Olfactory

Olfactory glands (Bowman glands) secrete a fluid that bathes the cilia of the receptors and acts as a solvent for odorant molecules.

Reside in the nasal cavity.
Olfactory receptor cells (first-order neurons) are stimulated by the binding of odor molecules to their cilia

G protein activation and activation of adenylyl cyclase → a rise in intracellular cAMP → causes opening of a cyclic-nucleotide gated ion channel → influx of Na+ and Ca2 + causing neuronal depolarization.
The axons of the olfactory receptor cells form CN I (olfactory nerve); these project through the cribriform plate at the base of the cranium to synapse with the mitral cells of the olfactory bulb in olfactory glomeruli.

The map of glomerular activation patterns within the olfactory bulb are thought to represent the quality of the odor being detected.

The mitral cells of the olfactory bulb are excitatory
The output axons of the mitral cells form the olfactory tract + lateral olfactory stria, both of which project to the primary olfactory cortex (prefrontal cortex) and the amygdala.
Because the olfactory bulb is composed of secondary, rather than primary, sensory neurons, it is, strictly speaking, a central nervous system (CNS) tract and not a cranial nerve.

Cortical brain regions which receive the mitral and tufted cell axon projections.

A predominantly two-layered cortical-like structure with connections to the olfactory tract.
Has an

Reciprocally connects with a number of brain regions involved with behaviour and emotion and is critical for processing basic olfactory information.
Learning and memory of odors
Encodes representations of odor quality, identity, familiarity, and hedonics (plesure/displeasure).
Multisensory integration

For example, piriform activity becomes elicited by visual stimuli after they are paired with a pleasant food odor.

When food associated with the odor is eaten to satiety, this response is attenuated.

Amygdala is positioned deep within the medial temporal lobe.
It is closely and reciprocally related to the hypothalamus, and is intimately associated with sympathetic nervous system activity and emotion, such as fear.
Its connections with the ventral tegmental area, locus coeruleus, and laterodorsal tegmental nucleus influence the release of such neurotransmitters as dopamine, norepinephrine, and epinephrine.
Recent neuroimaging studies suggest that the amygdala responds to the intensity of emotionally significant, that is, pleasant or unpleasant, odors.

The most caudal temporal lobe region that receives axonal projections from the olfactory bulb is the lateral entorhinal cortex.
This six-layered cortex is a transitional cortex between the three-layered allocortex and the six-layered neocortex.
This brain region has strong reciprocal connections with the piriform cortex.
It preprocesses information entering the hippocampus and is intimately involved in learning and memory.

In animals, conditioned odor-aversion learning is disrupted by lesions of the medial or lateral entorhinal cortex.

Definition: Cortical regions receiving projections from the primary olfactory cortex.

The structure most commonly termed secondary olfactory cortex in humans is the Orbitofrontal cortex.

Receives projections from, and sends projections to, all primary olfactory regions,

In addition to these direct connections, the orbitofrontal cortex also reciprocally connects to a number of these structures via the dorsomedial nucleus of the thalamus.

This cortical region has extensive connections with brain regions associated with vision, touch, taste, and visceral sensations, providing cross-modal integration and associative learning.

In addition to integrating food-related and odor-guided behaviours, the orbitofrontal cortex is intimately associated with judgments of odour familiarity, intensity, hedonicity, and quality, and facilitates the perception of flavour sensations