OLFACTORY NERVE

Olfactory nerve or nerve of smell is the first cranial nerve.


ORIGIN

It originates as the central process of olfactory receptor nerve cells in the mucous membrane of upper part of the nose(above the superior concha).

OLFACTORY BULB

Bundles of these nerve fibers pass through openings in the cribriform plate of ethmoid bone and end in the olfactory bulb in the anterior cranial fossa.


OLFACTORY TRACT
Emerging from the posterior end of olfactory bulb is a white band the olfactory tract which passes backward to the olfactory area of cerebral cortex.


PRIMARY OLFACTORY CORTEX

The second order neurons (mitral cells) project centrally together with pyramidal cells of olfactory nucleus down olfactory tracts and stria to Primary olfactory cortex (medial temporal lobe) and ipsilateral amygdaloid body anterior perforated substance and septial area.

The primary olfactory cortex has numerous connections with hypothalamus reticulatr system, limbic lobe.

TESTING THE SENSE OF SMELL

· Check that nasal passages are clear
· Test sense of smell for each nostril separately
· Occlude one nostril by digital pressure
· Ask patient with closed eyes to sniff and identify the substance

INTERPRETATION
ANOSMIA:
It means loss of sense of smell; commonest cause is obstruction of nasal passages. If due to neurological lesion it may be due to
· Head injury
· Tumors of anterior cranial fossa
· Tuberculous meningitis
PAROSMIA:
It is the perversion of smell. Offensive smells are perceived as pleasant and vice versa.
Cause
Psychogenic in origin

HALLUCINATION:
Sometimes occur in temporal lobe palsy.