#10. Cranial Nerves Flashcards
Are the cranial nerves part of the PNS or the CNS?
PNS
List the route of the olfactory nerve from periphery to central
olfactory receptors in the olfactory epithelium –olfactory nerve – olfactory foramina in the cribriform plate – olfactory bulbs – olfactory tracts – primary olfactory area (28), limbic system and hypothalamus – frontal lobe (11)
Define anosmia
-loss of sense of smell
How does anosmia occur?
from infections of nasal mucosa, head injuries, lesions along olfactory pathway, meningitis, smoking, cocaine use
Define hyposmia
decreased sense of smell
Define hyperosmia
increased sense of smell
Where is the olfactory nerve?
- superior part of nasal cavity
- inferior surface of the cribriform plate
- along the superior nasal concha
What is the route of the Optic nerve from periphery to central?
rods and cones – optic nerves – optic foramen – optic chaism – optic tract (a few axons exit and go to the superior colliculi) – lateral geniculate nucleus – 1 degree visual area
Where is the optic chiasm?
in the sella turcica
What is the process in which light is translated and sent to the optic nerve?
light travels through the blood vessels, ganglion cells, and bipolar cells to get the the rods and cones on the back of the retina. the rods and cones then translate the light into electrical signals and pass that signal to the bipolar cells. the bipolar cells pass the signal on to the ganglion cells and the axons of the ganglion cells leave the retina as the optic nerve
What are the three layers of the retinal neurons?
ganglion cells, bipolar cells and rods/cones
What is the purpose of photoreceptors?
to start the process of converting light rays to nerve impulses
What is the location of cones on the retina?
concentrated in the center of the retina
What stimulates cones?
bright light
What is the acuity of cones?
high
Do cones see black/white/grey or in color?
Cones see in color. Rods see in black/white/grey
What is the location of rods on the retina?
concentrated in the periphery
What is the significance of rods?
they allow us to see in dim light
What is the acuity of rods?
low
Define acuity
resolution
Why do we have blind spots?
the blind spot is created due to the optic nerve exiting the eye
Define anopia
blindness due to a defect or loss of 1 or 2 eyes
What causes anopia?
from fractures in the orbit, brain lesions, damage along pathway, disease of the nervous system, pituitary gland tumours, cerebral aneurysm
Which extrinsic eye muscle makes you look down and out?
the superior oblique
Which extrinsic eye muscle makes you look up and out?
the inferior oblique
Which cranial nerve innervates the superior oblique?
CN IV trochlear
Which cranial nerve innervates the lateral recuts?
CN VI abducens
What does CN III innervate?
medial recuts, superior rectus, inferior rectus, inferior oblique, levator palpebrae suerioris
What is the route of the motor part of the oculomotor nerve starting from the nucleus in the midbrain?
nucleus - superior orbital fissure - superior branch and inferior branch.
superior branch innervates superior rectus and levator palpebrae suerioris.
inferior branch innervates medial rectus, inferior rectus, and inferior oblique.
What is the route of the autonomic portion of the oculomotor nerve starting from the nucleus in the midbrain?
motor nucleus - superior orbital fissure - inferior branch - ciliary ganglion - splits to innervate the ciliary muscle and the circular muscle of the iris
What does the ciliary muscle do?
- changes the shape of the lens for near vision. “accomodation”
- makes the lens fatter
What does the circular muscle of the iris do?
- changes the shape of the pupil
- contraction = smaller pupil
What nerves move the eye?
oculomotor, trochlear and abducens
What are is the significance of CN IV?
- smallest cranial nerve
- the only one that arises from the back of the brainstem
What is the route of the trochlear nerve starting at the nucleus?
trochlear nucleus in midbrain - superior orbital fissure - superior oblique muscle of eyeball
What is the route of CN VI starting at the nucleus?
abducens nucleus - superior orbital fissure - lateral rectus muscle
What happens if the oculomotor nerve is damaged?
- strabismus
- ptosis
- dilation of pupil
- mvmt of eyeball downward and outward on damaged side
- loss of accommodation for near vision
- diplopia
What is strabismus?
- lazy eye
- a condition in which both eyes do not fix on the same object, since one or both eyes may turn inward or outward
Define diplopia
double vision
What happens with damage to the trochlear nerve?
- strabismus
- diplopia
What happens with damage to the abducens nerve?
- affected eyeball can’t move laterally beyond midpoint and eyeball is usually directed medially
- this leads to strabismus and diplopia
What are the branches of CN V?
- opthalamic
- maxillary
- mandibular
What does the opthalamic branch of the trigeminal nerve do?
-sensory from skin over upper lid, cornea, lacrimal glands, upper nasal cavity, side of nose, forehead, anterior half of scalp
What does the maxillary branch of the trigeminal nerve do?
-sensory from muscosa of nose, palate, part of pharynx, upper teeth, upper lip, lower eyelid
What does the mandibular branch of the trigeminal nerve do?
-sensory from anterior 2/3 of tongue (not taste. only temperature and feeling), cheek and its mucosa, lower teeth, skin over mandible and side of head anterior to eat, mucosa of floor of mouth.
What is the route of the sensory portion of the trigeminal nerve starting at the pons nuclei?
pons nuclei - trigeminal ganglion - splits into 3 branches.
What branch or branches carries the motor functions the trigeminal nerve?
the mandibular branch
What does the motor branch of the trigeminal nerve supply and do?
- it supplies the muscles of mastication
- mainly control chewing
What is tic douloureaux?
- aka trigeminal neuralgia
- sharp cutting, intense pain that lasts for a few seconds to a minute.
- pain is within the nerve’s distribution
What causes trigeminal neuralgia?
- anything that presses on the trigeminal nerve or its branches
- local compression
- herpes zoster, vascular lesions, tumours, demyelinating conditions with subsequent scarring (MS), idiopathic
What are the symptoms of tic douloureaux?
- sudden painful attacks that last for seconds or minutes
- pain often occurs in clusters
- unilateral
- along one or more distributions of the nerve (usually V2 or V2 and V3)
- any mechanical stimulation, chewing, smiling, a breeze felt on the cheek can trigger an attack
- trigger zone may be lips, face, tongue (temp, touch, facial mvmt)
What is the theory of how trigeminal neuralgia occurs? (I don’t think she will ask about this but just in case)
- demyelinated fibers become hyperexcitable
- light mechanical stimulation recruits nearby pain fiberrs causing them to discharge and create the sensation of intense pain.
What is the route of CN VII sensory branch?
taste buds of ant 2/3 of tongue – stylomastoid foramen – geniculate ganglion – pons – thalamus – gustatory area of cerebral cortex (43)
(sensory branch also has axons from the skin in the ear canal)
What is the route of CN VII motor branch?
nucleus in pons – stylomastoid foramen – facial expression mm, stylohyoid mm, posterior digastric mm, stapedius mm
What does the stapedius muscle do?
when the muscle contracts it dampens that vibrations of the bone to lessen what you are hearing to protect your hearing.
What is the route of CN VII autonomic branch?
superior salivatory nucleus – (splits) pterygopalatine ganglion then to the lacrimal, nasal and palatine gland.
OR
superior salviatory nucleus – (split) submandibular ganglion – submandibular and sublingual glands
What gland do the CN VII go through but not innervate?
the parotid gland
What is Bell’s Palsy?
- a condition involving the facial nerve.
- results in paralysis of the muscles of facial expression on the same side as the lesion
- is one of the most common neurological conditions
- affects at least 25/100 000 people each year.
What are the symptoms for Bell’s Palsy?
- unilateral weakness followed by flaccid paralysis of mm of facial expression
- onset of symptoms from weakness to flaccid paralysis is quite rapid
- if sensory and autonomic affected can’t control lacrimation, usually decrease in salivation, can’t taste on anterior 2/3 of tongue, heightened sensitivity of hearing
- sagging of face and eyelid with possible pulling toward unaffected side.
What can cause Bell’s Palsy?
- nerve damage from viral infection (shingles) or from bacterial infection (lyme’s dx)
- compression from edema with pregnancy, middle ear infection, diabetes, HTN, hypothyroidism, leprosy
- condition involving the parotid gland
- trauma
- exposure to chill or draft
What is the prognosis for Bell’s Palsy?
- if only segmental demyelination (as with compression) recovery is usually in 2-8 weeks
- if Wallerian degeneration = poorer prognosis
What is the tx for Bell’s Palsy?
wait.
-self-limiting
What is the difference between Bell’s Palsy and a stroke?
with a stroke you can still control the forehead and the eye and with Bell’s you can’t.
What are the branches of CN VIII?
vestibular and cochlear branches
What does the vestibular branch of CN VIII do?
controls equilibrium impulses
What is the route of the vestibular branch of CN VIII?
semicircular canals, the saccule and the utricle of inner ear – vestibular ganglion – vestibular nuclei in pons and medulla
What does the cochlear branch of CN VIII do?
hearing impulses
What is the route of the cochlear branch of CN VIII?
spiral organ (organ of corti) – spiral ganglion – medulla – thalamus – primary auditory area (41, 42)
What happens with injury to the vestibular branch of CN VIII?
- veritgo
- ataxia
- nystagmus
Define vertigo
a subjective feeling that one’s own body of the environment is rotating
Define ataxia
loss of muscle coordination
Define nystagmus
involuntary rapid mvmt of the eyeball
What happens with injury to the cochlear branch of CN VIII?
- tinnitus
- deafness
What can cause damage to CN VIII?
trauma, lesions, middle ear infections
What does the sensory branch of CN IX do?
- taste buds on posterior 1/3 of tongue
- proprioceptors from some swallowing muscles
- baroreceptors in carotid sinus that monitor BP
- chemoreceptors measuring o2 and co2 in the blood
- external ear to convey tough, pain, heat, and cold
What is the route of the sensory branch of CN IX?
from the various endings – superior and inferior ganglia – jugular foramen – medulla
What is the route of the motor branch of CN IX?
nuclei in medulla – jugular foramen – stylopharyngeus muscle
What does the stylopharyngeus muscle do?
elevates the pharynx and larynx for swallowing
What is the route of the autonomic branch of CN IX?
inferior salivary nucleus in medulla – otic ganglion – parotid gland
What happens if CN IX is injured?
- dysphagia
- aptyalia
- loss of sensation in throat
- ageusia
define dysphagia
difficulty swallowing
define aptyalia
reduced saliva secretions
define ageusia
loss of taste sensation
What is Glossopharyngeal neuralgia?
- recurrent attacks of pain in nerve distribution
- rare
- more common in men usually after 40 yoa
- unilateral, painful
- pain lasts a few minutes usually beginning in the tonsil area or base of tongue. may radiate to ipsilateral ear
What is the name of the other pathology that is very similar to glossopharyngeal neuralgia?
- trigeminal neuralgia
- distinguished by location of pain
Where does the sensory branch of CN X start?
- skin of external ear
- a few taste buds in epiglottis and pharynx
- proprioceptors in mm of neck and throat
- baroreceptors and chemoreceptors
What is the route of the sensory branch of CN X?
mainly from visceral sensory receptors in most organs of thoracic and abdominal cavities – superior and inferior ganglia – medulla
What nerves are involved in taste buds?
- CN X Vagus
- CN IX Glossopharyngeal
- CN VII Facial
What is the route for the motor branch of CN X?
from the medulla – pharynx, larynx, and soft palate muscles
What does the autonomic branch of CN X supply and where does it start?
- the axons start in the medulla
- supplies: lungs, heart, glands of GI tract, smooth mm of respiratory passageways, esophagus, stomach, gallbladder, small intestine, most of large intestine
What happens with injury to CN X?
- vagal paralysis
- dysphagia
- tachycardia
What is the route of CN XI?
motor axons from anterior grey horn of C1-C5 – ascend through foramen magum – exit through jugular foramen – SCM and trapezius
What happens with injury to CN XI?
paralysis to SCM and trapezius
What is the route of CN XII?
hypoglossal nucleus in medulla – hypoglossal canal – mm of tongue
What happens with injury to CN XII?
- difficulty chewing
- dysarthria
- dysphagia
- the tongue, when protruded, curls toward the affected side and that side atrophies.
