Transcript Cranial Nerve Anatomy

SCRUBS – Cranial Nerves
Chun Kit Poh
08 February 2010
Objectives
• Cranial nerves I – XII
• Parasympathetic
• Pupillary light reflex
• Cranial Nerve nuclei
• Accommodation reflex
• Examples
• Visual field defects
• (not covering CN clinical examination)
• Trigeminal Neuralgia
• Corneal reflex
• Pseudo / bulbar palsy
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
Cranial Nerves
Cranial Nerve I (Olfactory)
CN I
• 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
• 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
Cranial Nerve II (Optic)
CN II
• 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)
• 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
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
Visual field defects
Where would the lesion be to produce these?
1
2
3
Meyer’s loop
4
5
6
Cranial Nerves III (Oculomotor), IV (Trochlear) and VI (Abducens)
CN III
CN IV
• 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
• 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
CN VI
• 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)
Cranial Nerve V (Trigeminal)
Motor innervation
CN V
• Motor innervation to muscles of mastication
• Motor innervation to tensor levi palatini, tensor tympani and digastric (anterior
belly)
Sensory innervation
Cranial Nerve V (Trigeminal) – sensory innervation
CN Va
• Forehead, eye brow, upper eyelid
CN Vb
• 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 Vc
• Cornea
• Upper palpebral conjunctiva
• Bulbar conjunctiva
• Nose – naris, nasal vestibule and tip
(external nasal nerve)
• Paranasal sinuses (except maxillary
sinus)
CN Va
• 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
CN Vb
Cranial Nerve V (Trigeminal) – dural innervation
Meningeal branches of CN V innervates the dura mater.
CN Va
• Falx cerebri and tentorium cerebelli
Falx cerebri - CN Va
CN Vb
• Middle cranial fossa medially
CN Vc
• Middle cranial fossa laterally
Tentorium cerebelli - CN Va
CN Vc
CN Va
CN Vb
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)
Cranial Nerve VII (Facial)
CN VII
• 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
• 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
Cranial Nerve VII (Facial)
CN VII
• 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
Cranial Nerve VII (Facial)
CN VII
• 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
• 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  Bell’s 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
Cranial Nerve VIII (Vestibulocochlear)
CN VIII
• 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
• 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)
Cranial Nerve IX (Glossopharyngeal)
CN IX
• 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
• 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
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
Cranial Nerve X (Vagus)
CN X
• 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
Cranial Nerve XI (Accessory)
CN XI
• 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
Cranial Nerve XI (Accessory)
CN XI
• 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)
Cranial Nerve XII (Hypoglossal)
CN XII
• 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)
• 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
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
Parasympathetic supply
Cranial nerves
CN Va
III
Cell in EdingerWestphal nucleus
(midbrain)
Ciliary ganglion
CN VII with greater petrosal nerve
CN Vb
VII
Cell in superior
salivatory nucleus
(pons)
CN VII with chorda tympani
Pupillary constriction (iris muscles),
accommodation (ciliary muscles)
Lacrimal gland, glands in mucosa of nasal
cavity and paranasal sinuses
Pterygopalatatine
ganglion
CN Vc
Submandibular and sublingual glands
Submandibular
ganglion
CN Vc
IX
Cell in inferior
salivatory nucleus
(pons / medulla)
Parotid gland
Otic ganglion
↓ Heart rate
X
↑ gut activity
Cell in dorsal motor
nucleus of vagus
(medulla)
Constricts airways
Ganglia in wall of
organ being
innervated
Soft palate – motor innervation
• Tensor veli palatini
CN Vc
• Levator veli palatini
• Palatoglossus
CN X
• Palatopharyngeus
• Musculus uvulae
Cranial Nerve Nuclei locations
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.
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.
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
Posterior tongue, oropharynx, taste (posterior tongue), middle ear,
carotid body and sinus
Stylopharyngeus
Motor
Parasympathetic
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