Brainstem And Cranial Nerves Flashcards
Brainstem contains nuclie controlling…
CN LOC Cerebellar circuits Muscle tone Posture CP
Midbrain rectus
Superior colliculus
Inferior colliculus
Floor of 4th ventricle
Facial colliculus
CN IV on brainstem
Exits dorsally
Travels laterally around midbrain
CN I olfactory nerve pathway
Special chemoreceptors detect odor —> axons via short olfactory nerves through cribiform plate —> synapse on olfactory bulb—> sensory info relayed vial olfactory tracts to primary olfactory cortex in temp lobe
CN I Anosmia
Los of olfaction
Unilateral - not noticeable because compensation
Bilateral - c/o decreased tasted
CN I anosmia casued by
Head trauma Viral infection Nasal obstruction Neurodegenerative disease Intracranial lesion at base of frontal lobe
CN II pathway
Optic nerve
Carries visual info form retinal to LGN to extrageniculate pathways and PVS
Optic nerve - anterior to chiasm
Optic tract - posterior to chiasm
Travels from orbit to intracranial vanity via optic canal
Control of extraocular muscles
CN III
CN IV
CN VI
CN III extraocular
Levator palpebrae superior (elevates eyelid)
PS fibers - pupillary constrictor muscles, ciliary muscles (near vision)
All other extraocular muscles besides LR and SO
CN IV extraocular
Superior oblique
Intorsion and depression
CN VI extraocular
Lateral rectus (abduction)
CN III course
Exits centrally at interprendulcar fossa —> preganglionic PS synapse in ciliary ganglion in orbit —> postganglionic PS continue to pupillary constrictor muscles and ciliary muscles of lens in orbit
CN IV exits
Dorsally at inferior tectum
CN VI exits
Centrally at pontomedullary junction
CN V facial sensation
Touch, pain, temp, joint position, vibration
Face, mouth, ant 2/3 tongue, nasal sinuses, cornea, meninges
CN V muscles of mastication
Just know they’ve innervates by this
Major branches of CN V
Ophthalmic division V1
Maxillary division V2
Mandibular division V3
CN V nuclei are primarily in
The pons
CN V course
Exits ventrolateral pons and then enters small fossa
Ophthalmic division - enters cavernous sinus to texit at superior orbital fissue
Maxillary division - exits via foramen rotundum
Mandibular division - exits via foramen ovale
CN V incoming sensory info synapses - mesensephalic trigeminal nucleus
In midbrain
Proprioception
Jaw jerk reflex
Cross and ascend via msesncephalic trigeminal tract
CN V incoming sensory info synapses - chief trigeminal sensory nurcleus
In pons
Fine/discriminative touch and dental pressures
Cross and ascend via trigeminal leminisucus —> VPM—> PSC
CN V incoming sensory info synapses - spinal trigeminal nucleus
In pons and medulla
Pain, temp, crude touch
Cross and ascend via trigeminothalamic tract —> VPM —> PSC
CN V motor fx
UMN control to CN motor nucleus is bilateral
Unilateral lesion to cortex or corticobulbar tract
No deficit in jaw movement
Lesion to LMN CN V
Ipsilateral jaw weakness
Deviation toward side of lesion (weak side)
Trigeminal neuralgia
** most common CN V disorder
Brief severe pain lasting from seconds to a few minutes
Cause is unknown
• Most often in V2 or V3 sensory distribution
• Painful episodes triggered by chewing, shaving, etc.
•Facial sensation is normal on exam
• Initial treatment is with medications
Lesion to the nerve of CN V sensor nucleus
Ipsilateral loss of facial sensations (primary sensory fibers do not cross before entering the nucleus)
Lesion to ascending tracts (CN V) or face area of PSC
Contralateral loss of facial sensation (fibers cross after exiting the nucleus)
Jaw jerk reflex
CN V
Tap on the chin with the mouth slightly open
• The reflex is minimal or absent in normal individuals
• The response is the jaw jerking slightly forward or absence of movement
• Bilateral UMN lesions could cause hyperactive (brisk) jaw jerk reflex
Monosynpatic pathway CN V
Sensory axons heading to the mesencephalic trigeminal nucleus also
send axons to synapse on the trigeminal motor nucleus
• Motor axons from trigeminal motor nucleus travel via V3 to the muscles
of mastication
CN VII: muscles
Of facial expression
CN VII PS fibers
Lacrimal glands and salivary glands
CV NII taste
Ant 2/3 of tongue
CN VII sensation
Small area near external auditory meatus
CN VII nucleus
In lower pons
Fibers loop dorsally around CN VI nucleus at floor of 4th ventricle to form facial colliculus
CN VII pathway
Course of CN VII: Nerve exits brainstem ventrolaterally at the pontomedullary junction in a region called the cerebellopontine angle Enters internal auditory meatus to travel in auditory canal along with CN VIII CN VII turns inferior to enter the facial canal and travels to the stylomastoid foramen to exit the skull
• Geniculate ganglion are located where CN VII turns (primary
sensory neurons for taste and sensation) Divides into five major branches to control muscles of facial expression
CN VII decides into
Temporal, zygomatic, buccal, mandibular, and cervical branches
Two branches of CN VII form superior salivatory nucleus
Greater petrosal nerve
Chorda tympani
CN VII taste
anterior 2/3 of tongue
• Primary sensory neurons synapse in nucleus
solitarius (gustatory nucleus) (green)
• Ascend via Central tegmental tract- > VPM -> Cortical
taste area (PSC, fronto-parietal operculum, and insula)
• Taste projects to bilateral cortical taste areas
Lesion to ipsilateral CN VII
Cause weakness of the ispislateral half of face
CN VII UMN facial weakness
LMNs to forehead and eye muscles get bilateral innervation from cortex (red UMNs- A) LMNs to muscles below eye get contralateral innervation only from cortex (purple UMNs- A)
Lesion to contralateral PMC cause 9CN VII)
LMNs to forehead and eye muscles get bilateral innervation from cortex (red UMNs- A) LMNs to muscles below eye get contralateral innervation only from cortex (purple UMNs- A)
Bell’s palsy
Most common CN VII disorder
Unilateral facial weakness of the LMN type
• Severe cases- eye will not close, loss of salivation, lacrimation, and
taste from ipsilateral anterior 2/3 of the tongue
• Cause unknown, can be from viral, inflammatory, or immune disorder • 80% recover neural control of facial muscles within 3 weeks-2 months • Recommended treatment is 10 days of oral steroids after onset
CN VII corneal reflex
Afferent- Sensation to the cornea of the eye is from CN V
• Efferent- Innervation to facial muscles is from CN VII
(including obicularis oculi) • Eye closure in response to lightly touching the cornea
