Title: Cranial nerves
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2Cranial nerves Cranial nerve nuclei
- There are 12, paired cranial nerves.
- The first 2 cranial Ns. attach directly to
forebrain (frontal lobe) , while the rest attach
to brain stem. - Olfactory system is attached to forebrain and is
referred to as the limbic system, / optic N. also
is discribed in visual pathway. - Cranial Ns. from 3 - 12 have nuclei (cranial
N.nucluei) in the brain stem , receiving
afferents Fs. Or send efferent Fs. as the cranial
Ns.
The base of the brain showing locations of
cranial nerves
3 Superficial attachements of Cranial nerves
- Occulomotor trochlear Ns. are attached to
midbrain. - Trigeminal N. is attached to antero-lateral
surface of pons. - Abducent, Facial vestibulo-cochlear Ns. are
lying between pons M.O. from medial to lateral. - Hypoglossal N. is attached to antero-lateral
sulcus of M.O. / but glossopharyngeal, vagus
accessory Ns. are attached to postero-lateral
sulcus of M.O.
The base of the brain showing locations of
cranial nerves
4 Afferent Nerve Nuclei
- Fibres carrying general sensation from the head
via trigeminal N. terminate in a large trigeminal
sensory nucleus that extends the whole length of
brain stem and cervical spinal cord. - Fibres carrying hearing motion/ positional
sense via vestibulo-cochlear N. terminate in
cochlear vestibular nuclei that are located in
upper M.O. - Visceral afferents carrying taste sensation via
facial glossopharyngeal Ns., terminate in
nucleus solitarius located in upper M.O.
Dorsal aspect of brain stem showing locations of
Afferent cranial N. nuclei (left) , and Efferent
cranial N.nuclei (right) , in which the same
colours have a common embryological origin.
5 Efferent Nerve Nuclei
- Somatic efferent column supplies striated Ms.
in head, including yellow colour
1- Oculomotor
nucleus.2-Trochlear nucleus.
3-Abducent nucleus. 4-Hypoglssal nucleus. - Branchiomotor (special visceral) efferent column
supplies striated Ms. derived from branchial
arches, including orange 1-
Trigeminal motor nucleus.
2- Facial motor nucleus.
3- Nucleus ambiguus. - Parasympathetic (general visceral) efferent
column supplies glands smooth Ms. of
viscera , including pink colour
1- Edinger- Westphal
nucleus. 2- Sup. Inf. Salivary
nuclei. 3- Dorsal nucleus of
vagus.
6 Somatic efferent Nerve Nuclei
- Oculomotor nucleus lies at the base of
periaqueductal grey of midbrain at the level of
superior colliculus. Its efferent Fs. run in
oculomotor N. to innervate levator palpebrae
superiooris all extraocular Ms. Except L.R
S.O - Trochlear nucleus lies at the ventral part of
periaqueductal grey of midbrain at the level of
inferior colliculus. Its efferent Fs. run in
trochlear N. to innervate S.O.muscle.
7Oculomotor trochlear Nerves
- Oculomotor nerve emerges from the medial aspect
of each cerebral peduncle e.g. through the
interpeduncular fossa. - Trochlear nerve emerges from back of midbrain,
caudal to inferior colliculus and then passes
laterally around cerebral peduncle to appear on
the anterior view of midbrain.
Anterior view of midbrain
Posterior view of midbrain
8 Somatic efferent Nerve Nuclei
- Abducent nucleus lies in the caudal pons ,
beneath floor of 4th vent. Its efferent Fs. run
in abducent N. to supply L.R. - Hypoglossal nucleus lies in the rostral M.O.
its efferent Fs. run in hypoglossal N. to supply
all Ms. of tongue Except palatoglossus muscle.
9 Branchiomotor efferent Nerve Nuclei
- Trigeminal motor nucleus lies in the tegmentum
of the mid-pons and its motor Fs. run in
mandibular branch of trigeminal N. to supply
structures of 1st pharyngeal arch as Ms. of
mustication, mylohyoid, ant.belly of digastric,
tensor tympani (middle ear) tensor veli
palatini.(soft palate). - Facial motor nucleus lies in the caudal pontine
tegmentum, its motor Fs. run in facial N. to
innervate Ms. of facial expression, stapedius
muscle (middle ear) other Ms.derived from 2nd
pharygeal arch (stylohyoid,post.belly of
digastric). - Nucleus ambiguus it is a long nucleus lies in
M.O., sending motor Fs. in 9th ,10th cranial
root of 11th nerves to innervate Ms. of pharynx
larynx derived from 3,4 6 pharyngeal arches.
10 Parasympathetic efferent Nerve Nuclei
- Edinger-Westphal nucleus lies in midbrain
adjacent to oculomotor nucleus. It is the
parasymp. part of oculomotor nucleus. It gives
preganglionic parasymp. motor Fs. Via oculomotor
N. into ciliary ganglion, which sends
postganglionic Fs. to innervate sphincter
pupillae ciliary Ms. in the eye. - Superior salivary nucleus lies in pontine
tegmentum, it gives preganglionic Fs. Via facial
N. into pterygo-palatine submandibular ganglia
, which gives postganglionic Fs. to innervate
lacrimal gl., Nasal and oral M.Ms.
submandibular and sublingual salivary glands.
respictevly
11 Parasympathetic efferent Nerve Nuclei
- Inferior salivary nucleus lies in pontine
tegmentum, sends pre-ganglionic Fs. Via
glosso-pharyngeal N. into otic ganglion , which
sends post-ganglionic Fs. to parotid gland. - Dorsal motor nucleus of vagus lies in the
rostral M.O. lateral to hypoglossal nucleus, it
gives preganglionic parasymp.Fs. Via vagus N. to
innervate thoracic abdominal viscera.
12Cranial Nerves III Oculomotor N.
- This N. contains 2-types of fibres 1- Somatic
motor efferent Fs. from oculomotor nucleus to
all extrinsic eye Ms. Except S.O L.R.
2- Preganglionic parasymp.
motor Fs. from Edinger-Westphal nucleus to
constrictor pupillae ciliary muscle via
postganglionic Fs. of short ciliary nerves
arise from ciliary ganglion. - This N. lying in the lateral wall of cavernus
sinus before passes to orbit through sup.orbital
fissure.
13Eye movements brought about by the extraocular
muscles
- Oculomotor nerve supplies sup.rectus, inf.rectus
, medial rectus , inferior oblique levator
palpebrae superioris, so it elevates ,depresses
and adducts the eyeball. - Trochlear N. supplies S.O, it depresses eyeball
down medial - Abducent N. supplies L.R , it abdducts eyeball.
14T.S of midbrain at the level of sup.colliculus
to illustrate the
pathway of pupillary light reflex.
- If the light is illuminated on one eye , it
causes constriction of the pupil of the same
eye due to contraction of constrictor pupillae
muscle. This is called
direct light reflex. - The constriction of the pupil of the
non-illuminated eye is called
consensual (indirect) light reflex. - During the visual pathway ,small Fs. leave the
optic tract to synape in the pretectal nucleus,
which projects bilaterally Fs. to
Edinger-Westphal nuclei of occulomotor ,that send
efferent parasympathetic Fs. Via oculomotor
nerves on both sides to sphincter pupillae ms.
Note that pretectal area involves in mediation of
pupillary light reflex.
15Accomodation Reflex
- Fixation upon a nearby object, involves
contraction of ciliary muscles to increase the
convexity of lens, thus focusing the image. - It is also accompanied by pupillary constriction
due to activation of constrictor pupillae m. - Also, Cortico-bulbar Fs.( visual frontal cortex)
activate the parasymp. Edinger-Westphal nuclei on
both sides to supply ciliary sphincter pupillae
Ms.
Optic pathway and Visual reflexes (pupillary
light R. accomodation R.)
16IV Trochlear Nerve
- This N. carries only somatic motor efferent Fs.
from the trochlear nucleus in midbrain (level of
inferior colliculus) to supply the S.O. of
opposite side. - Trchlear N. ,the only nerve emerges from the
post.surface of brain - stem ,then appears on
the ventral aspect of the midbrain. - It runs in lateral wall of cavernus sinus and
enter the orbit through sup. orbital fissure to
supply S.O.
T.S of midbrain at the level of inferior
colliculus ,showing the location of trochlear
nucleus (at the base of periaquaductal grey
matter) and course of trochlear N.Fs.
17VI Abducens Nerve
- Like trochlear N., contains only somatic motor
neurones in the abducens nucleus ,which located
in caudal pons beneath the floor of 4th
ventricle. - Fibres emerge from the ventral surface of brain
stem at the junction between the pons pyramid
of M.O - The nerve then passes in the cavernous sinus and
enter orbit through sup. orbital fissure to
supply L.R muscle to abduct the eyeball.
18Lesions of cranial nerves III,IV and VI
- Oculomotor N. palsy by a lesion of occulomotor
nucleus in mibrain or compression by aneurysm or
tumour leads to ptosis , dilatation of pupil
that is unresponsive to light accommodation
reflexes and inability to move eyeball upwards,
downwards and inwards (adduction). - Abducens N. palsy leads to inability to move the
eyeball outwards (abduction). - Combined unilateral palsies of III, IV,and VI
during their course in cavernous sinus , sup.
Orbital fissure or within the orbit , lead to
1-ptosis.
2-dilatation of
pupil. 3-paralysis
of all eye movements
- Note right ptosis .
- Note with elevation of eyelid, the eyeball can be
seen abducted and the pupil dilated. - Note failure of left eyeball abduction due to
lesion of left abducent N.
19 V Trigeminal Nerve
- It is the largest cranial N., it has both
sensory Fs. that are distributed via ophthalmic,
maxillary and mandibular to the head ---
motor Fs. to Ms.of mastications (Ms.of 1st
arch). - It attaches to the ventrolateral aspect of pons
by 2 roots (a large sensory
laterally a smaller motor medially).
Superficial distribution of sensory fibres of
the 3 divisions of trigeminal nerve.
20V Sensory components of Trigeminal Nerve
- Trigeminal sensory nucleus consists of
3-subnuclei 1-Chief
(principle) sensory nucleus lies in pontine
tegmentum (mid-pon), it recevies touch sensation.
2-Spinal nucleus extends caudally
through the medulla and upper cervical spinal
cord to become continuous with substantia
gelatinosa, it recevies pain temp.sensation
from face scalp.
3-Mesencephalic nucleus in midbrain, it recevies
proprioception (deep) sensation from head.
Brain stem and location of
trigeminal sensory nucleus
its major connections.
21 Sensory components of Trigeminal nerve
(for touch/pressure
pain/temperature)
- Afferent Fs. of touch, pressure, pain
temperature are recevied from skin of face
,scalp, via peripheral processes
(ophthalmic,maxillarysensory part of
mandibular) whose cell bodies (first neurones)
are situated in trigeminal ganglion, located at
the convergence of ophthalmic , maxillary and
mandibular nerves. - Afferent Fs.(centeral axons) conveying touch
terminate in principal nucleus, and those
carrying pain temp. end in nucleus of spinal
tract of trigeminal.
Brain stem and location of trigeminal sensory
nucleus its major connections.
22Sensory components of Trigeminal nerve
(for proprioceptive sensation)
- 1st neurone for Proprioceptive
peripheral afferents (via mandibular nerve)
from Ms.of mustication temporo-mandibular joint
have their cell bodies not in trigeminal ganglion
but in mesencephalic nucleus of trigeminal (
the only primary afferents to have cell bodies
within C.N.S). - The centeral axons of the cells of mesencephalic
nucleus descend medially to synapse around Motor
Nucleus of Trigeminal (2ND neurone) in pons. - Axons arising from 2nd neurones in trigeminal
nuclei (sensory motor) decussate to form
contralateral trigemino-thalamic tract, which
terminates in contralateral (VP) nucleus of
thalamus that sends Fs. to sensory cortex.
Brain stem and location of trigeminal sensory
nucleus its major connections.
23Motor components of Trigeminal Nerve
- The motor Fs.of trigeminal N. arise from the
trigeminal motor nucleus , which lies in pontine
tegmentum. - The axons leave the pons to join the mandibular
division of trigeminal , to innervate
1- 4 Ms. of
mastication. 2- 4 other Ms.
mylohyoid, anterior belly of digastric, tensor
palati (soft palate) tensor tympani (middle
ear).
T.S of pons at the level of Trigeminal nuclei.
24 Lesions of Trigeminal Nerve
- Herpes Zoster infection of sensory root of
trigeminal N. .. Leads to severe stabbing pain
eruption of vesicles localised to skin supplied
by its branches ophthalmic , or maxillary or
mandibular N.. Trigeminal Neuralgia. - Syringo-bulbia ,it is a disease of unknown
etiology which affects the closed M.O, causes
central cavitation of medulla caudal to 4th V. ,
leading to destruction damage of decussating
trigemino-thalamic Fs., causing selective loss of
pain temp. sensation in the face
( dissociated
sensory loss), mostly leading to destruction of
the cervical spinal cord (syringomyelia)
cavitation of spinal cord.
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26VII Facial Nerve
- It carries 3-types of fibres 1- Efferent motor
(branchiomotor) Fs. From facial motor nucleus in
pons to Ms. of 2nd arch , Ms.of facial
expression stapedius. 2-Afferent Taste sensory
Fs. From anterior 2/3 of tongue. These Fs. are
processes of cells in sensory geniculate ganglion
in middle ear , and run in nervus intermedius
to end in nucleus solitarius in M.O.
3-Efferent parasympathetic secretomotor Fs.
Carried by lateral root of facial nerve (nervus
intermedius) From sup.salivary nucleus in pons
to pterygopalatine submandibular ganglia to
lacrimal gland , palate, nasal oral m.m, /and
submandibular sublingual salivary glands.
27VII Facial Nerve
- The lateral root contains sensory parasymp.Fs.
is called nervus intermedius , / but the medial
root is the motor root. - The sensory Fs. ends in nucleus solitarius in
medulla and then Fs. project to V.P.nucleus of
thalamus, which sends Fs. to sensory cortex of
parietal lobe.
28VII Facial Nerve
- Motor Fs. of facial nucleus in pons , via facial
N. looping over abducens nucleus , then leaving
the brain stem to supply Ms.of facial
expression ,platysma ,stylohyoid , post.belly of
digastric stapedius of middle ear. - Facial motor nucleus receives other afferents
from area of brain stem for mediation of certain
reflexes and also from cerebral cortex ,
(cortico-bulbar pyramidal tract).
29VII Facial Nerve
- Reflex connections mediate 1- protective eye
closure in response to sudden strong stimuli
through tectobulbar Fs. descending from sup.
Colliculus (tectum of midbrain) to end in facial
motor nucleus, then, via facial N. to supply
orbicularis oculi to close protect the eye.
2- corneal reflex through Fs. from
trigeminal sensory nucleus, to motor nucleus of
facial, then via facial N. to orbicularis oculi
in response to tactile stimulation of cornea. - Afferents from cortical motor areas
(cotico-bulbar Fs.) supply Ms. of upper face
which are distributed bilaterally (from Rt. left
C.hemispheres) , but those supplying Ms. of
lower face are crossed. So, Unilateral upper
motor neurone lesion (UMNL) leads to lower
facial Ms. paralysis of opposite side only, but
upper Ms. are intact.
30Bells Palsy LMN facial paralysis
- It is due to acute unilateral inflammation of
facial nerve within the skull (in facial canal). - Manifested by paralysis of facial muscles of
upper lower parts of face on the same side of
lesion.. - Manifested by pain around ear , - failure to
close eye, absent corneal reflex, - loss of
taste sensation in anterior 2/3 of tongue,
hyperacusis increased sound perception due to
paralysis of stapedius. (action
of stapedius damping down the intensity of high
pitched sounds by damping down movement of
stapes) - If herpes zoster virus is the inflammatory
agent , a vesicular rash appear in ext.
auditory canal m.m of oropharynx (Ramsay
Hunt syndrome).
31VIII Vestibulocochlear Nerve
- It is purely sensory nerve.
- It has 2-components ,
1- Vestibular N., which carries balance sensation
from utricle, sacule semicercular canals.
2- Cochlear N., which carries hearing
sensation. - It emerges from ponto-medullary junction at
cerebello-pontine angle with the facial N.
32 VIII Vestibular Nerve
- Cells of origin vestibular
ganglion ,lying in internal acoustic meatus. - The peripheral process carries sensation from
utricle,saccule semicircular canals (membranous
labyrinth). - Central process leaves vestibular ganglion and
joins cochlear N. - They enter the brain in groove between pons
M.O. to end in the Vestibular nuclei in M.O.
Distribution of Vestibular Nerve
33Vestibular Nerve Fibres
- 1-Efferent Fs. From the 4 vestibular nuclei to
cerebellum ( flocculo-nodular lobe)
through inferior cerebellar peduncle to control
body balance (equilibrium). - 2-Efferent Fs. descend uncrossed to spinal cord
from lateral vestibular (Deiters)nucleus) to
form vestibulo-spinal tract , assist to maintain
balance by influencing muscle tone of body. - 3-Efferent Fs. Also pass to ocular nuclei of
oculomotor , trochlear abducent through medial
longitudinal fasciculus , for coordination of
head eye movements.
Vestibular nerve nuclei their central
connections (rostral M.O.)
34Vestibular Nerve Fibres
4-Efferent Fs. ascend from vestibular nuclei to
relay in (VP) nucleus of thalamus to reach the
cerebral cortex , at the vestibular area of
sensory cortex which is uncertain but is
probably adjacent to primary sensory cortex area
in parietal lobe at inferior parietal lobule just
above lateral fissure or adjacent to auditory
cortex in temporal lobe.
Vestibular nerve nuclei their central
connections
35Lateral aspect of cerebral hemisphere
location of vestibular area in cerebral cortex
probably adjacent to the sensory cortex in
parietal lobe/ or adjacent to auditory cortex
in temporal lobe.
36- Cochlear Nerve
- 1st order neurones conduct impulses of sound from
the organ of Corti in the cochlea. - Fs. of cochlear N. are the central processes of
nerve cells located in spiral ganglion. - The Fs. bifurcate to end in dorsal venteral
cochlear nuclei , which lie close to
inf.cerebellar peduncle.
Ascending connections of auditory
component of vestibulo-cochlear nerve.
37- 2nd order neurones arise from cochlear nuclei
into pons, some Fs. Cross to opposite side as
trapezoid body.
- At trapezoid body some Fs.may terminate in
superior olivary nucleus. - Most Fs. Ascend from sup.olivary nuclei to form
the lateral lemniscus in pons, then ascend to
end in inferior colliculus of midbrain. - Some Fs. end in nucleus of lateral lemniscus in
pons to establish reflex connections with motor
trigeminal facial nuclei, mediating cotraction
of tensor tympani stapedius Ms. In response to
loud noise.
Ascending connections of auditory
component of vestibulo-cochlear nerve.
38- The inferior colliculus sends axons to medial
geniculate nucleus of thalamus. - 3rd order neurone axons arise from MGN pass
through internal capsule to primary auditory
cortex, which is located in Heschls gyri lying
in superior temporal gyrus and hidden within the
lateral fissure - Auditory association cortex ( Wernicks area)
is an area of temporal lobe surrounding the
primary auditory cortex , in which the auditory
information is interpreted ( for knowing the
meaning of sounds).
Ascending connections of auditory
component of vestibulo-cochlear nerve.
39Lateral aspect of cerebral hemisphere
Note primary auditory cortex Wernickes area
in superior temporal gyrus.
40Acoustic Neuroma
- It is a benign tumour of vestibulocochlear nerve
leads to compression of the nerve adjacent
structures in cerebello-pontine angle. - So, there is attacks of dizziness deafness.
- With expansion of tumour, ataxia (disturbances of
voluntary movement) paralysis of cranial
Ns.(especially V-VII) and the limbs follow due
to damage of pyramidal Fs.
41IX Glossopharyngeal Nerve
- It is a mixed N. ,attached lateral to olive in
rostral medulla and leaves the skull through
jugular foramen. - It receives afferent Fs. From 1-Receptors of
general sensation in pharynx, post.1/3 of tongue,
eustachian tube middle ear.
2- Taste buds of pharynx post.1/3 of
tongue. 3- Chemoreceptors
in carotid body Baroreceptors in the carotid
sinus.
Glossopharyngeal nerve nuclei
their central connections
42IX Glossopharyngeal Nerve Fibres
1-Afferent Fs. for general sensation end in
trigeminal sensory nucleus.
-Fibres carrying touch sensation
from back of tongue pharynx are important for
mediating gag reflex, through connection with
nucleus ambiguus hypoglossal nucleus.
2-Afferent visceral (chemo- baroreceptors)
taste Fs. end in nucleus solitarius
of medulla.
Glossopharyngeal nerve nuclei
their central connections. Red
motor, brownparasymp.,bluesensory
43IX Glossopharyngeal Nerve Fibres
3-Efferent motor Fibres
arises from its motor nucleus in the rostral
part of nucleus ambiguus of medulla to supply
stylopharyngeus involved in swallowing.
4-Efferent Parasympathetic Fibres arises from
inferior salivary nucleus of rostral medulla to
synapse in otic ganglion, then via
post-ganglionic Fs.innervate parotid gland.
Glossopharyngeal nerve nuclei
their central connections. Red motor,
brownparasymp.,bluesensory
44X Vagus Nerve
- It is mixed nerve, attached lateral to olive of
medulla caudal to glosso-pharyngeal N. in
groove between olive inf.cerebellar peduncle. - It recevies afferent Fs.from 1-Receptors for
general sensation in pharynx, larynx, tympanic
membrane, ext.acoustic meatus. 2-
Chemoreceptors in aortic bodies and
baroreceptors in aortic arch.
3-Receptors in
thoracic abdominal viscera.
Vagus nerve Nuclei their central connections.
45X Vagus Nerve Fibres
1-Afferent Fs.for general sensation end in
sensory nucleus of trigeminl and - visceral
sensory afferents end in nucleus
solitarius. 2-Efferent Motor Fs. arise from
nucleus ambiguus of medulla (main motor nucleus
of vagus) to innervate Ms. of soft palate,
pharynx, larynx to control swallowing and
speech. 3-Efferent Parasymp. Fs. arise from
dorsal motor nucleus of vagus to supply CVS, RS,
GITS.
Vagus nerve Nuclei their central connections.
46XI Accessory Nerve
- It is purely motor , consists of cranial part
spinal part. - The cranial part emerges from lateral aspect of
medulla below vagus N. It arises from caudal
part of nucleus ambiguus of medulla.
At the level of jugular foramen it joins
vagusN. to supply Ms. of soft palate, pharynx
larynx. - Spinal root of accessory arises from upper 5
cervical spinal cord segments. It ascends to the
side of medulla to join the cranial root till the
jugular F., it separates to supply sternomastoid
trapezius Ms.
Diagram of caudal medulla rostral spinal cord
to illustrate origin and course of vagus
accessory nerves.
47XII Hypoglossal Nerve
- It is purely motor , supplying all extrinsic
intrinsic Ms. of tongue except palatoglossus (by
pharyngeal plexus). - It arises from hypoglossal nucleus in medulla (
beneath floor of 4th V.). - It emerges from M.O. between olive pyramid.
- It also receives coticobulbar Fs. from
contralateral motor cortex, which subserve
voluntary movements of tongue as occur in speech.
T.S.of medulla to illustrate origin course of
hypoglossal nerve.
48Motor neurone disease and lesions of cranial
nerves IX-XII
- Occures in those over 50 years due to chronic
degeneration of cortico-bulbar tracts projecting
to nucleus ambiguus (sends motor Fs.in 9,10,11
nerves) hypoglossal nucleus , leading to
dysphonia (difficulty in phonation), dysphagia
(difficulty in swallowing) , dysarthria (
difficulty in articulation) and weakness
spasticity of tongue (pseudobulbar palsy). - There is also degeneration of nucleus ambiguus
hypoglossal nucleus themselves, leading to
dysphonia,dysphagia, dysarthria and weakness,
wasting fasciculation of tongue (bulbar palsy).
- IX-XII nerves can be damaged by tumours in skull
foramina, lead to dysphonia, weakness, wasting
fasciculation of tongue and depression of gag
reflex wasting of sternomastoid trapezius
Ms.
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