ABSTRACT
The axons of the olfactory receptor neurons (ORNs) run in the olfactory nerve to make excitatory synapses on the dendrites of mitral cells or tufted cells and short axon periglomerular cells in the olfactory bulb. Olfactory bulb circuitry mediates at least two kinds of activity: Interglomerular processing enhances contrast between neighboring glomeruli and intraglomerular processing involves positive feedback to enhance signals in mitral cells or tufted cells (M/T) cells within a glomerulus. A large part of the olfactory cortex is the pyriform cortex. This is concerned with olfactory discrimination. It send axons which terminate in the medial dorsal thalamus, which in turn projects to the orbitofrontal cortex. This cortex mediates the conscious perception of smell. Olfactory processing is subject to considerable modulation. The olfactory bulb receives inputs from noradrenergic and serotonergic neurons in the brainstem and cholinergic neurons in the forebrain.
