Cranial Nerves Flashcards
What are the cranial nerves?
• CRANIAL NERVES= peripheral nerves that emerge directly from the brain (particularly BRAINSTEM= midbrain, pons, & medulla) except CN I & II which emerge from the cerebrum (forebrain)
o Have somatic motor, somatic sensory, and parasympathetic fibers
o Communicate brain with body, targets in head & neck
What are the differences between cranial nerve & spinal nerve?
• Cranial nerves emerge directly from the brain/brainstem
o spinal nerves emerge from the spinal cord
• Cranial nerve targets= in head & neck
o spinal nerve targets= in body & limbs
• Cranial nerves can be purely sensory, purely motor, or a mixture both
o spinal nerves are mixed nerves (sensory + motor)
• Some sensory cranial nerves are special sensory (vision, hearing/balance, smell, taste)
o all spinal sensory nerves are general sensory (pain, touch, temperature, & pressure)
• Some motor cranial nerves are branchial motor (supply skeletal muscles derived from embryonic gill arches)
o all spinal motor nerves are general motor (voluntary/somatic; visceral/autonomic)
• Cranial nerves never contain sympathetic fibers as an integral component of their fiber composition
o Sympathetics will follow CN to their target
What are common to cranial nerve & spinal nerve?
• Sensory nerves have their cell bodies outside of CNS
o cranial= sensory ganglion outside of brainstem
o spinal= dorsal root ganglion
• Motor nerves have their cell bodies within the CNS
o cranial= within brainstem (cranial nerve motor nuclei)
o spinal= within spinal cord (ventral horn)
List the name and roman numeral of each cranial nerve. Outline what bony foramen or foramina each cranial nerve travels through along its course from the brainstem to its target/targets
• CN I= Olfactory Nerve
o Point of Exit: Cribiform plate of ethmoid bone (congregate as olfactory bulb & travel in olfactory tract)
• CN II= Optic Nerve
o Point of Exit: Optic Canal
• CN III= Oculomotor Nerve:
o Point of Exit: Superior Orbital Fissure
• CN IV= Trochlear Nerve
o Point of Exit: Superior Orbital Fissure
• CN V= Trigeminal Nerve
o Point of Exit:
♣ Opthalmic (V1)= Superior Orbital Fissure
♣ Maxillary (V2)= Foramen Rotundum
♣ Mandibular (V3)= Foramen Ovale
• CN VI= Abducens Nerve
o Point of Exit: Superior Orbital Fissure
• CN VII= Facial Nerve
o Point of Exit: Internal Acoustic Meatus
• CN VIII= Vestibulocochlear Nerve
o Point of Exit: Internal Acoustic Meatus
• CN IX= Glossopharyngeal Nerve
o Point of Exit: Jugular Foramen
• CN X= Vagus Nerve
o Point of Exit: Jugular Foramen
• CN XI= Spinal Accessory Nerve
o Point of Exit: Jugular Foramen
• CN XII= Hypoglossal Nerve
o Point of Exit: Hypoglossal Canal
Which cranial nerves are PURELY SENSORY?
• 3 Purely Sensory Nerves:
o Olfactory Nerve (CN I)
o Optic Nerve (CNII)
o Vestibulocochlear Nerve (CN VIII)
Which cranial nerves are PURELY MOTOR?
• 5 Purely Motor Nerves: o Oculomotor Nerve (CN III) o Trochlear Nerve (CN IV) o Abducens Nerve (CN VI) o Spinal Accessory Nerve (CN XI) o Hypoglossal Nerve (XII)
Which cranial nerves carry SPECIAL SENSORY component?
• 6 Nerves carry Special Sensory Component: o Olfactory (CN I) Smell o Optic (CN II) Vision o Facial (CN VII) Taste (anterior 2/3 of tongue) o Vestibulocochlear (CN VIII) Hearing (& balance) o Glossopharyngeal (CN IX) Taste (posterior 1/3 of tongue) o Vagus (CN X) Taste (root of tongue; taste buds of epiglottis)
Which cranial nerves carry BRANCHIAL MOTOR component? (aka special visceral efferent)
• 5 Nerves carry Branchial Motor Component: o Trigeminal (CN V) Muscles of Mastication (1st Pharyngeal Arch) o Facial (CN VII) Muscles of Facial Expression (2nd Pharyngeal Arch), large component of facial o Glossopharyngeal (CN IX) Stylopharyngeus muscle (3rd Branchial Arch), poor man’s facial nerve o Vagus (CN X) Pharyngeal & Laryngeal muscles, one extrinsic tongue muscle (4th Branchial Arch) o Accessory (CN XI) Sternocleidomastoid & Trapezius muscles (6th Branchial Arch)
Which cranial nerves carry PARASYMPATHETIC nerve fibers?
• 4 Nerves carry Parasympathetic Nerve Fibers: o Oculomotor (CN III) corresponding ganglion= Ciliary o Facial (CN VII) corresponding ganglion= Pterygopalatine & Submandibular o Glossopharyngeal (CN IX) corresponding ganglion= Otic o Vagus (CN X) synapses in wall of organs
How do parasympathetic nerves in the head differ from those in the body?
- Parasympathetic nerves in the head reach their ganglia & synapse outside of their target organs whereas parasympathetic nerves synapse intramurally (within the target organ’s wall) in the rest of the body
- all autonomic ganglia in the head are parasympathetic
- preganglionic parasympathetic fibers reach their target in the head via branches of CN III, VII, or IX
- postganglionic parasympathetic fibers reach their end organs by hitch-hiking along branches of CN V
What & where are the sensory ganglia of the cranial nerves equivalent to dorsal root ganglia of the spinal nerve?
• Cranial Nerve Sensory Ganglia= equivalent to spinal ganglia; located outside the brainstem
o have a peripheral process that is associated with a receptor & a central process that terminates in a cranial nerve sensory nucleus
What is the brainstem’s equivalent of dorsal, ventral, & lateral horns?
• Instead of having dorsal (sensory), ventral (motor), or lateral (autonomic) horns like the spinal cord, the brainstem consists of cranial nerve nuclei which correspond to the different fiber types within each cranial nerve (motor, sensory, & parasympathetic)
o Cranial Nerve Motor Nuclei= origin for somatic motor fibers that innervate skeletal muscles of the neck & face
♣ equivalent to ventral horn of spinal cord
o Cranial Nerve Sensory Nuclei= termination of afferent sensory fibers from central processes of cranial nerve sensory ganglia
♣ equivalent to dorsal horn of spinal cord
o Cranial Nerve Parasympathetic Nuclei= CN II, VII, IX, & X; where preganglionic parasympathetic fibers must synapse in the head
♣ equivalent to lateral horn of spinal cord
♣ COPS ganglia ciliary; otic; pterygopalatin; submandibular)
Describe the 4 cranial parasympathetic ganglia & with what cranial nerve each ganglion is associated?
• Ciliary Ganglion corresponding nerve= Oculomotor (CN III)
o located in posterior orbit
o preganglionic fibers run with Oculomotor nerve
o postganglionic fibers run in short ciliary nerves to innervate 2 eye muscles:
♣ Sphincter Pupillae= constricts pupil (Miosis)
♣ Ciliaris= accommodation (when it contracts, releases tension on zonular fibers making the lens more convex to allow for near vision)
• Pterygopalatine & Submandibular Ganglia corresponding nerve= Facial (CN VII)
o Pterygopalatine Ganglion= located in pterygopalatine fossa
♣ receives preganglionic fibers from greater petrosal branch of CN VII/Facial
• axons project to lacrimal glands & nasal mucosa
• also innervates venous plexus of nasal conchae to heat/cool air in nose
o Submandibular Ganglion= situated above deep portion of submandibular glans on the hyoglossus muscle near the posterior border of the mylohyoid muscle
♣ receives preganglionic fibers from chorda tympani & lingual nerve branches/tributaries of CN VII/Facial
♣ sends postganglionic fibers to oral mucosa & submandibular & sublingual salivary glands
• Otic Ganglion corresponding nerve= Glossopharyngeal (CN IX)
o small, oval-shaped, flattened parasympathetic ganglion of a reddish-gray color; immediately below the foramen ovale in the infratemporal fossa
o innervates the parotid gland (largest paired salivary gland)
o preganglionic fibers travel along lesser petrosal nerve
o postganglionic fibers travel along auriculotemporal nerve (CN V3)
What cranial nerve do most cranial preganglionic parasympathetic fibers hitchhike along to reach their targets?
PREganglionic PARAsympathetic fibers reach their target ganglia in the head via branches of CN III, VII, or IX
Are the sympathetic nerves in the head preganglionic or postganglionic?
• ALL SYMPATHETIC NERVES IN THE HEAD ARE POSTGANGLIONIC because they already synapsed at the superior cervical ganglion
What is the superior cervical ganglion? How are postganglionic fibers from this ganglion distributed to the head & neck?
• PREganglionic sympathetic fibers ascend in sympathetic chain & terminate in SUPERIOR CERVICAL GANGLION (superior termination of chain) at base of skull adjacent to INTERNAL CAROTID ARTERY as it enters the carotid canal
o originate in upper thoracic levels of IML column (T1-T4)
• POSTganglionic sympathetic fibers from the superior cervical ganglion can reach their target organs by:
o 1) jumping on internal carotid arteryfollow if inferiorly to bifurcation from common carotidthen travel along the external carotid artery & its branches to reach target organ
o 2) follow internal carotid artery into craniumfollow branches of TRIGEMINAL SYSTEM
o 3) travel on their own before joining with other nerves
What is Horner’s Syndrome? How is it characterized clinically?
• HORNER’S SYNDROME interruption of cervical sympathetic trunk that manifests as the absence of sympathetically stimulated functions on the ipsilateral (same) side of the head
o Symptoms= constriction of pupils (miosis) from dilator pupillae not working (sympathetic) and sphincter pupillae (parasympathathetic, constriction) being opposed ; drooping of superior eyelid (ptosis) from superior tarsal (sympathetic, tone of eyeline) damage, redness & increased temperature of skin (vasodilation, no sympathetic); absence of sweating (anhydrosis, no sympathetic)
Trace the path of CN III parasympathetics from the brainstem to their targets (sphincter pupillae & ciliaris muscles)
• PARAsympathetic (GVE) fibers innervate smooth muscular sphincter pupillae & ciliaris
o PREganglionic parasympathetic cell bodies are located in the Edinger Westfall (accessory oculomotor) nucleus
o fibers travel in the INFERIOR DIVISION OF III & synapse on POSTganglionc cell bodies in the CILIARY GANGLION
o POSTganglionic fibers travel directly to the eye via SHORT CILIARY NERVES (branches of CN VI)
What function does sphincter pupillae serve? What does ciliary muscle do when it contracts? What is the process of accommodation in the eye?
• Sphincter Pupillae constricts the pupil= Miosis
• Ciliary Muscle contraction/relaxation changes the shape of the lens to adjust the focus of their vision= ACCOMMODATION
o when relaxed the lens lies flatFar vision
o when contracted the lens becomes convex Near vision (parasympathetic stimulation)
How does an oculomotor nerve lesion present? How will the pupil & upper eyelid appear?
• When lesioned, results in dilated pupil, ptosis (droopy upper eyelid), pupil is directed “down & out”
o innervates levator palpebrae superioris (lifts lid); superior rectus (lifts eyeball); inferior rectus (downward motion of eyeball); medial rectus (ADduction of eyeball); inferior oblique (upward motion of eyeball-attaches to back of eyeball)
Which cranial nerve exits the DORSAL side of the brainstem?
• TROCHLEAR NERVE (CN IV) purely somatic motor nerve supplying superior oblique muscle that arises from the DORSAL aspect of the brainstem (unlike the other CN, which exit the ventral side of the brain)
o enters the orbit via the SUPERIOR ORBITAL FISSURE
o cell bodies originate in trochlear nucleus of the pons
How will a patient with a trochlear nerve lesion present clinically?
• Trochlear Nerve Lesion= patient is unable to look down when the eye is adducted (isolate the superior oblique by adducting the eye; puts the axis of the eyeball/optic nerve in line with the axis of the superior oblique muscle)
How will a patient with an abducens nerve lesion present clinically?
• Abducens Nerve (CN VI)= purely somatic motor nerve supplying the lateral rectus muscle
o pass through the cavernous sinus & enter the orbit via the SUPERIOR ORBITAL FISSURE
• Abducens Nerve Lesion patient is unable to ABduct the eye
What 2 openings in the skull does CN XI travel through?
• SPINAL ACCESSORY NERVE (CN XI)= purely somatic motor nerve supplying trapezius & sternocleidomastoid
o spinal rootlets from the upper 5 segments of spinal cord coalesce & enter the skull through the FORAMEN MAGNUM & then travel along the inner wall to exit the skull via the JUGULAR FORAMEN
