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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