Neuro - cranial nerves - quiz 2

Brainstem general functions

conduit, CN III - XII, integrative - reticular formation

divisions of the brainstem

midbrain, pons, medulla

regions of the brainstem

basilar, tegmentum, tectum

Basilar brainstem

ventral surface

motor aspect of the brain

tegmentum region of the brainstem

nuclei of CN III - XII

reticular formation

Tectum region of the brainstem

midbrain only

dorsal to cerebral aqueduct

cerebellum is the chamber of what ventricle?

ventricle 4

How many pairs of cranial nerves are there?

12

all of the CN are visible on the inferior view of the brain except

CN IV

the CN are generally numbered in order from

rostral (CN I) to caudal (CN XII)

all CN innervate structures in the head and neck EXCEPT

CN X (vagus)

axons and receptors outside of the brainstem/cerebrum are part of

the PNS

nuclei organization - dorsal structures are associated with _____ processing

central

nuclei organization - ventral structures are associated with _____ processing

motor

CN I

Olfactory

CN I sensory function

Smell: the only sensory system that does not transmit sensory information through the thalamus.

CN I motor function

none

CN I - CNS entry/exit location

inferior frontal lobe

pathway of CN I

nasal chemoreceptors in the olfactory mucosa (olfactory epithelium) connect via the olfactory nerve through the cribriform plate > olfactory bulb > olfactory tract (some fibers go to the anterior olfactory nucleus)

THEN 2 options

2 options of CN I pathways following intial

OPTION 1: medial olfactory stria > anterior commissure > contralateral olfactory bulb (bulbs ultimately receive information from both sides)

or

OPTION 2: lateral olfactory stria > olfactory tubercle; medial temporal lobe, & amygdala

All sensory information is sent to the thalamus EXCEPT

olfaction

CN I - testing

Using familiar, non-irritating odors: coffee, vanilla, etc.

Test one nostril at a time

Pathology of CN I

Anosmia - loss of sense of smell

Hyperosmia - increase in olfactory sensitivity

Trauma - fracture of cribriform plate, possible CSF leakage (pathway for meningitis)

Infection, neoplasm, metabolic disease, drug ingestion

CN II

Optic

sensory function of CN II

vision

motor function of CN II

none

CN II - CNS entry/exit location

diencephalon

CN II pathway

Retinal cells > optic nerve > optic chiasm > optic tract >

Lateral geniculate body (part of the thalamus) > optic radiation > primarily visual cortex (vision)

or

brainstem nuclei (midbrain): pupil reflexes, light/dark awareness, and head orientation in space

T/F: you are not consciously aware of what you are seeing until it reached the occipital region of occipital lobe (area 17 of brochman's area)

TRUE

CN II - testing

field of view (lateral ~90 degrees, medial ~60 degrees)

pupil reflexes (light reaction) ; consensual (opposite eye)

accommodation: eyes adjusting to nearby objects (adduction, pupils constrict, the lens becomes more convex)

CN II - pathology

blindness, hemianopsia, loss of 1/2 visual field

CN III

Oculomotor

sensory function of CN III

none

motor function of CN III

Levator palpebrae superioris m. (lifts upper eyelid) and all extraocular eye m. except for the lateral rectus and superior oblique

sphincter pupillae (constriction of the pupil), ciliary mm. (contraction thickens the lens)

CN III - CNS entry/exit location

ventral midbrain (cerebral penducles between the PCA & SCA arteries)

CN III pathway

2 nucleis that play a part: come out between cerebral penducles > enter superior orbital fissure > from there is depends on the muscle it is going to:

Oculomotor nucleus (GSE; rostral midbrain; motor part) > superior orbital fissure > extraocular muscles

Oculomotor nucleus (GVE; midbrain; parasympathetic part)(Edinger-Westphal nucleus; posterior to motor part of the oculomotor nucleus) > ciliary ganglion & pupillary sphincter > intrinsic muscles of the eye.

CN III - testing

finger following test

pupil size and pupil reflex

opening eyelid

CN III - pathology

diabetes mellitus vascular lesions

external (lateral) strabismus (visual axis of eyes not parallel; misaligned) : eyeball deviating laterally (outward or abducted) due to unopposed lateral rectus

diplopia (double vision)

paralysis of medially directed gaze

ptosis ('drooping' eyelid)

dilation of the pupil (mydriasis)

CN IV

Trochlear

sensory function of CN IV

none

motor function of CN IV

Superior Oblique m. (contralateral to the nucleus)

Moves eye inferio-medially

if the eye is adducted the superior oblique will

turn pupils down

if the eye is abducted, superior oblique will

rotate the eye

CN IV - CNS entry/exit location

posterior (dorsal) midbrain

CN IV - pathway

Contralateral trochlear nucleus ( midbrain; level of inferior colliculus) runs dorsally from the nucleus and decussates in anterior medullary velum > emerges from posterior tectum (caudal to inferior colliculi) > through the superior orbital fissure to the superior oblique m.

Decussating fascicles of CN IV

where R and L pieces of CN IV cross

CN IV - testing

Finger following test: pt. adducts the eye and then rotates it downward

note head alignment- anterior view, head may deviate opposite side

CN IV - pathology

rarely have lesions that are limited to only the trochlear nerve.

Impaired down and in gaze; Diplopia (double vision from eyes no longer being parallel) > difficulty descending stairs

CN V

Trigeminal

3 branches of trigeminal nerve

ophthalmic (V1) : forehead

maxillary (V2) : mid face

mandibular (V3) : lower jaw

sensory function of CN V

touch, pain, temperature, position for face (cornea)

Anterior 2/3 tongue touch

Nasal sinuses and cornea

meninges

motor function of CN V

muscles of mastication and tensor tympani

CN V - CNS entry/exit location

mid-lateral pons

Motor pathway of CN V

Right and left motor cortex--(UMN) > Motor nucleus V (lateral tegmentum; rostral pons) > mandibular branch > m. of mastication (temporalis; masseter; med/lat pterygoid; tensor tympany; and others)

Sensory touch pathway of CN V

innervated tissue > trigeminal ganglion (primary cell bodies) > main sensory nucleus V (mid pons) > cross midline & travel with contralateral medial lemniscus fibers > thalamus (VPM) > SI cortex (also some uncrossed fibers that travel to ipsilaterally VPM)

sensory proprioception pathway of CN V

M. of mastication (ipsilateral; innervated tissue) > mesencephalic nucleus (dorsolateral tegmentum; location of the neuron cell body in the brainstem; unusual for primary nerves) with axon to motor nucleus V (reflex) > reticular formation

sensory nociceptive pathway of CN V

Pain receptors > trigeminal ganglion (primary cell bodies) > enter and descend and form the spinal tract of trigeminal n. > cross midline > thalamus (VPM) > SI (primary somatosensory cortex) > reticular formation

specific nuclei in the thalamus:

VPM - ventro-posterior medial : sensory info from the face

VPL - ventro-posterior lateral : sensory info from the body

CN V - testing

Jaw jerk

Corneal reflex

CN V - pathology

Hyperaccusis (tensor tympani)

weakness and atrophy of mastication m.

Lateral medulla + lower pons: loss of ipsilateral pain and temp.

Lesion in upper pons/midbrain: contralateral anesthesia

Trigeminal neuralgia (tic douloureux): unbearable pain over the n. distribution; trigger zone in sensory distribution pattern

CN VI

Abducens

CN VI sensory function

none

CN VI motor function

lateral rectus m. > abducts the eye; ipsilateral to the nucleus

CN VI - CNS entry/exit location

between pons and medulla (pons-medulla junction) at the pyramids

CN VI pathway

Abducens nucleus (dorsal and caudal pons in pontine tegmentum) > emerges between pons and pyramids > superior orbital fissure > lateral rectus m.

CN VI - testing

Finger following test , abduction

CN VI - Pathology

Internal/medial strabismus 2 to unopposed medial rectus à eye deviates medially

Diplopia

Nuclear lesion: lateral paralysis à disruption of the nucleus itself causes ipsilateral lateral gaze paralysis

In testing; medial strabismus shows at rest, lateral paralysis shows in finger following test

what CN help to regulate eye movements

3, 4, 6

CN VII

Facial

CN VII sensory function

Outer ear (touch, pain, pressure) - spinal trigeminal (V) nucleus (STTN)

Special -taste (anterior 2/3 of tongue; solitary nucleus)

CN VII motor function

Closes eyes (orbicularis oculi), moves lips, muscles used for facial expression, and Stapedius

salivary & lacrimal glands

CN VII - CNS entry/exit location

between pons and medulla (lateral)

CN VII - facial motor nucleus pathway

§ Facial motor nucleus (caudal pontine tegmentum) > passes dorsally encircling (internal genu) abducens nucleus > emerges in the junction between pons and cerebellum (cerebellopontine angle) > internal auditory canal > facial canal > stylomastoid foramen > muscles used for facial expression. [Stapedius, too, but it comes off earlier in the facial canal]

CN VII - UMN motor pathway

· Part of the Facial motor nucleus controlling the upper face (above the eyes) - receives UMN neuron input from the bilateral motor cortex

· Part of the Facial motor nucleus controlling the lower fact (below the eyes) receives UMN neuron input only from the contralateral cortex

CN VII - parasympathetic pathway

Superior salivary nucleus (medulla; preganglionic cell bodies) > Nervus Intermedius (smaller of two divisions of VII) > internal acoustic meatus > facial canal (geniculate ganglion located in a sharp bend in the canal) > chorda tympani and lingual nerves > salivary, nasal, and lacrimal glands

CN VII - taste pathway

Taste receptors on the tongue > facial canal (geniculate ganglion located in a sharp bend in the canal) > internal acoustic meatus) > Nervus Intermedius (smaller of two divisions of VII) > Solitary tract nucleus (in the reticular formation)

4 different nuclei

facial motor

STTN (spinal trigeminal nucleus)

Solitary nucleus

Superior salivatory nucleus

facial motor nucleus

same level as abducens level ; big player in motor control of facial muscles

STTN

through facial nerve before now coming here

Solitary nucleus

sensory information (taste)

superior salivatory nucleus

parasympathetic, distributed to salivary and lacrimal glands

CN VII - testing

taste (anterior 2/3 of the tongue, sweet and salt)

Corneal blink reflex: touch the cornea, and the eyes blink automatically

Close eyes, smiling (facial expressions)

CN VII - pathology

Cheeks puff out, lack of facial expression

Bell's palsy: loss of function overnight; swelling in the distal facial canal; spon. recovery in 1-2 mo.

Proximal lesion (ipsilateral):

hyperacusis: secondary to stapedius m paralysis

Absent taste anterior 2/3 tongue

Disturbed secretion of tears and salivation

LMN: paralysis or weakness

UMN (corticobulbar; 'bulbar' loosely refers to the brainstem) lesion:

Sparing of forehead/brow area - receives input from bilateral cortex

Involuntary contraction still possible (reflexes)

Lower parrt of the face is driven ONLY by ______ side of brain

contralateral

Peripheral lesion of facial nerve

Lesion B - both top and bottom affected

UMN lesion of facial nerve

only contralateral lower face affected

CN VIII

Vestibulocochlear

sensory function of CN VIII

Cochlear: hearing (ipsilateral nuclei)

Vestibular: head position/ movement; equilibrium (ipsilateral nuclei)

motor function of CN VIII

none

CN VIII - CNS entry/exit location

between the pons and the medulla (most laterally)

Hearing pathway of CN VIII

Hair cells in the cochlear duct > internal auditory meatus > connects to Cochlear nuclei > becomes bilateral at this point (auditory info goes up on both side of the nervous system)

vestibular pathway of CN VIII

semicircular canals (hair cells in the maculae of the utricle and saccule; cristae in the ampullae) > internal auditory meatus > Vestibular nuclei (four)

CN VIII - testing

Hearing (tuning fork, snapping, may need an audiologist)

Vestibular for postural control (put in different positions, balance testing)

CN VIII - pathology

loss of hearing

vertigo; disequilibrium

once you get to CN VIII and its totality you may have a combo of both hearing and vestibular impairment (at apparatus level = may have only one)

cerebellopontine angle

this angle is where you describe CN VIII exiting

CN IX

Glossopharyngeal

CN IX sensory function

Outer Ear (STTN - spinal trigeminal tract and nucleus) - CN 7, 9, 10

middle ear, pharynx, touch post. 1/3 tongue (Sol. N. & STTN)

carotid body & sinus (Sol. N.)

chemoreceptors - posterior 1/3 tongue. (Sol. N.)

CN IX motor function

Stylopharyngeus m. (elevates pharynx) (Nucleus Ambiguus)

parotid salivary gland (Inf. Salivatory N)

CN IX - CNS entry/exit location

medulla

Five branches of CN IX pathway

inferior salivatory

solitary nucleus

STTN

nucleus ambiguus

solitary nucleus