Cranial nerves

1
Cranial nerves Cranial nerve nuclei

• There are 12, paired cranial nerves.
• The first 2 cranial Ns. attach directly to
  forebrain, 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
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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. lies between olive pyramid in
  the M.O. / but glossopharyngeal, vagus
  accessory Ns. are attached to postero-lateral
  sulcus of M.O., lateral to olive.

The base of the brain showing locations of
cranial nerves
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Afferent Nerve Nuclei

• Large Trigeminal Sensory nucleus, extends the
  whole length of brain stem and cervical spinal
  cord. receiving general sensation from the head
  via trigeminal N.
• Vestibular Cochlear nuclei that are located in
  upper M.O., receiving hearing positional sense
  via vestibulo-cochlear N.
• Nucleus solitarius located in upper M.O.,
  receiving taste sensation via facial
  glossopharyngeal Ns.

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.
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Efferent Nerve Nuclei

• Somatic efferent column supplies striated Ms.
  in head, including
  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
  1- Trigeminal motor nucleus.
  2- Facial motor nucleus.
  3- Nucleus ambiguus.
• Parasympathetic (general visceral) efferent
  column supplies glands smooth Ms. of
  viscera , including
  1- Edinger- Westphal nucleus.
  2- Sup. Inf. Salivary nuclei.
  3- Dorsal nucleus of vagus.
  

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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.

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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.

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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.

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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 caudal
  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

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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.
  via Vagus N. to supply mucous gland of G.I.T
  respiratory glands.
• Dorsal motor nucleus of vagus lies in the
  rostral M.O. lateral to hypoglossal nucleus, it
  gives preganglionic parasymp.Fs. Via vagus N. to
  supply ms. of abdominal respiratory viscera.

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Cranial 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 into
  ciliary ganglion which sends postganglionic Fs.
  via short ciliary nerves into constrictor
  pupillae ciliary ms.

11
T.S of midbrain at the level of sup.colliculus
to illustrate the
pathway of pupillary light reflex.

• During the visual pathway ,small Fs. leave the
  optic tract to synape in 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.
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Accomodation 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 activation of
  sphincter pupillae m.
• Fibres from 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.)
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IV 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.

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.
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VI Abducens Nerve

• 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.

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Lesions of cranial nerves III,IV and VI

• Oculomotor N. palsy by a lesion of occulomotor
  nucleus in midbrain 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 right eyelid, the eyeball
  can be seen abducted and the pupil dilated.
• Note failure of left eyeball abduction due to
  lesion of left abducent N.

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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. Via mandibular N. 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.
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V 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.
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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.
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Sensory 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 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.
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Motor 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
  1st pharyngeal arch drevatives
  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.
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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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1. All of the following are corresponding to
parasympathetic efferent nuclei EXCEPT
a.Superior salivary nucleus. b.Inferior salivary
nucleus. c.Abducent nucleus. d.Edinger-Westphal
nucleus. e.Dorsal motor nucleus of vagus.
2. Which of the following is Corresponding to
branchiomotor efferent nuclei ?


a.Edinger-Westphal nucleus.



b.Dorsal motor nucleus of vagus.


c.Oculomotor
nucleus. d.Nucleus ambiguus. e.Hypoglossal
nucleus.
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3.Bulbar palsy is confirmed by
degeneration of one of the following Nuclei
a.Oculomotor nucleus.
b.Mesencephalic nucleus. c.Abducent
nucleus. d.Trochlear nucleus. e.Nucleus
ambiguus. 4.Syringobulbia leads to destruction of
a.The lateral lemniscus.
b.The trigeminal lemniscus. c.The
corticobulbar tract. d.The
spinothalamic tract. e.The trapezoid body.
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VII Facial Nerve

• It consists of 2 roots

1-The lateral root (Nervous intermedius) contains
sensory parasymp.Fs.

2- The medial
root is the motor root.
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VII 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-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.
  3-
  Sensory Taste Fs. from anterior 2/3 of tongue,
  cell bodies in sensory geniculate ganglion in
  middle ear , and run in nervus intermedius to
  end in Nucleus Solitarius in M.O. projecting
  into (v.p) of thalamus then to sensory cortex

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VII Facial Motor 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 brain stem for mediation of certain reflexes
  and from cerebral cortex for
  cortico-bulbar pyramidal tract.

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VII Facial Motor Nerve

• Reflex connections mediate 1- protective eye
  closure in response to sudden strong stimuli 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.

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Bells 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).

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VIII Vestibulocochlear Nerve

• It is purely sensory nerve.
• It has 2-components ,
  1- Vestibular N., which carries balance sensation
  from utricle, sacule semicircular canals.
  
  2- Cochlear N., which carries hearing
  sensation.
• It emerges from ponto-medullary junction at
  cerebello-pontine angle

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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.
• It enters the brain in groove between pons M.O.
  to end in the Vestibular nuclei in M.O.

Distribution of Vestibular Nerve
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Vestibular Nerve Fibres

• 1-Efferent Fs. From the 4 vestibular nuclei to
  cerebellum ( flocculo-nodular lobe)
  through inferior cerebellar peduncle to control
  balance.
• 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. 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.)
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Vestibular 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 adjacent to primary sensory
cortex in parietal lobe at inferior parietal
lobule just above lateral fissure.
Vestibular nerve nuclei their central
connections
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Lateral aspect of cerebral hemisphere
location of vestibular area in cerebral cortex
adjacent to primary sensory cortex in inferior
parietal lobe/ or above lateral fissure, adjacent
to auditory cortex in temporal lobe.
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• Cochlear Nerve
• 1st order neurones it is formed by the cells of
  spiral ganglion.
• Peripheral Fs. conduct sound from the organ of
  Corti in the cochlea.
• The axons of these cells bifurcate to end in
  dorsal venteral cochlear nuclei , which lie
  close to inf.cerebellar peduncle.

Ascending connections of auditory
component of vestibulo-cochlear nerve.
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• 2nd order neurones it is formed of cells of
  cochlear nuclei.
• Most axons of these cells Cross to opposite side
  of pons 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 then ascend to end in
  inferior colliculus of midbrain.

• The inferior colliculus sends axons to medial
  geniculate nucleus of thalamus.

Ascending connections of auditory
component of vestibulo-cochlear nerve.
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• 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.
38
Lateral aspect of cerebral hemisphere
Note primary auditory cortex Wernickes area
in superior temporal gyrus.
39
Acoustic Neuroma

• It is a benign tumour of vestibulocochlear nerve
  in cerebello-pontine angle.
• So, there is attacks of dizziness, deafness
• ataxia (disturbances of voluntary movement).

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IX Glossopharyngeal Nerve Fibres

• It is a mixed N. ,attached lateral to olive in
  rostral medulla and leaves the skull through
  jugular foramen.
• It contains

1-Afferent Sensory Fs. for Taste sensation from
post.1/3 of tongue general sensation from
phartnx end in trigeminal sensory nucleus.

2-Afferent visceral (chemo- baroreceptors
in carotid body sinus) taste Fs. end in
Nucleus Solitarius of medulla.
Glossopharyngeal nerve nuclei
their central connections. Red motor, brown
parasymp., blue sensory
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IX Glossopharyngeal Nerve Fibres
3-Efferent motor Fibres
arises from its main 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
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X 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- Visceral
  receptors in thoracic abdominal viscera.

Vagus nerve Nuclei their central connections.
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X 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.
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XI 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.
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XII 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.

T.S.of medulla to illustrate origin course of
hypoglossal nerve.
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Motor 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, dysphagia, wasting
  of sternomastoid trapezius Ms. Weakness
  wasting of tongue.