Nerve
Olfactory nerve (CN I)
Receptor axons connecting the nose to the olfactory bulb
High-yield
Olfactory information can reach primary olfactory cortex without an obligatory first relay in the thalamus; later processing does involve thalamic connections. Injury near the cribriform plate may impair smell, but neither permanent anosmia nor a CSF leak is inevitable.
Overview
Smell begins in receptor neurons in the upper nasal olfactory epithelium. Their fine unmyelinated axons collect into bundles called olfactory fila and pass through the ethmoid cribriform plate. They synapse within olfactory-bulb glomeruli. These peripheral receptor axons should be distinguished from the bulb and tract, which are parts of the brain.
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Reference facts
- Origin
- Bipolar receptor neurons in olfactory epithelium high in the nasal cavity; their first central connections are with bulb neurons, including mitral and tufted cells.
- Skull exit
- Multiple openings in the cribriform plate transmit the fila into the anterior cranial fossa.
- Course
- Receptor axons end in the bulb. Bulb projection neurons form the olfactory tract, whose branches connect with piriform and other olfactory-associated cortical and limbic regions.
- Motor
- No skeletal motor or glandular motor supply is assigned to CN I.
- Sensory
- Smell from olfactory epithelium near the nasal roof, superior concha and upper septum. Trigeminal pathways separately detect irritation and general sensation, so an irritant response does not establish intact olfaction.
Mnemonic
Follow the smell pathway: nasal receptor → cribriform plate → olfactory bulb → olfactory cortex.
Clinical correlation
Head trauma, nasal disease and several neurological disorders can reduce smell. Cribriform-region injury may also tear the barrier containing CSF; a persistent leak increases infection risk. Loss of smell changes perceived food flavor, although basic taste can remain. Olfactory-groove masses can compress the bulb or tract.
Frequently asked questions
Where does the olfactory nerve (CN I) arise?
Bipolar receptor neurons in olfactory epithelium high in the nasal cavity; their first central connections are with bulb neurons, including mitral and tufted cells.
What muscles does the olfactory nerve (CN I) supply?
No skeletal motor or glandular motor supply is assigned to CN I.
What is the sensory distribution of the olfactory nerve (CN I)?
Smell from olfactory epithelium near the nasal roof, superior concha and upper septum. Trigeminal pathways separately detect irritation and general sensation, so an irritant response does not establish intact olfaction.
Where does the olfactory nerve (CN I) leave the skull?
Multiple openings in the cribriform plate transmit the fila into the anterior cranial fossa.