Cranial Nerves I, II, V, VII
CN I: The Olfactory Nerve
•First cranial nerve
•Unique - Constituting the only examples of
neuronal regeneration in humans
- The olfactory cells = Receptor cells =
Bipolar neurons
- Olfactory impulses reach the cerebral
cortex without relay through the thalamus
The primary olfactory cortex=medial and
cortical nuclei of the amygdaloid complex
and the prepiriform area
↓
Connected with the neighboring entorhinal
cortex and medial dorsal nucleus of the talamus
•To be perceived as an odor, an inhaled sustance must be volatile
Disturbances of olfaction
1. Quantitative abnormalities: anosmia, hyposmia, hyperosmia
2. Qualitative abnormalities: distortions or illusions of smell – dysosmia or parosmia
3. Olfactory halucinations
4. Olfactory agnosia
Anosmia
•If unilateral – usually not recognized by the patient
•Categories –
Nasal: odorants do not reach the olfactory receptors - hypertrophy and hyperemia of the
nasal mucosa (heavy smoking, chronic rhinitis and sinusitis)
1
, - Neuroepithelial: destruction of receptors or their axon filaments – influenza, herpes
simplex, hepatitis virus infections; local radiation therapy; esthesioneuroblastoma;
Kallman syndrome; toxic agents (benzen); head injury
- Central: olfactory pathway lesions, head injury, tumors, aneurysms
The Foster Kennedy syndrome
•A meningioma of the olfactory groove may implicate the olfactory bulb and tract and
may extend posteriorly to involve the optic nerve
•Clinical - ipsilateral: anosmia and optic atrophy
- Opposite site: papilledema
Anosmia or hyposmia in Parkinson disease and Multiple sclerosis – for reasons that are
quite unclear
Hyperosmia
•Migraine attacks, aura in epilepsy, neurotic individuals
Dysosmia or Parosmia
•Pervertion of the sense of smell - in local nasopharingeal conditions such as empyema
of the nasal sinuses – ex: cacosmia and cacogeuzia in ozena
- In middle-aged and elderly persons with depression
Olfactory halucinations
•Are always of central origin
•Episodic – in temporal lobe seizures or as aura in epilepsy
•In combinations with delusions – in psychiatric illnesses (endogenous in depression and
exogenous in schizophrenia) or in dementia
•In alcohol withdrawal syndrome
2
CN I: The Olfactory Nerve
•First cranial nerve
•Unique - Constituting the only examples of
neuronal regeneration in humans
- The olfactory cells = Receptor cells =
Bipolar neurons
- Olfactory impulses reach the cerebral
cortex without relay through the thalamus
The primary olfactory cortex=medial and
cortical nuclei of the amygdaloid complex
and the prepiriform area
↓
Connected with the neighboring entorhinal
cortex and medial dorsal nucleus of the talamus
•To be perceived as an odor, an inhaled sustance must be volatile
Disturbances of olfaction
1. Quantitative abnormalities: anosmia, hyposmia, hyperosmia
2. Qualitative abnormalities: distortions or illusions of smell – dysosmia or parosmia
3. Olfactory halucinations
4. Olfactory agnosia
Anosmia
•If unilateral – usually not recognized by the patient
•Categories –
Nasal: odorants do not reach the olfactory receptors - hypertrophy and hyperemia of the
nasal mucosa (heavy smoking, chronic rhinitis and sinusitis)
1
, - Neuroepithelial: destruction of receptors or their axon filaments – influenza, herpes
simplex, hepatitis virus infections; local radiation therapy; esthesioneuroblastoma;
Kallman syndrome; toxic agents (benzen); head injury
- Central: olfactory pathway lesions, head injury, tumors, aneurysms
The Foster Kennedy syndrome
•A meningioma of the olfactory groove may implicate the olfactory bulb and tract and
may extend posteriorly to involve the optic nerve
•Clinical - ipsilateral: anosmia and optic atrophy
- Opposite site: papilledema
Anosmia or hyposmia in Parkinson disease and Multiple sclerosis – for reasons that are
quite unclear
Hyperosmia
•Migraine attacks, aura in epilepsy, neurotic individuals
Dysosmia or Parosmia
•Pervertion of the sense of smell - in local nasopharingeal conditions such as empyema
of the nasal sinuses – ex: cacosmia and cacogeuzia in ozena
- In middle-aged and elderly persons with depression
Olfactory halucinations
•Are always of central origin
•Episodic – in temporal lobe seizures or as aura in epilepsy
•In combinations with delusions – in psychiatric illnesses (endogenous in depression and
exogenous in schizophrenia) or in dementia
•In alcohol withdrawal syndrome
2
