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

• Related article: "Types of neurons: characteristics and functions"

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.

Sensory neuron processes 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 bulb olfactory. in this structure information is received primarily by two cell types: mitral cells and tufted cells.

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

Olfactory bulb and glomeruli

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

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 neuronal bodies) of the glomeruli olfactory.

After the olfactory bulb, the axons of the mitral cells transmit information to other areas of the brain.. Among these regions, it is worth highlighting the piriform cortex, the area responsible for detecting odors and involved in storing memories; the amygdala, the main nucleus of emotion control; and the entorhinal cortex, related to memory, smell and orientation.

• You may be interested in: "Olfactory bulb: definition, parts and functions"

mitral cell morphology

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. Generally, they usually show a single primary dendrite (extension of the neuron dedicated to receiving nerve impulses from other neurons) that projects to a single glomerulus.

Besides, this type of cells show a few lateral dendrites that project to the outer plexiform layer (region connecting photoreceptor cells and bipolar cells).

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

Principal functions

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

But what happens in the main olfactory information processing nucleus? These are the main functions carried out by the olfactory bulb:

1. odor differentiation

the olfactory bulb It is mainly responsible for distinguishing between different types of odors. This differentiation is made through different patterns of activation of neurons responsible for the olfactory perception, which react depending on the smell perceived and the shape and structure of the particles olfactory.

2. Emotional information processing

The amygdala, the brain's main emotion control center, has connections to the medulla. olfactory both directly and indirectly, through the primary olfactory cortex or cortex piriformis, and 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 take over from 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 the smells.

3. taste perception

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

In this sense, the olfactory bulb also plays a relevant role in the perception of flavor due to this very fact. An example of how these two senses are related to each other is the inability of people suffering from anosmia (loss of the sense of smell) to capture flavors.

Synaptic connections with other cells

The mitral cells have a significant role in the olfactory bulb connection circuit, since they receive information from at least four cell types: olfactory sensory neurons, outer tuft cells, periglomerular neurons, and cells granular. 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 tuft cells. In addition, they also receive inhibitory signals from granule cells. in their lateral dendrites or in the soma, and from periglomerular cells in the dendritic tuft.

Apparently and according to the investigations, the tufted cells receive a strong innervation from the olfactory nerve and fire their action potentials near the onset of inhalation and their firing frequency is relatively insensitive to the concentration of smells; instead, mitral cells receive little innervation from the olfactory nerve and strong inhibition periglomerular (from around the glomeruli), which delays their firing with respect to cells in plume.

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

Bibliographic references:

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