cranial nerves - medicine 12345678911223

cranial nerves

4. CRANIAL NERVES
Cranial nerves are
nerves that emerge directly from the brain,
in contrast to spinal nerves which emerge from segments of the spinal
cord.
In humans, there are 12 pairs of cranial nerves.
Only the first and the second pair emerge from the cerebrum,
the remaining 10 pairs emerge from the brainstem.

5. CRANIAL NERVES
•The 12 pairs of cranial nerves are part of the peripheral nervous system (PNS) and
pass through foramina or fissures in the cranial cavity.
• All nerves except one, the accessory nerve [XI], originate from the brain.
•In addition to having similar somatic and visceral components as spinal nerves,
some cranial nerves also contain special sensory and motor components.
•The special sensory components are associated with hearing, seeing,
smelling, balancing, and tasting.
•Special motor components include those that innervate muscles derived
embryologically from the pharyngeal arches.

6.  CLASSIFICATION OF
CRANIAL NERVES
1. Primarily or exclusively sensory nerves (I, II, VIII) that contain special
sensory fibers for  smell (I), vision (II), and  hearing and equilibrium (VIII).  

2. Primarily motor nerves (III, IV, VI, XI, XII) that contain somatic motor
fibers to skeletal muscles of the eye, neck, and tongue.  

3. Mixed (motor and sensory) nerves (V, VII, IX, X).  These mixed nerves
supply  sensory innervation to the face  (through general somatic sensory
fibers) and to the  mouth and viscera  (general visceral sensory),  including
the taste buds  for the sense of taste  (special visceral sensory). 

7. -  These nerves also  innervate pharyngeal arch
muscles (somatic motor),  such as the chewing muscles (V) and
the muscles of facial expression (VII). 
-Four of the cranial nerves (III, VII, IX, X) contain visceral
motor fibers that regulate visceral muscle and glands throughout
much of the body. These motor fibers belong to the
parasympathetic division of the autonomic nervous system
(ANS) 

8. Sensory (afferent) Modalities:
1. General somatic sensory (GSS) – carry general sensation of
pain, touch and temperature from skin.
2. General visceral sensory (GVS) – general sensation of dissension
and ischemic pain from viscera.
3. Special somatic sensory (SSS) – carry special senses derived
from ectoderm (e.g. sight, sound, balance).
4. Special visceral sensory (SVS) – carry special senses derived
from endoderm (e.g. taste, smell).

9.   Motor (efferent) Modalities:
 General somatic motor (GSM) – supply skeletal muscles.
General visceral motor (GVM) –  supply smooth muscles of gut
and autonomic motor.
Special visceral motor (SVM) – muscles derived from pharyngeal
arches.

21. Olfactory nerve [I]
•The olfactory nerve [I] carries special afferent (SA)  fibers  for the sense of   smell.
•Its sensory neurons have:
–peripheral processes that act as receptors in the nasal mucosa;
–central processes that return information to the brain.
vThe receptors are in the roof and upper parts of the nasal  cavity and the central
processes, after joining into small  bundles, enter the cranial cavity by passing
through the  cribriform plate of the ethmoid bone.
vThey terminate by synapsing with secondary neurons in  the olfactory
bulbs.

22. Cranial nerves exiting the cranial cavity

23. Cranial nerves on the base of the
brain

24. FEATURES
The primary sensory neurons of
olfactory nerve(olfactory
neurons) lie on the body surface
in the epithelial lining of the
nasal cavity and their dendrites
lie free in the mucous film. 

25. ANATOMICAL
COURSE
It passes from its  receptors in
the nasal mucosa to the
forebrain. 
It enters the skull through
the cribriform plate of
the ethmoid bone to enter the
anterior cranial fossa, where
they terminate in the olfactory
bulb. 

26.  CLINICALS
  ANOSMIA
Absence of sense of smell.
Can be temporary, permanent, progessive or congenital.

27. Optic nerve [II]
•The   optic nerve [II] carries SA   fibers for vision.  These    fibers return information to
the brain  from photoreceptors in the retina.
•Neuronal processes leave the retinal  receptors, join into small bundles,
and are  carried by the optic nerves to other  components of the visual
system in the brain.
•The  optic nerves enter the cranial cavity  through the optic canals.

28.   Unique Features 
     -Are paired, anterior extensions of the forebrain
(diencephalon), 
    -It consists of second-order sensory neurons. 
   -Its fibres are myelinated by oligodendrocytes. 
    -It is surrounded by meninges. 
    -Its fibres cannot regenerate if cut/damaged. 


29.   ANATOMICAL
COURSE
-The information received from the
external environment passes to the rods
and cones on the  retina, and then to
bipolar cells,  ganglion cells, and
ultimately to the optic nerve.
-The optic nerve then passes through
the optic canal, onward to the optic
chiasma, and then to terminate in
the occipital lobes. 
-At the optic chiasma, some
information crosses to the opposite side
aiding  binocular vision
-The nerve passes posteromedially in
the orbit, exiting through the optic
canal to enter the middle cranial fossa,
where it forms the optic chiasm 

30. --Here, fibers from the nasal (medial) half of  each retina
decussate in the chiasm and join uncrossed fibers from the
temporal (lateral) half of the retina to form the  optic tract. 
- The partial crossing of optic nerve fibers in the chiasm is a
requirement for binocular vision, allowing depth-of-field
perception (three-dimensional vision). 
Therefore, fibers from the right halves of both retinas form the
right optic tract. 
The decussation of nerve fibers in the chiasm results in the right
optic tract conveying impulses from the left visual field and vice
versa.
Most fibers in the optic tracts terminate in the lateral
geniculate bodies of the thalamus. From these nuclei, axons are
relayed to the visual cortices of the occipital lobes of the brain. 

31.   Thus, visual pathway consists of
the following compo- nents in
craniocaudal order :
Retina → optic nerve → optic
tract → lateral geniculate body →
optic radiation → visual cortex. 

32. CLINICAL
RELEVANCE
   PITUITARY ADENOMA
  Compression to the optic
chiasm particularly affects the
fibres that are crossing over
from the nasal half of each
retina. 
This produces visual defect
affecting the peripheral vision in
both eyes, known as
a bitemporal hemianopia.

33. Oculomotor nerve [III]
•The oculomotor nerve [III] carries two  types  of fibers:
–general somatic efferent (GSE) fibers  innervate most of the
extraocular muscles;
–general visceral efferent (GVE) fibers  are  part of the
parasympathetic part of the  autonomic division of the
peripheral  nervous system (PNS).

35.   NUCLEUS
ORIGIN:
The occulomotor nerve emerges from
upper part of the midbrain/
Mesencephalon.
It lies in the deep periaqueductal grey
matter at the level of the superior
colliculus, anterior to the cerebral
aqueduct.
TWO NUCLEUS:
1. OCULOMOTOR NUCLEUS:
Somatic motor fibres( general somatic
efferents)
2. EDINGER-WESTPHAL NUCLEI
Visceral motor fibres ( general visceral
efferent)

36.   ANATOMICAL COURSE
-  Emerges from the midbrain, pierces the dura mater lateral to
the diaphragma sellae roofing over the hypophysis and then runs through
the roof and lateral wall of the cavernous sinus .
- leaves the cranial cavity and enters the orbit through the superior
orbital fissure. 
- Within this fissure, it divides into 
1. superior division (which supplies the superior rectus and levator
palpebrae superioris) and 
2. inferior division (which supplies the inferior and medial rectus and
inferior oblique). 
-The inferior division also carries presynaptic parasympathetic (visceral
efferent) fibers to the ciliary ganglion, where they synapse .
- Postsynaptic fibers from this ganglion pass to the eyeball in the short
ciliary nerves to innervate the ciliary body and sphincter pupillae 

38. Oculomotor nerve [III] 2/2
•The oculomotor nerve [III] leaves the anterior surface of
the brainstem between the midbrain and the
pons.
•It enters the anterior edge of the tentorium cerebelli,
continues in an anterior direction in the lateral wall of the
cavernous sinus, and leaves the cranial cavity through the
superior orbital fissure.
•In the orbit, the GSE fibers in the oculomotor nerve
innervate levator palpebrae superioris, superior rectus,
inferior rectus, medial rectus, and inferior oblique muscles.
•The GVE fibers are preganglionic parasympathetic fibers
that synapse in the ciliary ganglion and ultimately
innervate the sphincter pupillae muscle, responsible
for pupillary constriction, and the ciliary muscles,
responsible for accommodation of the lens for near
vision.

39.  MOTOR FUNCTIONS
The oculomotor nerve innervates many of the extraocular
muscles. These muscles move the eyeball and upper eyelid.
Superior Branch
Superior rectus – elevates the eyeball
Levator palpabrae superioris – raises the upper eyelid.
Additionally, there are sympathetic fibres that travel with the
superior branch of the oculomotor nerve. They innervate
the superior tarsal muscle, which acts to keep the eyelid
elevated after the levator palpabrae superioris has raised it.

40. Inferior Branch:
Inferior rectus – depresses the
eyeball
Medial rectus  – adducts the
eyeball
Inferior oblique – elevates,
abducts and laterally rotates the
eyeball

41. PARASYMPATHETIC
FUNCTIONS
There are two structures in the eye that receive
parasympathetic innervation from the oculomotor
nerve:
Sphincter pupillae – constricts the pupil, reducing
the amount of light entering the eye.
Ciliary muscles  – contracts, causes the lens to
become more spherical, and thus more adapted to
short range vision.
The pre-ganglionic parasympathetic fibres travel in
the inferior branch of the oculomotor nerve. Within
the orbit, they branch off and synapse in the ciliary
ganglion. The post-ganglionic fibres are carried to
the eye via the short ciliary nerves

42. CLINICAL RELEVANCE
OCCULOMOTOR NERVE PALSY
1. Ptosis(drooping upper eyelid)
2. ‘Down and out‘ position of the eye at rest 
3. Accomadation is lost

45. Trochlear nerve [IV]
•The trochlear nerve [IV] is a cranial nerve that
carries GSE fibers to innervate the superior oblique
muscle, an extraocular muscle in the orbit.
•It arises in the midbrain and is the only cranial nerve
to exit from the posterior surface of the
brainstem.
• After curving around the midbrain, it enters the
inferior surface of the free edge of the tentorium
cerebelli,
• continues in an anterior direction in the lateral wall
of the cavernous sinus, and enters the orbit,
through the superior orbital fissure.

47. CLINICAL CORELATION
 TROCHLEAR NERVE PALSY
Injury of trochlear nerve.-causes paralysis of the superior
oblique muscle of eyeball.
Clinical features:
a. Extorsion of the eyeball and weakness of downward 
gaze. 
b. diplopia (double vision) which occurs when the patient 
looks laterally and in glances on looking downward

48. Trigeminal nerve [V] 1/3
•The trigeminal nerve [V] is the major general
sensory nerve of the head, and also innervates
muscles that move the lower jaw.
•It carries general somatic afferent (GSA) and
branchial efferent (BE) fibers:
•the GSA fibers provide sensory input from the face,
anterior one-half of the scalp, mucous membranes of
the oral and nasal cavities and the paranasal
sinuses, part of the tympanic membrane, the eye and
conjunctiva, and the dura mater in the anterior and
middle cranial fossae;
•the BE fibers innervate the muscles of
mastication, the tensor tympani, the tensor veli
palatini, the mylohyoid, and the anterior belly of
the digastric.

49. Trigeminal nerve [V] 2/3
•The trigeminal nerve exits from the anterolateral surface of
the pons as a large sensory root and a small motor root.
•These roots continue forward out of the posterior cranial
fossa and into the middle cranial fossa by passing over the
medial tip of the petrous part of the temporal bone.
•In the middle cranial fossa the sensory root expands
into the trigeminal ganglion, which contains cell
bodies for the sensory neurons in the trigeminal nerve
and is comparable to a spinal ganglion.
•The ganglion is in a depression (the trigeminal
depression) on the anterior surface of the petrous part
of the temporal bone, in a dural cave (the trigeminal
cave).
•The motor root is below and completely
separate from the sensory root at this point.

50. Trigeminal nerve [V] 3/3
•Arising from the anterior border of the
trigeminal ganglion are the three terminal
divisions of the trigeminal nerve, which in
descending order are:
•the ophthalmic nerve (ophthalmic division
[V
1]);
•the maxillary nerve (maxillary division
[V
2]);
•the mandibular nerve (mandibular division
[V
3]).

51. Cavernous sinus

52. Ophthalmic nerve [V
1]
•The ophthalmic nerve [V
1] passes forward in the
dura of the lateral wall of the cavernous
sinus, leaves the cranial cavity, and enters the
orbit through the superior orbital fissure.
•The ophthalmic nerve [V
1] carries sensory
branches from the eyes, conjunctiva, and orbital
contents, including the lacrimal gland.
•It also receives sensory branches from the
nasal cavity, frontal and ethmoidal sinuses,
upper eyelid, dorsum of the nose, and the
anterior part of the scalp.

53. Maxillary nerve [V
2]
•The maxillary nerve [V
2] passes forward in the dura
mater of the lateral wall of the cavernous sinus just
inferior to the ophthalmic nerve [V
1],
•
leaves the cranial cavity through the foramen
rotundum, and enters the pterygopalatine
fossa.
•The maxillary nerve [V
2] receives sensory
branches from the dura in the anterior and
middle cranial fossae, the nasopharynx, the
palate, the nasal cavity, teeth of the upper
jaw, maxillary sinus, and skin covering the
side of the nose, the lower eyelid, the cheek,
and the upper lip.

54. Mandibular nerve [V
3] 1/2
•The mandibular nerve [V
3] leaves the inferior
margin of the trigeminal ganglion and leaves the
skull through the foramen ovale.
•The motor root of the trigeminal nerve
also passes through the foramen ovale and
unites with the sensory component of the
mandibular nerve [V
3] outside the skull.
•Thus, the mandibular nerve [V
3] is the only
division of the trigeminal nerve that contains a
motor component.

55. Mandibular nerve [V
3] 2/2
•Outside the skull the motor fibers innervate the
muscles of mastication, including the temporalis, the
masseter, and the medial and lateral pterygoid muscles,
•as well as the tensor tympani, the tensor veli palatini,
the anterior belly of the digastric, and the mylohyoid
muscles.
•The mandibular nerve [V
3] also receives sensory
branches from the skin of the lower face, cheek,
lower lip, the ear, the external acoustic meatus and the
temporal region, the anterior two-thirds of the tongue,
the teeth of the lower jaw, the mastoid air cells, the
mucous membranes of the cheek, the mandible, and
dura in the middle cranial fossa.

56.   CLINICAL
SIGNIFICANCE
Trigeminal neuralgia
- presents as episodes of
severe stabbing pain of sudden
onset & short duration in the
area of distribution of one or
more of the three  divisions of
the trigeminal nerve.
- most commonly  associated
with maxillary (CN V2) and
mandibular divisions (CN V3) of
the trigeminal nerve

57.  Abducent nerve [VI]
It is the 6th cranial nerve.
It has purely somatic motor function
Provides innervation to only one extra ocular muscle- lateral
rectus muscle.

59. Abducent nerve [VI]
•The abducent nerve [VI] carries GSE fibers
to innervate the lateral rectus muscle in the
orbit.
•It arises from the brainstem between the pons
and medulla and passes forward, piercing the
dura covering the clivus.
• Continuing upward in a dural canal, it crosses
the superior edge of the petrous temporal
bone, enters and crosses the cavernous
sinus just  inferolateral to the internal
carotid artery,
•
and enters the orbit through the superior
orbital  fissure to supply the lateral rectus
muscle.

61. •CLINICAL RELEVANCE
1. Examination of the abducens nerve
2. Abducens nerve palsy-can be due
to any structural pathology which leads
to downwards pressure on the
brainstem .
- diplopia
- affected eye resting in adduction
-inability to abduct the eye.

62. Facial nerve [VII]1/2
•The facial nerve [VII] carries GSA, SA, GVE, and BE fibers:
•The GSA fibers provide sensory input from the external
acoustic meatus and a small amount of skin posterior to the
ear;
•The SA fibers are for taste from the anterior two-thirds of
the tongue;
•The GVE fibers are part of the parasympathetic part of the
autonomic division of the PNS and stimulate secretomotor
activity in the lacrimal gland, submandibular and
sublingual salivary glands, and mucous membranes
of the nasal cavity, and hard and soft palates;
•The BE fibers innervate the muscles of the face
(muscles of facial expression) and scalp derived from the
second pharyngeal arch, and the stapedius, the posterior
belly of the digastric, and the stylohyoid muscles

63. It is mixed nerve with motor and sensory roots.
Motor: Innervates the muscles of facial expression, the posterior
belly of the digastric, the stylohyoid and the stapedius muscles.
Sensory: A small area around the concha of the auricle.
Special Sensory: Provides special taste sensation to the anterior
2/3 of the tongue.
Parasympathetic: Supplies many of the glands of the head and
neck, including:
◦Submandibular and sublingual salivary glands.
◦Nasal, palatine and pharyngeal mucous glands.
◦Lacrimal glands.

65. Facial nerve [VII] 2/2
•The facial nerve [VII] attaches to the lateral surface of the
brainstem, between the pons and medulla
oblongata.
•It consists of a large motor root and a smaller sensory root
(the intermediate nerve):
•the intermediate nerve contains the SA fibers for taste, the
parasympathetic GVE fibers and the GSA fibers;
•the larger motor root contains the BE fibers.
❑The motor and sensory roots cross the posterior cranial fossa and
leave the cranial cavity through the internal acoustic meatus.
❑After entering the facial canal in the petrous part of the temporal
bone, the two roots fuse and form the facial nerve [VII].
❑Near this point the nerve enlarges as the geniculate
ganglion, which is similar to a spinal ganglion
containing cell bodies for sensory neurons.

66. Facial nerve [VII] 2/2
•At the geniculate ganglion the facial nerve [VII] turns
and gives off the greater petrosal nerve, which
carries preganglionic parasympathetic (GVE) fibers.
•The facial nerve [VII] continues along the bony canal,
giving off the nerve to stapedius and the chorda
tympani, before exiting the skull through the
stylomastoid foramen.
•The chorda tympani carries taste (SA) fibers
from the anterior two-thirds of the tongue and
preganglionic parasympathetic (GVE) fibers
destined for the submandibular ganglion.

68. MOTOR FUNCTIONS
Branches of the facial nerve are responsible for innervating
many of the muscles of the head and neck. All these muscles
are derivatives of the second pharyngeal arch.
The first motor branch arises within the facial canal; the  nerve
to stapedius. 
The nerve passes through the pyramidal eminence to supply the
stapedius muscle in the  middle ear

69. Between the stylomastoid foramen, and the parotid gland, three more
motor branches are given off:
Posterior auricular nerve – Ascends in front of the mastoid process, and
innervates the intrinsic and extrinsic muscles of the outer ear. It also
supplies the occipital part of the occipitofrontalis muscle.
Nerve to the posterior belly of the digastric muscle  – Innervates the
posterior belly of the digastric muscle (a  suprahyoid muscle of the neck).
It is responsible for raising the hyoid bone.
Nerve to the stylohyoid muscle  – Innervates the stylohyoid muscle
(a suprahyoid muscle of the neck). It is responsible for raising the hyoid
bone.

70. Within the parotid gland, the facial nerve terminates by bifurcating
into five motor branches. 
These innervate the muscles of  facial expression:
1. Temporal branch –  Innervates the frontalis, orbicularis oculi
and corrugator supercilii
 2. Zygomatic branch  – Innervates the orbicularis oculi.
3. Buccal branch – Innervates the orbicularis oris, buccinator and
zygomaticus muscles.
4. Marginal Mandibular branch  – Innervates the mentalis muscle.
5. Cervical branch  – Innervates the platysma.

72. SPECIAL SENSORY FUNCTIONS
 The chorda tympani branch of the facial nerve is responsible for
innervating the anterior 2/3 of the tongue with the special
sense of taste.

73. PARASYMPATHETIC FUNCTIONS
The parasympathetic fibres of the facial nerve are carried by
the greater petrosal and chorda tympani branches.

77.  Extracranial Lesions
-Extracranial lesions occur during the extracranial course of the
facial nerve (distal to the stylomastoid foramen). Only the motor
function of the facial nerve is affected, therefore resulting in
paralysis or severe weakness of the muscles of facial expression.
-There are various causes of extracranial lesions of the facial
nerve:
Parotid gland pathology – e.g a tumour, parotitis, surgery.
Infection of the nerve – particularly by the herpes virus.
Compression during forceps delivery – the neonatal mastoid
process is not fully developed, and does not provide complete
protection of the nerve.

78. Vestibulocochlear nerve [VIII]
•The vestibulocochlear nerve [VIII] carries SA fibers for
hearing and balance, and consists of two divisions:
–a vestibular component for balance;
–a cochlear component for hearing
❖The vestibulocochlear nerve [VIII] attaches to the
lateral surface of the brainstem, between the pons
and medulla, after emerging from the internal
acoustic meatus and crossing the posterior cranial
fossa.
❖The two divisions combine into the single nerve seen in
the posterior cranial fossa within the substance of the
petrous part of the temporal bone.

79. CLINICAL RELEVANCE
1. LESIONS OF VESTIBULOCOCHLEAR NERVE:
Present as:
- Tinnitus  (ringing or buzzing in the ears)
- Damage or loss of hearing
-Decline of balance (vertigo)
2. VESTIBULAR NEURITIS
inflammation of the vestibular branch of the vestibulocochlear nerve.
Presents with:
Vertigo
Nystagmus
Loss of equilibrilium
Nausea and vomitting
3.LABYRINTHITIS

80. Glossopharyngeal nerve [IX] 1/2
•The glossopharyngeal nerve [IX] carries GVA, SA, GVE, and BE
fibers:
•The GVA fibers provide sensory input from
• The carotid body and sinus, posterior one-third of the
tongue, palatine tonsils, upper pharynx, and mucosa
of the middle ear and pharyngotympanic tube;
•The SA fibers are for taste from the posterior one-third of
the tongue;
•The GVE fibers are part of the parasympathetic part of
the autonomic division of the PNS and stimulate
secretomotor activity in the parotid salivary
gland;
•The BE fibers innervate the muscle derived from the
third pharyngeal arch (the stylopharyngeus muscle).

81. Glossopharyngeal nerve [IX] 2/2
•The glossopharyngeal nerve [IX] arises as several rootlets on the
anterolateral surface of the upper medulla oblongata.
•The rootlets cross the posterior cranial fossa and enter the jugular
foramen.
• Within the jugular foramen, and before exiting from it, the
rootlets merge to form the glossopharyngeal nerve.
•Within or immediately outside the jugular foramen are two
ganglia (the superior and inferior ganglia), which contain the cell
bodies of the sensory neurons in the glossopharyngeal nerve [IX].

82. Tympanic nerve
•Branching from the glossopharyngeal nerve [IX] either within or
immediately outside the jugular foramen is the tympanic
nerve.
•This branch re-enters the temporal bone, enters the middle
ear cavity, and participates in the formation of the tympanic plexus.
•Within the middle ear cavity it provides sensory innervation
to the mucosa of the cavity, pharyngotympanic tube, and mastoid
air cells.
•The tympanic nerve also contributes GVE fibers,
which leave the tympanic plexus in the lesser petrosal
nerve-a small nerve that exits the temporal bone,
❑The lesser petrosal nerve
•enters the middle cranial fossa, and descends through the
foramen ovale to exit the cranial cavity carrying
preganglionic parasympathetic fibers to the otic ganglion.

83. Glossopharyngeal nerve branches
Tympanic – sensory innervation to the mucosa of the middle ear,
turning into the lesser petrosal nerve to supply parasympathetic fibres
to the parotid gland*
Stylopharyngeus – motor innervation to the stylopharyngeus
Tonsillar – sensory and parasympathetic innervation to the tonsils and
oropharynx
Nerve to carotid sinus – sensory innervation to the carotid sinus
Nerve to dorsal 1/3 of the tongue – special sense of taste from
the dorsal 1/3 of the tongue
Lingual branch – sensory information from the dorsal 1/3 of the tongue
Vagal communicating branch – parasympathetic communicating
branches with the vagus nerve

84. CLINICAL CORELATION
1. Lesions of glossopharyngeal nerve:
The lesion of the glossopharyngeal nerve is rare in isolation since there is
often associated involvement of the vagus nerve. However, the complete
lesion of the glossopharyngeal nerve results in: 
◦(a)  the loss of taste and general sensations over the posterior one-third of the
tongue, 

◦(b)  difficulty in swallowing, 

◦(c)  the loss of the salivation from the parotid gland, and 

◦(d)  the unilateral loss of the gag reflex


2. Glossopharyngeal neuralgia

85. Vagus nerve [X] 1/2
•The vagus nerve [X] carries GSA, GVA, SA, GVE, and BE fibers:
•The GSA fibers provide sensory input from the skin posterior to the ear
and the external acoustic meatus, and the dura mater in the posterior
cranial fossa;
•The GVA fibers provide sensory input from the aortic
body chemoreceptors and aortic arch baroreceptors,
and the mucous membranes of the pharynx, larynx,
esophagus, bronchi, lungs, heart, and abdominal viscera
in the foregut and midgut;
•The SA fibers are for taste around the epiglottis;
•The GVE fibers are part of the parasympathetic part of the autonomic
division of the PNS and stimulate smooth muscle and glands in the pharynx,
larynx, thoracic viscera, and abdominal viscera of the foregut and midgut;
•The BE fibers innervate one muscle of the tongue (palatoglossus),
the muscles of the soft palate (except tensor veli palatini), pharynx
(except stylopharyngeus), and larynx.

88. Vagus nerve [X] 1/2
•The vagus nerve arises as a group of rootlets on
the anterolateral surface of the medulla
oblongata just inferior to the rootlets arising to
form the glossopharyngeal nerve [IX].
• The rootlets cross the posterior cranial fossa and
enter the jugular foramen.
•Within this foramen, and before exiting from it,
the rootlets merge to form the vagus nerve [X].
• Within or immediately outside the jugular
foramen are two ganglia, the superior (jugular) and
inferior (nodose) ganglia, which contain the cell
bodies of the sensory neurons in the vagus nerve [X].

90. CLINICAL CORRELATION
1. Alderman’s nerve phenomenon
2. Lesions of vagus nerve: The bilateral lesions of vagus nerve cause: 
(a)  nasal regurgitation of the swallowed liquids, 

(b)  nasal twang of voice, 

(c)  hoarseness of voice, 

(d)  flattering of palatal arches, 

(e)  cadaveric position of vocal cards, 

(f)  dysphagia,and 

(g)  loss of cough reflex. 


91. Accessory nerve [XI] 1/2
•The accessory nerve [XI] is a cranial nerve that carries BE
fibers to innervate the sternocleidomastoid and trapezius
muscles.
• It is a unique cranial nerve because its roots arise
from motor neurons in the upper five segments of
the cervical spinal cord.
•These fibers leave the lateral surface of the spinal cord and,
joining together as they ascend, enter the cranial cavity
through the foramen magnum.
• The accessory nerve [XI] continues through the
posterior cranial fossa and exits through the
jugular foramen.
• It then descends in the neck to innervate the
sternocleidomastoid and trapezius muscles from their deep
surfaces.

92. Course of the spinal accessory
nerve

93. Cranial root of the accessory nerve 2/2
•Some descriptions of the accessory nerve [XI] refer to a few
rootlets arising from the caudal part of the medulla
oblongata on the anterolateral surface just inferior to the
rootlets arising to form the vagus nerve [X] as the 'cranial'
root of the accessory nerve.
•Leaving the medulla, the 'cranial' roots course with the
'spinal' roots of the accessory nerve [XI] into the jugular
foramen, at which point the 'cranial' roots join the vagus
nerve [X].
• As part of the vagus nerve [X], they are distributed to the
pharyngeal musculature innervated by the vagus nerve [X]
and are therefore described as being part of the vagus
nerve [X].

94. Hypoglossal nerve [XII]
•The hypoglossal nerve [XII] carries GSE fibers
to innervate all intrinsic and most of the
extrinsic muscles of the tongue.
•It arises as several rootlets from the anterior
surface of the medulla, passes laterally across
the posterior cranial fossa and exits through the
hypoglossal canal.
•
This nerve innervates the hyoglossus,
styloglossus, and genioglossus muscles and all
intrinsic muscles of the tongue.

98. Cranial Nerves
Examination