1 - Cranial Nerves Flashcards
What Cranial Nerves exit the midbrain?
What Cranial Nerves exit the pons?
What Cranial Nerves exit the medulla?
What cranial Nerves exit the spinal cord?
Midbrain: III, IV
Pons: V, VI, VII, VIII
Medulla: IX, X, XII
Spinal Cord: XI
CN II exit from CNS? (important regions from table)
Thalamus, Hypothalamus
Pretectal Area, Superior Colliculus
What are the two exceptions to the rule that CN nuclei are the same level as the nerve entry/exit?
2/4 Trigeminal Nuclei
Spinal Trigeminal Nucleus extends caudally (to cervical spinal cord)
Mesencephalic Trigeminal Nucleus extends into midbrain
What is the general location of sensory vs motor of CN nuclei?
Sensory = Lateral
Motor = Medial
What is unique about CN II?
What is it formed by?
Where do they project to?
Only cranial nerve that is a CNS pathway, not a peripheral nerve
Formed by axons of retinal ganglion cells
- - -
Project to suprachiasmatic nucleus of hypothalamus, superior colliculi, and lateral geniculate nucleus of thalamus
What is the importance of the pretectal area?
Important for relay in pupillary light reflex pathway
Two Components and of CN III (Oculomotor)?
Nuclei?
Somatic Motor:
All extraocular muslces (ex. sup oblique/lat rectus), Levator palpebrae superior
Oculomotor Nucleus
- - -
Visceral Motor (via Ciliary Ganglion)
Parasympathetic innervaion of pupil constrictor and ciliary muscles
Edinger-Westphal Nucleus
Pupullary Reflex Pathway
Sensory Input?
Key Region?
Motor Output?
Sensory Input: CN II (light hits eye)
Key Region: Pretectal Area (between superior colliculus and thalamus)
Relays bilaterally to preganglionic parasympathetics neurons in Edinger-Westphal Nucleus; contralateral projection is through post. commissure (mediates consenual light response)
Motor Output: Edinger-Westphal Nucleus to ciliary ganglion to pupillary constrictor
Direct and Consensual Response: Oculomotor Lesion
Pupil will not constrict on side of lesion
Direct and Consensual Response: Horner’s Syndrome
Pupil can not dilate on impaired side
Other Symptoms: Ptosis, Anhydrosis
*Lesion of Sympathetics = Deficit in Dilation*
Direct and Consensual Response: Afferent Nerve defect
Sensory Loss
Impaired direct and consensual response on affected side.
Normal response on unaffected side.
Direct and Consensual Response: Benign Anisorcoria
Pupil Asymmetry; no clinical pathology
Clinical: Unilateral LMN Lesion of CN III
Common Causes?
Complete Loss of Function = “Down and Out” Eye
Ptosis = eyelid droop
Blown Pupil, no response to light (loss of parasympathetic constrictor)
Common Causes: Diabetes, tumors, compression of Posterior Communicating Artery, uncal herniation
What is unique about CN IV (Trochlear)
Main role?
Only CN to exit dorsal surface
Function: Innervates Superior Oblique (contralateral to nucleus) – Fibers will decussate
Clinical: Unilateral LMN Lesion of CN IV
Loss of Function?
Common Causes?
Loss of Function: Elevation and Extorion of affected eye–causes diplopia; clinical sign of Head Tilt
Common Causes: Head trauma (nerve vulnerable to shearing injury), tumor of midbrain/tectum, diabetes
Trigeminal Nerve (CN V) Components
Somatic Sensory:
Touch, pain, temperature, joint position, vibration
Face, mouth, anterior 2/3 of tongue (not taste), nasal sinuses, meninges (related to Migraines)
Branchial Motor: Muscles of mastication, tensor tympani, tensor veli palatini, mylohyoid, anterior digastric
Trigeminal Sensory Nuclei
Location
Input
Output
Location: Lateral mid-Pons
Input: large diameter sensory fibers from face; analogous to dorsal column; discriminative touch, vibration, proprioception
Output (Trigeminal Lemniscus): Second order neurons, crosses and joins medial lemniscus, projects to VPM of thalamus
Trigeminal (CN V) Sensory Nuclei: Spinal Trigeminal Nucleus
Input
Output
Spinal Trigeminal Nucleus
Located laterally from mid-pons to upper cervical spinal cord, w/input from small diameter sensory fibers (crude touch, pain, temperature)
Spinal trigeminal tract carriers descending sensory fibers
Output (Trigeminothalamic tract): Second order neurons, joins anterolateral system
Topographic Representation of Face
Face represented in “onion skin” pattern
Concentric rings centered around mouth
Trigeminal Sensory Nuclei: Mesencephalic Trigeminal Nucleus
Location?
Input
Output
Location: Laterally from mid-pons to midbrain long lateral edge of periaqueductal grey
Input: Cell bodies of large diameter sensory fibers that convery priprioceptive sensation – “centrally located sensory ganglion”
Output: Descends to trigeminal motor nucleus, mediates jaw-jerk reflex
Trigeminal Motor Nucleus
Contain LMN for branchiomotor functions of Trigeminal
Receives proprioceptive sensory input for jaw-jerk reflex (absent with UMN injury)
Clinical: Trigeminal Neuralgia (tic douloureux)
Chronic pain condition
Type 1: Typical Form - extreme sporadic burning or shock-lik pain; may repeat in short intervals
Type 2: Atypical Form - constant aching, burning, or stabbing pain (lower intensity that Type 1)
Pain can be incapacitating
Cause: May be from nerve compression/inflammation
Clinical: Trigeminal Disorders - Shingles
Cause: Herpes Zoster (chicken pox virus), virus reemerges (usually older adults), as shingles rash
Postherpetic Neuralgia: Severe pain in area which has shingles rash
Vision loss possible if eye affected
Vaccine available (rec’d for adults 50+)
Clinical: Trigeminal Disordrs - Sensory Loss
Peripheral lesion
CNS Lesion in Lateral Pons, Medulla
If Spinothalamic fibers in the anterolateral system are also injured – ipsilateral sensory loss in face, contralateral sensory loss in body
CN VI (Abducens)
Type
Type: Somatic Motor - lateral rectus (abduction of eye)
Clinical: Unilateral LMN Lesion of CN VI (Abducens)
Lateral gaze paralysis
Inability to abduct affected eye
At Rest: Medial Strabismus (cross eye), horizontal diplopia
CN VII (Facial)
Types? (4)
Branchiomotor: Muscles of face, stapedius, post. digastric, stylohyoid muscles–Facial Expression
Parasympathetics: Sublingual, Submandibular, Lacrimal
Visceral (Chem) Sensory: Ant. 2/3 tongue Taste
Somatic Sensory: Portion of outer ear
CN VII (Facial) Nuclei (4x)
Facial Nucleus: LMN innervating muscles of face (branchiomotor)
Superior Salivatory Nucleus: Salivary and Lacrimal glands (parasympathetics)
Spinal Trigeminal Nucleus: Somatic sensation from outer ear
Solitary Nucleus: Visceral (chemical) sensation from ant. 2/3 tongue
Corneal Reflex
Afferent Limb
Efferent Limb
Afferent Limb: Trigeminal Nerve (ophthalmic division), Chief Sensory/Spinal Trigeminal Nuclei
Note: Blink can be invoked by visual stimuli–input is CN II in this case
Efferent Limb: Facial Nucleus and Nerve, Orbicularis Oculi Muscles
Clinical: Unilateral LMN Lesion of CN VII
Ipsilateral Face Weakness from UMN lesion
- - -
Bell’s Palsy (most common)
Ipsilateral weakness, loss of taste sensation from ant. ipsilateral tongue
Hyperacusis, ear pain
Drooling
Dry eyes, mouth
“Crocodile Tears” due to recovery of paraysmpathetics
“Synkinesis”, or abnormal movements of face
CN VIII (Vestibulocochlear)
Type?
Somatic Sensory
CN IX (Glossopharyngeal)
Components (4x)
Branchiomotor: Stylopharyngeus
Parasympathetics: Parotic Gland
Somatic Sensory: Touch, pain, temperature from posterior 1/3 of tongue, pharynx, middle ear, portion of outer ear
Visceral Sensory: Baro- and chemo-receptors in carotid body, taste receptors in posterior 1/3 of tongue
CN IX (Glossopharyngeal) - Nuclei
Branchiomotor: LMNs in Nucleus Ambiguus
Parasympathetic: Preganglionic neurons in inferior salivatory nucleus
Somatic Sensory: Spinal trigeminal nucleus
Visceral Sensory:
Baro- and chemo-receptors: Caudal solitary nucleus
Taste Receptors: Rostral solitary nucleus
CN X (Vagus) - Types
Branchiomotor: Muscles of pharync and larynx (speech and swallowing)
Parasympathetic: Major portion of nerve, heart, lungs, digestive tract
Somatic Sensory: Pharynx, larynx, meninges, portion or outer ear
Visceral Sensory: Baro-and chemo-receptors in aortic arch, cardiorespiratory and digestive systems; taste receptors in epiglottis, posteriorpharynx
CN X (Vagus) - Nuclei
Branchiomotor: LMNs in nucleus ambiguss
Parasympathetic: Preganglionic neurons in dorsal motor nucelus of vagus
Somatic Sensory: Spinal trigeminal nucleus
Visceral Sensory:
Baro-and chemo-receptors: Causal solitary nucleus
Taste receptors: Rostral solitary nucleus
Clinical: Unilateral lesion of Nucleus Ambiguus
Ipsilateral paralysis of the soft palate, pharynx, and larynx
Uvula will deviate away from lesion
Symptoms: Dusphonia (difficulty speaking), Dyspnea (difficulty breathing), Dysphagia (difficulty swallowing)
Gag reflex diminished/absent ipsilaterally; afferent in CN IX, efferenct from nucleus ambiguss
CN XI (Accessory) - Type
Branchiomotor: Trapezius, Sternocleidomastoid
Clinical: Unilateral LMN Lesion of CN XI
Paresis/Paralysis of the ipsilateral sternocleidomastoid and ipsilateral trapezius
Patient unable to turn their head away from side of lesion
Ipsilateral shoulder drop, may have difficulty raising ipsilateral arm above horizontal
CN XII (Hypoglossal) - Type
Somatic Motor: Intrinsic and extrinsic muscles of tongue (except palatoglossus)
Clinical: Unilateral LMN Lesion of CN XII
Ipsilateral tongue weakness–tongue deviates TOWARD lesion
Ipsilateral fasciculations, Atrophy
