, antagonizes BMP signaling, forming boundaries where antagonists meet and limiting this signaling to a particular region of the mesoderm. Together, these pathways provide the initial specification of the paraxial mesoderm and maintain this identity. This specification process has now been fully recapitulated in vitro with the formation of paraxial mesoderm progenitors from pluripotent stem cells, using a directed differentiation approach. The tissue undergoes convergent extension as the primitive streak regresses, or as the embryo gastrulates. The notochord extends from the base of the head to the tail; with it extend thick bands of paraxial mesoderm. As the primitive streak continues to regress, somites form from the paraxial mesoderm by "budding off" rostrally. In certain model systems, it has been shown that the daughter cells of stem cell-like progenitor cells which come from the primitive streak or site of gastrulation migrate out and localize in the posterior paraxial mesoderm. As the primitive streak regresses and somites bud off anteriorly, new cells derived from these stem-cell like precursors constantly enter the posterior end of the paraxial mesoderm.

Derived tissues Many kinds of tissue derive from the segmented paraxial mesoderm by means of the somite. Among these are:

the sclerotome, which forms cartilage, the syndetome, which forms tendons, the myotome, which forms skeletal muscle, the dermatome, which forms the dermis as well as skeletal muscle, and endothelial cells.

Head mesoderm A particular kind of tissue deriving from the paraxial mesoderm is the head mesoderm, also known as cephalic mesoderm. This tissue derives from the unsegmented paraxial mesoderm and prechordal mesoderm. Tissues derived from the head mesoderm include connective tissues and the muscles of the face. The head mesoderm forms through a separate signaling circuit than the segmented paraxial mesoderm, though also involving BMP and fibroblast growth factor signaling. Here, retinoic acid interacts with these pathways. Early markers of somites exist but are not expressed in cephalic mesoderm, although the same cell types that are generated in somites are generated in cephalic mesoderm, such as angioblasts, myocytes, and a variety of connective tissues. The head is ultimately made from paraxial mesoderm and neural crest cells.

See also Somitomere Chordamesoderm Intermediate mesoderm Lateral plate mesoderm Mesenchyme Triploblasty List of human cell types derived from the germ layers

References This article incorporates text in the public domain from page 50 of the 20th edition of Gray's Anatomy (1918)

External links "Paraxial Mesoderm: The Somites and Their Derivatives" at the National Center for Biotechnology Information "Somite Development" at McGill University Diagram at Lippincott Williams & Wilkins

Illustrations

Worked examples

Example 1 — a first encounter with Paraxial mesoderm

Start with the simplest possible case. Write down what Paraxial mesoderm claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Paraxial mesoderm before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Paraxial mesoderm ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Paraxial mesoderm

In research: Paraxial mesoderm appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Paraxial mesoderm in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Paraxial mesoderm is common in secondary-school and first-year university syllabi. It links to neighbouring topics Embryology, Mesoderm, so understanding it makes those chapters shorter.
In everyday life: Look for Paraxial mesoderm outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Paraxial mesoderm in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Paraxial mesoderm means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Paraxial mesoderm out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Paraxial mesoderm in simple terms?

Why does Paraxial mesoderm matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Paraxial mesoderm?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Paraxial mesoderm.