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Olfactory bulb

Olfactory bulb 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 Olfactory bulb rather than just read about it. In short: The olfactory bulb (Latin: bulbus olfactorius) is a neural structure in the forebrain of vertebrates that is involved in olfaction, or the sense of smell. It transmits olfactory information to the other brain regions including the amygdala, orbitofrontal cortex (OFC) and hippocampus where it contributes to emotion, memory and learning.

Olfactory bulb — main illustration
Olfactory bulb — illustration

Key takeaways

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

Reference excerpt

The olfactory bulb (Latin: bulbus olfactorius) is a neural structure in the forebrain of vertebrates that is involved in olfaction, or the sense of smell. It transmits olfactory information to the other brain regions including the amygdala, orbitofrontal cortex (OFC) and hippocampus where it contributes to emotion, memory and learning. The bulb is divided into two distinct structures: the main olfactory bulb and the accessory olfactory bulb. The main olfactory bulb connects to the amygdala via the piriform cortex of the primary olfactory cortex and directly projects from the main olfactory bulb to specific amygdala areas. The accessory olfactory bulb resides on the dorsal-posterior region of the main olfactory bulb and forms a parallel pathway. Destruction of the olfactory bulb results in ipsilateral anosmia, while irritative lesions of the uncus can result in olfactory and gustatory hallucinations.

Structure In most vertebrates, the olfactory bulb is the most rostral (forward) part of the brain, as seen in rats. In humans, however, the olfactory bulb is on the inferior (bottom) side of the brain. The olfactory bulb is supported and protected by the cribriform plate of the ethmoid bone, which in mammals separates it from the olfactory epithelium, and which is perforated by olfactory nerve axons. The bulb is divided into two distinct structures: the main olfactory bulb and the accessory olfactory bulb.

Layers The main olfactory bulb has a multi-layered cellular architecture. In order from surface to the center the layers are:

Glomerular layer External plexiform layer Mitral cell layer Internal plexiform layer Granule cell layer The olfactory bulb transmits smell information from the nose to the brain, and is thus necessary for a proper sense of smell. As a neural circuit, the glomerular layer receives direct input from afferent nerves, made up of the axons from approximately ten million olfactory receptor neurons in the olfactory mucosa, a region of the nasal cavity. The ends of the axons cluster in spherical structures known as glomeruli such that each glomerulus receives input primarily from olfactory receptor neurons that express the same olfactory receptor. The glomerular layer of the olfactory bulb is the first level of synaptic processing. The glomerular layer represents a spatial odor map organized by chemical structure of odorants like functional group and carbon chain length. This spatial map is divided into zones and clusters, which represent similar glomeruli and therefore similar odors. One cluster in particular is associated with rank, spoiled smells which are represented by certain chemical characteristics. This classification may be evolutionary to help identify food that is no longer good to eat. The spatial map of the glomerular layer may be used for perception of odor in the olfactory cortex. The next level of synaptic processing in the olfactory bulb occurs in the external plexiform layer, between the glomerular layer and the mitral cell layer. The external plexiform layer contains astrocytes, interneurons and some mitral cells. It does not contain many cell bodies, rather mostly dendrites of mitral cells and GABAergic granule cells are also permeated by dendrites from neurons called mitral cells, which in turn output to the olfactory cortex. Numerous interneuron types exist in the olfactory bulb including periglomerular cells which synapse within and between glomeruli, and granule cells which synapse with mitral cells. The granule cell layer is the deepest layer in the olfactory bulb. It is made up of dendrodendritic granule cells that synapse to the mitral cell layer.

Function This part of the brain receives sensations of smell. As a neural circuit, the olfactory bulb has one source of sensory input (axons from olfactory receptor neurons of the olfactory epithelium), and one output (mitral cell axons). As a result, it is generally assumed that it functions as a filter, as opposed to an associative circuit that has many inputs and many outputs. However, the olfactory bulb also receives "top-down" information from such brain areas as the olfactory cortex, amygdala, neocortex, hippocampus, locus coeruleus, and substantia nigra. Its potential functions can be placed into four non-exclusive categories:

… excerpt ends here. Continue reading the full article.

Illustrations

Olfactory bulb illustration
Olfactory bulb illustration
Olfactory bulb: Coronal image of mouse main olfactory bulb cell nuclei.Blue – Glomerular layer; Red – External Plexiform and Mitral cell layer;Green – Internal Plexiform and Granule cell layer.Top of image is dorsal aspect, right of image is lateral aspect. Scale, ventral to dorsal, is approximately 2mm.
Coronal image of mouse main olfactory bulb cell nuclei.Blue – Glomerular layer; Red – External Plexiform and Mitral cell layer;Green – Internal Plexiform and Granule cell layer.Top of image is dorsal aspect, right of image is lateral aspect. Scale, ventral to dorsal, is approximately 2mm.
Olfactory bulb: Flow of olfactory information from receptors to glomeruli layer
Flow of olfactory information from receptors to glomeruli layer
Olfactory bulb: Fossil endocast of a Tyrannosaurus cranial vault, showing extensive olfactory bulb (structure to the left). Tyrannosaur dinosaurs, as well as carnivorous animals in general, have highly developed olfactory bulbs to seek out prey.
Fossil endocast of a Tyrannosaurus cranial vault, showing extensive olfactory bulb (structure to the left). Tyrannosaur dinosaurs, as well as carnivorous animals in general, have highly developed olfactory bulbs to seek out prey.

Worked examples

Example 1 — a first encounter with Olfactory bulb

Start with the simplest possible case. Write down what Olfactory bulb 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 Olfactory bulb 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 Olfactory bulb 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 Olfactory bulb

In research
Olfactory bulb 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 Olfactory bulb 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
Olfactory bulb is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cerebrum, Limbic system, Olfactory system, so understanding it makes those chapters shorter.
In everyday life
Look for Olfactory bulb 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 Olfactory bulb in 20 minutes

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

Frequently asked questions

What is Olfactory bulb in simple terms?

The olfactory bulb (Latin: bulbus olfactorius) is a neural structure in the forebrain of vertebrates that is involved in olfaction, or the sense of smell. It transmits olfactory information to the other brain regions including the amygdala, orbitofrontal cortex (OFC) and hippocampus where it contri…

Why does Olfactory bulb 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 Olfactory bulb?

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 Olfactory bulb.

Tags

  • Cerebrum
  • Limbic system
  • Olfactory system
  • Otorhinolaryngology

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