Cranial Nerves

Question 1

Describe Cranial nerves:

Answer 1

12 pairs in number containing mixed nerves: Sensory, motor, and parasympathetic

Arises from brain stem except for first two pairs. They are extensions of the brain itself.

Leaves cranium by passing through foramina at base of cranial fossae.

Numbered in roman numerals (opposite of spinal nerves)

Question 2

Where do CN III, and IV arise from?

Answer 2

Highest part of brain (mid Brain)

Question 3

Where does CN V arise from?

Answer 3

Second part of the brain stem AKA pons

Question 4

Where does CN VI, VII, and VIII arise from?

Answer 4

The pontomedullary sulcus

Question 5

Where does CN IX, X, XI, and XII arise from?

Answer 5

Different parts of the medulla

Question 6

Define Olfactory Nerve

Answer 6

Cranial Nerve 1:
Pure Sensory (Smell)
Starts as bipolar neurons at the level of cribriform plate of ethmoid bone.

These neurons end at the olfactory bulb which inturn gives rise to olfactory tract.

Olfactory tract ends to enthorhinal area (frontal Lobe)

Question 7

Describe Foramen Cecum:

Answer 7

Small vein passes through. The vein connects veins from the outside of the skull to the veins inside the skull.

Also supplies triangle area around nose.

Infection (pimple pop) to this area could affect the meninges (Meningitis)

Question 8

Cribriform Plate:

Answer 8

Provides access to Cranial nerve 1 (Olfactory)

Question 9

Optic Canal:

Answer 9

Passage for Cranial Nerve 2 (Optic)

Question 10

Sub Orbital Fissure:

Answer 10

Passage for Cranial Nerve 3, Cranial Nerve 4, one division of Cranial Nerve V (5) known as V1, or Ophthalmic nerve

Question 11

Foramen Rotundum

Answer 11

Passage for V2 Maxillary Nerve of CN V (5)

Question 12

Foramen Ovale

Answer 12

Passage for V3 mandibular nerve of CN V (5)

Question 13

Foramen Spinosum

Answer 13

Passage for middle meningeal artery (supplies meninges)

Question 14

Carotid Canal

Answer 14

Passage for internal Carotid Artery

Question 15

Internal Auditory meatus

Answer 15

Passage for CN VII (7) and CN VIII (8)

Question 16

Jugular Foramen

Answer 16

Internal Jugular Vein starts here: Passage for CN IX (9), X (10) and XI (11)

Question 17

Hypoglossal canal:

Answer 17

Passage for CN XII (12)

Question 18

Foramen Magnum

Answer 18

Passage for Medulla of brainstem and vertebral arteries

Question 19

Accessory Nerve: CN XI (11)

Answer 19

Pure motor nerve
Arises from medulla (cranial Root) and upper four segments of spinal cord (spinal root)
Passes through jugular foramen, where cranial root joins CN X (10) and distributes to laryngeal muscles via vagus.
Spinal Roots supplies SCM and Trapezius muscles.

Passes deep to SCM and becomes s/f at junction between upper third and distal 2/3 of scm. Lev scap sits deep to accessory nerve.

Junction between proximal 2/3 and distal 1/3 of the ant. border of trapezius.

Question 20

Optic Nerve CN II (2)

Answer 20

Pure Sensory Nerve (Vision)

Arise from retina (cone and rods to bipolar cells to ganglion cells to optic nerve)

Left and right optic nerves exchange some fibers at optic chiasm and turn into optic tract

Optic tract ends to lateral geniculate body (thalamus) and continues as optic radiation

Optic radiation ends to visual cortex (occipital Lobe)

Question 21

Occulomotor N CN III (3)

Answer 21

Mixed (motor & Parasympathetic nerve)

Arise from midbrain and passes thru superior orbital fissure.

Motor fibers supply some of the extraocular muscles (sup, inf, med, recti, and inf. oblique plus levator palpebra superioris)

Parasympathetic fibers: reach iris of the eye (after synaps in ciliary ganglion) supplies sphincter muscle of pupil (constricts iris)

Question 22

Trochlear N (CN IV) 4

Answer 22

Pure motor nerve

Only cranial nerve that shows up posterior to brainstem

Smallest of all cranial nerves

Arises from midbrain and passes through superior orbital fissure

Only supplies one of the extraocular muscles (sup. Oblique)

Question 23

Trigeminal N CN. V (5)

Answer 23

Only CN that has dermatome

Arise from pons and enters semilunar ganglion and then divides into three divisions:
Opthalmic (V1) Pure (General) Sensory - Enters the orbital Cavity through the superior orbital fissure.

Divides into following branches:

Lacrimal for Lacrimal Gland

Naso-ciliary: Supplies eyeball, nasal cavity mucous membrane

Supra-orbital for the skin of forehead (highest point of skull is called vertex)

nerve exits through supraorbital foramen

Question 24

Maxillary CN (V2)

Answer 24

Pure general sensory nerve.

Passes through foramen rotundum and enters pterygo-palatine fossa

Divides into following branches:

1. Pharyngeal (naso-pharynx)
2. Nasal (Nasal Cavity Postero-lateral Wall)
3. Superior Alveolar (upper Teeth)
4. Palatine (palate)
5. Infra-Orbital (Skin of the face between lower eyelid and upper lip)

Question 25

Mandibular CN (V3)

Answer 25

A mixed (motor and general sensory) nerve. Passes through foramen ovale and enters the infra-temporal fossa

Divides into following branches:

1. Inferior alveolar (lower teeth & skin of chin, mylohyoid and ant. belly of digastric)
2. Motor Branches to muscles of mastication tensor lympani and tensor velli palatini
3. Buccal (Sensory to skin and mucous of cheek)
4. Lingual (sensory for tongue, parasympathetic fibers from CN VII for submandibular and sublingual glands)
5. Auriculotemporal (a strip of skin in front of the ear and parasympathetic fibers from CN IX to parotid gland)

Question 26

Abducent N CN. VI (6)

Answer 26

Name comes from muscle it supplies (Lat rectus) Abduction of eye.

Pure motor nerve

Arises from midbrain and passes through superior orbital fissure.

Only supplies one of the extraocular muscles (lat. rectus)

Question 27

Facial N CN VII (7)

Answer 27

Mixed (Sensory, motor, Parasympathetic) passes through internal auditory meatus and enters geniculate ganglion. Different fibers choose different passages to leave the cranium

Motor fibers pass through stylo-mastoid foramen to supply muscles of expression, stylo-hyoid, and posterior belly of digastric

Damage to motor fiber causes bells palsy

Sensory and some parasympathetic fibers pass via petro-tympanic fissure (as chorda tympani nerve) to joint the lingual nerve (V3) will carry sense of taste from anterior 2/3 of the tongue (taste) and also supplies submandibular and sublingual glands

Other parasympathetic fibers form the greater petrosal nerve that passes through a synonymous groove to get into the pteryogo-palatine ganglion. Then it distributes to the lacrimal gland and mucosal glands of nasal cavity and palate

Question 28

Vestibulo-Cochlear N CN VIII (8)

Answer 28

Pure (special) sensory Nerve

Arises between medulla and pons

Passes through internal auditory meatus and ends to vestibule and cochlea of the inner ear. Carries sense of hearing (cochlear ganglion) and equillibrium/balance (Vestibular ganglion)

Question 29

Glosso-Pharyngeal N CN IX (9)

Answer 29

mixed sensory motor and parasympathetic nerve

Arises from medulla and passes thru jugular foramen

Joints two sensory ganglia

Sensory fibers either end to posterior 1/3 of tongue (general and taste) or to the oropharynx (general) , carotid body/sinus (has mechano sensors that senses the pressure of the carotid Artery)

Motor Fibers only supply stylo-pharyngeus

parasympathetic fibers will supply the parotid gland through auriculo-temporal nerve.

Question 30

Vagus N CN X (10)

Answer 30

Only cranial nerve to extend to thoracic viscera and abdomen (kidneys, pancreas, liver, biliary system are all controlled by vagus)

Stops at left 1/2 of transverse colon.

Is a mixed (sensory, motor and P/S) nerve

Arises from medulla and passes through jugular foramen

Joins two sensory ganglia

General sensory ganglia distribute to laryngo-pharynx, larynx and external ear while the sense of taste is collected from the back of the oral cavity.

Motor Fibers supply muscles of soft palate, pharynx, and larynx (not true)

Parasympathetic fibers regulate function of smooth muscles and glands of GI tract down to left 1/3 of transverse colon and thoracic Viscera

Question 31

Hypoglossal N CN XII (12)

Answer 31

pure motor nerve

Arises from medulla and passes through hypoglossal canal

Nerve enters the tongue and supplies all intrinsic and extrinsic muscles.