ppt

1. Neuroanatomy and
Neurolocalization of CN VII-XII
Presenter: Dr. Abebe G. (NR-2)
Moderator: Dr. Nebiyu B.(Consultant Neurologist)
Dr. Guadie B. (Consultant Neurologist)
July 12, 2022

2. Outline
• Neuroanatomy of each CN
• Neurolocalization of each CN
• Clinical correlation of each CN
• Reference

3. Objectives
• At the end of the presentation, we should be able to know:
Neuroanatomy and neurolocalization of each CN
Common clinical syndromes

4. Facial Nerve (CN VII)
• It is a mixed nerve with both motor and sensory components.
• Predominantly motor nerve supplying
muscles of facial expression
the stapedius
the stylohyoid
posterior belly of the digastric

5. cont.
• A smaller branch ( nervus intermedius) carries fibers for
 the parasympathetic (tears and salivation)
 visceral sensory (taste)
 general somatosensory functions ( external auditory meatus)
• The neuronal cell bodies that form he facial nucleus are situated in the
pons.

7. Course of the Facial Nerve
• Both components of CN VII emerge from the brain stem at the
pontomedullary junction, cross the subarachnoid space, and enter the
internal acoustic meatus.
• At the entrance to the IAC, the facial nerve motor root lies in a groove
on the anterosuperior surface of the CN VIII with the NI in between.
• At the lateral end of the meatus, the facial nerve enters its own canal,
named the “facial canalˮ.

9. cont.
• The first branch given off in the facial nerve’s course is the greater
(superficial) petrosal nerve, which carries preganglionic
parasympathetic fibers.
• Pass through the ganglion and goes forward through the hiatus of the
facial canal to join the deep petrosal nerve from the carotid
sympathetic plexus to form the vidian nerve or the nerve of the
pterygoid canal, which runs the lacrimal gland.

10. cont.
• Distal to the geniculate ganglion, the facial nerve continues to descend
and the nerve to the stapedius arises from the distal tympanic
segment.
• The chorda tympani usually leaves the main trunk slightly above the
stylomastoid foramen; it carries taste and general visceral afferent
(GVA) fibers as well as preganglionic parasympathetic.
• The chorda tympani runs downward to exit the skull and join the
lingual nerve, a branch of the mandibular division of CN V.

11. cont.
• Taste sensation from the anterior two-thirds of the tongue is carried
through the lingual nerve to the chorda tympani then to the geniculate
ganglion.
• Central processes carrying taste and GVA sensation terminate in the
nucleus of the solitary tract.

13. cont.
• Fibers subserving taste sensation ascend with the contralateral medial
lemniscus to the thalamus.
• Temporofrontal, zygomatic, buccal, marginal mandibular, and cervical
branches supply all the facial mimetic muscles.

14. Segments of facial nerve
1. Brainstem (intramedullary )segment
 from the brainstem nuclei to the exit point
2. Cisternal segment
 from the exit point to the entrance into the IAC
3. Meatal (canal )segment
 course through the IAC to the entrance to the facial canal
4. Labyrinthine segment
 from entrance of facial canal to the geniculate ganglion

15. cont.
5. Short horizontal segment
 from the geniculate ganglion to the posterior wall of the tympanic
cavity
6. Mastoid segment
 from the pyramidal eminence to the stylomastoid foramen
7. Extratemporal (peripheral )segment
 from the stylomastoid foramen to the pes anserinus

17. Branchial Motor (Efferent) Component
• Signals for voluntary movements of the facial muscles originate in the
motor areas of the cerebral cortex.
• They travel through the posterior limb of the internal capsule as part of
the corticobulbar tract and project to the ipsilateral and contralateral
motor nuclei of CN VII in the tegmentum of the caudal pons.
• Upper motor neurons that project to the parts of the nucleus
innervating upper facial muscles project bilaterally.

18. cont.
• Those that project to the parts of the nucleus innervating the lower
facial muscles project mainly contralaterally.
• Branchial motor axons from the facial nucleus pass through the
internal acoustic meatus to the facial canal.
• The nerve to stapedius is given off in the vertical part of the canal.

19. cont.
• Stylomastoid foramen
Nerve to stylohyoid and the posterior belly of digastric muscles
posterior auricular nerve to the occipitalis muscle
temporal, zygomatic, buccal, mandibular, and cervical branches

24. cont.
• The facial nuclei also receive bilateral extrapyramidal, basal ganglia,
and hypothalamic innervations that are concerned with maintaining
facial muscle tone and with automatic and emotional movements.

25. Parasympathetic Motor (Visceral Efferent) Component
• The parasympathetic component of CN VII is responsible for control
of the lacrimal, submandibular, and sublingual glands and the mucous
glands of the mouth, pharynx, and nose.
• The cell bodies are scattered in the pontine tegmentum and are
collectively called the “superior salivatory nucleus.”

28. General Sensory (Afferent) Component
• The general sensory component of CN VII is very small
• Innervates the external ear, the external acoustic meatus, and the
external (lateral) surface of the tympanic membrane
• The nerve cell bodies are located in the geniculate ganglion

30. Special Sensory (Afferent) Component
• There are five basic tastes: salt, sour, sweet, bitter, and savory (umami)
• The special sensory axons of CN VII carry signals from taste buds on
the anterior two-thirds of the tongue via the chorda tympani nerve and
from a small population of taste buds on the soft palate via the greater
petrosal nerve.
• Their cell bodies are located in the geniculate ganglion within the
facial canal

31. cont.
• Unlike other sensory projections, the ascending (secondary) fibers
from this nucleus project ipsilaterally to reach the ventral posterior
nucleus of the thalamus.
• Then project through the posterior limb of the internal capsule to the
cortical area for taste, which is located in the most inferior part of the
sensory cortex in the postcentral gyrus and extends onto the insula.

34. Facial weakness

35. cont.
• Facial nerve dysfunction results in unilateral upper and lower facial
weakness manifested by flattening of the nasolabial fold, an
asymmetrical smile, poor eyebrow elevation, decreased forehead
wrinkling, and weak eye closure
• Two types of neurogenic facial nerve weakness peripheral or lower
motor neuron and central or upper motor neuron.

36. Facial Weakness of Central Origin
• weakness of the lower face, with relative sparing of the upper face.
• The upper face has both contralateral and ipsilateral supranuclear
innervation
• cortical innervation of the facial nucleus may be more extensive for
the lower face than the upper.
• The upper face is not necessarily completely spared, but it is always
involved to a lesser degree than the lower face.
• Lesions are most often in the cortex or internal capsule

37. cont.
• Facial asymmetry more apparent with spontaneous expression as when
laughing, is called a mimetic or emotional facial palsy (EFP)
• Weakness more marked on voluntary contraction, when the patient is
asked to smile or bare his/her teeth is a volitional facial palsy (VFP)
• Volitional facial paresis may occur with corticobulbar interruption
from lesions of the lower precentral gyrus, internal capsule,
cerebral peduncle, or upper pons (above the facial nucleus)
• The reverse dissociation, emotional paresis occurs with frontal lobe
lesions anterior to the precentral gyrus, especially if they affect the
right cerebral hemisphere

39. Peripheral Facial Palsy
• PFP can occur from a lesion involving the facial nerve nucleus in the
pons at any point along the infranuclear segment.
• Flaccid weakness of all the muscles of facial expression on the
involved side, both upper and lower face and the paralysis is usually
complete (prosopoplegia).
• The affected side is smooth, no wrinkles on the forehead, the eye is
open, the inferior lid sags, the nasolabial fold is flattened and the angle
of the mouth droops

40. cont.
• Lack of tearing may signal proximal involvement above the origin of
the greater superficial petrosal nerve
• Weakness of the stapedius- hyperacusis
• With PFP the direct corneal reflex is impaired but the consensual is
intact; in the opposite eye the direct response is intact and the
consensual impaired
• Labials (b, p, m, w) and vowels (o ,u, i, e, a) are produced by pursing
the lips, patients with peripheral facial weakness have difficulty in
articulating these sounds.

41. Localization of PFN palsy
Nuclear & Fascicular Lesions (Pontine Lesions)
• At the nucleus of the facial nerve or its intrapontine axons (fascicles)
• usually affect neighboring structures, such as the abducens fascicle
the paramedian pontine reticular formation (PPRF) (paralysis of
conjugate gaze to the ipsilateral side), the corticospinal tract
(contralateral hemiplegia)
• occasionally the spinal tract and nucleus of the trigeminal nerve and
the spinothalamic tract (ipsilateral facial and contralateral body
sensory disturbances)

42. cont.
Millard-gubler Syndrome:
• lesion in the ventral pons affecting CN VII, CN VI and the corticospinal tract
 Ipsilateral peripheral-type facial paralysis
 Ipsilateral lateral rectus paralysis
 Contralateral hemiplegia
Eight-and-a-half Syndrome:
• lesion in the dorsal tegmentum of the caudal pons involving the PPRF and the
MLF as well as the nucleus of the facial nerve
 Internuclear ophthalmoplegia (INO) in addition to horizontal gaze palsy (one-
and-a-half syndrome)
 Ipsilateral lower motor neuron-type facial palsy

43. Cerebellopontine angle lesions
• Lesions in this location (e.g. acoustic neuroma, meningioma) result in:
 Ipsilateral peripheral-type facial nerve paralysis
 Ipsilateral loss of taste
 Ipsilateral tinnitus, deafness, and vertigo

44. Ramsay Hunt Syndrome:
• Involvement of the geniculate ganglion by zoster virus (VZV)
• results in facial paralysis, hyperacusis, and loss of taste associated
with geniculate neuralgia and herpetic vesicles on the eardrum,
external auditory meatus or palate
• facial paralysis can develop without herpetic eruption, a condition
known as zoster sine herpete.

45. Lesions Distal to the Stylomastoid Foramen
• produce isolated facial motor paralysis.
• Individual motor branches of the facial nerve may be affected causing
paralysis of individual facial muscles.
• the fibers of the facial nerve may be involved by inflammation of the
retromandibular lymph nodes or by tumors or infections of the
parotid gland.
• The facial nerve or its branches are also susceptible to facial trauma
• Bell’s palsy is one of the most common conditions seen accounting for
approximately 50% of the cases of peripheral facial paralysis

46. Bell’s Palsy:
• Idiopathic facial paralysis
• frequently follows a viral infection or an immunization
• Facial nerve pathology in Bell’s palsy is consistent with an
inflammatory and possibly infectious cause
• ? herpes simplex,? herpes zoster
• antiviral treatment has not proved efficacious
• is more prevalent in women who are pregnant or have recently gave
birth

48. Sensory Involvement
• Taste may be affected with lesions of the facial nerve proximal to the
takeoff of the chorda tympani.
• Permanent taste disturbances may follow Bell’s palsy.

49. Autonomic dysfunction
• lesions of the nerve at or proximal to the geniculate ganglion can cause
abnormalities of lacrimation and salivation
• Absence of salivation occurs only with bilateral lesions
• Schirmer’s test: hanging litmus or filter paper on each lower lid
• lacrimal reflex , usually bilateral, caused by stimulating the cornea
• nasolacrimal reflex is elicited by mechanical stimulation of the nasal
mucosa

50. Cranial Nerve VIII: The Vestibulocochlear Nerve

51. Two separate functional components:
the auditory (cochlear) nerve concerned with hearing, and
the vestibular nerve concerned with equilibrium ,coordination and
orientation in space

52. • Sound waves converge on the tympanic membrane and are
transmitted by the auditory ossicles (malleus, incus, and stapes) to
the inner ear, or labyrinth
• Labyrinth is a complex of interconnecting cavities, tunnels, ducts,
and canals that lies in the petrous portion of the temporal bone
• The bony labyrinth is filled with perilymph, a thin watery fluid

53. • The membranous labyrinth is an arrangement of sacs and ducts that
lies within the bony labyrinth, generally follows its outline, and is
filled with endolymph (Scarpa’s fluid)
• The membranous labyrinth has two major components: the vestibular
apparatus and the cochlear duct
• The ossicles span the middle ear cavity and transmit the oscillations of
the tympanic membrane to the footplate of the stapes

56. • The ossicles function as an amplifier and compensate for the loss of
energy as sound waves are transmitted from the air to the perilymph
behind the oval window
• The tensor tympani muscle(inserts on the malleus) and the
stapedius(inserts on the stapes) provide reflex protection against
sudden and loud noise.
• The oval window opens into the vestibule of the inner ear, which
connects on one side to the cochlea and on the other to the
semicircular canals.

57. • The cochlea spirals for 2.5 to 2.75 turns to reach its apex.
• The base of the cochlea faces the internal acoustic meatus and contains
fenestrations that admit the filaments of the cochlear nerve
• Tonotopic organization( high frequency tones vibrate cochlear region
near the base and, low frequency tones vibrate the region near the
apex)

58. The Auditory Pathways
Four-tiered neuronal network:
1) Auditory (cochlear) nerve extending from the organ of Corti to the
cochlear nucleus
2) Fibers from the cochlear nucleus crossing to the contralateral
inferior colliculus
3) Fibers from the inferior colliculus extending to the medial
geniculate body
4) Fibers from the medial geniculate body projecting to the auditory
cortex in the superior temporal gyrus

61. 1st order neurons
• The auditory receptors are the neuroepithelial hair cells of the organ
of Corti.
• Hair cells located at the cochlear apex are stimulated by low-
frequency tones, whereas those located at the base are stimulated by
high-frequency tones
• These fibers then enter the brainstem at the level of the ventral
cochlear nuclei as the cochlear nerve.

62. 2nd order neurons
• On entry into the lower brainstem at the junction between the medulla
and pons, the afferent cochlear nerve fibers divide, innervating the
dorsal cochlear nucleus and the anteroventral and posteroventral
nuclei of the cochlear complex
• This innervation follows a tonotopic pattern.
• The more dorsal aspects of these nuclei receive fibers that have
innervated “high-frequency” (basal) hair cells, whereas the ventral
aspects receive fibers from “low-frequency” (apical) hair cells.

63. • The dorsal and ventral cochlear nuclei contain the second-order
neurons and give rise to several projections to the contralateral
brainstem, which ascend as the lateral lemniscus, a fiber tract that
projects to the central nucleus of the inferior colliculus
• These projections include the dorsal acoustic striae (from the dorsal
cochlear nucleus), the intermediate acoustic striae (from the dorsal
part of the ventral cochlear nucleus), and the ventral acoustic striae
(from the ventral cochlear nucleus)

64. 3rd order neurons
• The inferior colliculus, located in the midbrain tectum caudal to the
superior colliculus, contains the third-order neurons and serves as the
central relay nucleus in the auditory pathway receiving ascending
and descending input
• The projections from the inferior colliculus terminate in the medial
geniculate body, with the low-frequency fibers ending in the apical–
lateral areas and the high-frequency fibers ending in the medial
portions of this nuclear mass

65. 4th order neurons
• The medial geniculate body is the thalamic auditory relay nucleus,
and chiefly gives rise to the geniculotemporal fibers or auditory
radiations.
• Most fibers terminate in the primary auditory cortex (AI,
Brodmann’s area 41), located in the transverse temporal gyri of
Herschel, but some end in the association auditory cortex (AII,
Brodmann’s area 42).
• The primary auditory cortex terminations conform to a tonotopic
pattern, with high-frequency tones terminating medially and low-
frequency tones terminating laterally.

66. • There are connections between the two cochlear nuclei, connections
between the two dorsal nuclei of the lateral lemniscus through the
commissure of Probst
• Connections between the inferior colliculus on each side through the
commissure of the inferior colliculus
• Connections between the central nucleus of the inferior colliculus
and the contralateral medial geniculate body through the brachium
of the inferior colliculus

68. • The blood supply to the cochlea and auditory brainstem nuclei arises
from the internal auditory (labyrinthine) artery, usually a branch of the
anterior inferior cerebellar artery.

69. The Vestibular System
• Monitors angular and linear accelerations of the head
• These accelerations are transduced into neuronal signals within a
specialized structure, the membranous labyrinth which consists the
otolith organ (utricle and saccule) and the three semicircular
canals
• Linear acceleration is monitored by the utricle and saccule
• angular acceleration is monitored by the ampullae of the
semicircular canals.

70. • The semicircular canals are three in number and are oriented at
approximately right angles to each other to detect angular
accelerating movements of the head
• The utricle and saccule are arranged at right angles also, with the
utricle parallel to the base of the skull and the saccule parallel to
the sagittal plane
• Horizontal head movements stimulate the utricle linearly, whereas
tilting the head activates the saccule.

71. • The information from the membranous labyrinth is transmitted into the
two different components of the vestibular nerve.
• The superior portion of the nerve carries input from the anterior and
horizontal semicircular canals and from the utricle
• The inferior portion of the nerve transmits information from the
posterior semicircular canal and the saccule.

72. • The vestibular nerve enters the brainstem at the pontomedullary level
and terminates in the vestibular nuclei which lie in the rostral
medulla and caudal pons
• The vestibular nuclei initiate contralateral vestibulo-ocular
responses(VOR) and ipsilateral vestibulospinal reflexes(VSR) to
maintain a stable vision during head movements and a stable posture
during body movements.
• The semicircular canals relate preferentially to the superior and
medial vestibular nuclei
• The macular fibers project mainly to the medial and inferior
vestibular nuclei

73. • Other afferents of the vestibular nerve enter the cerebellum by way of
the inferior cerebellar peduncle and terminate in the
vestibulocerebellum.
• Most of the vestibular nuclei output is concerned with feedback
integration with the cerebellum, spinal cord, and brainstem.
• The main vestibular connections include:
Medial Longitudinal Fasciculus
 Medial Vestibulospinal Tract
 Lateral Vestibulospinal Tract
Cerebellum
Reticular Formation

74. MEDIAL LONGITUDINAL FASCICULUS
 Exert an influence on conjugate eye movements and on head posture
 All vestibular nuclei send fibers to the contralateral MLF except the superior
nucleus which projects to the ipsilateral MLF
MEDIAL VESTIBULOSPINAL TRACT
 Arises primarily from the medial vestibular nucleus, and to a lesser extent,
from the inferior and lateral vestibular nuclei
 Exerts an excitatory and inhibitory effect on the cervical and upper
thoracic levels of the contralateral spinal cord.

75. LATERAL VESTIBULOSPINAL TRACT
 Originates primarily from the lateral and inferior vestibular nuclei and
projects to the ipsilateral spinal cord
 Facilitates extensor trunk tone and the action of antigravity axial muscles
CEREBELLUM
 Receives afferent fibers from the vestibular nuclei of the same side.
 Also has reciprocal connections with the vestibular nuclei
RETICULAR FORMATION
 Neurons in the superior lateral and inferior vestibular nuclei project bilaterally
to the ventral posterolateral and posterior nuclear group of the thalamus

76. • The cortical representation of vestibular function is located in the
postcentral gyrus near areas 2 and 5 of the cerebral cortex.
• Other receptive areas include the frontal lobe (area 6) and the superior
temporal gyrus.
• The blood supply to the membranous labyrinth is from the internal
auditory or labyrinthine artery, which usually arises from the anterior
inferior cerebellar artery but occasionally branches directly from the
basilar artery.

77. Clinical Evaluation of Cranial Nerve VIII
Function and Lesion localization
• Weber’s test
• Rinne’s test Otoscopic examination should be done first.
• Schwabach’s test
• Conductive hearing loss is that due to impaired conduction of
sound to the cochlea
• Sensorineural hearing loss Involves the cochlea (sensory), the
cochlear nerve and nuclei (neural), or the central auditory
pathways.

78. SNHL vs CHL

79. Localization of Lesions Causing Vertigo
Components of clinical exam:
(a) Observation for spontaneous and gaze-evoked nystagmus
(b) Evaluation of extraocular movement
(c) vestibulo-ocular reflex testing
(d) Dix-Hallpike and static positioning (side lying) tests
(e) Limb coordination, primarily searching for past pointing and ataxia
(f) Gait and Romberg

81. vestibule-ocular reflex

82. Benign Paroxysmal Positioning Vertigo
• Disorder of the inner ear in which brief attacks of acute and severe
vertigo with concomitant nystagmus and autonomic symptoms is
precipitated by certain head movements (often while patients turn in
bed).
• Commonly, BPPV involves the posterior semicircular canal.
• BPPV may follow head trauma, viral labyrinthitis, Ménière’s disease,
migraines, or inner ear surgery, but most cases (50%–70%) are
primary or idiopathic

83. Ménière’s Disease
• Progressive disorder characterized by episodic acute and disabling
attacks of vertigo, fluctuating SNHL and tinnitus
• The hearing loss in the early stages of the disease affects only low
frequencies, fluctuates, and increases during the acute attack.
• Often unilateral, although it may be bilateral in approximately 20% to
45% of cases.
• The etiology is unknown.
• ???excess fluid and pressure in the endolymphatic system

84. CN IX: Glossopharyngeal nerve

85. • Contains motor, sensory, and parasympathetic fibers.
• The nerve emerges from the posterior lateral sulcus of the medulla
dorsal to the inferior olive in close relation with cranial nerve X and
the bulbar fibers of cranial nerve XI
• Travel through the jugular foramen

86. • The nerve winds around the lower border of the stylopharyngeus
muscle and then penetrates the pharyngeal constrictor muscles to
reach the base of the tongue
• The motor fibers originate from the rostral nucleus ambiguus and
innervate the stylopharyngeus muscle (a pharyngeal elevator) and
(with the vagus nerve) the constrictor muscles of the pharynx
• Taste afferents and general visceral afferent fibers have their cell
bodies in the petrous ganglion and terminate mainly in the nucleus of
the solitary tract

87. • The sensory fibers carried in the glossopharyngeal nerve include taste
afferents, supplying the posterior third of the tongue and the pharynx
• General visceral afferents from the posterior third of the tongue,
tonsillar region, posterior palatal arch, soft palate, nasopharynx, and
tragus of the ear.
• The parasympathetic fibers carried in the glossopharyngeal nerve
originate in the inferior salivatory nucleus

88. Has six terminal branches:
• (a) The tympanic nerve (Jacobson nerve)
• (b) Carotid
• (c) Pharyngeal
• (d) Muscular
• (e) Tonsillar
• (f) Lingual branches

91. Clinical Evaluation of Cranial Nerve IX
Motor Function:
 Stylopharyngeus function is difficult to assess.
 Motor paresis may be negligible, although mild dysphagia may
occur and the palatal arch may be somewhat lower at rest on the
side of injury.
Sensory Function:
 The integrity of taste sensation may be tested over the posterior
third of the tongue
 Is lost ipsilaterally with nerve lesions

92. Autonomic Function:
 Salivary secretion (from the parotid gland) may be decreased,
absent, or occasionally increased with glossopharyngeal lesions
 Specialized quantitative studies
Reflex Function:
The pharyngeal or gag reflex is tested by stimulating the
posterior pharyngeal wall, tonsillar area, or base of the tongue.
The response is tongue retraction associated with elevation and
constriction of the pharyngeal musculature.

93. Glossopharyngeal (Vagoglossopharyngeal)
Neuralgia
• Unilateral pain (usually stabbing, sharp, and paroxysmal) located in
the field of sensory distribution of the glossopharyngeal or vagus
nerves
• An abrupt ,severe pain in the throat or ear that lasts seconds to
minutes and is often triggered by chewing, coughing, talking,
yawning, swallowing, and eating certain foods
• Etiologies:
 often “idiopathic”(may be related to ephaptic excitation of the
glossopharyngeal and vagus nerves)
 posterior fossa lesions( tumor, infection, trauma, compression,
MS,…)

94. Anatomy of Cranial Nerve X (Vagus Nerve)
• The longest and most widely distributed CN
• Contains motor, sensory, and parasympathetic nerve fibers
• It connects with four brainstem nuclei: the nucleus ambiguous, the
DMNX, the nucleus of the spinal tract of CN V, and the nucleus of the
solitary tract.

96. • Rootlets of the vagus nerve emerge from the posterior sulcus of the
lateral medulla dorsal to the inferior olive in close association with
the CN IX
• These vagal rootlets form a single trunk that leaves the skull through
the jugular foramen
• Inferior to the jugular foramen are the two vagal ganglia: the jugular
(general somatic afferent) and nodose (special and general visceral
afferent)

97. • It conveys exteroceptive GSA sensation from the pharynx, larynx,
ear, and meninges, and
• GVA fibers from the larynx, viscera of the thorax and abdomen, and
receptors in the aorta.
• Carries skeletomotor axons from the nucleus ambiguus to the
pharynx and larynx
• parasympathetic axons from the DMNX to the smooth muscles and
glands of the pharynx and larynx and to the thoracic and abdominal
viscera.

100. Clinical Evaluation of Cranial Nerve X
Motor Functions:
 The striated muscles of the soft palate, pharynx, and larynx are
innervated by the vagus nerve.
 The soft palate and uvula are examined at rest and with phonation
 Observing pharyngeal contraction during phonation and swallowing
 with phonation, the palate should elevate symmetrically with no
uvular deviation
With acute unilateral lesions, the speech may have a nasal quality
and dysphagia is often present(more marked for liquids than solids)
 Direct observation of laryngeal movements during laryngoscopy

101. Reflex Function:
The efferent limb of the pharyngeal reflex (gag reflex) runs in the
glossopharyngeal and vagus nerves
Hiccup (singultus) is a sudden reflex contraction of the diaphragm ,the
phrenic nerves are the major pathway, but CN X contributes
The carotid sinus reflex is produced by stimulation of the carotid sinus at the
carotid bifurcation, Causing
 slowing of the HR
 a fall in BP
 a decrease in CO
 peripheral vasodilation

102. Disorders of Function
• Bilateral UMNL result in pseudo-bulbar palsy
 Dysphagia
 Spastic dysarthria
“Emotional incontinence” with pathologic crying
 Depressed or exaggerated gag reflex

103. Cranial Nerve XI: The Spinal Accessory Nerve

104. • Purely motor nerve originates partly from the medulla (cranial part
or internal ramus) and partly from the spinal cord (spinal root or
external ramus).
• Its fibers emerge from the lateral medulla below the roots of the vagus.
• The spinal part arises from a column of cells (“accessory nucleus”)
that extends from the 1st -6th cervical cord segments in the dorsolateral
part of the ventral horn of the spinal cord

105. • The cranial and spinal roots unite and exit from the skull through the
jugular foramen.
• The external ramus enters the neck between the internal carotid artery
and the internal jugular vein.
• Somatotopicaly arranged:
C1 and C2 innervate predominantly the ipsilateral SCM
C3 and C4 innervate primarily the ipsilateral trapezius

107. • The supranuclear innervation of the trapezius and sternocleidomastoid
muscles probably originates in the lower precentral gyrus.
• The corticobulbar fibers to the trapezius are crossed and thus one
cerebral hemisphere supplies the contralateral trapezius muscle.
• Corticobulbar fibers orientation in the brain stem:
 Trapezius…ventral
 SCM…..tegmentum

108. CLINICAL EXAMINATION
 One SCM acts to turn the head to the opposite side or to tilt it to the
same side.
 Acting together, the SCMs thrust the head forward and flex the neck

110. Weakness of SCM and trapezius muscles
1) Weakness of the trapezius on one side & weakness of the SCM on
the other side (dissociated weakness) indicates an UMLN ipsilateral
to the weak SCM, above the oculomotor complex.
2) Weakness of the trapezius on one side, sparing of SCM muscles
indicates a ventral brainstem lesion, a lower cervical cord lesion or a
lower spinal accessory root lesion
3) Weakness of the SCM, sparing trapezius indicates a lesion of the
lower brainstem tegmentum, or upper cervical accessory roots

111. 4) Weakness of the SCM and the trapezius muscles on the same side
indicates a contralateral brainstem lesion, an ipsilateral high cervical
cord lesion, or an accessory nerve lesion before the nerve divides
into its branches
5) Weakness in one muscle only ( SCM or trapezius ) may occur with
lesions of the accessory nerve distal to its bifurcation (e.g., lesion of
the branch of the accessory nerve to the trapezius).

112. Cranial Nerve XII: The Hypoglossal Nerve
• Is a purely motor nerve supplying the tongue
• Its cells of origin are in the hypoglossal nuclei, which are upward
extensions of the anterior gray columns of the spinal cord
• The nucleus is somatotopically organized, with different cell groups
innervating different tongue muscles
• From rostral to caudal, the innervation is intrinsic tongue muscles,
genioglossus, hyoglossus and styloglossus
• The nerve leaves the skull through hypoglossal foramen

115. • Supranuclear control of the tongue is mediated by corticobulbar
fibers that originate mainly within the lower portion of the precentral
gyrus (perisylvian) area
• The corticobulbar fibers controlling the genioglossus muscles are
crossed
• The other corticobulbar fibers controlling the other tongue muscles
have bilateral supranuclear control

116. • Protrusion of the tongue requires the action of extrinsic tongue
muscles
• Lateral movements of the non protruded tongue are
accomplished by intrinsic muscles
• Lesions in the primary motor cortex or internal capsule will cause
contralateral tongue weakness
• Lesions of the hypoglossal nucleus, exiting fascicles or nerve
cause ipsilateral tongue weakness.

117. • Lesions of the hypoglossal nerve result in paresis, atrophy, furrowing,
fibrillations, and fasciculations that affect the corresponding half of the
tongue.
• Bilateral LMNL result in:
 Atrophy, weakness, and fibrillations of the tongue
 Marked difficulty with articulation( esp. pronunciation of d & t
phonemes)
 Dysphagia and breathing difficulties (flaccid tongue falls
backward to obstruct the pharynx)

118. Reference