biology

Sternalis muscle

Sternalis muscle is a biology 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 Sternalis muscle rather than just read about it. In short: The rectus sternalis muscle is an anatomical variation that lies in front of the sternal end of the pectoralis major parallel to the margin of the sternum. The sternalis muscle may be a variation of the pectoralis major or of the rectus abdominis.

Key takeaways

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

Reference excerpt

The rectus sternalis muscle is an anatomical variation that lies in front of the sternal end of the pectoralis major parallel to the margin of the sternum. The sternalis muscle may be a variation of the pectoralis major or of the rectus abdominis.

Structure The sternalis is a muscle that runs along the anterior aspect of the body of the sternum. It lies superficially and parallel to the sternum. Its origin and insertion are variable. The sternalis muscle often originates from the upper part of the sternum and can display varying insertions such as the pectoral fascia, lower ribs, costal cartilages, rectus sheath, aponeurosis of the abdominal external oblique muscle. It may be present unilaterally or bilaterally. There is still a great deal of disagreement about its innervation and its embryonic origin. In a review, it was reported that the muscle was innervated by the external or internal thoracic nerves in 55% of the cases, by the intercostal nerves in 43% of the cases, while the remaining cases were supplied by both nerves. However, innervation by the pectoral nerves has also been reported. This appears to indicate that the sternalis is not always derived from the same embryonic origin.

Prevalence Cadaveric studies have shown that the sternalis muscle has a mean prevalence of around 7.8% in the population, with a significantly higher incidence of unilateral rather than bilateral presentation and a slightly higher incidence in females. The prevalence among subpopulations ranges from 0.5% to 23.5%⁠—a possible reason for this sizable range could be that small, ill-defined, or tendinous fibers may or may not be accepted as constituting a sternalis muscle.

Variations A 2014 study classified the sternalis into three types depending on morphology.

Type I (single head and single belly) Type II (double-headed/multi-headed) Type III (double-bellied/multi-bellied) Type I, the single head and single belly was seen in the majority of reported cases (58.5%), type II in 18.1%, and type III in 23.4%. In addition to the above classification, triple-bellied/double-headed sternalis has also been reported.

Function There is no apparent physiological function of the sternalis muscle. However, there are many theories for a function. It may function as a proprioceptive sensor for thoracic wall movements. It may also take part in the movement of the shoulder joint or have an additional role in elevation of the chest wall.

Clinical significance

The presence of the sternalis is asymptomatic but aesthetic complaints have been reported as it was reported to cause chest asymmetry or deviation of the nipple-areola complex. The presence of the sternalis may cause alterations in the electrocardiogram or confusion in mammography. However, there is a potential benefit of the muscle as it can be used as a flap in a reconstructive surgery of the head and neck and the anterior chest wall.

History The sternalis was first reported by Carbolius in 1604 and the name was first given by Turner in 1867. Different terminologies have been given to the sternalis due to its highly varied morphology and the disagreement on its embryonic origin. The sternalis was referred to as the rectus sternalis, sternalis brutorum, musculus sternalis, episternalis, parasternalis, presternalis, rectus sterni, rectus thoracis, rectus thoracicus superficialis, superficial rectus abdominis, japonicas, and thoracicus depending on studies.

Additional images

References

Illustrations

Worked examples

Example 1 — a first encounter with Sternalis muscle

Start with the simplest possible case. Write down what Sternalis muscle claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, 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 Sternalis muscle 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 Sternalis muscle 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 Sternalis muscle

In research: Sternalis muscle appears in biology 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 Sternalis muscle 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: Sternalis muscle is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1640 in science, 1867 in biology, Accessory muscle, so understanding it makes those chapters shorter.
In everyday life: Look for Sternalis muscle 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 Sternalis muscle in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sternalis muscle 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 Sternalis muscle out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sternalis muscle in simple terms?

Why does Sternalis muscle matter?

Because it connects several biology 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 Sternalis muscle?

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 Sternalis muscle.