Olfactory (I) Nerve

OLFACTORY NERVE: Ist CRANIAL NERVE

• Special visceral afferent nerve 
• Mediates sense of smell (olfaction).
• Pure sensory nerve.

Olfactory nerve has following unique features:-

1. The primary olfactory neurons lie at the body surface in the epithelium lining the roof of nasal cavity (olfactory epithelium).
2. The primary olfactory neurons undergo continuous turnover being replaced from stem cells in the olfactory epithelium.
3. It is the only cranial nerve that projects directly to forebrain (telencephalon).
4. The olfactory neurons enter the allocortex directly without relaying through thalamus.
5. The olfactory pathway to highest cortical center is ipsilateral.

Termination– Glomerulus of the olfactory bulb.

Olfactory Pathway:

First order neuron

(Present in olfactory epithelium)

Olfactory nerve

↓

Second order neuron

(Present in olfactory bulb)

↓

Olfactory tract

↓

Ends in Pre-piriform & piriform cortex

(Primary olfactory cortex)

Receives smell sense

↓

Uncus & para hippocampus

(Secondary olfactory cortex)

↓

Receives smell sense

APPLIED ANATOMY:

1. During fracture of anterior cranial fossa- olfactory nerves may separate from olfactory bulb and cerebrospinal fluid (C.S.F) leaks through nose-Rhinorrhoea.
2. Anosmia- loss of smell sensation-eg. in Rhinitis.
3. Parosmia– Preverted sense of smell.
4. Caprosmia-unpleasent odour due to decomposition of the tissue of the individiual- bad smell is felt during expiration.

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