Mitral cell: what it is and characteristics of this type of neuron

A mitral cell is a type of neuron that is part of the olfactory system.

These cell types are a major exit channel for the olfactory bulb and work by sending signals to various peripheral cortical structures. This type of cell is known in more detail.

    What is a mitral cell

    Within the olfactory system, the flow of information from the periphery to the mitral cells is mediated by direct synaptic inputs from olfactory sensory neurons.

    Extensions of sensory neurons form a bundle of nerve fibers (the olfactory nerve) that transmits information about the volatile compound to the central nervous system, and more specifically to the olfactory bulb. In this structure information is received mainly by two types of cells: mitral cells and feather cells.

    The mitral and feather cells are functionally similar and together constitute the sensory neurons which, along with their axons, connect the olfactory bulb to the central nervous system.

    The olfactory bulb and the glomeruli

    The contact sites between primary sensory neurons and olfactory bulb cells give rise to a series of spherical structures called glomeruli. These play an important role, because it is the place where information converges from all the sensory cells which perceive the same volatile compound at the same time.

    Mitral cells, which have received information from axons of olfactory neurons, are involved in the synapse with the neuropil (the region between several cell bodies or sums of neurons) of olfactory glomeruli.

    After the olfactory bulb, axons of mitral cells transmit information to other areas of the brain. These regions include the pear-shaped bark, an area responsible for detecting odors and involved in storing memories; the amygdala, the main nucleus of emotional control; and the entorhinal cortex, related to memory, smell and orientation.

      Morphology of mitral cells

      A mitral cell is distinguished by the position of its soma (the cell body) in an orderly row in the mitral cell layer of the olfactory bulb. They usually show a single primary dendrite (Extension of the neuron dedicated to receiving nerve impulses from other neurons) projecting onto a single glomerulus.

      Outraged, these cell types show a few lateral dendrites that project into the outer plexiform layer (Region connecting photoreceptor cells and bipolar cells).

      The morphology of the mitral cells was an advantage in the first synaptic processing studies performed as it is possible to independently stimulate both the soma and the main dendrite using electrodes conveniently located in different layers of the olfactory bulb.

      main duties

      Once the information from the odor molecules has been captured, transformed and sent to the olfactory bulb, it is processed in the glomeruli and the mitral cells send this information to the relevant brain regions.

      But what happens at the heart of the processing of olfactory information? Here are the main functions performed by the olfactory bulb:

      1. Differentiation of odors

      The olfactory bulb it is mainly responsible for distinguishing between different types of odors. This differentiation takes place through different patterns of activation of neurons responsible for olfactory perception, which react according to the perceived smell and the shape and structure of the olfactory particles.

      2. Emotional processing of information

      The amygdala, the primary center for controlling emotions in the brain, has connections to the olfactory bulb both directly and indirectly, via the primary olfactory cortex or the piriformis cortex, and it allows certain emotions to be linked to certain olfactory stimuli.

      In addition, our sense of smell, unlike other senses such as sight or hearing, does not need to be demonstrated in the thalamus; this is why their connection to the limbic system is more direct, generating more powerful and explicit connections, which allows us to more easily evoke intense memories of past experiences through scents.

      3. Perception of taste

      The senses of smell and taste are closely related and interconnected. Many times we have the feeling that we are savoring something when we just sniff it.

      In this sense, the olfactory bulb also plays an important role in the perception of taste by this very fact. An example of the relationship between these two senses is the inability of people with anosmia (loss of smell) to capture flavors.

      Synaptic connections with other cells

      Mitral cells play an important role in the connection circuit of the olfactory bulb, as they receive information from at least four types of cells: olfactory sensory neurons, outer plume cells, periglomerular neurons, and granule cells. The first two are excitatory, while the other two are inhibitory.

      Through their primary dendrites, mitral cells receive excitatory synapses from olfactory sensory neurons and outer plume cells. In addition, they also receive inhibitory signals from granule cells in its lateral dendrites or in the soma, and periglomerular cells in the dendritic plume.

      According to the opinion and according to research, the feather cells receive a strong innervation from the olfactory nerve and draw their action potentials towards the beginning of inhalation and their firing frequency is relatively insensitive to the concentration of odors; on the other hand, mitral cells receive little innervation from the olfactory nerve and strong periglomerular inhibition (around the glomeruli), which delays their ignition compared to the cells of the feathers.

      One hypothesis treated in animals is that mitral cells they transform the strength of the olfactory signal into a synchronized code, Where the odor concentration is coded to the frequency of triggering action potentials relative to the inhalation cycle.

      Bibliographical references:

      • Bradford, HF (1988). Fundamentals of Neurochemistry. Job.
      • Dhawale et.al (2010) Coding of non-redundant odors by sister mitral cells revealed by glomeruli directed towards the lumen of the mouse. Nature Neuroscience 13, pages 1404-1412.

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