FIRST CRANIAL NERVE - OLFACTORY

1. CRANIAL NERVES
-NITHIN
NAIR

2. 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

4. 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

5. OLFACTORY NERVE

6. OBJECTIVES
 Anatomy and functions
 Purpose of the test
 How to test
 Interpretations

7. Anatomy and functions
First cranial nerve -- concerned with sense of smell.

8. 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.

9. 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.

11. 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.

14. 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

17. 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.

18. HOWTO TEST

19. PROCEDURE

20. INTERPRETATIONS

21. 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

22. 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.

23. 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.

24. 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

25. References...
BD CHAURASIA’S HUMAN ANATOMY
NEUROLOGICAL EXAMINATION BY
NAVNEET KUMAR
BICKERSTAFF’S NEUROLOGICAL
EXAMINATION
NEUROLOGICAL EXAMINATION MADE
EASY – GERAINT FULLER
PJ MEHTA’S PRACTICAL MEDICINE
PRACTICAL PHYSIOLOGY – VD JOSHI
WWW.GOOGLE.COM