Olfactory Nerve

Structure

• The olfactory nerve, or cranial nerve I, is unique among cranial nerves.
• It's composed of sensory nerves for smell.

Origin

• Originates in the olfactory epithelium in the upper part of the nasal cavity.

Pathway

• Axons pass through the cribriform plate of the ethmoid bone.
• They end in the olfactory bulb on the inferior surface of the frontal lobe.

Segments of the Olfactory Nerve

Segment Name	Path	Involved Cisterns	Length (Approx.)	Blood Supply
Olfactory Receptor Neurons	Located in the olfactory epithelium of the nasal cavity.	Not applicable, as this segment is extracranial.	Variable, depends on nasal cavity size.	Branches of the anterior ethmoidal artery, a branch of the ophthalmic artery.
Olfactory Filaments	Pass through the cribriform plate of the ethmoid bone.	Not directly associated with any specific cistern but traverse from nasal cavity to cranial cavity.	Around 2 cm (varies).	Supplied by small branches from the anterior ethmoidal artery.
Olfactory Bulb	Situated on the inferior surface of the frontal lobe, immediately above the cribriform plate.	Lies within the anterior cranial fossa, no specific cistern involved.	Approximately 1-1.5 cm in length.	Anterior cerebral artery (ACA), specifically the fronto-orbital branch. Anterior ethmoidal artery also contributes.
Olfactory Tract	Extends posteriorly from the olfactory bulb.	Located in the subarachnoid space, no specific cistern involved.	About 2-3 cm in length.	Primarily supplied by the anterior cerebral artery, particularly its orbital frontal branches.

Olfactory Bulb

• The olfactory bulb is part of the brain where the olfactory nerves begin.
• It processes odor information and sends it to the brain.

Intracranial Course

• From the olfactory bulb, the olfactory tract extends posteriorly.
• The tract divides into medial and lateral striae.

Central Connections

• The medial striae connect to the contralateral olfactory area.
• The lateral striae project to the ipsilateral primary olfactory cortex.

Clinical Significance

• Anosmia, loss of smell, can occur with damage to the olfactory nerves.
• Important in assessing frontal lobe lesions and skull base fractures.