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Type:
Educational Exhibit
Keywords:
Neuroradiology brain, MR, Education, Education and training
Authors:
A. I. Fernández Martín1, E. Dominguez Franjo2, N. Alegre Borge3, A. Paniagua Bravo1, L. Ibañez Sanz1, J. C. Paniagua4; 1Madrid/ES, 2Arganda del Rey/ES, 3San Sebastián de los Reyes/ES, 4Salamanca/ES
DOI:
10.1594/ecr2015/C-1732
Background
There are twelve cranial nerves numbered in order as they emerge from cranial to caudal in the brain.
These are: olfactory (I),
optic (II),
oculomotor (III),
trochlear (IV),
trigeminal (V),
abducens (VI),
facial (VII),
vestibulocochlear(VIII),
glosopharyngeal (IX),
vagus (X),
accesory (XI) and hypoglossal(XII) nerves.
The I and II cranial nerves are not true nerves but extensions of the brain.
Therefore they are myelinated by oligodendrocytes and not by Schwann cells like the rest of the cranial nerves,
and are covered by meninges.
The neurosensory cells (neurons) of the olfactory nerve are placed in the nasal vault,
whose axons,
fila olfactoria,
traverse the cribiform plate (transethmoidal segment).
It is followed by an intracranial segment in the olfactory sulcus,
where it can be subdivided into olfactory bulb,
tract and cortex.
Optic nerve comprises four segments: intraocular,
intraorbital,
intracanalicular and intracranial.
Afterwards the nerve fibers from the medial half of the retina cross to the opposite side in the optic chiasm.
The remaining cranial nerves can be divided in four segments (intraaxial,
cisternal,
cranial/skull base and extracranial segments) as summarized in the diagrams:
Fig. 1
Fig. 2: IAC = Internal Auditory Canal
ICA = Internal Carotid Artery
Fig. 3: ICA = Internal Carotid Artery