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Cranial Nerves: Overview

Part of PNS
Sensory, motor, and parasympathetic nerve fibers that innervate the head and viscera


Where do cranial nerves originate?

Brain or brainstem


How are the cranial nerves named?

Named in order, from anterior to posterior, where they emerge from the brain


How many cranial nerve (pairs) are there?

12 pairs (CN 1 - CN 12)


How many sensory, motor, and mixed nerve pairs exist?

3 pairs of sensory nerves
5 pairs of motor nerves
4 pairs of mixed nerves (both sensory and motor)


List all 12 cranial nerves in order (CN 1 - CN 12)

1. Olfactory (CN 1)
2. Optic (CN 2)
3. Oculomotor (CN 3)
4. Trochlear (CN 4)
5. Trigeminal (CN 5)
6. Abducens (CN 6)
7. Facial (CN 7)
8. Vestibulocochlear (CN 8)
9. Glossopharyngeal (CN 9)
10. Vagus (CN 10)
11. Spinal Accessory (CN 11)
12. Hypoglossal (CN 12)


What is the mnemonic for the cranial nerves?

On [Olfactory (CN 1)]
On [Optic (CN 2)]
On [Oculomotor (CN 3)]
They [Trochlear (CN 4)]
Traveled [Trigeminal (CN 5)]
And [Abducens (CN 6)]
Found [Facial (CN 7)]
Voldemort [Vestibulocochlear (CN 8)]
Guarding [Glossopharyngeal (CN 9)]
Very [Vagus (CN 10)]
Secret [Spinal Accessory (CN 11)]
Horcruxes [Hypoglossal (CN 12)]


Which 2 cranial nerves attach to the forebrain?

Olfactory (CN 1) and Optic (CN 2)


Where do the rest of the cranial nerves attach?

At the brainstem


Which is the only cranial nerve to extend past the head and neck?

Vagus nerve (CN 10)


What are the 3 axons cranial nerves can carry?

Sensory axons (S)
Motor axons (M)
Both axons (B)


Which 3 cranial nerves carry sensory axons?

Olfactory (CN 1)
Optic (CN 2)
Vestibulocochlear (CN 8)


Which 5 cranial nerves carry motor axons?

Oculomotor (CN 3)
Trochlear (CN 4)
Abducens (CN 6)
Spinal Accessory (CN 11)
Hypoglossal (CN 12)


Which 4 cranial nerves carry both sensory and motor axons?

Trigeminal (CN 5)
Facial (CN 7)
Glossopharyngeal (CN 9)
Vagus (CN 10)


What's the mnemonic for determining which cranial nerves carry S, M, or B axons?

Some [Olfactory (CN 1)]
Say [Optic (CN 2)]
Money [Oculomotor (CN 3)]
Matters [Trochlear (CN 4)]
But [Trigeminal (CN 5)]
My [Abducens (CN 6)]
Brother [Facial (CN 7)]
Says [Vestibulocochlear (CN 8)]
Big [Glossopharyngeal (CN 9)]
Brains [Vagus (CN 10)]
Matter [Spinal Accessory (CN 11)]
Most [Hypoglossal (CN 12)]


3 Sensory Cranial Nerves

Olfactory (CN 1), Optic (CN 2), Vestibulocochlear (CN 8)

Innervation for special sensory structures (smell, vision, equilibrium, and hearing)


Olfactory Nerve (CN 1) [S]

Sensory: olfaction (smell)
Origin: olfactory epithelium of nose (terminate in posterior olfactory cortex)


Optic (CN 2) [S]

Technically not a nerve but a brain tract (we still call it a nerve)

Sensory: vision
Origin: retina of eye (terminal in primary visual cortex [posterior part of occipital lobe])


Vestibulocochlear (CN 8) [S]

Sensory: hearing and balance (equilibrium)
Origin: inner ear, enters brain stem at pons


5 Motor Cranial Nerves

Oculomotor (CN 3), Trochlear (CN 4), Abducens (CN 6), Spinal Accessory (CN 11), and Hypoglossal (CN 12)

Somatic motor fibers to skeletal muscles of eye, neck/back, and tongue


Oculomotor (CN 3), Trochlear (CN 4), Abducens (CN 6) [M]

Oculomotor (CN 3):
--origin: midbrain
--also parasympathetic

Trochlear (CN 4):
--origin: midbrain

Abducens (CN 6):
--origin: pons

Fxn: all of these are primarily motor nerves to extrinsic eye muscles


Problems with Eye Innervation

When the nerve(s) that control the muscles that move the eye are damaged, lots of potential issues. Conditions include strabismus (eyes not parallel), ptosis (drooping eyelids), and diplopia (double vision)


Spinal Accessory Nerve (CN 11) [M]

Motor nerve to trapezius and sternocleidomastoid muscles

Origin: rootlets at cervical region of spinal cord


Hypoglossal (CN 12) [M]

(Hypo = below; global = tongue)

Motor to tongue muscles
Origin: medulla oblongata


4 Mixed Cranial Nerves (sensory and motor)

Trigeminal (CN 5), Facial (CN 7), Glossopharyngeal (CN 9), and Vagus (CN 10)

Mixed nerves: sensory innervation to face, mouth, and viscera and also motor innervation to pharyngeal arch muscles (chewing, facial expression)


Trigeminal (CN 5) [B]

3 branches: V1 (ophthalmic), V2 (maxillary), V3 (mandibular)

Motor: V3 only
--muscles of mastication

Sensory: V1, V2, and V3
--somatic sensory for face, oral cavity, nasal cavity, anterior 2/3 of tongue (NOT taste)

Origin: sensory receptors to pons


Facial (CN 7) [B]

Somatic motor: muscles of facial expression (5 major motor branches)

Visceral Motor (parasympathetic)
--lacrimal gland (tears), submandibular and sublingual salivary glands (digestion), + nasal and palatine glands

Sensory: anterior 2/3 of tongue, small patch at ear for somatic sensory

Origin: pons


Glossopharyngeal (CN 9) [B]

Somatic motor: stylopharyngeas muscle (swallowing)

Visceral motor (parasympathetic): parotid salivary gland (involved with digestion)

Sensory: general visceral sensory, taste posterior 1/3 of tongue

Origin: medulla oblongata


Vagus (CN 10) [B]

Somatic motor: larynx and pharyngeal muscles

Visceral motor (parasympathetic): thoracoabdominal viscera through 2/3 of the intestines, regulates HR, breathing, and digestive system activity

Sensory: external auditory meatus (EAM) and laryngopharynx. Also visceral sensory form most thoracoabdominal viscera

Origin: medulla oblongata

Vagus (aka the wanderer) is the only cranial nerve to extend beyond head/neck!


Summary: Cranial nerves

3 sensory: olfactory (CN 1), optic (CN 2), vestibulocochlear (CN 8)
5 motor: oculomotor (CN 3), trochlear (CN 4), abducens (CN 6), spinal accessory (CN 11), and hypoglossal (CN 12)
4 mixed (sensory and motor): trigeminal (CN 5), facial (CN 7), glossopharyngeal (CN 9), and vagus (CN 10)

Know where they come from and where they innervate!