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Encyclopedia > Olfactory bulb
Brain: Olfactory bulb
Vesalius' Fabrica, 1543. Olfactory Bulbs and Olfactory tracts outlined in red
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.
Latin bulbus olfactorius
Gray's subject #189 826
NeuroNames hier-261
MeSH Olfactory+Bulb
Dorlands/Elsevier b_26/12200284

The olfactory bulb is a structure of the vertebrate forebrain involved in olfaction, the perception of odors. Image File history File links 1543,Vesalius'OlfactoryBulbs. ... Andreas Vesalius (portrait from the Fabrica). ... The olfactory tract is a narrow white band, triangular on coronal section, the apex being directed upward. ... Image File history File links Download high-resolution version (677x1025, 173 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Olfactory bulb ... Feral mouse A mouse (plural mice) is a mammal that belongs to one of numerous species of small rodents. ... Mitral cells are neurons that make up a part of the olfactory system. ... In neuroscience, granule cells are tiny cells found within the granular layer of the cerebellum. ... In anatomy, the dorsum is the upper or back side of an animal, as opposed to the ventrum. ... The term lateral can refer to: an anatomical definition of direction. ... Latin is an ancient Indo-European language originally spoken in Latium, the region immediately surrounding Rome. ... NeuroNames is a system of nomenclature for the brain and related structures. ... Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. ... Elseviers logo. ... Classes and Clades See below Male and female Superb Fairy-wren Vertebrates are members of the subphylum Vertebrata (within the phylum Chordata), specifically, those chordates with backbones or spinal columns. ... In the anatomy of vertebrates, the prosencephalon is a part of encephalon, or brain. ... Olfaction (the sense of smell) is the detection of chemicals dissolved in air. ... Odor receptors on the antennae of a Luna moth An odor is the object of perception of the sense of olfaction. ...

Contents

Anatomy

In most vertebrates, the olfactory bulb is the most rostral (forward) part of the brain. 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 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. In zootomy, several terms are used to describe the location of organs and other structures in the body of bilateral animals. ... The anatomical planes The anatomical position is a schematic convention for describing the relative morphology of the human body. ... Your skull is in your back (this is obviously not true, I was just testing the website to see if it really works) The ethmoid bone (os ethmoidale) is a bone in the skull that separates the nasal cavity from the brain. ... The olfactory epithelium is a specialized epithelial tissue inside the nasal cavity that is involved in smell. ... The olfactory nerve is the first of twelve cranial nerves. ...


Main olfactory bulb

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

The glomerular layer receives direct input from olfactory 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. Glomeruli 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 glomerulus (plural glomeruli) in olfaction is structure in the olfactory bulb. ... Mitral cells are neurons that make up a part of the olfactory system. ... In neuroscience, granule cells are tiny cells found within the granular layer of the cerebellum. ... An olfactory receptor neuron, also called an olfactory sensory neuron, is the primary transduction cell for olfaction in the olfactory system. ... The olfactory mucosa is an organ made up of the olfactory epithelium and the mucosa, or mucus secreting glands, behind the epithelium. ... The nasal cavity (or nasal fossa) is a large air-filled space above and behind the nose in the middle of the face. ... The glomerulus (plural glomeruli) in olfaction is structure in the olfactory bulb. ... Olfactory receptors are a type of G protein-coupled receptor in olfactory receptor neurons. ... Mitral cells are neurons that make up a part of the olfactory system. ... In anatomy of animals, the piriform cortex, or pyriform cortex is a region in the brain. ...


Accessory olfactory bulb

The accessory olfactory bulb, which resides on the dorsal-posterior region of the main olfactory bulb, forms a parallel pathway independent from the main olfactory bulb. It receives axonal input from the vomeronasal organ, a distinct sensory epithelium from the main olfactory epithelium that detects pheremones, among other chemical stimuli. Like the main olfactory bulb, axonal input to the accessory olfactory bulb forms synapses with mitral cells within glomeruli. However, mitral cells in the accessory olfactory bulb project their axons to targets in the amygdala and hypothalamus where they may influence aggressive and mating behavior. The vomeronasal organ (VNO) or Jacobsons organ (sometimes misspelled Jacobsens) is an auxiliary olfactory sense organ in some vertebrates, all of which are tetrapods. ... The olfactory epithelium is a specialized epithelial tissue inside the nasal cavity that is involved in smell. ... Fanning honeybee exposes Nasonov gland (white-at tip of abdomen) releasing pheromone to entice swarm into an empty hive A pheromone is any chemical produced by a living organism that transmits a message to other members of the same species. ... This article or section does not cite its references or sources. ... The hypothalamus (from Greek ὑποθαλαμος = under the thalamus) is a region of the mammalian brain located below the thalamus, forming the major portion of the ventral region of the diencephalon and functioning to regulate certain metabolic processes and other autonomic activities. ...


Function

Nerves of septum of nose. Right side. ("Olfactory T. Bulb" visible at upper left.)
Nerves of septum of nose. Right side. ("Olfactory T. Bulb" visible at upper left.)

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 amygdala, neocortex, hippocampus, locus coeruleus, and substantia niagra. With this in mind, its potential functions can be placed into four non-exclusive categories: Image File history File links Gray858. ... Image File history File links Gray858. ... Television signal splitter consisting of a hi-pass and a low-pass filter. ... This article or section does not cite its references or sources. ... The neocortex (Latin for new bark or new rind) is a part of the brain of mammals. ... The hippocampus is located in the medial temporal lobe of the brain. ... The Locus ceruleus, also spelled locus coeruleus, (Latin for the blue bit) is a nucleus in the brain stem apparently responsible for the physiological reactions involved in stress and panic. ... The substantia nigra, (Latin for black substance, Soemering) or locus niger is a heterogeneous portion of the midbrain, separating the pes (foot) from the tegmentum (covering), and a major element of the basal ganglia system. ...

  • enhancing discrimination between odors.
  • enhancing sensitivity of odor detection.
  • filtering out many background odors to enhance the transmission of a few select odors.
  • permitting higher brain areas involved in arousal and attention to modify the detection or the discrimination of odors.

While all of these functions could theoretically arise from the olfactory bulb's circuit layout, it is unclear which, if any, of these functions are performed exclusively by the olfactory bulb. By analogy to similar parts of the brain such as the retina, many researchers have focused on how the olfactory bulb filters incoming information from receptor neurons in space, or how it filters incoming information in time. At the core of these proposed filters are the two classes of interneurons; the periglomerular cells, and the granule cells. Human eye cross-sectional view. ...


Mitral cells are connected by interneurons known as granule cells, which by some theories produce lateral inhibition between mitral cells. It is not clear what the functional role of lateral inhibition would be, though it may be involved in boosting the signal-to-noise ratio of odor signals by silencing the basal firing rate of surrounding non-activated neurons. The synapse between mitral and granule cells is of a rare class of synapses that are "dendro-dendritic" which means that both sides of the synapse are dendrites that release neurotransmitter. In this specific case, mitral cells release the excitatory neurotransmitter glutamate, and granule cells release the inhibitory neurotransmitter Gamma-aminobutyric acid (GABA). As a result of its bi-directionality, the dendro-dendritic synapse can cause mitral cells to inhibit themselves (auto-inhibition), as well as neighboring mitral cells (lateral inhibition). To meet Wikipedias quality standards, this article or section may require cleanup. ... In neuroscience, granule cells are tiny cells found within the granular layer of the cerebellum. ... simply; your nose receives messages from the environment sending them to the olfactory centre which is present in the cerebrum the largest part of brain: then you either smell a good smell or a bad smell stink with parts of seconds. ... Glutamate is the anion of glutamic acid. ... Gamma-aminobutyric acid (usually abbreviated to GABA) is an inhibitory neurotransmitter found in the nervous systems of widely divergent species. ...


Evolution

Comparing the structure of the olfactory bulb between species such as the fruit fly (where it is called the antennal lobe), the Leopard Frog and the lab mouse reveals that they all share the same fundamental layout (five layers containing the nuclei of three major cell types, see "Anatomy" for details), despite being dissimilar in shape and size. It is quite possible, however, that function has not been conserved with structure, indicating that olfactory bulbs of distant species may be paralogs of each other. An intriguing alternative possibility states olfactory bulb structure is conserved because it contains an optimal solution to a computational problem experienced by all olfactory systems, and thus may have evolved independently in different species. Binomial name Drosophila melanogaster Meigen, 1830 [1] Drosophila melanogaster (from the Greek for black-bellied dew-lover) is a two-winged insect that belongs to the Diptera, the order of the flies. ... Antennal Lobe is the deutocerebral neuropil of the insect which receive the input from the sensory neurons on the antenna. ... Species Rio Grande Leopard Frog, Plains Leopard Frog, Chiricahua Leopard Frog, Vegas Valley Leopard Frog, Relict Leopard Frog Northern Leopard Frog, Southern Leopard Frog, Ramsey Canyon Leopard Frog, Lowland Leopard Frog, Leopard frogs, which are also called meadow frogs and grass frogs, are a collection of so-called true frogs... Binomial name Mus musculus Linnaeus, 1758 Mus musculus is the common house mouse. ... Used to describe two genes which share significant homology within the same species. ...


References

  • Shepherd, G. The Synaptic Organization of the Brain, Oxford University Press, 5th edition (November, 2003). ISBN 0-19-515956-X
  • Halpern M, Martinez-Marcos A, Structure and function of the vomeronasal system: an update. Progress in Neurobiology; 70(245-318), 2003.
  • Ache BW, Young JM, Olfaction: Diverse Species, Conserved Principles. Neuron; 48(417-430), 2005.

Additional images

External links


  Results from FactBites:
 
How Rats and Mice—and Probably Humans—Recognize Odors (688 words)
This synapse actually forms in the olfactory bulb, which is a part of the brain.
A round, knob-like structure, the olfactory bulb is quite large in animals with an acute sense of smell but decreases in relative size as this ability wanes.
In the olfactory epithelium of the nose, Axel and Buck's groups found, neurons that make a given odorant receptor do not cluster together; instead, these neurons are distributed randomly within certain broad regions of the epithelium, called expression zones, which are symmetrical on the two sides of the animals' nasal cavities.
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The olfactory bulb is located on top of the cribriform plate at the base of the frontal lobe in the anterior cranial fossa.
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The axons of olfactory receptor cells are delicate and pass through small foramina of the cribriform plate at the base of the skull and synapse directly in the olfactory bulb.
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