SCRUBS

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SCRUBS Cranial Nerves
Chun Kit Poh 08 February 2010
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Objectives

• Cranial nerves I XII
• Pupillary light reflex
• Accommodation reflex
• Visual field defects
• Trigeminal Neuralgia
• Corneal reflex
• Pseudo / bulbar palsy

• Parasympathetic
• Cranial Nerve nuclei
• Examples
• (not covering CN clinical examination)

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Cranial Nerves
CN I Olfactory Sensory
CN II Optic Sensory
CN III Oculomotor Motor Parasympathetic
CN IV Trochlear Motor
CN V Trigeminal Sensory Motor
CN VI Abducens Motor
CN VII Facial Sensory Motor Parasympathetic
CN VIII Vestibulocochlear Sensory
CN IX Glossopharyngeal Sensory Motor Parasympathetic
CN X Vagus Sensory Motor Parasympathetic
CN XI Accessory Motor
CN XII Hypoglossal Motor
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Cranial Nerves
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Cranial Nerve I (Olfactory)

• Attached to the forebrain telencephalon
  (cerebral hemispheres), under the surface of the
  frontal lobe
• Axons from olfactory receptors in the nasal
  cavity enter cranial cavity through foramina of
  cribriform plate (of the ethmoid bone)
• Does not project via the thalamus

CN I

• Conveys olfactory information (smell)
• Damage
• Anosmia follows damage of CN I (e.g. fracture of
  cribriform plate) ? loss of sense of smell and
  also flavour of foods, but sense of taste (sweet,
  salt, bitter and sour) is preserved
• Can be due to head trauma or when meningiomas
  invade CN I

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Cranial Nerve II (Optic)

• Attached to the forebrain an outgrowth of
  diencephalon (thalamic structures surrounding the
  3rd ventricle)
• Axons from nasal retinal field decussate at
  optic chiasma and pass into contralateral optic
  tract
• Axons from temporal retinal field remain
  ipsilateral
• Mainly terminate in lateral geniculate nucleus
  of thalamus (some to pretectal area)

CN II

• Conveys visual information
• Damage
• Blindness on affected side
• Relative afferent pupillary defect / Marcus Gunn
  pupil to subtle optic nerve defect (observed
  during the Swinging Light Test)
• Pupils constrict less (hence appear to dilate)
  when light swings from unaffected side to
  affected side

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Cranial Nerves II, III
Pupillary light reflex

• Tests CN II and III, midbrain function
• Direct light reflex constriction of
  illuminated eye
• Consensual light reflex constriction of
  non-illuminated eye
• Pathway
• Retina ? Optic Nerve (CN II) ? Optic chiasma ?
  Optic tract ? Some optic tract fibres (CN II)
  branch to ? Pretectal area ? Bilateral projection
  to Edinger-Westphal nuclei ? CN III ? Ciliary
  ganglion ? Short ciliary nerve ? Sphincter
  pupillae

Accommodation reflex

• Focussing on a near object causes pupil to
  constrict
• Pathway
• Retina ? Optic Nerve (CN II) ? Optic chiasma ?
  Optic tract ?
• Lateral geniculate body ? Optic radiation ?
  Visual Cortex ? Association fibres ?
• Frontal lobes ? Descend via anterior limb
  of internal capsule ? Superior colliculus ?
• Edinger-Westphal nuclei ? CN III ?
  Ciliary ganglion ? Muscles of iris and ciliary
  body

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Visual field defects
Meyers loop
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Cranial Nerves III (Oculomotor), IV (Trochlear)
and VI (Abducens)

• Motor innervation to superior, medial and
  inferior rectus muscles
• Motor innervation to levator palpebrae
  superioris muscle
• Preganglionic parasympathetic neurons (via
  ciliary ganglion) to sphincter pupillae (pupil
  constriction) and ciliary muscles (accommodation)
• Damage
• Eye is down and out
• Drooping eyelid (ptosis)
• Dilatation of pupil, unresponsive to light and
  accommodation

CN III
CN IV

• The only cranial nerve to emerge from dorsal
  aspect of brain stem (axons cross midline)

• Purely somatic motor innervation to superior
  oblique muscle (depression, abduction and
  intorsion of the eye)
• Damage
• Eye unable to look down when adducted (primary
  action of inferior rectus cancelled out in this
  position) most notable when trying to walk down
  stairs!
• Causes contralateral symptoms if the trochlear
  nucleus in the brainstem on one side is damaged

• Purely somatic motor innervation to lateral
  rectus muscle (abduction of the eye)
• Longest intracranial course for any CN often
  first to be affected by fractures of base of
  skull / intracranial disease. Most important CN
  to test!
• Abducens nucleus lies beneath floor of 4th
  ventricle
• Damage
• Eye unable to abduct (convergent squint)
• Close to Internal Carotid Artery in the cavernous
  sinus ICA aneurysm, cavernous sinus thrombosis,
  Tolosa-Hunt syndrome (inflammation of cavernous
  sinus)

CN VI
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Cranial Nerve V (Trigeminal)
Motor innervation

• Motor innervation to muscles of mastication
• Motor innervation to tensor levi palatini,
  tensor tympani and digastric (anterior belly)

CN V
Sensory innervation
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Cranial Nerve V (Trigeminal) sensory innervation

• Forehead, eye brow, upper eyelid
• Cornea
• Upper palpebral conjunctiva
• Bulbar conjunctiva
• Nose naris, nasal vestibule and tip (external
  nasal nerve)
• Paranasal sinuses (except maxillary sinus)

CN Va

• Lower palpebral conjunctiva
• Lower eyelid
• Mucosa in posteroinferior part of nasal cavity
• Oral mucosa posterior to incisor teeth
  (nasopalatine nerve)
• Soft palate
• Maxillary sinus
• Maxillary teeth
• Upper lip

CN Vb
CN Va
CN Vb
CN Vc

• Lower lip
• Chin
• Temple
• Mandibular teeth (inferior alveolar nerve)
• Middle to deep part of External Acoustic Meatus
  (EAM)
• General sensation of anterior 2/3 of tongue

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Cranial Nerve V (Trigeminal) dural innervation
Meningeal branches of CN V innervates the dura
mater.

• Falx cerebri and tentorium cerebelli

CN Va
Falx cerebri - CN Va

• Middle cranial fossa medially

CN Vb

• Middle cranial fossa laterally

CN Vc
Tentorium cerebelli - CN Va
CN Vc
CN Va
CN Vb
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Trigeminal neuralgia

• Common in CN Vb, less common in CN Vc, but not in
  CN Va
• Management
• Drugs Carbamazepine, Lamotrigine, Phenytoin,
  Gabapentine, Amitriptyline
• Stereotactic gamma knife
• Ablative procedures (Rhizolysis) to destroy part
  of the trigeminal nerve to block the electrical
  activity that is causing the pain side effect is
  permanent numbness to part of the face
• Radiofrequency
• Glycerol injection into the trigeminal cistern
  (subarachnoid space)

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Cranial Nerve VII (Facial)

• Sensory part (nervus intermedius) smaller,
  more lateral roots, between CN VII and CN VIII
• Motor part more medial roots
• From cerebellopontine angle - lateral part of
  pontomedullary junction ?
• crosses posterior cranial fossa ? leaves
  cranial cavity through internal acoustic meatus
• (where motor and sensory part fuse to form CN
  VII) ? enlarges to form geniculate ganglion ?
• facial canal in petrous part of temporal bone ?
  emerges through stylomastoid foramen

CN VII

• Before stylomastoid foramen, branches into
• Greater petrosal nerve
• Chorda tympani
• Nerve to stapedius
• After stylomastoid foramen, enters the parotid
  gland (but does not supply it), branches into
• (think TEN ZULUS BEAT MY CAT)
• Temporal
• Zygomatic
• Buccal
• Marginal mandibular
• Cervical

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Cranial Nerve VII (Facial)

• Motor innervation to muscles of facial
  expression
• Somatic sensory from skin around ear lobe and
  EAM
• Taste sensation from anterior 2/3 of tongue
• Intracranial course close to CN VIII
• Preganglionic parasympathetic neurons (via
  pterygopalatine ganglion) to lacrimal gland
  (lacrimation), and glands in mucosa of nasal
  cavity and paranasal sinuses, and (via
  submandibular ganglion) to submandibular and
  submental glands (salivation)
• Damage
• Parotid gland removal, mumps, parotitis, tumour
  may damage CN VII
• Acoustic neuroma ? paralysis of facial muscles,
  deafness, dizziness
• Damage to nerve to stapedius ? hyperacusis

CN VII
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Cranial Nerve VII (Facial)

• Facial motor nucleus supplying frontalis and
  orbicularis oculi receive bilateral innervation
  from the motor cortex
• Facial motor nucleus supplying the lower facial
  muscles receives contralateral innervation

CN VII

• Damage
• Therefore, a unilateral Upper Motor Neurone (UMN)
  lesion of CN VII causes contralateral paralysis
  of lower facial muscles (e.g. stroke)
• A Lower Motor Neurone (LMN) lesion, either in the
  pons or any part of the peripheral course ?
  complete paralysis of facial muscles on one side
  (Facial palsy)
• A facial palsy of unknown aetiology ? Bells palsy

Corneal reflex

• Tests CN Va and VII
• Pathway
• Cornea ? Nasociliary nerve (branch of CN Va) ?
  Principal sensory nucleus of CN V ?
• (brain stem interneurons) ? Facial motor
  nucleus ? CN VII ? Orbicularis oculi muscle
• Both eyes should blink if either cornea is
  stimulated

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Cranial Nerve VIII (Vestibulocochlear)

• Both divisions (dendrites which make contact
  with hair cells of vestibular or auditory
  apparatus of inner ear) pass through internal
  auditory meatus (together with CN VII)
• Attach to brain stem at cerebellopontine angle

CN VIII

• Sensory, carries information related to position
  and movement of the head (vestibular nerve) and
  auditory information (cochlear nerve)
• Damage
• Dizziness
• Deafness (profound if Lower Motor Neuron (LMN)
  lesion supply is bilateral higher up, at all
  levels rostral to cochlear nuclei at the medulla)

Acoustic neuroma

• Benign tumour of CN VIII (Schwann cells) leading
  to compression of the nerve and structures at the
  cerebellopontine angle
• Dizziness
• Deafness
• Paralysis of CN V-VII ? facial palsy and loss of
  cutaneous sensation on ipsilateral face
• (Ataxia)

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Cranial Nerve IX (Glossopharyngeal)

• From lateral aspect of olive and through jugular
  foramen
• Descends into the neck and passes between
  internal and external carotid arteries to enter
  the pharynx (pharyngeal plexus) to supply the
  mucosa of pharynx and posterior tongue
• General sensory afferents end in sensory nuclei
  of trigeminal nerve
• Carotid body / sinus and taste fibres terminate
  in nucleus solitarius
• Motor from nucleus ambiguus

CN IX

• Principally a sensory nerve general sensation
  from pharynx, middle ear, posterior 1/3 of tongue
• Taste sensation from posterior 1/3 of tongue
• Chemoreceptors in carotid body (oxygen, CO2, and
  pH) and baroreceptors in carotid sinus
• Motor innervation to stylopharyngeus
• Preganglionic parasympathetic (via otic
  ganglion) to parotid gland
• Damage
• Loss of sensation of taste and general sensation
  from posterior 1/3 of tongue
• Loss of function of stylopharyngeus (elevation of
  pharynx/larynx in swallowing)
• Loss of ipsilateral gag reflex

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Cranial Nerve X (Vagus)
CN X

• From rootlets lateral to olive in the medulla
  and through jugular foramen
• Motor from nucleus ambiguus
• General sensory afferents end in sensory nuclei
  of trigeminal nerve whilst visceral afferents in
  nucleus solitarius
• Auricular branch conveys sensory fibres from
• EAM
• Tympanic membrane
• Descends in carotid sheath pharyngeal branches
  and superior laryngeal nerve
• Internal (sensory above vocal chords)
• External (motor to cricothyroid)
• Recurrent laryngeal nerves laryngeal muscles
  (not cricothyroid), sensory below vocal chords
• Left related to ligamentum arteriosum
• Right related to right subclavian artery
• Forms the oesophageal plexus .
• Preganglionic parasympathetic from dorsal motor
  nucleus of vagus

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Cranial Nerve X (Vagus)

• General sensation in the laryngopharynx, larynx,
  oesophagus, tympanic membrane, EAM, part of ear
  lobe
• Chemoreceptors in aortic bodies (oxygen, carbon
  dioxide not pH) and baroreceptors in aortic
  arch
• Thoracic and abdominal visceral sensation
• Motor to soft palate, pharynx, larynx, upper
  part of oesophagus
• Preganglionic parasympathetic to cardiovascular,
  respiratory and GI systems
• Damage
• Loss of ability to speak voice changes,
  hoarseness
• Loss of gag reflex and other vagal reflexes such
  as coughing, vomiting and fainting from
  irritation of posterior wall of external auditory
  meatus
• Damage to recurrent laryngeal nerve (near
  inferior thyroid artery) nearly always affects
  abductors of vocal cords ? difficulty in breathing

CN X
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Cranial Nerve XI (Accessory)

• Cranial part from lateral aspect of medulla as
  rootlets caudal to rootlets of vagus, joins vagus
  at jugular foramen to supply larynx and pharynx
  (hence accessory)
• Spinal part from motor neurons in ventral horn
  of spinal grey matter at C1-C5, emerge from
  between ventral and dorsal nerve roots and
  ascends through foramen magnum to enter posterior
  cranial fossa
• Briefly runs with cranial CN XI before emerging
  through jugular foramen, passes deep to SCM which
  it supplies
• Enters roof of posterior triangle of neck from
  1/3 down of posterior border of SCM to 1/3 up
  anterior border of trapezius

CN XI
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Cranial Nerve XI (Accessory)

• Spinal part supplies motor innervation to
  sternocleidomastoid (SCM) and trapezius muscles
• Damage
• Vulnerable in posterior triangle of the neck ?
  paralysis of trapezius (but not SCM which it has
  already supplied), abduction of arms beyond 90o
  (e.g. hair grooming) is impaired
• If injury is higher up (before posterior angle) ?
  inability to tilt head on affected side, and to
  turn head away from affected side (remember SCM
  pulls to turn head to the other side)

CN XI
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Cranial Nerve XII (Hypoglossal)

• From hypoglossal nucleus (beneath floor of 4th
  ventricle), emerge as a series of rootlets
  between the pyramid and the olive
• The hypoglossal nucleus receives afferents from
  nucleus solitarius and trigeminal sensory nucleus
  involved in control of reflex movements of
  chewing, sucking and swallowing
• Also receives corticobulbar fibres from
  contralateral motor cortex voluntary movements
  of tongue (e.g. speech)

CN XII

• Purely motor to the intrinsic and extrinsic
  muscles of the tongue
• Damage
• In a LMN lesion (e.g. damage to nerve in the
  neck), the tongue is pushed to the affected side
  ? difficulty chewing, dysarthria
• Carotid artery surgery (e.g. endarterectomy), CN
  XII is near the origin of occipital artery from
  external carotid artery

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Cranial Nerve XII (Hypoglossal)
CN XII
Lesions and motor neuron disease of CN IX-XII

• Due to
• Motor neuron disease
• Multiple Sclerosis
• Vascular cause
• Bulbar palsy ipsilateral LMN lesion
• Degeneration of nucleus ambiguus and hypoglossal
  nucleus
• Dysphonia (difficulty in phonation)
• Dysphagia (difficulty in swallowing)
• Dysarthria (difficulty in articulation
• Weakness, wasting and fasciculation of the tongue
• Pseudobulbar palsy
• Lesions to corticobulbar tracts projecting to
  nucleus ambiguus and hypoglossal nucleus
• Bilateral lesion is clinically significant
• Dysphonia, dysphagia, dysarthria
• Weakness and spasticity of the tongue

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Parasympathetic supply
Cranial nerves
CN Va
Pupillary constriction (iris muscles),
accommodation (ciliary muscles)
III
Cell in Edinger-Westphal nucleus (midbrain)
Ciliary ganglion
CN Vb
CN VII with greater petrosal nerve
Lacrimal gland, glands in mucosa of nasal cavity
and paranasal sinuses
VII
Pterygopalatatine ganglion
Cell in superior salivatory nucleus (pons)
Submandibular and sublingual glands
CN VII with chorda tympani
CN Vc
Submandibular ganglion
CN Vc
IX
Parotid gland
Cell in inferior salivatory nucleus (pons /
medulla)
Otic ganglion
? Heart rate ? gut activity Constricts airways
X
Cell in dorsal motor nucleus of vagus (medulla)
Ganglia in wall of organ being innervated
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Soft palate motor innervation

• Tensor veli palatini
• Levator veli palatini
• Palatoglossus
• Palatopharyngeus
• Musculus uvulae

CN Vc
CN X
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Cranial Nerve Nuclei locations
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Example
1. Ramsay Hunt syndrome (type II), also called
herpes zoster oticus, is a form of herpes zoster
affecting the facial nerve, associated with
muscle paralysis and loss of sensory modalities.
Pain is experienced in the distribution of the
nerve. Describe the motor pathway of the facial
nerve from the brainstem to its point of action.
State and briefly explain the symptoms of the
syndrome.

• From ventrolateral aspect between pons and the
  medulla (crosses posterior cranial fossa), exits
  cranial cavity through internal acoustic,
  (through facial canal in petrous part of temporal
  bone, enlarges to form the geniculate ganglion),
  supplies stapedius (before going through
  stylomastoid foramen) and then innervates muscles
  of facial expression (after branching in the
  parotid gland into temporal, zygomatic, buccal,
  marginal mandibular and cervical).
• Symptoms paralysis of facial muscles
  unilaterally with failure to close the eye,
  absent corneal reflex (loss of efferent limb),
  hyperacusis on affected side (loss of stapedius),
  loss of taste sensation in anterior two-thirds of
  tongue, dry mouth and eyes, pain is experienced
  around the ear, vesicular rash in EAM and mucous
  membrane of oropharynx.

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Example
2. Briefly describe the structures within the
cavernous sinus, paying particular reference to
the cranial nerves within and the surrounding
structures. Cavernous sinus thrombosis may occur
as a result of an infection of the any part of
the head (e.g. face, ear) that drains into the
cavernous sinus. Explain the clinical outcome of
a cavernous sinus thrombosis.

• Draw!
• All cranial nerves passing through or in the
  walls affected
• CN III, CN IV, CN Va, CN Vb, CN VI.
• Abducens nerve usually affected first because it
  passes through the sinus paralysis of lateral
  rectus resulting in medial squint.
• Involvement of ophthalmic and maxillary nerves
  causes severe pain in its distribution.
• Pupil may be dilated and sluggish.
• Condition may also result in visual loss
  (resulting from impaired venous drainage from
  orbit) and papilloedema.

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Cranial Nerves
CN I Olfactory Sensory Smell
CN II Optic Sensory Vision
CN III Oculomotor Motor Parasympathetic Medial, superior and inferior rectus, inferior oblique, levator palpebrae superioris
CN IV Trochlear Motor Superior oblique
CN V Trigeminal Sensory Motor Cranial dura mater CN Va (ophthalmic), CN Vb (maxillary), CN Vc - face CN Vc (mandibular) muscles of mastication, tensor tympani, tensor levi palatini, digastric (anterior belly)
CN VI Abducens Motor Lateral rectus
CN VII Facial Sensory Motor Parasympathetic Taste (anterior tongue) Muscles of facial expression, stapedius, stylohyoid, platysma, digastric (posterior belly)
CN VIII Vestibulocochlear Sensory Hearing, balance
CN IX Glossopharyngeal Sensory Motor Parasympathetic Posterior tongue, oropharynx, taste (posterior tongue), middle ear, carotid body and sinus Stylopharyngeus
CN X Vagus Sensory Motor Parasympathetic Larynx, hypopharynx, heart, lungs, (taste) Muscles of larynx, pharynx (speech, swallowing)
CN XI Accessory Motor Sternocleidomastoid, trapezius
CN XII Hypoglossal Motor Muscles of the tongue