The Olfactory Nerve (CN I)
The Olfactory Nerve (CN I)
Objectives
By the end of these revision notes, you should:
The Basics
Anatomy of the Olfactory Nerve
The olfactory nerve consists of specialised sensory neurones located in the nasal cavity that extend directly into the brain. The pathway of the olfactory nerve can be divided into three main regions: the olfactory epithelium, the olfactory bulb, and the olfactory tract.
The olfactory epithelium
The olfactory epithelium is located in the upper part of the nasal cavity. It is composed of pseudostratified columnar epithelium and contains olfactory receptor neurones. These have tiny hair-like projections, known as cilia, that detect molecules dissolved in the mucous – this will trigger a smell. The olfactory epithelium also includes supporting cells and basal cells that replenish olfactory neurones.
The axons of the olfactory receptor neurones converge to form small bundles known as the olfactory nerve filaments. These filaments pass through tiny openings in the cribriform plate of the ethmoid bone to reach the olfactory bulb.
The olfactory bulb
The olfactory bulb is located on the ventral surface of the frontal lobe, just above the cribriform plate. Within the bulb, olfactory receptor neurones synapse with other neurones, including mitral and tufted cells, in structures called glomeruli. The glomeruli act as processing units for different smell signals.
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