week 6 practical

name the twelve cranial nerves in order from cn i to cn xii

olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, hypoglossal

state in order from cn i to cn xii whether they are purely sensory, motor or mixed and which four carry parasympathetic fibers

sensory, sensory, motor, motor, both, motor, both, sensory, both, both, motor, motor and cranial nerve 3, 7, 9, 10

state the origin and skull exit for cn i (olfactory nerve)

olfactory bulb (forebrain, not brainstem) and cribriform plate of the ethmoid

state the origin and skull exit for cn ii (optic nerve)

retinal ganglion cells (a cns tract, not a true peripheral nerve) and optic canal

state the origin and skull exit for cn iii (oculomotor nerve)

midbrain, at the level of the superior colliculus (emerges from interpeduncular fossa) and superior orbital fissure (inside the annulus of zinn)

state the origin and skull exit for cn iv (trochlear nerve)

midbrain, inferior colliculus (decussates and exits dorsally) and superior orbital fissure (outside the annulus of zinn)

state the origin and skull exit for cn v (trigeminal nerve, all divisions)

pons, at the middle cerebellar peduncle and v1 via superior orbital fissure, v2 via foramen rotundum, v3 via foramen ovale

state the origin and skull exit for cn vi (abducens nerve)

pontomedullary junction (runs free within the cavernous sinus) and superior orbital fissure (inside the annulus of zinn)

state the origin and skull exit for cn vii (facial nerve)

pontomedullary junction and internal acoustic meatus where motor exits stylomastoid foramen and parasymoathetic is greater petrosal nerve

state the origin and skull exit for cn viii (vestibulocochlear nerve)

pontomedullary junction and internal acoustic meatus (does not leave the skull)

state the origin and skull exit for cn ix (glossopharyngeal nerve)

medulla and jugular foramen

state the origin and skull exit for cn x (vagus nerve)

medulla and jugular foramen

state the origin and skull exit for cn xi (accessory nerve)

medulla and upper cervical cord and jugular foramen

state the origin and skull exit for cn xii (hypoglossal nerve)

medulla and hypoglossal canal

what is the function of cn i (olfactory nerve)

detection of odorant molecules and transmission of olfactory information (smell) to the brain

what is the function of cn ii (optic nerve)

transmission of visual information (vision) from the retina to the brain

what is the function of cn iii (oculomotor nerve)

motor control of superior rectus, inferior rectus, medial rectus, inferior oblique, and levator palpebrae superioris (lps), parasympathetic to iris sphincter (pupil constriction) and ciliary muscle (accommodation) via ciliary ganglion

what is the function of cn iv (trochlear nerve)

motor control of superior oblique muscle (eye movement: intorsion, depression, and abduction)

what is the function of cn v (trigeminal nerve, overall)

general sensation from face, scalp, cornea, oral and nasal cavities and motor control of muscles of mastication

what is the function of cn v1 (ophthalmic division of trigeminal)

sensation from cornea, conjunctiva, upper eyelid, and forehead, serves as afferent limb of the corneal reflex

what is the function of cn v2 (maxillary division of trigeminal)

sensation from lower eyelid, cheek, and upper jaw carries cn vii parasympathetic fibers onward to the lacrimal gland

what is the function of cn v3 (mandibular division of trigeminal)

motor control of muscles of mastication sensation from lower jaw, teeth, and tongue

what is the function of cn vi (abducens nerve)

motor control of lateral rectus muscle (eye abduction)

what is the function of cn vii (facial nerve)

motor control of facial expressions (including orbicularis oculi to close lid) taste from anterior 2/3 of tongue, parasympathetic secretomotor to lacrimal, submandibular, and sublingual glands

what is the function of cn viii (vestibulocochlear nerve)

vestibular system: detection of head position and movement for balance (drives vestibulo-ocular reflex), cochlear system: detection of sound waves for hearing

what is the function of cn ix (glossopharyngeal nerve)

sensation and taste from posterior 1/3 of tongue, oropharynx, and middle ear, motor to stylopharyngeus muscle, parasympathetic secretomotor to parotid gland via otic ganglion

what is the function of cn x (vagus nerve)

parasympathetic innervation to thorax and abdomen (heart, lungs, gi tract), motor to pharyngeal and laryngeal muscles, sensation from larynx, pharynx, and external ear

what is the function of cn xi (accessory nerve)

motor control of head and shoulder movements via sternocleidomastoid and trapezius muscles

what is the function of cn xii (hypoglossal nerve)

motor control of intrinsic and extrinsic tongue muscles for speech, swallowing, and chewing

which cranial nerve is the only one to emerge from the dorsal surface of the brainstem, and where does it exit

cn iv trochlear nerve it emerges from the dorsal midbrain immediately below the inferior colliculi

which fact about cn iv explains why it is the nerve most often damaged in closed head trauma

its long, slender intracranial course wrapping around the brainstem makes it uniquely susceptible to shearing forces against the rigid edge of the tentorium cerebelli during brain displacement

what are the main cranial nerves are relevant to the eye

cn ii to cn vii

which extraocular muscles and ocular structures are innervated by cn iii and which is from the superior and inferior division

superior division is superior rectus and superior levator palpebrae, inferior is inferior and medial rectus, inferior oblique and parasympathetic fibers to iris sphincter and ciliary muscle via the ciliary ganglion

which single muscle does cn iv supply, and what is its action

superior oblique which depresses, intorts, and abducts the eye (moves eye down and in)

which single muscle does cn vi supply, and what is its action

lateral rectus (lr), abducts the eye (moves eye outward)

name the three main branches of v1 (ophthalmic nerve) within the orbit and state which ones pass inside vs outside the annulus of zinn

lacrimal and frontal nerves pass outside (above) the annulus, nasociliary nerve passes inside the annulus

what are the sensory and afferent functions of v1 relevant to the eye

provides general sensation from the cornea, conjunctiva, upper eyelid, and forehead

trace the complete parasympathetic secretomotor pathway to the lacrimal gland step-by-step from cn vii

cn vii -> greater petrosal nerve -> crosses foramen lacerum -> travels in pterygoid canal -> relays in pterygopalatine ganglion -> joins v2 -> zygomatic branch of v2 -> communicating branch -> lacrimal nerve (v1 branch) -> lacrimal gland

from which cranial nerve does the greater petrosal nerve originate

cn vii (facial nerve)

into which anatomical space does the anterior end of the pterygoid canal open

the pterygopalatine fossa

which fibers relay in the ciliary ganglion, and which fibers merely pass through

parasympathetics from cn iii relay onto sphincter pupillae and ciliary muscle via short ciliary nerves for pupil constriction and accommodation. sympathetics pass through to dilator pupillae for pupil dilation and sensory fibers from V1 pass through for eye/corneal sensation

which fibers relay in the pterygopalatine ganglion, and which fibers merely pass through

parasympathetics from cn vii via greater petrosal nerve & pterygoid canal relay and sympathetics from deep petrosal nerve and v2 sensory fibers pass through

what cell bodies sit inside the trigeminal (semilunar) ganglion, and which fibers pass through without synapsing

contains sensory neuron cell bodies for all three divisions (v1, v2, v3), the motor root of v3 passes through

which cranial nerves pass inside (through) the tendon ring of the annulus of zinn at the superior orbital fissure

cn ii (in optic canal), cn iii (superior & inferior divisions), cn vi, and nasociliary nerve (v1 branch)

which cranial nerves pass outside (above/below) the annulus of zinn at the superior orbital fissure

cn iv, frontal nerve (v1), lacrimal nerve (v1), and superior ophthalmic vein

which nerves would be spared by a lesion confined strictly to the interior of the annulus of zinn

cn iv, frontal and lacrimal nerve (v1) because they pass outside the annulus

which structures run directly within the center (lumen) of the cavernous sinus

internal carotid artery, cn vi (abducens nerve) and the carotid sympathetic plexus

which cranial nerves run in the lateral wall of the cavernous sinus

cn iii (oculomotor), cn iv (trochlear), v1 (ophthalmic), and v2 (maxillary)

why is cn vi the most vulnerable nerve in early cavernous sinus lesions or raised icp

because it runs freely within the central sinus lumen adjacent to the internal carotid artery rather than protected inside the fibrous dural lateral wall

why can a tumor of cn viii in the internal acoustic meatus affect cn vii, and what is the ocular consequence

cn vii and cn viii travel together through the internal acoustic meatus so a cn viii tumour compresses cn vii which paralyses orbicularis oculi. this causes inability to fully close eyelid and loss of blink reflex leading exposure keratopathy as without blinking tears can no longer sweep across the cornea to keep it lubricated causing corneal drying and damage

describe the eye position, movement deficit, pupil status, and key clinical signs of a complete cn iii palsy

down and out, loss of adduction, elevation, and depression, pupil dilated and unreactive (if parasympathetics involved) causing complete ptosis (loss of lps) and loss of accommodation

explain why a compressive cn iii palsy involves the pupil while an ischemic cn iii palsy typically spares the pupil

parasympathetic fibers run superficial of cn iii while motor fibers run in the deep central core with both getting seperate blood supply. compressive lesion such as pcoa aneurysm pushes from outside which compresses the superficial parasympathetics first causing a dilated, unreactive pupil. with an ischemic lesion such as diabetes, microvascular blockages starves the deep core first causing motor fibers to die from lack of oxygen causing muscle paralysis but the superficial parasympathetic fibers on the outside survive because they receive blood from a different supply allowing pupil to be spared

describe the presentation and key clinical signs of a cn iv palsy

affected eye elevated (hypertropia), especially in adduction, loss of depression in adduction, pupil normal, vertical diplopia that worsens when looking down and compensatory head tilt away from affected side

describe the presentation and key clinical signs of a cn vi palsy

eye adducted (esotropia), loss of abduction, pupil normal, horizontal diplopia worse on ipsilateral gaze, acts as a "false localizing sign" in raised icp

describe the presentation and key clinical signs of a cn vii palsy relevant to the eye

eye position, movement and pupil all normal but inability to close eyelid, loss of blink, risk of corneal exposure keratopathy and reduced tear secretion if lesion is proximal to greater petrosal nerve

describe presentation and key clinical signs of horner's syndrome (ocular sympathetic pathway lesion)

eye movement and position is normal, pupil constricted with dilation lag, mild ptosis due to loss of muller's muscle innervation and occasional facial anhidrosis (reduced sweating)