cranial nerves -- neuro 500 Flashcards
development o nervous sytem begins whne
begins in 3rd week of gestation
development of nervous system starts with
starts with a thickening of the ectoderm called the neural plate
what does neural plate do
-neural plate folds inward and forms a longitudinal groove, called the neural groove
raised edges of neural plate
-raised edges of the neural plate are called the neural folds
neural tube
-as the whole thing grows and forms a tube, now called the neural tube
Layers of cells from walls
…
outer/marginal layer cells
= white matter of nervous system
middle/mantle layer cells
= gray matter
inner/ependymal layer cells
= lining of central canal (spinal cord) and ventricles of brain
Neural crest
= mass of tissue between the neural tube + skin ectoderm
neural crest becomes
-posterior (dorsal) root ganglia of spinal nerves
-spinal nerves
-ganglia of cranial nerves
-cranial nerves
-ganglia of autonomic nervous system
-adrenal medulla
-meninges
cranial nerves
12 pairs of cranial nerves
cn originate
originate in the brain and pass through various foramina in
cranial/facial bones
cranial nerves part of which division
part of the PNS
how are cn numbered
the numbers indicate the order (rostral to caudal) that nerves arise from the brain
how are cn named
the name indicates the nerve’s distribution or function
sensory nerves – WHERE ARE CELL BODIES
sensory nerves – their cell bodies are outside the brain
(w/ dendrites)
motor nerves - where are cell bodies
motor nerves – their cell bodies are within the brain
shortest cranial nerve
olfactory
olfactory epithelium
WHERE?
-superior part of nasal cavity
inferior surface of the cribriform plate
along the superior nasal concha
olfactory epithelium
3 cell types
1) Olfactory receptors
2) Supporting cells
3) Basal cells
olfactory sensory signal pathway
axons of olfactory receptors
—> FORM olfactory nerve
axons “ go through olfactory FORAMINA in cribriform plate
–> join olfactory bulbs
–> become olfactory tracts
then enter … (next slide)
where does olfactory signal go from olfactory tracts?
to primary olfactory area
+ limbic system
+ hypothalamus
—> Frontal lobe
WHAT makes the olfactory sensory pathway unique?
THEY DON’T SYNAPSE @ THALAMUS
Olfactory sensations are the only sensations that
reach the cerebral cortex without first synapsing
in the THALAMUS
Hyperosmia
Anosmia
Hyperosmia – increased sense of smell
Anosmia - loss of sense of smell
anosmia potential causes
infections of nasal mucosa,
head injuries,
lesions along olfactory pathway,
meningitis,
smoking,
cocaine use
sense of smell vs gender
-women often have a keener sense of smell than
men do
during which time is sense of smell most sharp for women?
especially during ovulation
smoking vs olfactory function
-smoking impairs smell in the short term
and may cause long-term damage to olfactory
receptors
age vs olfactory function
-sense of smell deteriorates with age
Hyposmia
reduced ability to smell
hyposmia – demographics
affects 50% of those over 65
and 75% of those over 80
hyposmia, like anosmia can also be caused by
can also be caused by neurological changes
retina
“a layer at the back of the eyeball containing cells that are sensitive to light and that trigger nerve impulses that pass via the optic nerve to the brain, where a visual image is formed.”
3 layers of retina (3 layers of retinal neurons)
- Photoreceptors
- Bipolar cell layer
- Ganglion cell layer
- Photoreceptors
function
start the process of converting light to nerve impulses
photoreceptors types
cones
rods
cones
stimulated in bright light
colour vision
high acuity
concentrated in the center of retina
acuity define
“sharpness or keenness of thought, vision, or hearing.”
cones, concentrated in centre of retina
for this reason, when it’s dark, the centre of vision may be less clear (?)
rods
- allow us to see in dim light
- no colour (black/white/grey)
- low acuity
- concentrated in the periphery
- bipolar cell layer
also has horizontal + amacrine cells
(they form lateral connections,
involved in modifying signals)
- Ganglion cell layer
their axons extend posteriorly to optic disc and exit the eye as the optic n
optic disc
“The optic disc or optic nerve head is the point of exit for ganglion cell axons leaving the eye”
optic sensory feedback pathway
rods + cones (then to bipolar cells – then to ganglion cells)
—> Optic nerve
—> Through the optic foramen/canal
—> via Optic chiasm
—> to Optic tract
from OPTIC tract, sensory feedback goes to ____ & ____
LATERAL GENTICULATE NUCLEUS
& superior colliculi
via the lateral genticulate nucleus, optic sensory information goes to ____
primary visual area of the cerebral cortex
anopia
blindness due to a defect or loss of 1 or 2 eyes
anopia possible causes
fractures in orbit,
brain lesions,
damage along the pathway,
disease of the nervous system,
pituitary gland tumours,
cerebral aneurysm
extrinsic eye muscles
extrinsic eye muscle extend from the bony orbit
to the sclera
sclera
“the white outer layer of the eyeball. At the front of the eye it is continuous with the cornea.”
sclera function
“The sclera is the supporting wall for your eyeball. It maintains your eye’s shape and protects it from injuries. Muscles attached to the sclera help you move your eyeball.”
cornea define
“The transparent part of the eye that covers the iris and the pupil and allows light to enter the inside.”
cornea function
“In addition to protecting the eye from outside infiltrates and ultraviolet radiation, the cornea is responsible for approximately 65% to 75% of the refraction of light as it passes through the eye. The cornea performs the initial refraction onto the lens, which further focuses the light onto the retina.”
vitreous humor
“the transparent gelatinous tissue filling the eyeball behind the lens.”
function:
“The vitreous humor, a gel-like substance filling the space between the lens and retina, provides structural support, acts as a shock absorber, maintains image clarity, and acts as a metabolic buffer for the eye.”
extrinsic eye mm
Superior rectus
Inferior rectus
Lateral rectus
Medial rectus
Superior oblique
Inferior oblique
(levator palpebrae superioris)
levator palpebrae superioris
technically for the eyelid not eye
capsulopalpebral fascia
“The capsulopalpebral fascia is a fibrous expansion originating from the fascial sheaths surrounding the inferior rectus and inferior oblique muscles. It assists with the depression of the lower eyelid when the inferior oblique and inferior rectus muscles contract.”
superior oblique muscle of eye action
abducts & depresses eye
medially rotates eye
inferior oblique muscle of eye action
abducts & elevates eye
laterally rotates eye
cranial nerve 3 oculomotor, motor pathway
Motor nucleus in midbrain
–> via Superior orbital fissure
—> divides into:
SUPERIOR BRANCH
INFERIOR BRANCH
superior branch of oculomotor n, supplies ___
superior rectus
levator palpebrae superioris
inferior branch of oculomotor supplies
medial rectus
inferior rectus
inferior oblique mm
what about …
lateral rectus
& superior oblique muscle of eye?
lateral rectus = abducens n
superior oblique = trochlear n
autonomic motor pathway of oculomotor n
Motor nucleus in midbrain
—> via Superior orbital fissure
—> via INFERIOR BRANCH of oculomotor n
—> to CILIARY GANGLION (via branch of oculomotor n to ciliary ganglion)
from ciliary ganglion, oculomotor motor signal goes to ____ & ____
ciliary mm
& circular mm of iris
ciliary mm function eye
“The ciliary muscle is a multi-unit smooth muscle in the eye responsible for adjusting the shape of the lens to enable focusing on objects at different distances”
why adjust lens shape?
As light enters the eye, it is refracted (bent) at the cornea.
The lens further refracts the light rays so they come into “exact” focus on the retina.
so how does changing shape of lens affect vision?
ACCOMODATION
Accommodation: when the eye is focusing on a close
object, the lens becomes more spherical, causing greater refraction of light rays.
so what happens to lens when ciliary mm contract?
becomes spherical
Adjusts the lens for near vision “accomodation”
why looking at close objects cause eye strain?
“When the ciliary muscle is contracted, the lens becomes more spherical – and has increased focussing power”
circular mm of iris
pupil diameter
circular vs radial mm of iris
circular mm constrict pupil
(parasympathetic)
radial mm dilate pupil
(sympathetic)
trochlear nerve cn4
motor function
thinnest cn
trochlear
only cn that arises from posterior brain stem
trochlear
trochlear nerve pathway
Trochlear nucleus in midbrain
—> through Superior orbital fissure
—> Superior oblique mm of eyeball
abducens (cn6) function & pathway
motor
abducens nucleus @ PONS
—> through superior orbital fissure
—> to LATERAL RECTUS MM OF EYE
damage to oculomotor n may result in …
strabismus
ptosis
dilation of pupil
Movement of eyeball downward + outward on damaged side
Loss of accommodation for near vision
Diplopia (double vision)
strabismus
a condition in which both eyes do not fix on the same object, since one or both eyes may turn inward or outward
etymology
“squint”
why movement of eyeball downward/outward?
uninhibited actions of lateral rectus & superior oblique mm of eye
why loss of accomodation for near vision?
loss of innervation to ciliary m of lens (oculomotor)
why diplopia (oculomotor n damage)
“because it disrupts the coordinated action of the eyes, leading to misalignment and a double image”
(AI)
damage to trochlear nerve may cause….
strabismus
diplopia
damage to abducens nerve ?
Affected eye can’t move laterally beyond midpoint and eyeball is usually directed medially
—> This leads to strabismus and diplopia
(Why? b/c abducens innervates lateral rectus)
LARGEST DIAMETER CN
TRIGEMINAL
TRIGEMINAL NERVE branches
ophthalmic
maxillary
mandibular
trigeminal function
sensory & motor
trigeminal nerve motor function
via mandibular branch
mm of mastication
control chewing
trigeminal neuralgia
-sharp cutting, intense pain that lasts for a few seconds
to a minute
pain is within the nerve’s distribution
trigeminal neuralgia causes
local compression
idiopathic,
herpes zoster,
vascular lesions,
tumours,
demyelinating conditions with subsequent scarring (e.g. MS)
trigeminal neuralgia SSx
sudden painful attacks
pain often occurs in clusters
unilateral
along one or more distributions of the nerve
trigeminal neuralgia quality of pain?
pain is knife-like, “like a lightening bolt inside [patient’s] head that lasts for seconds to minutes”
which branch of trigeminal n usually affected by trigeminal neuralgia?
usually CN V2
or CN V2 and CN V3
2 = maxillary
3 = mandibular
what can trigger trigeminal neuralgia attack?
any mechanical stimulation, chewing, smiling, a breeze
felt on the cheek can trigger an attack
triggerzone
patients avoid stimulating the trigger zone
trigger zone may be lips, face, tongue (touch, temp, facial mvt)
tirgeminal nerve sensory function
…
- Ophthalmic branch, sensory function
Sensory from skin over
upper lid, cornea,
lacrimal glands, upper
nasal cavity, side of nose,
forehead, anterior half of scalp
via SUPERIOR ORBITAL FISSURE
- Maxillary branch, sensory function
Sensory from mucosa
of nose, palate, part of
pharynx, upper teeth,
upper lip, lower eyelid
via FORAMEN ROTUNDUM
- Mandibular branch, sensory function
Sensory from anterior 2/3
of tongue (not taste),
cheek + its mucosa, lower
teeth, skin over mandible
+ side of head ant to ear,
mucosa of floor of mouth
via FORAMEN OVALE
all three branches of trigeminal nerve form ____
TRIGEMINAL GANGLION
goes to PONS
facial nerve function
sensory
motor
autonomic
facial nerve sensory function
taste buds of anterior 2/3 of tongue
through stylomastoid foramen
to GENTICULATE GANGLION
to pons —> thalamus
then to GUSTATORY AREA of cerebral cortex
other sensory function of facial nerve (CN7)
-also sensory axons from skin in ear canal (touch, pain, temp)
motor function of CN7
nucleus in pons
—> stylomastoid foramen’
facial expression muscles, stylohyoid mm,
posterior digastric mm, stapedius mm (ear)
facial nerve autonomic function
nucleus in pons
—>
pterygopalatine ganglion
& submandibular ganglion
pterygopalatine ganglion GOES TO ____
lacrimal glands
nasal gland
palatine gland
submandibular ganglion GOES TO ____
submandibular glands
sublingual glands
Bell’s palsy
-is 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
-it affects at least 25 people out of 100,000 each year
Bell’s palsy SSx
-unilateral weakness followed by flaccid paralysis of muscles of facial expression
-onset of symptoms from weakness to flaccid paralysis is quite rapid
-if sensory + 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
bell’s palsy cause
nerve damage from
-viral infection (shingles)
-bacterial infection (lyme’s dx)
compression from edema with
-pregnancy -middle ear infection -diabetes -hypertension -hypothyroidism -leprosy
-conditions involving the parotid gland
-trauma
-exposure to chill or draft
Bell’s palsy Px
-if only segmental demyelination (as with compression), recovery is usually in 2-8 weeks
-if Wallerian degeneration = poorer prognosis
Bell’s palsy Tx
- treat the cause, if known
- often no treatment because there is spontaneous recovery in 70% of cases
- protect the eye with eye patch and antibiotic drops
Bell’s palsy vs stroke DDx
- people often fear paralysis of one side of face is from stroke (UMN) but stroke generally affects the lower muscles of face (not frontalis or muscles around eye)
- so during a stroke, patient can close eye and wrinkle forehead but can’t smile
Vestibulocochlear Nerve
Type: sensory
Function: hearing and equilibrium
2 branches (vestibular, cochlear)
Vestibular branch – function
carries impulses for equilibrium
vestibular branch of cn8 – pathway
Semicircular canals, the saccule + utricle of inner ear
—> Vestibular ganglion
—> Vestibular nuclei in pons + medulla
Cochlear branch – function
carries impulses for hearing
cochlear branch of cn8 – pathway
Spiral organ (organ of Corti) in cochlea of internal ear
—> Spiral ganglion
—> Internal acoustic meatus
—> Cochlear nuclei in medulla (NOT PONS)
—> Thalamus
—> Primary auditory area
Injury to vestibular branch
Vertigo – a subjective feeling that one’s own body or the environment is rotating
Ataxia – muscular incoordination
Nystagmus – involuntary rapid movement of the eyeball
Injury to cochlear branch
Tinnitus – ringing in ears
Deafness
what can cause damage/injury to vestibulocochlear nerve (CN8) ?
trauma,
lesions,
middle ear infections
glossopharyngeal nerve functions
sensory
motor
autonomic
Sensory function cn9
1) Taste buds on posterior 1/3 of tongue
2) Proprioceptors from some swallowing muscles
3) Baroreceptors in carotid sinus that monitor BP
4) Chemoreceptors in carotid sinus
5) External ear to convey touch, pain, heat and cold
sensory feedback pathway for cn9
from above areas
—> to Superior and inferior ganglia
—> via jugular foramen
—> to MEDULLA
glossopharyngeal nerve motor function
nuclei in medulla
—> through jugular foramen
—> stylopharyngeus muscle
glossopharyngeal nerve autonomic function
inferior salivary nucleus in medulla
—> otic ganglion
—> parotid gland
injury to cn9 ?
Dysphagia
Aptyalia
Loss of sensation in throat
Ageusia
Aptyalia
“absence of or deficiency in secretion of saliva.”
“The term “aptyalia” comes from the Greek words “a-“ (meaning “without” or “lack of”) and “ptyalism” (meaning “salivation”)”
Ageusia
“The term “ageusia” refers to the loss of your sense of taste”
ageusia etymology
“Ageusia (from negative prefix a- and Ancient Greek γεῦσις geûsis ‘taste’) is the loss of taste functions of the tongue”
Glossopharyngeal Neuralgia
-recurrent attacks of severe pain in the CN IX nerve distribution (posterior pharynx, tonsils, back of tongue, middle ear)
-from nerve compression
-rare, more common in men, usually after 40
-(like in trigeminal neuralgia) get paroxysmal attacks of unilateral brief, excruciating pain
-occurs spontaneously or are precipitated by certain movements (eg, chewing, swallowing, talking, sneezing)
-pain lasts seconds to a few minutes, usually begins in tonsil area or at base of tongue and may radiate to ipsilateral ear
glossopharyngeal neuralogia vs trigeminal neuralgia distinguishing features
-is distinguished from trigeminal neuralgia by location of pain
-also, in glossopharyngeal neuralgia, swallowing or touching the tonsils with an applicator triggers pain
vagus nerve functions
sensory, motor, autonomic
cn 10 sensory function
- Skin of external ear for touch, pain, heat and cold
- Taste buds in epiglottis and pharynx
- Proprioceptors in mm of neck and throat
- Baroreceptors & chemoreceptors in carotid sinus & aortic bodies
- Most sensory axons come from visceral sensory receptors in most organs of thoracic & abdominal cavities that convey sensations (ie hunger, fullness, discomfort)
cn10 sensory pathway
from above
—> Superior and inferior ganglia
—> through Jugular foramen
—> medulla
motor pathway cn10
medulla
—> through jugular foramen
—> Muscles of the pharynx, larynx & soft palate (swallowing, vocalization, coughing)
autonomic pathway cn10
medulla
via jugular foramen
—>
smooth muscle of lungs
cardiac muscle
glands of GI tract
smooth mm of respiratory passageways
esophagus
stomach
gallbladder
small intestine
most of large intestine
Injury to Vagus nerve
Vagal paralysis – interruptions of sensations from many organs in thoracic and abdominal cavities
Dysphagia
Tachycardia
Accessory Nerve cn11
motor
Motor axons from anterior grey horn of C1-C5
—> ascend through foramen magnum
—> exit through jugular foramen
—> SCM & trapezius
hypoglossal nerve
motor
Hypoglossal nucleus in the medulla
—> Hypoglossal canal
—> muscles of tongue
cn12 injury
difficulty chewing
dysarthria
dysphagia
