HNS08 Cranial Nerves

Question 1

***12 pairs of cranial nerve

Answer 1

Sensory function only:

• Olfactory (CN1)
• Optic (CN2)
• Vestibulocochlear (CN8)

Motor function only:

• Oculomotor (CN3)
• Trochlear (CN4)
• Abducens (CN6)
• Accessory (CN11)
• Hypoglossal (CN12)

Both sensory and motor function:

• Trigeminal (CN5)
• Facial (CN7)
• Glossopharyngeal (CN9)
• Vagus (CN10)

Question 2

Functional components of cranial nerves

Answer 2

Sensory

1. General somatic sensory
   - touch, pain, temperature, pressure, vibration, proprioception
2. General visceral sensory
   - sensory input from the viscera (except pain)
3. Special sensory
   - smell, vision, taste, hearing, balance

Motor

4. General somatic motor
   - innervates muscles that develop from somites
5. Branchial motor
   - innervates muscles that develop from branchial (pharyngeal) arches (CN5,7,9,10,11)
6. General visceral motor
   - innervates viscera (including glands and all smooth muscles)

Question 3

Cranial nerve locations

Answer 3

See slide

Question 4

Cranial nerve nuclei

Answer 4

Sensory nuclei:
- developed from Alar plate —> as 4th ventricle and brainstem expands —> more lateral

Motor nuclei:
- developed from Basal plate —> as 4th ventricle and brainstem expands —> more medial

Question 5

CN1 Olfactory nerve

Answer 5

Olfactory system consist of:

1. Olfactory epithelium
2. Bulbs (belong to CNS)
3. Tracts (belong to CNS)
4. Olfactory areas of brain (collectively known as Rhinencephalon)

Peripheral processes of receptor cells —> small bundles
—> pass through Cribriform plate of ethmoid bone
—> synapse on secondary sensory neurons in Olfactory bulb (lie on Cribriform plate)
—> Olfactory bulb
—> Olfactory tract
—> Medial stria (terminates in anterior commissure to project to contralateral olfactory structure)
OR
—> Lateral stria (terminates in primary olfactory (piriform) cortex of the temporal lobe (ipsilateral))

Cells of origin:
***Bipolar cells in olfactory epithelium (special sensory)

Central connections (where cranial nerve neurons synapse in CNS):
Olfactory bulb (location of secondary olfactory neurons)

Peripheral distribution:
Cilia at surface of olfactory epithelium in superior nasal concha + upper third of nasal septum

Function:
Smell

Signs of damage:
Anosmia (loss of smell sensation)

Question 6

Primary olfactory receptor cells

Answer 6

• Bipolar nerve cells with a dendrite
  —> terminates in a knob and project numerous cilia
• Axons of olfactory neurons contact dendrites of secondary olfactory cells (Mitral cell + Tufted cell) in olfactory bulb
• Bipolar cells undergo continuous replacement throughout life

Question 7

CN2 Optic nerve (part of CNS)

Answer 7

Arise from retina of eye

Image of visual field projected onto retina upside-down and reversed
—> **Photoreceptors (Cone, Rod cells) —> electrical signals
—> **Bipolar cells
—> **Retinal ganglion cells
—> Optic nerve (pass through optic canals —> converge at optic chiasm)
—> Optic chiasm
—> Optic tract (fibres continue posteriorly around midbrain with most synapsing in **lateral geniculate nucleus of their respective thalamus / small portion enter **pretectal region of midbrain and participate in pupillary light reflex)
—> **Lateral geniculate nuclei of Thalamus —> secondary neuron / optic radiation fibres
—> Visual cortex

Cells of origin:
Retinal ganglion cells (special sensory)

Central connections:

• Lateral geniculate nuclei (in Thalamus)
• Superior colliculus + pretectal nuclei (afferent pathway of pupillary light reflex)

Peripheral distribution:
Retinal bipolar cells

Function:

• Vision
• Pupillary light reflexes

Signs of damage:

• Blindness
• Absent of pupillary constriction bilaterally on testing blind eye

Question 8

Projection of visual field to thalamus

Answer 8

Image on medial side of retina: Contralateral side of thalamus (cross at Optic chiasm)

Image on lateral side of retina: Ipsilateral side of thalamus at Lateral geniculate nuclei

Effect:
- Left side image perceived on Right side brain (vice versa)

Question 9

Pupillary light reflex

Answer 9

Optic nerve
—> Pretectal nuclei
—> Project bilaterally to both side of Edinger-Westphal nuclei
—> through Oculomotor nerve
—> Ciliary ganglion
—> short ciliary nerves
—> direct + consensual pupillary constriction

Question 10

CN3 Oculomotor nerve

Answer 10

• Emerges from medial side of midbrain, superior to pons
• Innervates all ***extraocular muscles except Superior oblique (CN4) and Lateral rectus (CN6) for precise movement of eyes, for visual tracking / fixation on object
• also supplies ***elevator of upper eyelid (Levator palpebrae superioris)

Cells of origin:

• Oculomotor nucleus (Somatic motor)
• Edinger-Westphal nucleus (Visceral motor)

Central connections:
NA (∵ nucleus already in CNS)

Peripheral distribution:

• Superior, Inferior, Medial rectus muscle; Inferior oblique; Levator palpebrae superioris (5 of 7 eye muscles)
• **Ciliary ganglion: postganglionic via short ciliary nerves to **sphincter of pupil + ***ciliary muscle

Function:

• Eye movement + elevates upper eyelid
• Contraction of pupil + Accommodation of lens

Signs of damage:

• Ophthalmoplegia with eye deviated down and out, severe ptosis (drooping eyelid)
• Mydriasis; loss of pupillary light and accommodation reflexes in ipsilateral eye

Question 11

Accommodation reflex

Answer 11

Adaptation of visual apparatus to facilitate NEAR vision which involves:

1. ↑ Curvature of lens by ciliary muscle contraction (↑ refractive power)
2. Pupillary constriction to help sharpen image on retina
3. Convergence of the eyes to fixate on target object

Question 12

CN4 Trochlear nerve

Answer 12

Emerges from dorsal brainstem (already crossed)

Cells of origin:
- Trochlear nucleus (Somatic motor)

Central connections:
NA (∵ nucleus already in CNS)

Peripheral distribution:
- Superior oblique muscle (***Contralateral, but already crossed in midbrain)

Function:
- Intorsion (向內擰); Depression of adducted eye

Signs of damage:
- Diplopia (double vision), head tilt to unaffected side (∵眼向外擰,頭唯有向相反方向擺), weakness in depression of ipsilateral (∵ already crossed) adducted eye

Question 13

CN6 Abducens nerve

Answer 13

Emerges from ventral medial brainstem, between pons and medulla oblongata

Cells of origin:
- Abducens nucleus (Somatic motor)

Central connections:
NA (∵ nucleus already in CNS)

Peripheral distribution:
- Lateral rectus muscle

Function:
- Abduction of eye (向外望)

Signs of damage:
- Diplopia, medial deviation, inability to abduct affected eye

Question 14

CN5 Trigeminal nerve

Answer 14

Emerges from lateral pons

3 divisions for ***general sensation towards Trigeminal ganglion (innervates different parts of face / forehead):

1. Ophthalmic division (V1) —> sensory ONLY
2. Maxillary division (V2) —> sensory ONLY
3. Mandibular division (V3) —> sensory + motor

4 nuclei:

1. Pontine trigeminal nucleus (sensory)
2. Spinal trigeminal nucleus (sensory)
3. Mesencephalic trigeminal nucleus (sensory)
4. Trigeminal motor nucleus (motor)

Cells of origin:

• Trigeminal ganglion (General sensory) —> Somatosensations
• Mesencephalic trigeminal nucleus (General sensory) —> Proprioceptive reflexes
• Trigeminal motor nucleus (Branchial motor) —> Mastication

Central connections:

• Spinal trigeminal nucleus (caudal part) + Pontine trigeminal nucleus
• NA
• NA

Peripheral distribution:

• Ophthalmic (V1), Maxillary (V2), Mandibular (V3) divisions to mucous membranes and skin of face and head
• Muscles of mastication, peridontal membrane, temporomandibular joint, external ocular muscle
• Temporalis, masseter, lateral and medial pterygoids + tensor veli palatini and tensor tympani, anterior belly of digastric, mylohyoid

Function:

• Somatosensations
• Proprioceptive reflexes
• Mastication (chewing)

Signs of damage:

• Loss of facial sensations and corneal reflex on stimulation ipsilaterally
• Insignificant
• Deviation of opened jaw to ipsilateral side

Question 15

CN7 Facial nerve

Answer 15

Facial nerve arises at junction between pons and medulla, cerebellopontine angle

6 major branches:

1. Temporal branch
2. Zygomatic branch
3. Buccal branch (=/ Buccal nerve (V3))
4. Marginal Mandibular branch
5. Cervical branch
6. Posterior auricular nerve

2 divisions:

• Motor root
• Intermediate nerve (smaller)

Cells of origin:

• Facial nucleus (Branchial motor) —> Facial expression
• Superior salivatory nucleus (Visceral motor) —> Nasal, Lacrimal, Salivary secretions
• Geniculate ganglion (Special sensory) —> Taste
• Geniculate ganglion (General sensory) —> Somatosensation

Central connections:

• NA
• NA
• Solitary nucleus (rostral part)
• Spinal trigeminal nucleus (caudal part)

Peripheral distribution:

• Facial muscles, buccinator, stapedius, stylohyoid, posterior belly of digastric, platysma, occipitalis
• 1. Greater petrosal nerve —> Nerve of pterygoid canal —> **Pterygopalatine ganglion —> postganglionic via Zygomaticotemporal nerve (CNV2) —> **Lacrimal gland + ***Mucosal glands of nasal cavity and palate
• 2. Chorda tympani —> Lingual nerve (CNV3) —> **Submandibular ganglion —> postganglionic to **Submandibular + ***Sublingual glands (記: CLS)
• Taste buds in anterior 2/3 of tongue
• Posterior auricular region, external auditory meatus, tympanic membrane

Function:

• Facial expression, articulation, winking, ingestion
• 1. Nasal and lacrimal secretions
• 2. Salivary secretion
• Taste
• Somatosensations

Signs of damage:

• Paralysis of ipsilateral upper and lower facial muscle
• 1. Loss of lacrimation (tears)
• 2. Decreased salivation; dry mouth
• Loss of taste in anterior 2/3 of tongue ipsilaterally
• Insignificant

Question 16

Summary of 4 functional components of Facial nerve (2 motor, 2 sensory)

Answer 16

1. Facial nucleus:
   - convey motor impulse to muscles of face (facial expression)
   - upper facial muscle: controlled bilaterally from both sides of brain
   - lower facial muscle: controlled contralaterally (left brain control right face)
2. Superior salivatory nucleus:
   - convey parasympathetic impulse to lacrimal, nasal, submandibular and sublingual salivary glands
3. Geniculate ganglion:
   - convey sensory impulse from taste buds of anterior 2/3 of tongue
4. Pontine trigeminal nucleus:
   - convey general sensory impulse from posterior auricular region

Question 17

CN8 Vestibulocochlear nerve

Answer 17

2 fibres:
1. Cochlear (hearing) fibres
2. Vestibular (balance) fibres
—> both leave lateral side between pons and medulla

Cells of origin:

• Vestibular ganglion (Special sensory) —> Balance
• Spiral ganglion (Special sensory) —> Hearing

Central connections:

• Vestibular nuclei (4) + Cerebellum
• Cochlear nucleus (Dorsal + Ventral)

Peripheral distribution:

• Hair cells of ampullary crests in semicircular ducts, maculae of saccule and utricle
• Hair cells of spiral organ of Corti

Function:

• Balance
• Hearing

Signs of damage:

• Vertigo, dysequilibrium, nystagmus (involuntary eye movement)
• Neural deafness

Question 18

Sense of body position in space

Answer 18

• Provided by information from:
  1. Visual system
  2. Conscious proprioceptive system
  3. Vestibular system

—> lack of good vision (e.g. closure of eyes) will lead to heavy fall if vestibular system is not functioning normally

Question 19

CN9 Glossopharyngeal nerve

Answer 19

Emerges from upper medial part of medulla

Cells of origin (5 functional components):

• Nucleus ambiguus (rostral part) (Branchial motor) —> Elevates pharynx
• Inferior salivatory nucleus (Visceral motor) —> Salivary secretion
• Inferior (petrosal) ganglion (Special sensory) —> Taste
• Inferior and superior ganglion (General sensory) —> Somatosensation
• Inferior ganglion (Visceral sensory) —> Reflex

Central connections:

• NA
• NA
• Solitary nucleus (rostral part)
• Spinal trigeminal nucleus
• Solitary nucleus

Peripheral distribution:

• Stylopharyngeus + Superior pharyngeal constrictor
• Tympanic plexus —> Lesser petrosal nerve —> **Otic ganglion —> Auriculotemporal nerve (CNV3) —> **Parotid gland (記: LOA)
• Taste buds in posterior 1/3 tongue
• Anterior surface of epiglottis, root of tongue, border of soft palate, uvula, tonsil, pharynx, auditory tube, middle ear
• Carotid sinus and bulb

Function:

• Elevates pharynx
• Salivary secretion
• Taste
• Somatosensation of tonsillar region
• Reflexes

Signs of damage:

• Slight dysphagia
• Dry mouth
• Loss of taste in posterior third of tongue ipsilaterally
• Anaesthesia of tonsillar region + loss of gag reflex from ipsilateral stimulus
• Insignificant

Question 20

Summary of Glossopharyngeal nerve

Answer 20

Mixed nerve with motor and sensory function

Motor:

1. Innervates part of tongue and pharynx —> elevates pharynx during swallowing
2. Provide motor fibres to ***Parotid salivary gland

Sensory:
1. Conduct taste (posterior 1/3 tongue) and general sensory impulse from tongue and pharynx

Question 21

CN10 Vagus nerve

Answer 21

• Only cranial nerve extend beyond head and neck
• Mixed nerve
• Most motor fibres are parasympathetic fibres to heart, lungs and visceral organs
• Supplies muscles for swallowing and vocalisation

Cells of origin (4 functional components):

• Nucleus ambiguus (Branchial motor) —> Deglutition (swallowing) + Phonation
• Dorsal motor nucleus of vagus + region of Nucleus ambiguus (Visceral motor) —> Cardiac depressor, Bronchoconstrictor, GI tract peristalsis + secretion
• Inferior (nodose) ganglion (Visceral sensory) —> Taste in epiglottis
• Inferior (nodose) ganglion (Visceral sensory) —> Visceral sensation + Reflexes
• Inferior (nodose) ganglion (Visceral sensory) —> Reflexes
• Superior (jugular) ganglion (General sensory) —> Somatosensation

Central connections:

• NA
• NA
• Solitary nucleus
• Solitary nucleus
• Solitary nucleus
• Spinal trigeminal nucleus (caudal part)

Peripheral distribution:

• Palate, pharyngeal constrictors, intrinsic muscles of larynx, ***Palatoglossus
• Cardiac nerves and plexus to heart; Pulmonary plexuses to ganglia of respiratory tree; Esophageal, Gastric, Celiac, Superior + Inferior mesenteric plexuses to myenteric and submucosal ganglia of digestive tract down to transverse colon
• Taste buds in regions of epiglottis
• Posterior epiglottis, pharynx, larynx, trachea, bronchi, esophagus, stomach, small intestine, ascending and transverse colon
• Aortic sinus and bulb
• External ear and meatus

Function:

• Deglutition (swallowing) + ***Phonation
• Cardiac depressor, Bronchoconstrictor, GI tract peristalsis + secretion
• Taste in epiglottis
• Visceral sensation + Reflexes
• Reflexes
• Somatosensation

Signs of damage:

• Dysphagia, hoarseness, paralysis of soft palate (with deviation of velum and uvula to contralateral side)
• Insignificant
• Insignificant
• Anaesthesia of ipsilateral pharynx and larynx
• NA
• Anaesthesia of ipsilateral external auditory meatus

Question 22

CN11 (Spinal) Accessory nerve

Answer 22

2 parts:

• Cranial part (emerging from medulla)
• Spinal part (arising from superior region of spinal cord, passes upward into cranium via foramen magnum)

Cells of origin:

• Nucleus ambiguus (caudal part) (Branchial motor)
• Motoneurons of spinal accessory nucleus in C1-6 (Branchial motor)

Central connections:
NA (∵ nucleus already in CNS)

Peripheral distribution:

• Communicates with vagal branches to ***muscles of pharynx and larynx
• Sternocleidomastoid + Trapezius muscle

Function:

• Swallowing + Vocalisation
• Movements of head and shoulder

Signs of damage:

• Insignificant
• Weakness in turning head toward opposite sides and shrugging shoulder

Question 23

CN12 Hypoglossal nerve

Answer 23

• Fibres arise from medulla (between pyramid and olive)
• Exit skull via Hypoglossal canal
• Innervates both extrinsic and intrinsic muscles of tongue —> contributes to swallowing and speech
• Supplies muscles for tongue movement

Cells of origin:
- Hypoglossal nucleus (Somatic motor)

Central connections:
NA (∵ nucleus already in CNS)

Peripheral distribution:
- Styloglossus, Hyoglossus, Genioglossus, intrinsic muscles of tongue

Function:
- Movement of tongue

Signs of damage:
- Wasting of ipsilateral tongue muscles and deviation to ipsilateral side on protrusion
(Only Genioglossus is controlled by contralateral upper motor neuron, rest of them controlled bilaterally)
(Genioglossus: contract to protrude tongue to contralateral side)

Question 24

Summary: Functional components and locations of nuclei

Answer 24

Sensory (上—>下; 外—>內):

1. Mesencephalic trigeminal
2. Pontine (Principal) trigeminal
3. Spinal trigeminal
4. Cochlear
5. Vestibular
6. Solitary

Motor (外—>內; 上—>下):
Midbrain region:
1. Edinger-Westphal
2. Oculomotor
3. Trochlear

Pons region:

4. Trigeminal motor
5. Facial
6. Superior salivatory
7. Abducens
8. Inferior salivatory

Medulla region:

9. Ambiguus
10. Dorsal motor vagal
11. Hypoglossal

Question 25

General sensory

Answer 25

1. CN5:
   - Ophthalmic (V1), Maxillary (V2), Mandibular (V3) divisions to mucous membranes and skin of face and head
   —> Trigeminal ganglion
   —> Spinal trigeminal nucleus (caudal part) + Pontine trigeminal nucleus

• Muscles of mastication, peridontal membrane, temporomandibular joint, external ocular muscle
  —> Mesencephalic trigeminal nucleus

2. CN7:
   - Posterior auricular region, external auditory meatus, tympanic membrane
   —> ***Geniculate ganglion
   —> Spinal trigeminal nucleus (caudal part)
3. CN9:
   - Tonsillar region (Anterior surface of epiglottis, root of tongue, border of soft palate, uvula, tonsil, pharynx, auditory tube, middle ear)
   —> **Inferior and **Superior ganglion
   —> Spinal trigeminal nucleus
4. CN10:
   - External ear and meatus
   —> ***Superior (jugular) ganglion
   —> Spinal trigeminal nucleus (caudal part)

Question 26

Visceral sensory

Answer 26

1. CN9
   - Carotid sinus and bulb —> ***Inferior ganglion —> Solitary nucleus
2. CN10
   - Taste in epiglottis / Visceral sensation + Reflexes (Posterior epiglottis, pharynx, larynx, trachea, bronchi, esophagus, stomach, small intestine, ascending and transverse colon) / Reflexes (Aortic sinus and bulb)
   —> ***Inferior (nodose) ganglion
   —> Solitary nucleus

Question 27

Special sensory

Answer 27

1. CN1
   - Smell —> Bipolar cells in olfactory epithelium —> Olfactory bulb
2. CN2
   - Vision —> Retinal ganglion cells —> Lateral geniculate nuclei
3. CN7 (anterior 2/3 tongue)
   - Taste —> Geniculate ganglion —> Gustatory / Solitary nucleus (rostral part)
4. CN8
   - Balance —> Vestibular ganglion —> Vestibular nuclei + Cerebellum
   - Sound —> Spiral ganglion —> Dorsal + Ventral Cochlear nucleus
5. CN9 (posterior 1/3 tongue)
   - Taste —> Inferior (petrosal) ganglion —> Gustatory / Solitary nucleus (rostral part)

Question 28

Somatic motor

Answer 28

1. CN3
   - Oculomotor nucleus —> Superior, Inferior, Medial rectus muscle; Inferior oblique; Levator palpebrae superioris (Ipsilateral)
2. CN4
   - Trochlear nucleus —> Superior oblique muscle (***Contralateral)
3. CN6
   - Abducens nucleus —> Lateral rectus muscle (Ipsilateral)
4. CN12
   - Hypoglossal nucleus —> Styloglossus, Hyoglossus, Genioglossus, intrinsic muscles of tongue (Palatoglossus by CN10) (Ipsilateral)

Question 29

***Branchial motor

Answer 29

1. CN5
   - Trigeminal motor nucleus
   —> Temporalis, Masseter, Lateral and Medial pterygoids + Tensor veli palatini and Tensor tympani, Anterior belly of digastric, Mylohyoid
2. CN7
   - Facial nucleus
   —> Facial muscles, Buccinator, Stapedius, Stylohyoid, Posterior belly of digastric, Platysma, Occipitalis
3. CN9
   - Nucleus ambiguus (rostral part)
   —> ***Stylopharyngeus + Superior pharyngeal constrictor
4. CN10
   - Nucleus ambiguus
   —> Palate, Pharyngeal constrictors, Intrinsic muscles of larynx, ***Palatoglossus
   —> Swallowing + Phonation
5. CN11
   - Nucleus ambiguus (caudal part)
   —> Sternocleidomastoid + Trapezius muscle / Communicates with vagal branches to ***muscles of pharynx and larynx

Question 30

Visceral motor (parasympathetic)

Answer 30

1. CN3
   - Edinger-Westphal nucleus
   —> **Ciliary ganglion: postganglionic via short ciliary nerves to **sphincter of pupil + ***Ciliary muscle
2. CN7
   - Superior salivatory nucleus
3. Greater petrosal nerve —> Nerve of pterygoid canal —> **Pterygopalatine ganglion —> postganglionic via Zygomaticotemporal nerve (CNV2)—> **Lacrimal gland + ***Mucosal glands of nasal cavity and palate
   —> Nasal and lacrimal secretions
4. **Chorda tympani —> **Lingual nerve (CNV3) —> **Submandibular ganglion —> postganglionic —> **Submandibular + ***Sublingual glands (記: CLS)
   —> Salivary secretion
5. CN9
   - Inferior salivatory nucleus
   —> Tympanic plexus —> **Lesser petrosal nerve —> **Otic ganglion —> **Auriculotemporal nerve (CNV3) —> **Parotid gland (記: LOA)
   —> Salivary secretion
6. CN10
   - Dorsal vagal nucleus
   - Nucleus ambiguus
   —> Cardiac depressor, Bronchoconstrictor, GI tract peristalsis + secretion

Question 31

CNV1 branches

Answer 31

1. Nasociliary nerve
   - Sensory root of ciliary ganglion
   - Posterior ethmoidal nerve
   - Long ciliary nerve
   - **Infratrochlear nerve
   - Anterior ethmoidal nerve —> **External nasal nerve
2. ***Lacrimal nerve
3. Frontal nerve
   - **Supratrochlear nerve
   - **Supraorbital nerve

Question 32

CNV2 branches

Answer 32

In the cranium
1. Middle meningeal nerve

From pterygopalatine fossa

1. Zygomatic nerve (Zygomaticotemporal nerve, Zygomaticofacial nerve), through the Inferior orbital fissure
2. Nasopalatine nerve
3. Posterior superior alveolar nerve
4. Greater palatine nerves
5. Lesser palatine nerves
6. Pharyngeal nerve

In the infraorbital canal

1. Middle superior alveolar nerve
2. Anterior superior alveolar nerve
3. Infraorbital nerve

Face:

1. Inferior palpebral nerve
2. Superior labial nerve
3. Lateral nasal nerve

Question 33

CNV3 branches

Answer 33

Trunk branches (before the division)

1. Muscular branches: motor nerves for Medial pterygoid, Tensor tympani, Tensor veli palatini
2. Meningeal branch (sensory)

Anterior division

1. ***Buccal nerve (sensory)
2. Masseteric nerve (motor)
3. Deep temporal nerves (motor)
4. Lateral pterygoid nerve (motor)

Posterior division

1. ***Auriculotemporal nerve (sensory)
2. ***Lingual nerve (sensory)
3. Inferior alveolar nerve (sensory + motor) —> Nerve to **Mylohyoid (motor, also supplies **Anterior belly of digastric) + Mental nerve