science

Semicircular canals

Semicircular canals 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 Semicircular canals rather than just read about it. In short: The semicircular canals are three semicircular interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the lateral, anterior and posterior semicircular canals.

Key takeaways

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

Reference excerpt

The semicircular canals are three semicircular interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the lateral, anterior and posterior semicircular canals. They are the part of the bony labyrinth, a periosteum-lined cavity on the petrous part of the temporal bone filled with perilymph. Each semicircular canal contains its respective semicircular duct, i.e. the lateral, anterior and posterior semicircular ducts, which provide the sensation of angular acceleration and are part of the membranous labyrinth—therefore filled with endolymph.

Structure

The semicircular canals are a component of the bony labyrinth that are at right angles from each other and contain their respective semicircular duct. At one end of each of the semicircular ducts is a dilated sac called a membranous ampulla, which is more than twice the diameter of the ducts. Each ampulla contains an ampullary crest, the crista ampullaris which consists of a thick gelatinous cap called a cupula and many hair cells. The superior and posterior semicircular ducts are oriented vertically at right angles to each other. The lateral semicircular duct is about a 30-degree angle from the horizontal plane. The orientations of the ducts cause a different duct to be stimulated by movement of the head in different planes, and more than one duct is stimulated at once if the movement is off those planes. The lateral semicircular duct detects angular acceleration of the head when the head is turned and the anterior and posterior semicircular ducts detect vertical head movements when the head is moved up or down. When the head changes position, the endolymph in the ducts lags behind due to inertia and this acts on the cupula which bends the cilia of the hair cells. The stimulation of the hair cells sends the message to the brain that acceleration is taking place. The semicircular canals open into the vestibule by five orifices, one of the apertures being common to two of them. Among species of mammals, the size of the semicircular canals is correlated with their type of locomotion. Specifically, species that are agile and have fast, jerky locomotion have larger canals relative to their body size than those that move more cautiously.

Lateral semicircular canal The lateral semicircular canal (also known as horizontal or external semicircular canal) is the shortest of the three canals. Movement of fluid within its duct corresponds to rotation of the head around a vertical axis (i.e. the neck), or in other words, rotation in the transverse plane. This occurs, for example, when one turns the head from side to side (yaw axis). It measures from 12 to 15 mm (0.47 to 0.59 in), and its arch is directed horizontally backward and laterally; thus each semicircular canal stands at right angles to the other two. Its ampullated end corresponds to the upper and lateral angle of the vestibule, just above the oval window, where it opens close to the ampullated end of the anterior semicircular canal; its opposite end opens at the upper and back part of the vestibule. The lateral canal of one ear is very nearly in the same plane as that of the other.

Anterior semicircular canal The anterior semicircular canal (also known as superior semicircular canal) contains the part of the vestibular system that detects rotations of the head in around the lateral axis, that is, rotation in the sagittal plane. This occurs, for example, when nodding one's head (pitch axis). It is 15 to 20 mm (0.59 to 0.79 in) in length, is vertical in direction, and is placed transversely to the long axis of the petrous part of the temporal bone, on the anterior surface of which its arch forms a round projection. It describes about two-thirds of a circle. Its lateral extremity is ampullated, and opens into the upper part of the vestibule; the opposite end joins with the upper part of the posterior semicircular canal to form the crus osseum commune, which opens into the upper and medial part of the vestibule.

Posterior semicircular canal The posterior semicircular canal contains the part of the vestibular system that detects rotation of the head around the antero-posterior (sagittal) axis, or in other words, rotation in the coronal plane. This occurs, for example, when one moves the head to touch the shoulders, or when doing a cartwheel (roll axis). It is directed superiorly and posteriorly, as per its nomenclature, nearly parallel to the posterior surface of the petrous part of the temporal bone. The vestibular aqueduct is immediately medial to it. The posterior semicircular canal is part of the bony labyrinth and its duct is used by the vestibular system to detect rotations of the head in the coronal plane. It is the longest of the three semicircular canals, measuring from 18 to 22 mm (0.71 to 0.87 in). Its lower or ampullated end opens into the lower and back part of the vestibule, its upper into the crus osseum commune.

Development Findings from a 2009 study demonstrated a critical late role for bone morphogenetic protein 2 (BMP-2) in the morphogenesis of semicircular canals in the zebrafish inner ear. It is suspected that the role of BMP-2 in semicircular canal duct outgrowth is likely to be conserved between different vertebrate species. Additionally, it has been found that the two semicircular canals found in the lamprey inner ear are developmentally similar to the superior and posterior canals found in humans, as the canals of both organisms arise from two depressions in the otic vesicle during early development. These depressions first form in lampreys between the 11 and 42 millimeter larval stages and form in zebrafish 57 hours post-fertilization

Function

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Illustrations

Worked examples

Example 1 — a first encounter with Semicircular canals

Start with the simplest possible case. Write down what Semicircular canals 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 Semicircular canals 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 Semicircular canals 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 Semicircular canals

In research: Semicircular canals 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 Semicircular canals 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: Semicircular canals is common in secondary-school and first-year university syllabi. It links to neighbouring topics Bones of the head and neck, Ear, Human head and neck, so understanding it makes those chapters shorter.
In everyday life: Look for Semicircular canals 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 Semicircular canals in 20 minutes

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

Frequently asked questions

What is Semicircular canals in simple terms?

Why does Semicircular canals 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 Semicircular canals?

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 Semicircular canals.