Anatomy of Cranial Nerves Flashcards
What is the function and modality of cranial nerve I?
Olfactory nerve- smell
Special sensory
Where is the extra cranial part of CN I?
Lays within olfactory mucosa in nasal cavity
What is the cranial foramina of CN I?
Cribriform plate of the ethmoid bone
Lies within anterior cranial fossa
Where is the intracranial part of CN I where is connects with the CNS?
Olfactory nerves synapse in the olfactory bulb
Then pass through the olfactory tract to cortical areas
What is the function and modality of CN II?
Optic nerve- vision
Special sensory
Where is the extra cranial part of CN II?
Neurons of retina travel posteriorly via optic nerve from posterior hemisphere of eye through orbit
What is the cranial foramina for CN II?
Optic canal in middle cranial fossa
Where is the intracranial part of CN II?
Optic nerve passes around pituitary stalk to optic chasm to form the optic tract
Where does CN II connect with the CNS?
Diencephalon
What are the only 2 structures running through the optic canal?
Optic nerve and ophthalmic artery
How is CN I clinically tested?
Not routinely tested!
Can ask patient to smell familiar smell whilst covering contralateral nostril
How is CN II clinically tested?
5 ways: Acuity (Snellen chart) Colour (Ishihara plates for colour blindness) Fields (Four quadrants) Reflexes (Pupillary light reflexes) Fundoscopy
What is the function and modality of CN III?
Oculomotor nerve Eye movement (motor) Pupil constriction (parasympathetic)
Where does CN III connect with the CNS?
Midbrain (mesencephalon)
Where is the intracranial part of CN III?
Towards the orbit in the lateral wall of the cavernous sinus
What is the cranial foramina for CN III?
Superior orbital tissue (SOF)
What is the extra cranial part of CN III?
Passed from SOF into orbit to supply all extra ocular muscles except 2
Parasympathetic part synapses in ciliary ganglion
What is the function and modality of CN IV?
Trochlear nerve Eye movement (Motor)
Where does CN IV connect with the CNS?
Midbrain (mesencephalon)
Where is the intracranial part of CN IV?
Nerve travels towards the orbit in the lateral wall of the cavernous sinus
What is the cranial foramina for CN IV?
Superior orbital fissure (SOF)
Where is the extra cranial part of CN IV?
Passes through SOF into orbit and supplies only superior oblique muscle
What is the function and modality of CN VI?
Abducent nerve Eye movement (motor)
Where does CN VI connect with the CNS?
Pontomedullary junction
Where is the intracranial part of CN VI?
Travels towards orbit within cavernous sinus
What is the cranial foramina for CN VI?
Superior orbital fissure (SOF)
Where is the extra cranial part of CN IV?
Passes through SOF into orbit and supplies only lateral rectus
How are eye movements tested?
The ‘H’ test
What is the function and modality of CN VIII?
Vestibulocochlear nerve
Hearing and balance (special sensory)
Where is the extra cranial part of CN VIII?
Axons from cochlear and vestibular apparatus
What is the cranial foramina for CN VIII?
Internal acoustic meatus
In posterior cranial fossa
Where is the intracranial part of CN VIII?
Travels posteromedially from internal acoustic to pontomedullary junction
Where does CN VIII connect with the CNS?
Pontomedullary junction
How do you clinically test VIII?
Rinne and Weber test
What is the function and modality of CN XI?
Spinal accessory nerve
Motor- sternocleidomastoid and trapezius muscle
Where does CN XI connect with the CNS?
Cervical spinal cord
Where is the intracranial part of CN XI?
Ascends through foramen magnum then travels towards jugular foramen in posterior cranial fossa
What is the cranial foramina for CN XI?
Jugular foramen in posterior cranial fossa
Where is the extra cranial part of CN XI?
Axons supply SCM on deep surface, then continue across posterior triangle to supply trapezius
How do you clinically test XI?
Ask patient to shrug shoulder
Ask patient to turn head to flex neck and turn towards the opposite side
What is the function and modality of CN XII?
Hypoglossal nerve
Motor ( all muscles of the tongue except palatoglossus)
Where does CN XII connect with the CNS?
Via rootlets lateral to pyramids of medulla oblongata
Where is the intracranial part of CN XII?
Passes anteriorly to hypoglossal canal
What is the cranial foramina for CN XII?
Hypoglossal canal in posterior cranial fossa
Where is the extra cranial part of CN XII?
Descends lateral to carotid sheath
At level of hyoid it turns anteriorly towards lateral aspect of tongue
How do you clinically test XII?
Ask patient to stick tongue straight out
Tongue tip will point towards side of injured nerve
Which cranial nerves are more complex?
Trigeminal
Facial
Glossopharyngeal
Vagus
What are the 3 divisions of CN V (Trigeminal) and what are their modalities?
CNV1- Ophthalmic- Sensory
CNV2- Maxillary- Sensory
CNV3- Mandibular- Sensory and Motor
Where does CN V connect with the CNS?
Pons (laterally)
Where is the intracranial part of CN V?
Inferior to edge of tentorium cerebella between posterior and middle cranial fossae
What are the cranial foramina for the 3 divisions of CN V?
CN V1- Superior orbital fissure
CNV2- Foramen rotundum
CNV3- Foramen ovale
Where is the extra cranial part of CN XII?
Sensory axons from all 3 divisions- from superficial and deep facial structures posteriorly towards respective cranial foramen
Motor axons- from CNV3 flow from foramen ovale towards skeletal muscle they supply
What areas of the face does CNV1 supply?
Upper eyelid
Cornea
All the conjunctiva
Skin of root/bridge/tip of nose
What areas of the face does CNV2 supply?
Skin of lower eyelid
Skin of maxilla
Skin of ala of nose
Skin/mucosa of upper lip
What areas of the face does CNV3 supply?
Skin over mandible and TMJ
What are the motor functions of CNV3 mandibular nerve?
Innervation of 3 pairs of jaw closing muscles- master, temporalis and medial pterygoid
Innervation of 1 pair of jaw opening muscles- lateral pterygoid
Tensor veli palatini and tensor tympani
How do you clinically test CNV?
Sensory: ask patient to close eyes and gently brush skin in each dermatome with fine top of cotton wool, compare both sides
Motor: Palpate strength of contraction of masseter & temporalis by asking patient to clench teeth
Ask patient to open jaw against resistance
What is the function and modality of CN VII?
Facial nerve- special sensory (taste), motor and parasympathetic
Where does CN VII connect with the CNS?
Anterolateral at pontomedullary junction
What is the cranial foramina for CN VII?
Temporal bone
Internal acoustic meatus (in)
Stylomastoid foramen (out)
Where is the extra cranial part of CN VII?
Most somatic motor axons pass into parotid gland then into 1 of 5 branches that supply muscles of facial expression
Where is the course of the facial nerve in the base of skull?
Through the petrous part of temporal bone
What does the branch of CN VII (chorda tympani) innervate?
Taste buds on anterior 2/3rds of tongue
Parasympathetic supply to submandibular & sublingual glands (salivation)
Which muscle in the inner ear is innervated by CN VII?
Stapedius muscle
Reduces stapes movement to protect the internal ear from excessive noise
The chorda tympani joins the lingual nerve (CNV3) to innervate what?
Anterior 2/3rds of tongue and parasympathetic fibres to glands of submandibular and sublingual
How do you clinically test CN VII?
Ask patient to: Raise eyebrows (frontalis) Close eyes tightly (orbicularis oculi) Smile (elevators of lips) Puff out cheeks and hold air (orbicularis oris)
What is the function and modality of CN IX?
Glossopharyngeal nerve Special sensory (Taste) Sensory Motor Visceral afferent Parasympathetic
Where does CN IX connect with the CNS?
Lateral aspect of superior medulla oblongata
What is the cranial foramina for CN IX?
Jugular foramen
Where is the extra cranial part of CN IX?
Descends towards pharynx and mouth To stylopharyngeus muscle To parotid gland From pharyngeal mucosa From carotid body and sinus From posterior 1/3rd of tongue
Where is the intracranial part of CN IX?
Directly towards jugular foramen in posterior cranial fossa
Which areas does CN IX innervate in general sensory?
Posterior 1/3rd of tongue Mucosa of most of nasopharynx and oropharynx Mucosa of some of laryngopharynx Palatine tonsil Eustachian tube Middle ear cavity
CN IX innervates what with special sensory?
Vallate papillae (taste buds) of posterior 1/3rd of tongue
CN IX innervates what with visceral afferent?
Carotid sinus baroreceptors
Carotid body chemoreceptors
CN IX innervates what with somatic motor?
Stylopharyngeus
CN IX innervate what with parasympathetic?
Secretomotor to parotid gland (salivary)
How do you clinically test CN IX?
Gag reflex in general sensory
Referred pain from pharynx to ear and vice versa
What is the function and modality of CN X?
Vagus nerve
Sensory, motor, visceral afferent and parasympathetic
Where does CN X connect with the CNS?
Lateral aspect of medulla oblongata
Immediately inferior to CN IX
Where is the intracranial part of CN X?
Directly towards jugular foramen in the posterior cranial fossa
What is the cranial foramina for CN X?
Jugular foramen
Where is the extra cranial part of CN X?
Axons supply lots of structures between the palate and the midgut
Which anatomical structures lie close to the CN X in the neck?
CN X runs within the carotid sheath
Posterior to and between the common carotid artery and internal jugular vein
Which anatomical structures lie close to the CN X in the thorax?
CN X runs inferiorly into the thorax then gives off the recurrent laryngeal nerve to turn back superiorly to supply the muscles of the larynx.
Which anatomical structures lie close to the left and right recurrent laryngeal nerves?
Left= curves under arch of aorta Right= curves under right subclavian artery
Which anatomical structures lie close to CN X in the abdomen?
Both CNs X pass onto surface of stomach
Vagus nerves very last parasympathetic axons pass to the splenic flexure of the colon
How do you clinically test CN X?
Ask patient to say ‘ahhhh”- muscles of palate- uvula should lift straight in the midline
Unilateral pathology will pull uvula away from non-functioning side
Ask patient to swallow water- splutter may suggest abnormal swallow
Listen to speech- hoarseness may suggest abnormal function of laryngeal muscles
