Cranial Nerves

Question 1

Cranial Nerves

Answer 1

12 pairs

• essentially run the functions of the head & neck
• pure sensory, pure motor, or mixed
• arise from & interact with nuclei (motor, sensory, parasympathetic) in brainstem (*NO SYMPATHETIC)
• cell bodies of sensory neurons live in CN ganglia (like dorsal root ganglia)

Question 2

The 12 Cranial Nerves

Answer 2

I - Olfactory
II - Optic 
III - Oculomotor
IV - Trochlear
V - Trigeminal
VI - Abducens
VII - Facial
VIII - Audiovestibular (Vestibulocochlear)
IX - Glossopharyngeal
X - Vagus
XI - Spinal Accessory
XII - Hypoglossal

Question 3

I - Olfactory Nerve

Answer 3

• pure sensory
• receptors in roof of nasal cavity
• olfactory nerves supply olfactory epithelium
• terminate in olfactory bulb –> olfactory tract
• only sensory system to bypass thalamus (sensory relay station)

Question 4

Damage/Disease to Olfactory Nerve

Answer 4

hyposmia - reduced sense of smell

anosmia - absence of sense of smell

Question 5

II - Optic Nerve

Answer 5

• pure sensory
• receptors in retina of eye
• axons of ganglion cells –> optic nerve
• optic nerve –> optic chiasm –> optic tract –> lateral geniculate nucleus (thalamus) –> optic radiations –> primary visual cortex
• visual fields projected onto visual cortex in inverted and reversed fasion

Question 6

Primary Visual Cortex

Answer 6

medial aspect of occipital lobe on either side of Calcarine Sulcus

Question 7

Damage/Disease to Optic Neve

Answer 7

results in visual field defects - depends on location of damage

Question 8

III - Oculomotor Nerve

Answer 8

• motor and parasympathetic (mixed)
• arises from midbrain
• motor to extra-ocular muscles (innervates all except LR6SO4 - lateral rectus CN VI, superior oblique CN IV)
• PS to pupillary constriction & accomodation

Question 9

Extra-Ocular Muscles supplied by Oculomotor Nerve

Answer 9

• medial rectus
• superior rectus
• inferior rectus
• inferior oblique
• levator palpebrae superioris (elevator of upper eyelid)

Question 10

Damage/Disease to Oculomotor Nerve

Answer 10

pupilarry dilation (unstopped sympathetics)
opthalmoplegia (eye movements weakened or paralyzed)

Question 11

IV - Trochlear Nerve

Answer 11

• smallest cranial nerve
• pure motor
• supplies superior oblique
• only CN to emerge from back of brainstem (midbrain)
• isolated damage uncommon (sandwiched btwn 2 layers of dura mater)

Question 12

VI - Abducent Nerve

Answer 12

• pure motor
• supplies lateral rectus (abducts eye = abducent)
• longest intracranial course of all CNs - more able to have function compromised

Question 13

Damage to Abducent Nerve

Answer 13

• paralysis of lateral rectus –> unopposed action of medial rectus –> eye deviates medially –> squint
  patients complain of double vision (diplopia)

Question 14

V - Trigeminal Nerve

Answer 14

• mixed nerve - sensory and motor from pons
• 3 divisions arising from trigeminal ganglion: V1 - opthalmic nerve (eye), V2 - maxillary nerve (cheek), V3 - mandibular nerve (mandible)
• serves as a conduit for parasympathetic functions of CNs III, VII, and IX

Question 15

Damage/Disease to Trigeminal Nerve

Answer 15

Trigeminal Neuraglia (Tic Douloureux)

• pain, mainly in V2 and V3
• sometimes only way to correct is to cut off sensation

Question 16

V1

Answer 16

Opthalmic Nerve –> eye

• pure sensory
• supplies sensation of frontal and ethmoidal paranasal air sinuses
• supplies sensory innervation (general - PTTP) to nasal cavity
• supplies sensation to the upper eyelid, side of the nose, forehead, and scalp (supraorbital nerve)
• has ciliary ganglion - parasympathetic for CN III

Question 17

V2

Answer 17

Maxillary nerve –> cheek

• pure sensory
• enters floor of orbit through inferior orbital fissue
• supplies sensation to: maxillary air sinus, nasal cavity, lower eyelid, skin of cheek, upper lip (infraorbital nerve), maxillary teeth and gums
• has pterygopalatine ganglion - PS for CN VII

Question 18

V3

Answer 18

Mandibular nerve –> mandible

• mixed nerve - sensory and motor
• submandibular (CN VII) & otic (CN IX) ganglia (PS)
• enters infratemporal fossa (medial to mandible)

Question 19

Functions of V3

Answer 19

Motor:
- supplies muscles of mastication
Sensory:
- lower lip, skin of mandible
- mandibular teeth & gums (inferior alveolar nerve)
- general sensation to anterior 2/3 of tongue (lingual nerve)
- ends as mental nerve
- carries proprioceptive info from muscles of mastication –> brainstem (force of bite)

Question 20

VII - Facial Nerve

Answer 20

• mixed nerve (motor, sensory & PS)
• attached to pons
• cell bodies in geniculate ganglion

Question 21

Damage/Disease to Facial Nerve

Answer 21

• may loose taste, salivation, or lacrimation in one eye

- Bell’s Palsy (hemi-facial paralysis)

Question 22

Functions of VII

Answer 22

Motor:
- muscles of facial expression
Sensory:
- taste to anterior 2/3 of tongue (via chordae tympani - joins lingual n)
- some sensory to skin around ear
PS:
- lacrimal gland for tearing vis pterygopalatine ganglion (V2)
- submandibular & sublingual salivary glands via submandibular ganglion (V3)

Question 23

VIII - Vestibulocochlear Nerve

Answer 23

• pure sensory, 2 components:
  1. Vestibular
  2. Conchlear

Question 24

Vestibular Component of VIII

Answer 24

• supplies vestibular aparatus (semicircular canals & vestibule) –> balance equilibrium
• disease: Meniere’s syndrome - vertigo, nausea, vomiting

Question 25

Cochlear Component of VIII

Answer 25

- supplies organ of Corti in cochlea --> hearing - bilateral central pathway in brainstem carries this info to the temporal lobe --> primary auditory cortex - damage/disease: difficulty in localizing sound (deafness rare)

Question 26

IX - Glossopharyngeal Nerve

Answer 26

- mixed (motor, sensory, & PS) - supplies tongue and pharynx - attached to medulla - regulates gag reflex

Question 27

Damage/Disease to IX

Answer 27

difficulty swallowing, loss of gag reflex

Question 28

Functions of IX

Answer 28

``` Motor to one Muscle: - stylopharyngeus (elevates pharynx) Sensory (general): - posterior 1/3 tongue, pharynx, palatine tonsils, carotid sinus & body (for carotid sinus reflex) Sensory (special): - taste to posterior 1/3 tongue PS: - supplies parotid gland via otic ganglion (V3) ```

Question 29

X - Vagus Nerve

Answer 29

- mixed (motor, sensory, & PS) | - attached to medulla

Question 30

Damage/Disease to Vagus Nerve

Answer 30

difficulty with speech and swallowing

Question 31

Vagus Nerve Functions

Answer 31

Motor: - to muscles of palate, pharynx, and larynx (from CN XI) Sensory: - to muscles of palate, pharynx, and larynx - sensory to eardrum (can induce a vagal response) - barareceptor to hollow organs (stomach and bowel) - carries visceral afferents from the organs to the CNS (gut feeling) PS: - functions as the PS nerve for the viscera - PS motor to smooth muscle in thoracic and abdominal organs up to distal part of transverse colon - regulates heart rate (slows it down)

Question 32

XI - Spinal Accessory Nerve

Answer 32

- motor function - attached to medulla & upper spinal cord Cranial Portion: - distributed with CNX (palate, pharynx, larynx) Spinal Portion: - spinal accessory nerve - supplies trapezius and sternocleidomastoid muscles in the neck

Question 33

Damage/Disease to XI

Answer 33

weakness when shrugging (elevating shoulders), turning head to one side against resistance

Question 34

XII - Hypoglossal Nerve

Answer 34

- pure motor - attached to medulla - supplies the muscles of the tongue

Question 35

Damage/Disease to XII

Answer 35

inability to protrude tongue symmetrically