Neuroanatomy lecture 6: Cranial nerves continued Flashcards
GSE (general somatic efferent):
motor fibers to skeletal muscle (voluntary)
GSA (general somatic afferent):
fibers that carry general sensation (touch, pressure, pain, proprioception, temp, tickle and vibration)
GVE (General visceral efferent):
motor fibers to smooth muscle, glands, and viscera (involuntary)
GVA (general visceral afferent):
fibers that carry visceral sensation
BE/SVE (brachial efferent/special visceral efferent):
motor fibers to skeletal, voluntary muscles that developed from brachial (pharyngeal) arches
SVA (special visceral afferent):
taste & smell
SSA (special somatic afferent):
vision, hearing, & balance
parasympathetic GVE fibers reside only in:
CN III: oculomotor
-ciliary ganglion
CN VII: facial
-pterygopalatine & submandibular ganglion
CN IX: glossopharyngeal
-otic ganglion
CN X: vagus
-various ganglia near visceral organs
Branchial motor (BE/SVE) fibers reside only in nerves associated with ___________ ___________ arches.
pharyngeal (branchial)
CN V: trigeminal nerve:
major sensory pathway for the face
pathway:
-begins at pons and travels superiorly/anteriorly towards face
-splits into three terminal divisions as trigeminal ganglion in middle cranial fossa
V1 = Opthalmic
V2 = maxillary
V3 = Mandibular
Each terminal branch exits the skull via a different foramen and innervates a different region of the face.
Trigeminal ganglion:
V1 =>
Opthalmic
GSA modality
-upper face
V2 =>
Maxillary
GSA Modality
-Mid face
V3 =>
Mandibular
GSA modality
-Lower face
BE/SVE modality
-Arch 1
-Muscles of mastication
Spinal nucleus of the trigeminal nerve:
pain, temp & light touch
Chief or principle nucleus or main sensory nucleus:
discriminative sensation and light touch as well as conscious proprioception
Mesencephalic nucleus:
proprioception
V1 opthalmic pathway:
passes through the cavernous sinus, exits via superior orbital fissure & has many additional branches from there.
Foramina: superior orbital fissure
Function: GSA modality
general sensory to:
-forehead
-anterior scalp
-upper eyelid
-tip of the nose
-anterior nasal cavity
-frontal and ethmoidal sinuses
-dura mater of anterior cranial fossa
Testing CN V1:
1) testing sensation of forehead
2) CN V1: corneal reflex
V2 maxillary pathway:
passes through the cavernous sinus, exits skull via foramen rotundum to innervate face
Foramina: Rotundum
Function: GSA Modality
general sensory to:
-the sides of the nose
-lower eyelids
-upper lip
-posterior nasal cavity
-teeth of the upper jaw
-maxillary sinus
-nasopharynx
-palate
-dura of the middle cranial fossa
Testing V2:
1) testing sensation of the lateral nose, cheek and upper jaw
V3 mandibular pathway:
not associated with cavernous sinus, exits skull via foramen ovale to innervate lower face
Foramina: Ovale
Function: GSA modality
general sensory to:
-lower lip
-chin
-lower face & cheek
-anterior external ear
-teeth of mandible
-mucous membranes of cheek
-anterior 2/3 of tongue
-dura in the middle cranial fossa
CN V extensively innervates the _________________
dura mater
-headache due to referring pain from some pathological conditions in the head region
V3 mandibular BE/SVE modality:
foramina: Ovale
Function:
-Arch 1
-Voluntary motor control to muscles of mastication:
-temporalis
-masseter
-medial pterygoid
-lateral pterygoid
Tensor tympani muscle:
innervated: mandibular branch of CN V
Connects to: auditory tube in malleus handle
Increases tension in the tympanic membrane and protects it from excessive vibration in response to loud sounds.
The muscle is contracted primarily to dampen the noise produced by chewing.
Trigeminal neuralgia:
sensation of pain elicited w/o presence of noxious stimuli
-often develops w/o any cause
-Intermittent attacks of severe, sharp, stabbing pain “electric shock”
-Most often affects CN V2 & V3
(affects the GSA code only*)
(no motor deficits)
-unilateral distribution
-Seen m/c distribution
Aggravated by:
-exposure to cold
-chewing
-brushing teeth
-talking
-touching face
Fiber types of the facial nerve:
1) BE/SVE: axons to muscle of fascial expression (arch II)
2) SVA: axons (taste) from the anterior 2/3rds of the tongue
3) GVE: axons to the submandibular, sublingual and lacrimal glands
4) GSA: axons for the “patch” of skin behind the ear
Foramina: internal acoustic meatus & stylomastoid
CN VII: Facial Nerve pathway:
Originates from the pons and first exits skull through the internal acoustic (auditory) meatus winding through the petrous portion of the temporal bone (facial canal)
Infection in the middle/inner ear can impact CN VII
Which temporal bone, nerve gives off several intracranial branches
remaining nerve will exit the cranial base via the stylomastoid foramen
Foramina: internal acoustic meatus & stylomastoid foramen
Once nerve exits skull: it gives rise to 6 extracranial branches
Intracranial branches of CN VII:
chorda tympani carries GVE and SVA:
-branches off main nerve in the facial canal (inside skull)
SVA=special visceral afferent
-carrying taste perception from the anterior 2/3rds of the tongue
GVE= general visceral efferent
-secretomotor of the submandibular and sublingual glands
via submandibular ganglion = saliva production
Greater petrosal nerve carries GVE
-exits the petrous portion of the temporal bone where parasympathetic axons synapse in the pterygopalatine ganglion
GVE = general visceral efferent
-secretomotor to lacrimal gland of eye (tear production)
The primary gustatory region of the cortex is found in:
The insula
1) 1st order neuron
2) 2nd order neuron
3) 3rd order neuron
GVE component of CN VII:
Extracranial branches of CN VII:
BE/SVE modality= voluntary motor control to muscles of facial expression
5 branches:
-temporal
-zygomatic
-buccal
-mandibular
-cervical
GSA modality = GAS to skin behind the ear
-posterior auricular branch
The stapedius attaches to the _________and helps dampen the sounds:
stapes
-protects from the intense/loud sounds and dampens endogenous sounds such as chewing, talking, and swallowing
Bell’s palsy:
results from trauma to the facial nerve, such a viral meningitis infection. A wide variety of symptoms can manifest, including:
weakness, twitching, or paralysis of facial muscles, including droopy eyelid and corner of the mouth.
These symptoms would result from damage of the SVE portion of the facial nerve.
Dry eye or mouth: result from damage from the GVE component of the nerve
Impairment of taste: damage to the SVA component of the nerve
Corneal reflex:
blinking an eye
protects eyes from foreign bodies
-sensory arc: CN V1 (touch to surface of cornea)
-motor arc: CN VII (orbicularis oculi)
Bilateral regardless of input side.
Test: cotton gauze touched to the cornea of R eye should result in blink/closure of both eyes
Clinical significance:
-cotton gauze to L eye and only R blinks: sensory signal worked but L motor didn’t work
-Cotton gauze to L eye, and no eyes blink: sensory input didn’t work
CN VIII: vestibulocochlear nerve pathway:
two separate nerves that travel together:
-begins at base of pons and exits cranium via internal acoustic meatus. Terminates as separate nerves in inner ear.
Foramina: Internal acoustic meatus
Function: special somatic afferent (SSA) for two senses:
-Hearing (cochlear)
-Balance & equilibrium (vestibular)
CN IX: glossopharangeal nerve pathway:
-nerve emerges from the brainstem in the lateral medulla and exits the posterior cranial fossa through the juguular foramina
-Majority if nerve remains extracranial to innervate structures of face and throat
Foramina: jugular foramen
Function:
(5 modalities)
1) BE/SVE: voluntary motor
-axons innervate stylopharyngeus (swallowing muscle)
2) SVA: special visceral afferent
-carry taste perception from the posterior 1/3 of the tongue
3) GVE: general visceral efferent
-innervate the parotid gland via otic ganglion (secretomotor function)
4) GVA: general visceral afferent
-from carotid body (visceral sensation from carotid body for chemoreception-maintaining BP)
5) GSA: general somatic afferent
-sensory from skin posterior to the ear, posterior 1/3 of tongue, and the afferent part of the gag reflex
CN X: vagus nerve pathway:
nerve emerges from the brainstem in the lateral medulla and exits the posterior cranial fossa through the jugular foramen.
Foramina: Jugular foramen
Function:
(5 modalities)
1) BE/SVE (voluntary motor):
-innervate the majority of the muscles of the pharynx, larynx, and soft palate (moving food towards esophagus during swallowing)
2) SVA (special visceral afferent):
-axons from skin posterior to ear, dura in posterior cranial fossa, mucous membranes of pharynx & larynx
3) GVE (general visceral efferent):
-axons from thoracic and abdominal viscera & aortic body
chemoreceptors: blood content
baroreceptors: blood pressure
4) GVA (general visceral afferent):
-axons (taste) from the root of tongue and epiglottis region
5) GSA (general somatic afferent):
-thoracic and abdominal viscera up to left colic flexure. Synapse is in or around target organ.
Vagus nerve injury:
Recurrent laryngeal nerve branch:
BE/SVE: branchial efferent/special visceral efferent:
-nerve supplies muscles of the larynx/voice box
-travels posterior to thyroid
Common causes of injury:
-Tumor or after surgical intervention of the thyroid
-Bronchial carcinoma
-Aortic arch aneurysm
Patient presentation includes:
-Hoarse voice
-Vocal changes (dysphonia)
-Difficulty producing speech
Vagus nerve GVE parasympathetic outflow:
The gag reflex is initiated by stroking the back of the throat and is mediated by:
the vagus nerve
Gag reflex:
help prevent choking
sensory arc: CN IX (touch base of throat)
Sensory arc: CN X (motor response to pharynx)
Bilateral regardless of input side
Test: touch one side of the oropharynx should result in contraction of soft palate muscles of both sides (sometimes this can be elicited by just asking patient to say “ahhhh”)
Clinical significance:
-CN X motor problems: uvula will deviate to the intact side (away from side of injury)
-CN IX sensory problem: NO response (soft palate muscles do not contract at all)
-Protective response that prevents oral contents from entering the throat except as part of normal swallowing
CN XI: spinal accessory pathway:
nerve begins at medulla and exits cranium via jugular foramen
Foramina: jugular foramen
Function: voluntary motor to sternocleidomastoid and trapezius muscles
SCM -contralateral rotation of head
Traps- shoulder “raises” (general somatic efferent)
CN XII: hypoglossal nerve pathway:
nerve begins at medulla and exits cranium via hypoglossal canal
Foramina: hypoglossal canal
Function: voluntary motor to muscles of the tongue
(general somatic efferent (GSE))
The cortex normally sends bilateral innervation to cranial nerve motor nuclei. The one exception is innervation of the ___________________ which is contralateral.
genioglossus muscle
CN XII: hypoglossal nerve injury:
Common causes of injury:
-fairly rare
-posterior neck dissection
-fracture of atlanto-occipital joint
Patient presentation includes:
-Tongue deviated to same side as injury due to atrophy of muscles
-“lick your wounds” presentation
-Dysphagia (difficulty swallowing)
-Slurred speech
-Fasciculation on the tongue “bag of worms” appearance
Testing CN XII: “stick out your tongue”
