Olfactory nerve

CRANIAL NERVES

-NITHIN NAIR

INTRODUCTION

• Cranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves, which emerge from segments of the spinal cord. In humans, there are traditionally twelve pairs of cranial nerves. Only the first and the second pair emerge from the cerebrum; the remaining ten pairs emerge from the brainstem

SIGNIFICANCE OF CRANIAL NERVE EXAMINATION

Important part of neurological examination.

Cranial nerve can get affected by primary disease of cranial nerve or by disease of brain or meninges

Each nerve may get affected in its intracranial or extracranial course

OLFACTORY NERVE

OBJECTIVES Anatomy and functions

Purpose of the test

How to test

Interpretations

Anatomy and functions

First cranial nerve -- concerned with sense of smell.

RECEPTORS AND THE FIRST NEURON

• The olfactory cells – bipolar neurons.

• Lie in the olfactory part of the nasal mucosa, serve both as receptors and first neurons in the olfactory pathway.

SECOND NEURON

• The mitral and tufted cells in the olfactory bulb --- fibres that form olfactory tract and reach primary olfactory areas (BA 28, 34)

THIRD NEURON• Located in the primary olfactory cortex –

includes the anterior perforated substance and small masses of grey matter around it.

FOURTH NEURON

• Fibres arising in primary olfactory cortex go to secondary olfactory cortex (or entorhinal area) located in uncus and anterior part of parahippocampal gyrus.

• Smell is perceived– primary and secondary olfactory areas.

• Some impulses from uncus travel via medial forebrain bundle and reticular formation to dorsal nucleus of vagus and salivatory nuclei in medulla oblongata.

OLFACTORY PATHWAY• Olfactory epithelium of nose olfactory ⇨

rootlets olfactory bulb lateral and medial ⇨ ⇨olfactory striae.

• Lateral olfactory stria pyriform lobe⇨

• Medial olfactory stria septal nuclei⇨

PURPOSE OF THE TEST

• To localize whether the loss of smell if any is due to pathology of the nose or is due to neural lesion.

• To determine whether any impairment of the sense of smell is unilateral or bilateral.

HOW TO TEST

PROCEDURE

INTERPRETATIONS

INTERPRETATIONS• Those who recognize and name

the odours quickly(usually women)

• Those who recognize, but cannot name them(usually men)

• Those who can detect a smell, and easily distinguish differences, but can neither recognize or name them.

NORMAL

INTERPRETATIONS

• The following terms are used to describe the degree of smell aberration

1) Anosmia: Absence of smell sensation.2) Hyposmia: Diminished sense of smell.3) Parosmia: Peverted sense of smell.4) Cacosmia: Perception of unpleasant odour in

the absence of olfactory stimuli.

INTERPRETATIONS

5) Hyperosmia: Acute sense of smell (lowered threshold of odour)

6) Presbyosmia: Decrease in sense of smell due to aging

7) Coprosmia: Cacosmia with a fecal sent.8) Phantosmia: Perception of smell that is not

real.

CAUSES OF ANOSMIA• Nasal polyps• Viral URTI• Rhinitis• Head trauma• Meningitis• Heavy smoking• Radiation • Zinc deficiency• Tumors of anterior

cranial fossa

• Subarachnoid haemorrhage

• Parkinson’s disease• Hypothyroidism• Kallmann syndrome• Hysteria• Idiopathic

References...BD CHAURASIA’S HUMAN ANATOMYNEUROLOGICAL EXAMINATION BY

NAVNEET KUMARBICKERSTAFF’S NEUROLOGICAL

EXAMINATIONNEUROLOGICAL EXAMINATION MADE

EASY – GERAINT FULLERPJ MEHTA’S PRACTICAL MEDICINEPRACTICAL PHYSIOLOGY – VD JOSHIWWW.GOOGLE.COM