Second year Anatomy topic mbbs

1. Cranial Nerves

3. Cranial Nerves
 There are 12 pairs of cranial nerves in our body.
 These are called as cranial nerve because the
originated directly from the brain; inside the cranium.
 Only the first and the second pair emerge from the
cerebrum; the remaining ten pairs emerge from the
brainstem.

4. Cranial Nerves
1. Olfactory nerve
2. Optic nerve
3. Oculomotor nerve
4. Trochlear nerve
5. Trigeminal nerve
6. Abducens nerve
7. Facial nerve
8. Vestibulocochlear nerve
9. Glossopharangeal nerve
10. Vagus nerve
11. Accessory nerve
12. Hypoglossal nerve

5. Classification
Pure Sensory Function: CN I, II and VIII
Pure Motor Function: CN III, IV, VI, XII
Mixed (Sensory and motor): CN V, VII, IX, X, XI

6. Olfactory nerve
Olfactory nerve is the first cranial nerve, which is
pure sensory in function.
It transmit the impulse that conveys the sense of
smell.
It is unique among the cranial nerve in that it
is capable of regeneration if damaged.

7. Olfactory nerve
It originates from the
olfactory mucosa in the roof
of nasal cavity.
Nerves pass through the
cribriform plate of ethmoid
bone to reach the brain.
Fibers run through the
olfactory bulb and
terminate in the primary
olfactory cortex.
Olfactory bulb Olfactory tract
Olfactory nerves

8. Olfactory Bulb
 The ovoid structure possess
several types of nerves
cells.
 The largest cells are mitral
cell which form synapse
with the incoming olfactory
nerve and form a rounded
area known as synaptic
glomeruli.
 Smaller nerve cells called
tufted cells and granular
cells also synapse with
mitral cell.

9. Olfactory Tract
 Olfactory tract divides into
lateral and medial olfactory
striae.
 The lateral stria carries the
axon to olfactory area of
cerebral cortex.
 The medial stria carries the
fibers that cross the median
plane to pass to the olfactory
bulb of opposite side.

10. Optic Nerve
 The optic nerve is 2nd cranial nerve which carries the
visual impulses from retina to the brain.
 To reach the brain it passes through the optic canal.
 The optic nerve starts from optic disc and ends at the
chiasma.
 The optic nerve leaves the orbital cavity through the
optic canal and unites with optic nerve of the
opposite side to form optic chiasma.

11. Optic Nerve
Optic Chiasma:
 The optic chiasma is situated at the junction of the anterior
wall and floor of the third ventricle.
 In the chiasma the fibers from nasal half of each retina cross
the midline and enter the optic tract of the opposite side.
 The fibers from temporal half of retina pass posteriorly in the
optic tract of the same side.
Optic tract:
 It emerges from the optic chiasma and passes posterolaterally
around the cerebral peduncle.
 Most of the fibers terminate by synapsing with nerve cells in
the lateral geniculate body.

12. Optic Nerve
Lateral Geniculate Body:
 Is a small, oval swelling projecting from thalamus.
 The axons of nerve cells within the geniculate body leave it to
form optic radiation.
Optic Radiation:
 The fibers of optic radiation are the axons of nerve cells of the
lateral geniculate body.
 The tract passes posteriorly through the internal capsule and
terminates in the visual cortex.

13. Optic Nerve

14. Oculomotor Nerve
The 3rd cranial nerve is entirely motor in
function.
The oculomotor nerve has two motor nuclei
1. Main motor nucleus
2. Accessory parasympathetic nucleus

15. Oculomotor Nerve
 The main nucleus is situated in the anterior part of
the gray matter that surrounds the midbrain.
 It lies at the level of superior colliculus.
 The accessory parasympathetic nucleus is situated
posterior to the main oculomotor nucleus.

16. Oculomotor nerve course
 It emerges on the anterior surface of the midbrain. It passes
forward between the posterior and superior cerebellar
arteries.
 Then it continues into the middle cranial fossa in the lateral
wall of cavernous sinus.
 It divides into superior and inferior ramus which enter the
cavity through superior orbital fissure.
 The 3rd cranial nerve supply all the extrinsic muscles of the
eye except the superior oblique and the lateral rectus muscle.

17. Oculomotor nerve

18. Oculomotor Nerve

19. Oculomotor Nerve
• Moritz Benedikt syndrome: Is a lesion of the oculomotor
nerve fibers as they pass through the red nucleus. A lesion
here will result in a contralateral tremor, due to damage to
the superior rectus input, and the typical oculomotor nerve
lesion symptoms:
Deviation of the ipsilateral eye downward and outward
(due to action of the intact superior oblique and lateral
rectus muscles)
A drooping of the ipsilateral eyelid (ptosis) due to a lack of
levator palpabrae superioris action
Diplopia (double vision)

20. Oculomotor Nerve
Weber syndrome:
• This syndrome results due to damage located more anteriorly
than in Moritz Benedikt syndrome, just before the nerve
fibers exit the brainstem.
• In this case, the typical oculomotor nerve lesion symptoms
are present but the contralateral tremor progresses to a
contralateral upper motor neuron paralysis affecting the
superior rectus.

21. Oculomotor Nerve Palsy
 Damage to the oculomotor nerve after it leaves the
brainstem results in a collection of symptoms known
as oculomotor nerve palsy. Symptoms include:
 Deviation of the ipsilateral eye out downward and outward
 Ptosis
 Double vision
 Ipsilateral pupil dilation
 Unresponsive light and accommodation reflexes in the
ipsilateral eye

22. Oculomotor Nerve Palsy

23. Trochlear Nerve
 The trochlear nerve is purely motor nerve.
 It is only cranial nerve to emerge from dorsal aspect of brain
Trochlear nerve nucleus:
 It is situated in the anterior part of gray matter .
 It lies inferior to the oculomotor nucleus at the level of
inferior colliculus.
 The nerves fibers after leaving the nucleus, pass posteriorly
around the central gray matter to reach the posterior surface
of midbrain.

24. Trochlear Nerve Course
 The 4th nerve emerges from the midbrain and
immediately decussates with the nerve of the
opposite side.
 The trochlear nerve passes forward through the
middle cranial fossa in the lateral wall of cavernous
sinus and enter the orbit via superior orbital fissure.
 It supplies the superior oblique muscle of eyeball and
assists in turning the eye downward and laterally.

25. Trochlear Nerve

26. Trigeminal Nerve

27. Trigeminal Nerve
 5th cranial nerve (CN5)
 Largest cranial nerve
 MIXED CRANIAL NERVE
 Sensory nerve to the greater part of the head.
 Motor nerve to several muscles including muscles of
mastication.
 The trigeminal nerve has four nuclei:
1. Main sensory nucleus
2. Spinal nucleus
3. Mesencephlic nucleus
4. Motor nucleus

28. Trigeminal Nerve
• Main sensory nucleus: Lies in the posterior part of the
pons, lateral to the motor nucleus.
• Main sensory nucleus: The spinal nucleus is continuous
superiorly with the main sensory nucleus in the pons and
extends through medulla oblongata and into the upper part of
spinal cord.
• Mesencephlic nucleus: is composed of column of unipolar
nerve cells situated in the lateral part of gray matter.
• Motor nucleus: Is situated in the pons medial to the
sensory nucleus.

29. Trigeminal Nerve

30. Trigeminal nerve course
 The 5th cranial nerves leaves the anterior aspect of the pons
as a small motor root and a large sensory root.
 The large sensory root now expands to form the crescent
shaped trigeminal ganglion.
 The ophthalmic, maxillary and mandibular nerves arise from
the anterior border of ganglion.
 The ophthalmic nerve contains only sensory fibers and leaves
the skull through superior orbital fissure to enter the orbital
cavity.
 The maxillary nerve also contains only sensory fibers and
leaves the skull through foramen rotundum.
 The mandibular nerve contains both sensory and motor fibers
and leave the skull through the foramen ovale.

31. Trigeminal Nerve Innervations
Ophthalmic nerve:
 Supply to the eyeball, lacrimal gland, conjuctiva, a
portion of nasal mucosa and forehead.
Maxillary nerve:
 Innervate the middle third of the face and upper
teeth.
Mandibular nerve:
 Divides into several branches to supply sensation to
the lower third of face and tongue, floor of mouth
and the jaw.
 The motor part innervates the four muscle of
mastication
1. Masseter
2. Temporalis
3. Lateral pterygoid
4. Medial pterygoid

32. Abducens Nerve
• The abducent nerve is a small, entirely motor
nerve that supplies the lateral rectus muscle of
the eyeball.
Abducens nerve nucleus:
 Small motor nucleus is situated beneath the floor of fourth
ventricle.
 The nucleus receives afferent corticonuclear fibers from both
cerebral hemispheres .
 Also receives fibers from the medial longitudinal fasciculus ,
by which it is connected to the nuclei of 3rd ,4th, and 8th cranial
nerves.

33. Abducens Nerve Course
 It emerges in the groove between the lower border of pons
and medulla oblongata.
 It passes forward through the cavernous sinus, lying below
and lateral to the internal carotid artery.
 The nerve enters the orbit via superior orbital fissure and
supplies the lateral rectus muscle.
 The nerve is responsible for lateral movement of eye.

34. Abducens Nerve

38. Facial Nerve Lesion
 Lesions that involve the facial motor nucleus or the
infranuclear portion of the facial nerve result in complete
paralysis of all the facial muscles on the ipsilateral side.
 The patient presents with mouth droop, flattening of the
nasolabial fold, inability to close eye, and smoothing of the
brow on the damaged side.

39. Bell's Palsy
 Bell's palsy is a condition that causes sudden weakness in the
muscles on one side of the face. In most cases, the weakness
is temporary and significantly improves over weeks.
 The weakness makes half of the face appear to droop. Smiles
are one-sided, and the eye on the affected side resists closing.

45. Clinical Aspects
• Sensorineural deafness is a deafness which results from the
disease of the cochlea or the vestibulocochlear nerve,
meaning that it is the middle ear deafness.
• It can be distinguished from conductive deafness after
performing both Rinne and Weber hearing tests.

52. Clinical aspects
Lesions of the vagus nerve
• The symptoms of a lesion along the vagus nerve are
dependent on where the lesion is located.
• The vagus nerve and its branches supply many different
structures in the body, symptoms may vary from palatal and
pharyngeal paralysis to abnormalities in the gastric acid
secretion and heart rate.

53. Clinical aspects
• Unilateral lesions of the recurrent laryngeal branch of the
vagus nerve can result in vocal cord paralysis in the
paramedian position. The result of this is a hoarse and
breathy voice, and diplophonia may also occur.
• Bilateral recurrent laryngeal lesions can result in paralysis of
both vocal cords, causing a whisper-type voice