olfactory bulb

Examples of olfactory bulb in the following topics:

• Olfactory (I) Nerve

  • The olfactory nerve, or cranial nerve I, is the first of the 12 cranial nerves.
  • The specialized olfactory receptor neurons of the olfactory nerve are located in the olfactory mucosa of the upper parts of the nasal cavity.
  • The olfactory nerves consist of a collection of many sensory nerve fibers that extend from the olfactory epithelium to the olfactory bulb, passing through the many openings of the cribriform plate of the ethmoid bone.
  • Olfactory receptor neurons continue to emerge throughout life and extend new axons to the olfactory bulb.
  • These interactions are transduced into electrical activity in the olfactory bulb, which then transmits the electrical activity to other parts of the olfactory system and the rest of the central nervous system via the olfactory tract.

• Overview of the Cerebrum

  • The cerebrum contains the cerebral cortex (of the two cerebral hemispheres), as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb.
  • The frontal lobe is located at the front of the brain, over the eyes, and contains the  olfactory bulb.
  • The olfactory sensory system is unique in that neurons in the olfactory bulb send their axons directly to the olfactory cortex, rather than to the thalamus first.
  • Damage to the olfactory bulb results in a loss of the sense of smell.
  • The olfactory bulb also receives "top-down" information from such brain areas as the amygdala, neocortex, hippocampus, locus coeruleus, and substantia nigra.

• Amoebic Meningoencephalitis

  • However, thus far the only route for Naegleria fowleri to enter the central nervous system is via deep insufflation of infected water as it attaches itself to the olfactory nerve, which is exposed only at the extreme vertical terminus of the paranasal sinuses.
  • When this occurs, it then migrates through the cribiform plate and into the olfactory bulbs of the forebrain, where it multiplies itself greatly by feeding on nerve tissue.
  • During this stage, occurring approximately 3–7 days post-infection, the typical symptoms are parosmia, rapidly progressing to anosmia (with resultant ageusia) as the nerve cells of the olfactory bulbs are consumed and replaced with necrotic lesions.
  • After the organisms have multiplied and largely consumed the olfactory bulbs, the infection rapidly spreads through the mitral cell axons to the rest of the cerebrum, resulting in onset of frank encephalitic symptoms, including cephalgia (headache), nausea, and rigidity of the neck muscles, progressing to vomiting, delirium, seizures, and eventually irreversible coma.
  • The parasite also demonstrates a particularly rapid late-stage propagation through the nerves of the olfactory system to many parts of the brain simultaneously (including the vulnerable medulla).

• Taste and Smell at Birth and in Old Age

  • Intrauterine olfactory learning is demonstrated by behavioral evidence that newborns respond positively to the smell of their own amniotic fluid.
  • The unique scent of the mother (to the infant) is referred to as her olfactory signature.
  • Studies demonstrate that the changes to the olfactory bulb and main olfactory system following birth are extremely important and influential for maternal behavior.
  • Pregnancy and childbirth result in a high state of plasticity of the olfactory system that may facilitate olfactory learning within the mother.
  • Human olfactory system. 1: Olfactory bulb 2: Mitral cells 3: Bone 4: Nasal epithelium 5: Glomerulus (olfaction) 6: Olfactory receptor cells

• Reception and Transduction

  • The olfactory epithelium is a collection of specialized olfactory receptors in the back of the nasal cavity that spans an area about 5 cm2 in humans.
  • An olfactory receptor, which is a dendrite of a specialized neuron, responds when it binds certain molecules inhaled from the environment by sending impulses directly to the olfactory bulb of the brain.
  • Olfactory neurons are bipolar neurons (neurons with two processes from the cell body).
  • Each olfactory sensory neuron has only one type of receptor on its cilia.
  • In the human olfactory system, (a) bipolar olfactory neurons extend from (b) the olfactory epithelium, where olfactory receptors are located, to the olfactory bulb.

• Sensory Areas

  • Olfactory information, however, passes through the olfactory bulb to the olfactory cortex, bypassing the thalamus.
  • The olfactory cortex is located in the uncus, found along the ventral surface of the temporal lobe.

• Limbic System

  • The septal nuclei receive reciprocal connections from the olfactory bulb, hippocampus, amygdala, hypothalamus, midbrain, habenula, cingulate gyrus, and thalamus.

• Neurons

  • Examples include (a) a pyramidal cell from the cerebral cortex, (b) a Purkinje cell from the cerebellar cortex, and (c) olfactory cells from the olfactory epithelium and olfactory bulb.

• Overview of Sensation

  • The olfactory system is the sensory system used for the sense of smell (olfaction).
  • In humans, olfaction occurs when odorant molecules bind to specific sites on the olfactory receptors in the nasal cavity.
  • They come together at a structure (the glomerulus) that transmits signals to the olfactory bulb in the brain.

• Olfaction: The Nasal Cavity and Smell

  • Olfactory sensitivity is directly proportional to spatial area in the nose—specifically the olfactory epithelium, which is where odorant reception occurs.
  • The area in the nasal cavity near the septum is reserved for the olfactory mucous membrane, where olfactory receptor cells are located.
  • This area is a dime-sized region called the olfactory mucosa.
  • Olfactory transduction is a series of events in which odor molecules are detected by olfactory receptors.
  • The olfactory nerve connects the olfactory system to the central nervous system to allow processing of odor information.