Cranial Nerves Pt 2 Flashcards
DESCRIBE orbit
place/socket = cone shaped cavity
bounded by 7 skull bones = neuro and viscerocranium
what does orbit contain
eyeball optic nerve, extraocular muscles, neurovascular structures,
lacrimal gland (superior lateral corner of orbit) & various amounts of adipose tissue (fat filler)
which nerve is in orbit
optic nerve
CNII
describe orbital fat
adipose tissue
cushions and protects orbit contents
promotes smooth eyeball movements
dampens movements of eyes (not shaking around)
name and describe all 7 bones that bound the orbit
frontal = roof of orbit
ethmoid = medial wall w/ maxilla (tiny)
lacrimal (ant to ethmoid) = medial wall w/ maxilla (tiny)
palatine = posterior wall near floor of orbit
maxilla = floor mostly, lateral wall too
zygomatic = floor, also lateral wall
sphenoid = posterior and lateral walls - wraps around back for posterior wall
describe eye
globe
organized into 3 concentric layers
name layers of eye - superficial to deep
sclera
uvea
retina
describe sclera
outer fibrous tunic - whites, tough = made of dense ct, protects/maintains shape (structural role - integrity)
continuous anteriorly with transparent cornea = front clear space, cornea part of sclera
describe uvea
middle vascular/muscular tunic
controls amount of light and focus
name the 3 components of uvuea
choroid
ciliary body/muscle
iris
describe choroid - part of uvea
vascular layer - supply eyeball and interior
describe ciliary body - part of uvea
muscle
can change shape of lens - for focus
bulge, pulls lens and adjusts concavity and shape = focus light on retina
Readjust image in front or back of retina
describe iris - part of uvea
pigmented muscular ring with 2 muscles
organized at 90 degrees to each other
pupillary sphincter
pupillary dilator
describe iris pupillary sphincter - part of uvea
concentric fibers - rings
constricts pupil, closes aperture, reduce diameter
when fibers shorten
Parasympathetic
describe iris pupillary dilator - part of uvea
radial fibers
dilates pupil, opens up
sympathetic
organized radially
describe retina
innermost photosensitive tunic - detects signal
Specialized photoreceptor cells that synapse with neuron whose axons travel together as optic nerve cn II
name parts of retina
optic disk
macula
describe optic disk - part of retina
WHERE neurons converge - enter optic nerve
NO photoreceptors here = creates small blind spot
describe macula - part of retina
area with highest density of photoreceptors
has a zone of peak visual acuity = fovea the (highest density rods and cones, best at detecting all forms of light, straight at back of pupils in anatomical position)
describe spaces - chambers of eye
space between iris and cornea = anterior chamber, contains AQUEOUS humour, maintains intraocular pressure and provides nutrition
space posterior to lens = vitreous chamber, contains VITREOUS humour, gel like, maintains shape of eye, metabolic functions
describe optic nerve - gen
relays visual stimuli to brain
describe optic nerve - passage
receptor cells in retina relay signals via optic nerves through optic anal
at optic chiasm X = left and right visual field signals sorted into optic tracts and projected to contralateral side of brain for processing (visual-occipital lobe)
bilaterally symmetrical but right has role in left and vice versa
describe optic nerve - exit
cn ii passes through optic canal (hidden under lesser wing of sphenoid) = immediately above superior orbital foramen
describe extraocular muscles
turn eye towards light
eyeball moved by 6 extraocular muscles = 4 rectus and 2 oblique
controlled by cn III, IV & VI = all pass through sof - mostly dedicated to things around eye (eyeball, eye muscles, skin around eye, skin of forehead)
describe intraocular muscles
pupillary dilator and sphincter and cilliary muscles of uvea
name rectus muscles - extraocular eye muscles
medial rectus
lateral rectus
superior rectus
inferior rectus
describe medial rectus
rotates eye medially in transverse plane
ADDUCTS
describe lateral rectus
rotates laterally = ABDUCTS
away from midline
describe superior rectus
elevates - rotates superiorly
intorsion = medial rotation in relation to superior
describe inferior rectus
depresses eyeball
rotates inferiorly
extorsion = lateral rotation in relation to superior side (north or noon)
name oblique muscles - extraocular eye muscles
superior oblique
inferior oblique
muscles complement superior and inferior rectus muscles
describe superior oblique
depresses, ABDUCTS and produces intorsion
describe inferior oblique
elevates, ABDUCTS and produces extorsion
what muscles produce pure elevation of eye
inferior oblique and superior rectus
(IO compensates for SR)
what muscles produce pure depression of eye
superior oblique and inferior rectus
SO compensates for adduction and extorsion of IR
describe attachment of rectus muscles
common tendinous ring around optic nerve to anterior half of eyeball at 4 cardinal points
common tendinous ring attached to sphenoid, around optic canal
describe attachment of superior oblique muscle
common tendinous ring to posterior/superior half of eyeball via trochlea
Changes course to attach to superior aspect of eyeball –> deep to superior rectus
describe attachment of inferior oblique muscle
infero-medial orbit wall (maxilla) to post/inf surface of eyeball between inferior and lateral rectus
off maxillary bone and runs laterally to insert itself on inferior of eye (inferior to inferior rectus)
describe innervation of
extraocular muscles
medial rectus, superior rectus, inferior rectus and inferior oblique = cn III oculomotor
superior oblique = cn VI trochlear
lateral rectus = cn VI abducens
(LR6SO4)3
describe cn III
oculomotor
levator palpebrae superioris
psns and sns
describe cn III psns/sns
in bright light = pupil constriction, parasym, craniosacral outflow, sphincter pupillae
in dim light = pupil dilation, symp, t1-t4, dilator pupillae
why do superior and inferior rectus muscles produce intorsion and extorsion respectively
orbital and visual axes not parallel
so SR and IR both cause adduction and axial rotation (torsion) of eye ball around visual axis
both positioned medially to visual axis
angle = misalignment of visual and orbit axis
describe levator palpebrae superioris
elevation of upper eyelid, above superior rectus, keeps eyes open
no inferior muscle to keep bottom lid open
where are middle and inner ear
in petrous portion temporal
describe external ear - functions
collect and direct- funnels soundwaves towards middle/inner ear- sound waves through auditory canal
describe external ear - structures
auricle - pinna (visible ear) and its supporting cartilages
includes external auditory meatus and external auditory canal
ends at tympanic membrane (eardrum)
describe middle ear - transduction
transduces sound pressure waves into mechanical vibrations = reduces energy loss at air to liquid transition (sound waves - mechanical sound pressure into waves/forces that inner ear can interpret)
Involves series of 3 linked ossicle
is middle ear open to nasopharynx
yes by auditory - eustachian tube
otherwise all energy lost when air wave hits liquid
the 3 ossicles turn sound –> mechanical waves
Describe middle ear structures
air filled cavity located in petrous portion of temporal
Inferior to middle cranial fossa
external opening sealed by tympanic membrane
contains 3 ear ossicles in sequence
describe middle ear - ossicles
malleus - handle embedded in tympanic membrane
incus - connects to stapes
stapes - linked to inner ear at (plate sits in) oval window
all responsible for sound transduction
describe middle ear - bony openings
3 covered = tympanic opening, oval and round window
1 open to nasopharynx via auditory tube = pressure equalization of middle ear and outside (yawn, airplane)
describe inner ear - gen
sensory component of ear-converts fluid waves to electrical impulses for hearing (cochlea) & balance (vestibular apparatus)
impulses transmitted to brain via CNVIII= Vestibulocochlear nerve via internal acoustic meatus (IAM)
describe inner ear - structures
consists of bony labyrinth = closed series of bony cavities (tubular spaces) in petrous temporal, filled with fluid (spiral up pyramid)
Divided into cochlea and vestibular apparatus (semicircular canals and vestibule)
encloses separate membranous labyrinth (tube within tube) - matches shape of bony labyrinth
describe cochlea
in membranous labyrinth, known as cochlear duct (blind ended at apex of cochlea)
Filled with endolymph - liquid outside it (within cochlear canal of bony labyrinth=perilymph)
describe cochlea duct separation
cochlear canal into 2 channels that meet at apex =
scala vestibuli = spirals up canal towards apex - ascending
scala tympani = spirals down to end at round window, blind end- descending
describe sound transduction steps 1-8
1- sound waves hit tympanic membrane
2 Makes chain of ossicles vibrate
3 - Stapes plate pushing back and forth into oval window
4 - moves perilymph”up” Scala vestibuli
5 - distance up spiral proportional to frequency of sound (and amplitude)
6 - perilymph in scala vestibuli pushes on cochlear duct (membranous labyrinth, liquids incompressible)= stimulating spiral organ receptors at that level
7- pressure waves on floor of cochlear duct passed on to scala tympani
8- move “down” cochlear canal to be dissipated at Round windows membrane
describe spiral organ (of corti)
embedded in cochlear duct floor against scala tympani
contains specialized receptor cells that stimulate the fibers of CN VIII (connected to)
describe vestibular apparatus
Occupies second half of bony labyrinth
bony labyrinth spaces here filled with a membranous labyrinth containing endolymph (location of sensory cells)
membranous labyrinth = semicircular ducts (3) and utricle and saccule
describe semicircular ducts - gen
located in semicircular canals of bony labyrinth
each at 90 degrees to each other (good at picking up head rotation in space along the 3 coronal planes)
at base - closest to vestibule of bony labyrinth = each duct has thickening = ampulla
describe semicircular ducts - detect movement
Specialized cells in ampullae detect movement of endolymph and stimulates cnVIII (brain interprets as head rotation)
each semicircular duct is best at detecting fluid motion along one axis in 3D (but works with others to achieve balance)
describe utricle and saccule - gen
located in vestibule of bony labyrinth between semicircular canals and cochlear canals
continuous with semicircular ducts (utricle) and cochlear duct (saccule)
describe utricle and saccule - detect motion
detects both linear accelerations as well as head position (like if upside down)
via stimulation of hair cells embedded in gel like thickening of endolymphatic duct walls
describe cn VIII
vestibulocochlear
relays auditory and balance stimuli to brain from hair cells in vesitbular organ (balance) or cochlea (hearing)
connects to membranous labyrinth and enters skull via IAM in petrous temporal bone onto brain–> between pons and medulla
