Clinical Neuroanatomy of cranial nerves

1. CRANIAL NERVES
Dr. Chirayu Regmi

2. EMBRYOLOGY
◦ ALAR PLATE [SENSORY]
◦ SULCUS LIMITANS
◦ DORSAL PLATE [MOTOR]

3. THE RULE OF 4
◦ The 4 medial structures are the
motor pathway, medial lemniscus
(ML), medial longitudinal
fasciculus (MLF), and motor
nuclei and nerves.
◦ The 4 lateral (side) structures are
the spinocerebellar tracts,
spinothalamic tract, sensory
nucleus of CN V, and
sympathetics.
◦ The 4 CNs in the medulla are IX,
X, XI, and XII; the 4 in the pons
are V, VI, VII, and VIII; and the
remainder are above the pons.

4. ◦ 1 MN, motor nucleus (3, 4, 6 or 12); 2
MLF, median longitudinal fasciculus; 3
ML, medial lemniscus; 4 MP, motor
pathway (corticospinal tract); 5 SC,
spinocerebellar; 6 SP, spinothalamic; 7
SY, sympathetic; 8 SV, sensory nucleus
of 5th cranial nerve.

5. ◦ The base of the brain

7. ◦ location of the various cell
columns that lie interiorly,
motor nuclei medially, and
sensory nuclei laterally,
separated by the sulcus
limitans.

12. CRANIAL NERVES
◦ 1. Olfactory
◦ 2. Optic
◦ 3. Oculomotor
◦ 4. Trochlear
◦ 5. Trigeminal
◦ 6. Abducens
◦ 7. Facial
◦ 8. Vestlbulocochlear
◦ 9. Glossopharyngeal
◦ IO. Vagus
◦ 11. Accessory
◦ 12. Hypoglossal

13. ◦ The olfactory, optic, and vestlbulocochlear nerves are entirely
sensory.
◦ The oculomotor, trochlear, abducens, accessory, and hypoglossal
nerves are entirely motor.
◦ The trigemlnal, facial, glossopharyngeal, and vagus nerves are both
sensory and motor nerves.

19. OLFACTORY NERVE

20. ◦The olfactory
nerves arise from
the olfactory
receptor nerve
cells in the
olfactory mucous
membrane located
in the upper part
of the nasal cavity
above the level of
the superior
concha.

21. ◦ 6 million olfactory receptor cells are located within a pseudostratified columnar neuroepithelium
lining the cribriform plate/ superior septum/ the middle turbinate, and the superior turbinate.
◦ Each receptor cell consists of a small bipolar nerve cell with a coarse peripheral process that passes to the
surface of the membrane and a fine central process.
◦ From the coarse peripheral process, a number of short cilia arise, the olfactory hairs, which project into
the mucus covering the surface of the mucous membrane. These projecting hairs react to odors in the air
and stimulate the olfactory cells.
◦ The fine central processes form the olfactory nerve. Bundles of these nerve fibers pass through the
openings of the cribriform plate of the ethmoid bone to enter the olfactory bulb. The olfactory nerve
fibers are unmyelinated and are covered with Schwann cells.

22. Olfactory Bulb
◦ Ovoid structure
◦ Several types of nerve
cells, the largest of which
is the mltral cell.
◦ The incoming olfactory
nerve fibers synapse with
the dendrltes of the mltral
cells and form rounded
areas known as synaptic
glomeruli.
◦ Smaller nerve cells, called
tufted cells and granular
cells, also synapse with the
mitral cells.
◦ The olfactory bulb, in
addition, receives axons
from the contralateral
olfactory bulb through the
olfactory tract.

23. Olfactory Tract
◦ Narrow band of white matter runs from the posterior end
of the olfactory bulb beneath the inferior surface of the
frontal lobe of the brain.
◦ Consists of the axons of the mitral and tufted cells of the
bulb and some centrifugal fibers from the opposite
olfactory bulb.
◦ reaches the anterior perforated substance, divides into
medial and lateral olfactory striae.
◦ The lateral stria carries the axons to the olfactory area of
the cerebral cortex, namely, the periamygdalold and
prepiriform areas.
◦ The medial olfactory stria carries the fibers that cross the
median plane in the anterior commissure to pass to the
olfactory bulb of the opposite side.

24. ◦The periamygdaloid and prepiriform areas= primary olfactory cortex.
◦The entorhinal area (area 28) of the parahippocampal gyrus receives
numerous connections from the primary olfactory cortex= secondary
olfactory cortex- responsible for the appreciation of olfactory
sensations.
◦Olfactory afferent pathway has only two neurons and reaches the
cerebral cortex without synapsing in one of the thalamic nuclei.
◦The primary olfactory cortex sends nerve fibers to many other
centers within the brain to establish connections for emotional and
autonomic responses to olfactory sensations.

26. ◦ Some Causes of Persistent Loss of
Smell

27. Foster Kennedy Syndrome
◦ optic atrophy in the ipsilateral eye and papilledema
in the contralateral eye
◦ Anosmia due to compression of olfactory nerve.

28. Terms and Definitions Related to Olfactory Abnormalities

29. The Snap & Sniff threshold test

30. References:
◦ Snell’s clinical neuroanatomy (8th edition)
◦ William Campbell, Richard J. Barohn - DeJong’s The Neurologic Examination (2019, LWW)
◦ Joseph Jankovic, John C. Mazziottam, Scott L. Pomeroy, Nancy J. - Bradley and Daroffs Neurology in Clinical Practice (2022,
Elsevier)