Olfactory system

Résumé

The olfactory system, or sense of smell, is the sensory system used for smelling (olfaction). Olfaction is one of the special senses, that have directly associated specific organs. Most mammals and reptiles have a main olfactory system and an accessory olfactory system. The main olfactory system detects airborne substances, while the accessory system senses fluid-phase stimuli. The senses of smell and taste (gustatory system) are often referred to together as the chemosensory system, because they both give the brain information about the chemical composition of objects through a process called transduction. Structure Peripheral The peripheral olfactory system consists mainly of the nostrils, ethmoid bone, nasal cavity, and the olfactory epithelium (layers of thin tissue covered in mucus that line the nasal cavity). The primary components of the layers of epithelial tissue are the mucous membranes, olfactory glands, olfactory neurons, and nerve fibers of the olfa

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https://en.wikipedia.org/wiki/Olfactory_system

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Structure and function of the olfactory bulb microcircuit

Michele Pignatelli

The aim of this study is to contribute to understand the physiology of the Olfactory System through detailed microcircuit investigation, adopting advanced electrophysiological and anatomical techniques. Multiple patch clamp recordings allow understanding the structural foundations supporting the network architecture, the biophysical rules adopted by the microcircuit connectivity and the fine dynamic of the synaptic transmission. The study focuses on the Olfactory Bulb microcircuit as a first neuronal processor of sensory inputs. The excitatory elements of the Olfactory Bulb microcircuit are anatomically defined by affiliation to the same receptive field: the Glomerulus. A correlated subthreshold activity between microcircuit elements defines the physiological signature of the microcircuit. We experimentally addressed three fundamental issues: origin of the correlated subthreshold activity, connectivity rules and dynamic of the synaptic transmission. In the first study we attribute the origin of correlated subthreshold activity to a class of pacemaker cells responsible for the synchronization of the population onset and acting therefore as a timer of the microcircuit response. In the second study we investigated the connectivity rules supporting the interaction between excitatory cells. The tight apposition between gap junctions and chemical synapses on the excitatory cells dendrites allows gap junctions to propagate postsynaptic potentials toward surrounding compartments. The result of the propagation is represented by an enhancement in the amplification of the sensory information and an increase in the speed of the reaction time. In the third study we extensively analyzed the mechanisms of the synaptic transmission and the activity dependent properties of synapses, revealing a potential role for the short-term plasticity in the development of the sensory processing. The results of our investigation are going to constitute the foundation of a database available for high definition multi-compartmental modeling of the Olfactory Bulb network.

EPFL2009

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Much information is conveyed to animals by the diverse molecules propagated in their environment. This information is transmitted and treated within the olfactory system to be utilized by the rest of the brain. In this process, the sensory flow arriving from the nose first encounters the olfactory bulb. This thesis studies different aspects of the encoding and treatment of olfactory information in the bulb by a combination of experimental and theoretical approaches. The olfactory bulb consists of two functional stages: an input stage where the nerve terminals from the sensory neurons of the nose are spatially arranged in a precise manner, and an output stage corresponding to the neurons which propagate the processed information towards the more central brain areas. The first part of this thesis is focused on the development of an image processing technique to precisely map the input stage. In a second part, output neurons activity in responsive areas of the bulb was recorded in anaesthetized mice. The data obtained indicate complex dynamics in neural activity on several time scales. We show that the combination of mean firing rates from a large enough ensemble of neurons allows to accurately predict the odor presented to the animal. We also show that temporal variables related to the dynamics give very little information complementary to the ensemble rate code, suggesting that these variables are not read by brain structures downstream to the bulb. In a third part, we developed a numerical model of the olfactory bulb to understand its fast oscillatory dynamics. The model proposes a mechanism based on the negative feedback from the interneurons that regulate output neurons. Some predictions of the model are checked experimentally. An analytical interpretation of the model is also proposed and its generalization to the analysis of fast oscillation in other parts of the brain is discussed.

EPFL2007

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Towards a Canonical Microcircuit of the Olfactory Bulb

Michele Pignatelli

2009

Chargement

Structure and function of the olfactory bulb microcircuit

Michele Pignatelli

EPFL2009