the first cranial nerve, or
simply CNI, carries the
sensory information for the
sense of smell. Derived from
the embryonic nasal
placode, the olfactory nerve
is capable of regeneration.
The olfactory nerve is
sensory in nature and
originates on the olfactory
mucosa in the anterosuperior
Lesions to the olfactory nerve can occur
because of blunt trauma, such as coupcontra-coup damage, meningitis, and tumors
of the frontal lobe. They often lead to a
reduced ability to taste and smell.
However, lesions of the olfactory nerve do
not lead to a reduced ability to sense pain
from the nasal epithelium. This is because
pain from the nasal epithelium is not carried
to the central nervous system by the
olfactory nerve; rather, it is carried to the
central nervous system by the trigeminal
(cranial nerve V).
|is the inability to perceive odor, or
in other words a lack of functioning
olfaction. Anosmia may be
temporary but traumatic anosmia
can be permanent. Anosmia is due
to an inflammation of the nasal
mucosa; blockage of nasal passages
or a destruction of one temporal
Damage to this nerve impairs the
sense of smell. To test the function
of the olfactory nerve, doctors
block one of the patient's nostrils
and place a pungent odor (such as
damp coffee essence) under the
open nostril. The test is then
repeated on the other nostril. If the
patient can smell the coffee, not
necessarily identify what it is, the
patient’s olfactory nerve is
The optic nerve, also known as
cranial nerve II, transmits visual
information from the retina to the
brain. Derived from the embryonic
retinal ganglion cell, a diverticulum
located in the diencephalon, the
optic nerve does not regenerate
Damage to the optic nerve typically causes permanent and potentially severe loss of vision, as
well as an abnormal pupillary reflex, which is diagnostically important. The type of visual field
loss will depend on which portions of the optic nerve were damaged. In general:
Damage to the optic nerve anterior to the optic chiasm causes loss of vision in the eye on the
same side as the damage.
Damage in the optic chiasm causes loss of vision laterally in both visual fields (bitemporal
hemianopsia). It may occur in large pituitary adenoma.
Damage to the optic tract posterior to the chiasm causes loss of vision in the visual field on the
side opposite to the damage.
Injury to the optic nerve can be the result of congenital or inheritable problems like Leber's
Hereditary Optic Neuropathy, glaucoma, trauma, toxicity, inflammation, ischemia, infection
(very rarely), or compression from tumors or aneurysms. By far, the three most common injuries
to the optic nerve are from glaucoma, optic neuritis (especially in those younger than 50 years
of age), and anterior ischemic optic neuropathy (usually in those older than 50).
Glaucoma is a group of diseases involving loss of retinal ganglion cells causing optic neuropathy
in a pattern of peripheral vision loss, initially sparing central vision.
Optic neuritis is inflammation of the optic nerve. It is associated with a
number of diseases, the most notable one being multiple sclerosis.
Anterior Ischemic Optic Neuropathy is a particular type of infarct that affects
patients with an anatomical predisposition and cardiovascular risk factors.
Optic nerve hypoplasia is the underdevelopment of the optic nerve causing
little to no vision in the affected eye.
Ophthalmologists and optometrists can detect and diagnose some optic
nerve diseases but, those sub-specialists that are neuroophthalmologists, are often best suited to diagnose and treat diseases of the
The International Foundation for Optic Nerve Diseases (IFOND) sponsors
research and information on a variety of optic nerve disorders and may
provide general direction.
known as the eighth cranial
nerve, transmits sound and
equilibrium (balance) information
from the inner ear to the brain. The
vestibulocochlear nerve is derived
from the embryonic otic placode.
Damage to the vestibulocochlear nerve
may cause the following symptoms:
1- hearing loss
3- false sense of motion
4- loss of equilibrium (in dark places)
6- motion sickness
7- gaze-evoked tinnitus.