UNIT 7: CN VIII + Development Flashcards
structures of the face and neck in the human embryo are derived from a series of
arches, clefts, pouches
arches and clefts arise …
externally at the anterior end of the embryo around the upper end of the foregut - primitive pharynx
pouches arise …
internally, are the “internal partners” of the external clefts
pharyngeal clefts are
slit like depressions bw the pharyngeal arches
1st cleft is the _______ and deepens to form…
hyomandibular cleft
deepens to form the external auditory meatus of the ear and external surface of the TM
2nd to 4th clefts are …
obliterated by rapid dev of tissue of the 2nd arch
if obliteration of the 2nd to 4th clefts are incomplete then…
a cervical cyst (space) may persist deep to the skin in the neck region
during 5th week 6 _____ of tissue develop on both sides of the ….
hillocks aka mounds
1st cleft
subsequent dev of the hillocks on either side of the 1st cleft leads to
formation of the auricle
external auditory meatus is formed from the
deepening of the 1st pharyngeal cleft
TM arises at
junction of 1st pharyngeal cleft and pouch
pharyngeal pouches are
pockets w/i the primitive pharynx (medial surface) that correspond to the pharyngeal clefts
in lower vertebrates, pharyngeal clefts and pouches are
open to each other to form gill slits
in human tissues …. tissue bw the 1st cleft and 1st pouch forms…
the TM … the remaining clefts are obliterated
distal end of the 1st pharyngeal pouch enlarges to form the
TC
distal end of 1st pharyngeal pouch that enlarges to form the TC, expands to enclose and surround…
the dev ossicles (from 1st and 2nd arches)
further posterior expansion of the TC gives rise to
the aditus (leads to mastoid antrum and air cells)
1st pharyngeal pouch continues to elongates and….
maintains opening into the pharynx, forming the eustachian tube
lining at the distal end of the 1st pharyngeal pouch forms the ….
internal layer of the TM
thickening of surface ectoderm at week 4 is recognized as the
otic placode
otic placode deepends into the ____ and eventually becomes _____ from surface ectoderm as the _____
otic pit
cut off
otic vesicle
otic vesicle gives rise to
membranous labyrinth
otic vesicle looks like an …. diverticulum forms….
inverted pear w small diverticulum
diverticulum forms the endolymphatic duct and sac
wider part of the otic vesicle gives rise to 3 …
flattened sacs … semicircular ducts
narrow ends of otic vesicle elongate and begin to ….
coil to form the cochlear duct
on the otic vesicle the utricle and saccule form bw
semicircular and cochlear ducts
auricular tags are
residual material along fusion line of 1st branchial arch; anterior to auricle
atresia
congenital absence of EAM
tympanic cavity may also be absent
microtia
small pinna; underdeveloped features
may still have an EAM
CN VIII is classified as a
special sensory nerve
end receptors in both systems of CN VIII are…
hair cells
dendrites of primary sensory neurones extend a very short distance in CN VIII from _____ to nerve cell bodies
bases of HCs
vestibular system’s of CN VIII ganglion is…
vestibular ganglion (only one! hence ganglion)
auditory sys of CN VIII has its ganglia in
spiral ganglia (many of them hence ganglia)
steps of hearing… (include what happens if sound it too loud)
Sound funneled by pinna to EAM which amplifies sound and now that acoustic energy is hitting the ear drum
Sound waves make TM move and vibrate which vibrates the malleus which then vibrates the incus and then the stapes
If the sound is too loud the tensor tympani would contract to dampen the vibration of the TM and if we rly need to do it more stapedius will pull on stapes and stop transmission
Stapes footplate pumps on fluid filled sys via the oval window, sets up travelling wave, high freq sounds pumping fast, low freq pumping slow, will move the perilymph … which bends the basilar membrane close to the base of the cochlea, the outer hair cells that are imbedded in the tectorial membrane this makes the endolymph move, then this makes the stereocilia in the IHCs move which makes up register sound
axons of primary neurons in CN VII travel through the …
IAM with CN VII
after primary neurons travel thru IAM, it enters the _____ at its junction with the pons and terminates in ___ vestibular nuclei and ___ cochlear nuclei
medulla
brainstem nuclei
4
2
name the 4 vestibular nuclei
superior
medial
lateral
inferior
name 2 cochlear nuclei
dorsal
ventral
input predominantly from the semicircular ducts goes to what nuclei…. and to coordinate what?
superior nucleus = to coordinate eye movements
medial nucleus = to coordinate postural head and neck movements
input predominantly from maculae goes to what nuclei.. to coordinate what?
lateral nucleus = to coordinate postural responses to gravity
inferior nucleus = projects to vestibular regions of cerebellum and other vestibular nuclei
all vestibular sub nuclei send a few secondary nerves to the ____ and a tertiary nerve to the _____…. this allows for ….
thalamus
somatosensory cortex
conscious appreciation of balance and head position
auditory NS is complex, involves two ascending systems called ____ and ____, and two descending systems called _____ and ____
classical
non-classical
corticofugal
olivocochlear
classical ascending auditory sys is….
tonotopic system; distinct freq tuning, neurons are organized anatomically according to freq to which they are tuned
non-classical auditory sys …
project to secondary auditory cortices
3 main nuclei of the classical ascending sys….. explain pathway
cochlear nuclei = dorsal and ventral nuclei in medulla
central nucleus of inferior colliculus in midbrain
medial geniculate body in thalamus
Synapse point at these nuclei
First one from the ear is the cochlear nuclei
Next one is in the midbrain
Then it synapses in the thalamus (medial geniculate body is part of the auditory pathway)
Then it goes to the primary auditory cortex
there are also 2 additional nuclei in the classical ascending pathway that have some synaptic connections… … what do they help w?
Not all fibres stop at SOC (which is next door to the cochlear nuclei) and not all stop at nuclei of the LL
Option stops begin sound localization (means we don’t have to wait for it to go to cortex for sound localization… ex. May not know which emergency vehicle is making a siren but we just need to be on alert, don’t need cortex for that, aka don’t need to know which emergency vehicle it is)
superior olivary complex
nuclei of the lateral lemniscus
classical ascending pathway contains connections bw the 2 sides of the… which is important for…
CNS at several levels in the ascending pathway - very important for directional hearing
how is the cochlea/heschel’s gyrus like a piano
High tones at base
Low tones at apex
Tonotopic organization
We don’t loose this detail
We keep it – and at heschel’s gyrus is also layed out by freq
Freq info given to cortex as is
The cochlea told us info about sound signal, but maintains that so the cortex doesnt have to do that again
in the auditory nerve, cell bodies of the primary sensory neuron are w/i the… in the…
spiral ganglia in the modiolus of the cochlea
all hair cells have both ____ and ____ innervation, but majority are ____
afferent and efferent
afferent
auditory nerve has type __ and ___ afferent nerve fibres…. _______ fibres in humans
type I and II
30,000
type I afferent nerve fibres are from ____, What ratio
IHCs
1 HC to many nerves
type II afferent fibres are from ____, ratio is…
OHCs
many hair cells to 1 nerve
type I fibres lead from IHCs to cells in the _______ nuclei
cochlear
type I fibres from IHCs is the pathway by which all …
auditory info is transmitted from the organ of corti to higher centres of the auditory CNS
for type I fibres, diameters are relatively _____; limits differences in ….
homogenous
limits diffs in conduction velocity across fibres leading to high degree of temporal coherence
homogeniety of type I fibres is important for
discrimination of complex sounds (speech) - and timing
variation in fibre size (and thus conduction velocity) inc w age, may explain some hearing probs not directly related to elevation of pure tone threshold
type II fibres innervate… what percentage of fibres are type II… where do they project…. function?
OHCs
1-5%
they project mostly to the dorsal cochlear nucleus (DCN); function is relatively unknown
one to many innervation =
type II fibres
many to one innervation =
type I fibres
cochlear nerve fibres terminate in the
ipsilateral cochlear nuclei
from the dorsal cochlear nuclei, the cochlear nerve mainly projects to …
the contralateral inferior colliculus by way of the lateral lemniscus
some cochlear nerve fibres travel to…. why?
facial motor nucleus and trigeminal motor nucleus
acoustic reflex and ossicular chain dampening
cochlear nuclei from left and right sides of the brainstem are _____ - most ____ connection
connected
peripheral
cochlear nuclei from L and R sides being connected allows for …..
bilateral pathways ensure redundancy of auditory info in the event of disease or damage
superior olivary complex is a ______ in the _____, where….
nucelus in medulla
only some fibres of the cochlear nerve synapse in this medullary nucleus before forming the LL
superior olivary complex receives bilateral input from _____ : it is the first group of neurons to… how?
cochlear nuclei
first group of neurons to integrate info from both ears; involved in directional hearing
compares arrival time of neural activity from 2 ears
compares intensity diffs from 2 ears
nuclei of SOC comprise some of the most…
complicated parts of the ascending pathways; largest inter-species variation
inferior colliculus …
a midbrain relay nucleus, where all ascending auditory info is channeled
caudal to superior colliculus
Lateral lemniscus fibres synpase in the
inferior colliculus
left IC and right IC are ….
connected - important communication for directional hearing based on diffs in sound intensity bw the 2 ears
medial geniculate body …
thalamic auditory relay nucleus
all fibres from the ICC are interrupted by the MGB
no connections bw left and right MGB
how is the non-classical ascending pathway diff from the classical
its a diffuse sys
not as clearly organized anatomically
receives input from other sensory systems
in non-classical pathway, the inferior colliculus synapses w the …. why?
superior colliculus
to coordinate eye movements and other motor responses to auditory stimuli that are important for directional hearing
neurons in non-classical ascending pathway respond to both… how is it diff to classical?
sound and other sensory stimuli such as touch and light
neurons in classical auditory pathway, up to and including the AI cortex, respond to sound stimulation
descending fibres are ____ abundant as ascending fibres, but…
abundant
much less is known about them
corticofugal descending pathway central part originates from
auditory cerebral cortex
olivocochlear descending pathway is from the ____ and ____ to _____ and ____
auditory cortex and SOC
to cochlear nuclei and cochlea
olivocochlear is a _____ auditory pathway, influences ability of ….
efferent
OHCs to amplify the motion of the basilar membrane
3 ways to test CN VIII
pure tone audiometry = detection of various sound freq
otoacoustic emissions = sounds produced by inner ear (spontaneous vs evoked)
evoked auditory brainstem responses = evoked potentials recorded in response to sounds
