Question #508
The first cranial nerve
The first cranial nerve is often referred to as the olfactory nerve. However, the “cranial nerve” component is not actually a nerve but rather an extension of the forebrain that is covered in meningeal layers (and therefore also CSF). The most proximal portion is called the olfactory tract, it passes forwards on the ethmoid bone to the cribriform plate where it swells and forms the olfactory bulb.
The olfactory bulb receives multiple olfactory nerves from the olfactory mucosa of the upper posterolateral nasal cavity. It is these olfactory nerves that pass through the cribriform plate and not the “cranial nerve”.
The first cranial nerve is the shortest of the cranial nerves (the trochlear nerve has the longest intracranial course, the vagus nerve the longest extracranial course and the trigeminal is the thickest cranial nerve).