Système olfactif: Neurones récepteurs

Local Wiring in the Olfactory System

• The olfactory system has a unique, highly organized structure. Olfactory receptor neurons (ORNs) project directly to the olfactory bulb, a non-synaptic pathway distinct from other sensory systems.
• ORNs with the same receptor type cluster to form glomeruli, synapse clusters in the olfactory bulb. This organized arrangement allows for the encoding of diverse odor qualities.
• Individual glomeruli receive input from specific ORN types expressing a single receptor type.

Olfactory Receptor Neurons (ORNs)

• ORNs are bipolar sensory neurons located in the olfactory epithelium, a specialised tissue lining the nasal cavity.
• Their apical dendrites contain cilia, highly sensitive structures interacting with odor molecules.
• Odor binding to receptors on the cilia initiates a signaling cascade leading to action potentials in the ORN axon, initiating the sensory signal.
• Each ORN expresses only one type of olfactory receptor (OR). The diversity of OR genes facilitates the detection of a wide range of odorants.

Olfactory Receptors (ORs)

• ORs are a large family of G protein-coupled receptors (GPCRs). They detect odorant molecules within the nose.
• Odorant binding to an OR triggers a cascade of intracellular signaling events.
• Different OR types are activated by unique odorants, allowing the olfactory system to distinguish various odor qualities.
• The vast array of OR types permits the olfactory system's remarkable ability to differentiate numerous odors.

Glomerular Organization

• Glomeruli are spherical clusters of synapses within the olfactory bulb.
• Each glomerulus receives input from ORNs expressing a specific olfactory receptor (OR) which often respond selectively to particular subsets of odor molecules.
• Glomerular arrangement creates a spatial representation of odors in the olfactory bulb, with similar odorants activating nearby glomeruli.
• The spatial pattern of neuronal activity within glomeruli defines the unique characteristics of an odor.

Olfactory Circuitry

• ORN axons project to the olfactory bulb, forming synaptic connections with neurons within the glomeruli.
• Interneurons within the olfactory bulb further process the olfactory signal.
• Signals then travel from the olfactory bulb to various brain regions, including the piriform cortex, amygdala, and entorhinal cortex.
• These brain regions are crucial for odor perception, memory formation, and emotional responses.
• The precise pathway and processing of olfactory information remain areas of ongoing research.

Importance of Local Wiring

• The organized local wiring within the olfactory system is crucial for efficient odor processing.
• The specific signal processing within glomeruli is essential for recognizing and discriminating different odors.
• It permits rapid transmission of olfactory information from the periphery to the brain, vital for survival behaviors and adaptive responses.
• The direct pathway and glomerular organization optimize odor information encoding.