Flashcards in Intro to Cranial Nerves Deck (51):
How many cranial nerves are there?
Which two cranial nerves are not actually nerves, but are tracts - extensions of the brain that are covered by meninges?
CN I (olfactory tract) and CN II (optic tract)
Which cranial nerve originates from spinal nuclei?
Are all cranial nerves both sensory and motor like spinal nerves are? Explain.
No, they don't form a union of dorsal and ventral roots, so they can be motor only, sensory only, or mixed.
Do cranial nerves form plexuses?
What makes up the brainstem? Which cranial nerves originate from the brainstem?
Midbrain + pons + medulla oblongata = brain stem.
All CNs except for I, II, and XI originate from the brainstem.
Groups of CNS cell bodies are called _______, while groups of cell bodies in the PNS are called ______.
Groups of cell bodies in the CNS = nuclei
Groups of cell bodies in the PNS = ganglia
Where are sensory cell bodies found in the peripheral nervous system? Where are sensory cell bodies found in the CNS?
In the PNS, they are found in dorsal root ganglion.
In the CNS they are found in ganglion just outside the brainstem.
-note that no synapses occur in these ganglia, they are pseudounipolar nerves.
Once a cranial nerve exits the brain and enters the _______ space, it is technically considered to be in the periphery.
Which cranial nerves have preganglionic parasympathetic fibers that piggyback on them? On which cranial nerve do postganglionic fibers piggyback?
CNs III, VII, IX, and X.
Postganglionic parasympathetic fibers piggyback on CN V.
What is the other term for the sympathetic nervous system?
What is the other term for the parasympathetic nervous system?
Sympathetic = thoracolumbar
Parasympathetic = craniosacral
What are the five types of fibers that cranial nerves might consist of? Which two CNs have all five of these fibers?
One or more of...
1. Special sensory (smell, sight, taste, etc.)
2. Visceral sensory
3. Somatic sensory
4. Somatic motor
5. Visceral motor (smooth muscle, glands, etc.)
CNs IX and X have all of these.
How will you remember which cranial nerves are sensory, motor, or mixed?
Some Say Marry Money, But My Brother Says Big Breasts Matter Most
B = both (mixed)
What is CN I?
The true olfactory nerves pass from the nose up through the ________ plate of the ________ bone to synapse with the olfactory bulb (CN I)
True olfactory nerves pass from the nose up through the cribiform plate of the ethmoid bone
What is CN II?
Axons of ______ ______ cells collectively make up the optic nerve.
retinal ganglion cells
Where in the brain do the axons of the retinal ganglion cells ultimately travel to?
Most go to the visual cortex within occipital lobes, and some synapse in the lateral geniculate nucleus (pupillary light reflex)
What is CN III?
Oculomotor - somatic and visceral motor
Fibers travel from the ocular motor nucleus to the eye through the ________ ________ fissure, and split to form a _______ and ______ division to innervate the ocular muscles.
superior orbital fissure, splits to form a superior and inferior division.
Name the five extraocular muscles that are innervated by CN III.
1. Superior rectus
2. Inferior rectus
3. Medial rectus
4. Inferior oblique
5. Levator palpebrae superioris
What do the parasympathetic fibers that follow CN III do?
They pass through the superior orbital fissure along with CN III, follow the inferior division, and synapse at the ciliary ganglion. The postganglionic fibers control the ciliary muscle and sphincter pupillae.
What do the ciliary and sphincter pupilae muscles do?
Ciliary muscle rounds the lens.
Sphincter pupilae constricts the iris (pupillary light reflex)
What does failure of pupillary constriction tell you? Should both pupils constrict when light is shone on one eye?
It may indicate CN III compression. Both should constrict - involuntary - should happen in an unconscious person.
On what bony structure in the skull can CN III be compressed in the setting of increased intracranial pressure?
On the petrous ridge of the temporal bone.
What artery does CN III travel next to? What is the clinical significance of this?
The posterior communicating artery (of the circle of Willis). A berry aneurysm can compress CN III --> slowed pupillary light reflex.
CN III only innervates five of the seven extraocular muscles. Which CNs innervate the other two?
CN IV (trochlear) innervates the superior oblique muscle. The nerve is named after the trochlea, the pulley that the muscle runs through.
CN VI (abducent) innervates the lateral rectus muscle. The nerve is named after the fact that contraction of the muscle moves the eye laterally (abduction - abducens).
-somatic motor only!
What are the three parts of the trigeminal nerve (CN V)? What hole in the skull does each go through?
V1 - ophthalmic, goes through the superior orbital fissure
V2 - maxillary, goes through the foramen rotundum
V3 - mandibular, goes through the foramen ovale
The trigeminal nerve is mixed. Where are its sensory and motor cell bodies found, respectively?
Sensory cell bodies are found in the trigeminal ganglion, and motor cell bodies are found in the brainstem.
Is the ophthalmic division (V1) of the trigeminal nerve sensory, motor, or mixed? What are its branches?
Somatic sensory. Its branches are the tentorial nerve, lacrimal nerve (which trifurcates to terminate as the supraorbital, supratrochlear, and infratrochlear nerves), frontal nerve, and nasociliary nerve.
Is the maxillary division (V2) of the trigeminal nerve sensory, motor, or mixed? What are its branches?
Somatic sensory. Its branches are the infraorbital, descending palatine, and superior alveolar nerves (posterior, middle, and anterior)
Is the mandibular division (V3) of the trigeminal nerve sensory, motor, or mixed? What are its branches?
Mixed somatic sensory and somatic motor. Its branches are the auriculotemporal, inferior alveolar, buccal, lingual, and mental nerves
What muscles do the motor component of CN V3 innervate?
8 muscles of mastication, 4 major, 4 minor ones:
3. Lateral pterygoid
4. Medial pterygoid
2. Anterior belly of digastric
3. Tensor tympani
4. Tensor veli palatini
Which nerve innervates the muscles of facial expression?
CN VII (motor division)
Name the six branches of CN VII (facial nerve).
6. Posterior auricular
Two Zebras Bit My Cat Posteriorly
Aside from the muscles of facial expression, name three additional muscles that CN VII innervates.
2. Posterior belly of digastric
3. Stapedius (smallest voluntary muscle in the body)
What does the stapedius do?
It dampens your ability to hear when it contracts (inhibits movement of the stapes)
i.e. it keeps your own voice from sounding super loud
What does the parasympathetic component of CN VII do?
Innervates glands in the eye, nose, and palate.
Describe the pathway of the parasympathetic fibers associated with CN VII as they travel to their targets.
They first enter the facial canal through the internal acoustic meatus, then split up. One pathway travels anteriorly to the eye, lacrimal gland, and nose (Greater petrosal). The other pathway travels inferiorly through the petrotympanic fissure to supply the sublingual and submandibular glands (Chorda tympani).
What is the special sensory component of CN VII?
Taste on the anterior 2/3 of the tongue (Chorda tympani)
Where is the special sensory (taste) cell body of the Chorda tympani (CN VII) located?
In the geniculate ganglion inside the facial canal.
What does CN VIII (vestibulocochlear) do?
Vestibular system - gives sense of balance.
Cochlea - hearing
CN IX has special sensory, visceral sensory, somatic sensory, somatic motor, and visceral motor fibers. Describe each that are associated with CN IX.
Special sensory: taste on the posterior 1/3 of the tongue.
Visceral sensory: carotid body and sinus.
Somatic sensory: pharynx and posterior 1/3 of tongue.
Somatic motor: stylopharyngeus muscle.
Visceral motor: parotid gland via the lesser petrosal (preganglionic parasympathetic) nerve.
Describe the neural pathway of visceral motor innervation of the parotid gland.
Preganglionic parasympathetic fibers piggyback CN IX until they both exit the jugular foramen, at which point the parasympathetic fibers take their own route, entering the tympanic canaliculus into the middle ear. This is where it changes its name to the lesser petrosal nerve. It passes out the middle ear through the foramen ovale and synapses at the otic ganglion near the V3 bundle, and post-ganglionic fibers follow the auriculotemporal nerve and innervate the parotid gland.
What are supplied by the somatic sensory fibers of CN X (vagus)?
Parts of the ear, larynx, and maybe parts of the meninges.
What is supplied by special sensory fibers of CN X?
Taste buds on the epiglottis
What is supplied by somatic motor fibers from CN X?
1. Pharyngeal constrictors
2. Laryngeal constrictors
3. Most palatal muscles
What does CN XI (spinal accessory nerve) do?
Somatic motor to SCMs and trapezius muscles.
Branches from the spinal nucleus send fibers up through the foramen magnum, which then come back out the jugular foramen to innervate the SCM and trapezius. Which nerve is this?
CN XI - spinal accessory nerve
What does CN XII do?
Somatic motor to the tongue