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

An overview of the characteristics of mitral cells, a type of neuron.

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

This type of cell is a main output channel of the olfactory bulb and acts by sending signals to various peripheral cortical structures. Let us know, in more detail, this type of cells.

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..

Prolongations of the 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 cell types: mitral cells and tufted cells..

The mitral and tufted cells are functionally similar and together constitute the sensory neurons that connect the olfactory bulb with the central nervous system with their axons.

Olfactory bulb and glomeruli

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

The mitral cells that have received information from the axons of the olfactory neurons are involved in the synapse with the neuropil (the region between several cell bodies or somas of neurons) of the olfactory glomeruli.

After the olfactory bulb, the axons of the mitral cells transmit information to other areas of the brain.. These regions include the piriform cortex, an area responsible for detecting odors and involved in the storage of memories; the amygdala, the main emotion control nucleus; and the entorhinal cortex, related to memory, olfaction and orientation.

Morphology of mitral cells

A mitral cell is distinguished by the position of its soma (the cell body) in an ordered row in the mitral cell layer of the olfactory bulb. Generally, they tend to show a single primary dendrite (prolongation of the neuron dedicated to the reception of the nerve impulse from other neurons) that projects to a single glomerulus.

In addition, these cells show a few lateral dendrites that project to the outer plexiform layer (region connecting the photoreceptor cells). (region connecting photoreceptor cells and bipolar cells).

The morphology of the mitral cells has been an advantage in the first synaptic processing studies carried out since it is possible to independently stimulate both the soma and the main dendrite by means of electrodes conveniently placed in different layers of the olfactory bulb.

Main functions

Once the information coming 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 in the main olfactory information processing nucleus? These are the main functions carried out by the olfactory bulb:

1. odor differentiation 2.

The olfactory bulb is mainly in charge of distinguishing between different types of odors.. This differentiation is carried out through different patterns of activation of neurons responsible for olfactory perception, which react according to the odor perceived and the shape and structure of the olfactory particles.

2. Emotional processing of information

The amygdala, the main emotion control center of the brain, has connections with the olfactory bulb both directly and indirectly, via the primary olfactory cortex or piriform cortex, and allows certain emotions to be linked to specific olfactory stimuli..

In addition, our sense of smell, unlike other senses such as sight or hearing, does not need to relay in the thalamus; that is why its connection with the limbic system is more direct, generating more powerful and explicit connections, which makes it easier for us to evoke intense memories of past experiences through smells.

3. Taste perception

The senses of smell and taste are closely related and interconnected.. Many times, we have the sensation that we are tasting something when we are simply smelling.

In this sense, the olfactory bulb also plays a relevant role in taste perception by this very fact. An example of how these two senses relate to each other is the inability of people suffering from anosmia (loss of the sense of smell) to pick up flavors.

Synaptic connections with other cells

The mitral cells play a significant role in the circuitry of the olfactory bulb, as they receive information from at least four cell types: olfactory sensory neurons, external tuft 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 external tuft cells. In addition, they also receive inhibitory signals from granule cells on their lateral dendrites or on in their lateral dendrites or in the soma, and from periglomerular cells in the dendritic tuft.

It appears from research that tufted cells receive strong innervation from the olfactory nerve and fire their action potentials near the onset of inhalation and their firing frequency is relatively insensitive to odor concentration; in contrast, mitral cells receive little innervation from the olfactory nerve and strong periglomerular inhibition (from around the glomeruli), which delays their firing relative to tufted cells.

One hypothesis in animals is that the mitral cells transform the olfactory signal strength transform the strength of the olfactory signal into a synchronized code, where odor concentration is encoded in the firing frequency of action potentials relative to the inhalation cycle.

Bibliographical references:

• Bradford, H.F. (1988). Fundamentals of Neurochemistry. Labor.
• Dhawale et.al (2010) Non-redundant odor coding by sister mitral cells revealed by light addressable glomeruli in the mouse. Nature Neuroscience 13, pp. 1404 - 1412.