Neurocranium

Key takeaways

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

Reference excerpt

In human anatomy, the neurocranium, also known as the braincase, brainpan, brain-pan, or brainbox, is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria or skullcap. The remainder of the skull is the facial skeleton. In comparative anatomy, neurocranium is sometimes used synonymously with endocranium or chondrocranium.

Structure The neurocranium is divided into two portions:

the membranous part, consisting of flat bones, which surround the brain; and the cartilaginous part, or chondrocranium, which forms bones of the base of the skull. In humans, the neurocranium is usually considered to include the following eight bones:

1 ethmoid bone 1 frontal bone 1 occipital bone 2 parietal bones 1 sphenoid bone 2 temporal bones The ossicles (three on each side) are usually not included as bones of the neurocranium. There may variably also be extra sutural bones present. Below the neurocranium is a complex of openings (foramina) and bones, including the foramen magnum which houses the neural spine. The auditory bullae, located in the same region, aid in hearing. The size of the neurocranium is variable among mammals. The roof may contain ridges such as the temporal crests.

Development The neurocranium arises from paraxial mesoderm. There is also some contribution of ectomesenchyme. In Chondrichthyes and other cartilaginous vertebrates this portion of the cranium does not ossify; it is not replaced via endochondral ossification.

Other animals The neurocranium is formed by the combination of the endocranium, the lower portions of the cranial vault, and the skull roof. Through the course of evolution, the human neurocranium has expanded from comprising the back part of the mammalian skull to being also the upper part: during the evolutionary expansion of the brain, the neurocranium has overgrown the splanchnocranium. The upper-frontmost part of the cranium also houses the evolutionarily newest part of the mammal brain, the frontal lobes.

In other vertebrates, the foramen magnum is oriented towards the back, rather than downwards. The braincase contains a greater number of bones, most of which are endochondral rather than dermal:

The singular basioccipital is the rear lower part of the braincase, below the foramen magnum. It is homologous to the basilar part of the occipital bone. In the ancestral tetrapod, the basioccipital makes up most of a large central knob-like surface, the occipital condyle, which articulates with the vertebrae as a ball-and-socket joint. This plesiomorphic ("primitive") state is retained by modern reptiles and birds. The underside of the basioccipital may have a pair of large projections which act as neck muscle attachments: the basitubera (also known as basioccipital tubera or basal tubera) The paired exoccipitals (singular: exoccipital) are visible at the rear of the braincase, adjacent to the foramen magnum and above the basioccipital. They are homologous to the lateral parts of the occipital bone. Modern amphibians and mammals have independently acquired inflated exoccipitals, acting as paired occipital condyles while the basioccipital is reduced and loses its connection to the vertebrae. The singular supraoccipital is the rear upper part of the braincase, above the foramen magnum and below or behind the parietals or postparietals. It is homologous to the squamous part of the occipital bone, which is greatly enlarged in humans. The paired opisthotics (singular: opisthotic) form most of the rear lateral part of the braincase, in front of the exoccipitals and above the foramen ovale. They also contribute to the paroccipital process, a lateral projection which acts as a buttress between the braincase and the outer skull bones. In many tetrapods, the opisthotic is fused to its corresponding exoccipital. The jugular foramen is usually found near the point of fusion. The paired prootics (singular: prootic) form the lateral part of the braincase, in front of the opisthotics. The front edge of the prootic is typically deeply notched by the exit hole for the trigeminal nerve (V). Many other nerve exits are scattered among the prootic, opisthotic, and exoccipital. The prootic is homologous to the petrous part of the temporal bone (in humans) or the petrosal bone (in other mammals). Some reptiles have a laterosphenoid in front of the prootic. This bone is present in archosaurs and a few other archosauromorphs, as well as the stem-turtle Proganochelys. The singular basisphenoid forms the front lower part of the braincase, in front of the basioccipital and below the prootics. Each side of the basisphenoid hosts a basipterygoid process, a lateral rod which bends down and out to link to the pterygoid bones of the bony palate. The basisphenoid may also act as a component of the basitubera. The singular parasphenoid is one of the few dermal components of the braincase, a flat plate below the basisphenoid. The parasphenoid acts as a component of the bony palate, wedging between the pterygoid bones and often ornamented with small tooth-like denticles. In many vertebrates the parasphenoid and basisphenoid are fused into a single bone, the parabasisphenoid. The front part of the parabasisphenoid is a blade-like structure, the cultriform process, which extends much further forward than the rest of the braincase.

Additional images

Illustrations

Worked examples

Example 1 — a first encounter with Neurocranium

Start with the simplest possible case. Write down what Neurocranium 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 Neurocranium 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 Neurocranium 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 Neurocranium

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

How to study Neurocranium in 20 minutes

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

Frequently asked questions

What is Neurocranium in simple terms?

In human anatomy, the neurocranium, also known as the braincase, brainpan, brain-pan, or brainbox, is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria or skullcap.

Why does Neurocranium 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 Neurocranium?

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 Neurocranium.