Semester B
Reviewed
name the sensory inputs that result in a sense of balance
vestibular system + vision + proprioception
describe the anatomy of the vestibular apparatus
inner ear, deep in petrous part of temporal bone, lateral/posterior to
cochlea = 3 semicircular canals (ant/lat/post) + 2 otolith organs
outer bony labyrinth = semicircular canals > apulla > ventricle + canal for
facial nerve > cochlea = perilymph inside (like ECF ie. high Na/low K)
inner membranous labyrinth = semicircular ducts > utricle > saccule >
ductus reuniens > cohlear ducts = endolymph inside (like ICF low Na/high
K)
pumps generates the conc gradient/membrane potential over the inner
membrane = greatest ~80mv at cochlea (fluids drained by endolymphatic
duct)
explain how hair cells respond to movement in semicircular canals and
otolithic organs and predict how directional movement increases or decreases
their firing rate
hair cells = sensory receptors in epithelial cell layer, polarised, I (chalice)
and II (cylindrical)
Semester B 1
, basal = glutamatergic synapse > tonic slow resting firing of primary
afferents to VC nerve
apical = 40-70 stereocilia (actin) on elastic cuticular plate (returns
sterocilia to position), getting shorter down axis of polarity, tallest =
kinocilium
top of lower connected to side of taller by tip links with
mechanotransducer ion channels - efferent input (ACh/CGRP) from
brainstem and myosin adjustment of tip link tension to control sensitivity
motion towards kinocilium > channels open > K influx from endolymph
(not AP) > depolarisation > VGCC open > NT release > inc firing down
CN8
motion away from kinocilium > channels close > hyperpolarisation > dec
firing
explain the different types of movement that the semicircular canals and
otolithic organs (saccule & utricle) respond to
1. semicircular ducts = angular/rotational acceleration
3 at 90 degrees = 3 axis directional info = v sensitive
ampullary crest = thickening of epithelia inside ampulla, topped with
gelatinous cupula embedded with hair cells all with axis in same direction
(towards utricle)
eg. head turns left > acceleration (not constant velocity) generates force >
shifts fluid in ducts to right > left side hair cells bend towards axis (fire) +
right side bend away (dec fire) = signals
dont detect linear as linear planes hit cupula from both sides so cancel out
otolith organs
2. utricle = static head tilt, linear acceleration
otoconia (calcium carbonate crystals) sit on top of gelatinous material =
otolith > otolithic membrane with sterocilia poking into otolith > soma of
hair cells embedded in thickened epithelium = macula (horizontal when
upright) > nerve fibres
Semester B 2
, cilia not all aligned but face TOWARDS curved landmark of striola
eg. head tilt to left/linear acceleration right > gravity drags otolithic mass
to left > shear causes left hair cells bend away from axis (dec fire) and
right side bend towards (fire)
frequent fluctuations = motion sickness
dont detect rotation as endolymph flow isnt strong enough to move heavy
mass
3. saccule = head position, vertical linear acceleration
as ^ but macula vertical when upright and cilia face AWAY from striola
list the connections of the vestibular nuclei and explain their relevance
CN8 (vestibulocochlear)
1. labyrinth > primary afferents (first axon) of bipolar vestibular ganglion >
other axon joins cochlear part to form CN8
2. CN8 through internal acoutus meatus and enters brainstem at
cerebellopontine angle
3. to ipsilateral nuclei in medulla (levels of inf cerebellar peduncle):
a) lateral vestibular nuclei = mainly from utricle(/saccule) > lateral
vestibulospinal/vestibulocerebellar to coordinate limb extensor/flexors for
balance
b) medial/superior vestibular nuclei = mainly from semicircular ducts >
medial vestibulospinal to innervate cervical (eg. neck extension on falling)
+ medial longitudinal fasciculus to CN3/4/6 nuclei to coordinate head/eye
movements (vestibuloocular reflex - head rotation rotates eyes in same
angle but opposite direction) + thalamus then motor cortex for conscious
perception of movement/space
5. also sends direct primary afferents to cerebellum (only sensory organ):
a) primary vestibulocerebellar fibres through juxtarestiform body and
medial inf cerebellar peduncle
b) to mossy fibres > fastigial nucleus
Semester B 3
, c) reciprocal connections with vestibular nuclei to regulate
head/eye/balance
provide a few examples for disorders that affect the vestibular system
assess with caloric test of warm water in ear
1. menieres disease
excess endolymph (endolymphatic hydrops) > distension of membranous
labyrinth > severe vertigo, nausea, nystagmus, progressive hearing loss,
tinnitus
2. benign positional vertigo
cupololithiasis = otoconia dislodged into posterior semicircular ducts >
movement causes abnormal fluid displacement = brief vertigo
3. acoustic neuroma/vestibular schwannoma
benign schwann cell tumour in C8 at cerebellopontine angle >
vestibular/hearing/cerebellar defects + facial palsy from CN7 compression
physics of auditory system
vibrations > pressure wave from source (sound) > transduced in ear into
neural signals > brain
frequency (Hz - cycle/s, humans 20-20000) = pitch = 1/T(period, time for
one full cycle)
amplitude (decibels, log ie. 60Db is 1millx 1Db) = volume
anatomy of external ear
elastic fibrocartilagenous pinna (helix, lobule, tragus) = collects sound and
discriminates direction
external auditory meatus (canal) = 2.5cm s shaped, air filled, first 1/3
cartilage then temporal bone, skin supplied by sensory from CN10
canal ends at concave (bulge out, shiny on light reflex test) tympanic
membrane (drum) lying at oblique angle, supplied by sensory from CN5
anatomy of middle ear
Semester B 4
Reviewed
name the sensory inputs that result in a sense of balance
vestibular system + vision + proprioception
describe the anatomy of the vestibular apparatus
inner ear, deep in petrous part of temporal bone, lateral/posterior to
cochlea = 3 semicircular canals (ant/lat/post) + 2 otolith organs
outer bony labyrinth = semicircular canals > apulla > ventricle + canal for
facial nerve > cochlea = perilymph inside (like ECF ie. high Na/low K)
inner membranous labyrinth = semicircular ducts > utricle > saccule >
ductus reuniens > cohlear ducts = endolymph inside (like ICF low Na/high
K)
pumps generates the conc gradient/membrane potential over the inner
membrane = greatest ~80mv at cochlea (fluids drained by endolymphatic
duct)
explain how hair cells respond to movement in semicircular canals and
otolithic organs and predict how directional movement increases or decreases
their firing rate
hair cells = sensory receptors in epithelial cell layer, polarised, I (chalice)
and II (cylindrical)
Semester B 1
, basal = glutamatergic synapse > tonic slow resting firing of primary
afferents to VC nerve
apical = 40-70 stereocilia (actin) on elastic cuticular plate (returns
sterocilia to position), getting shorter down axis of polarity, tallest =
kinocilium
top of lower connected to side of taller by tip links with
mechanotransducer ion channels - efferent input (ACh/CGRP) from
brainstem and myosin adjustment of tip link tension to control sensitivity
motion towards kinocilium > channels open > K influx from endolymph
(not AP) > depolarisation > VGCC open > NT release > inc firing down
CN8
motion away from kinocilium > channels close > hyperpolarisation > dec
firing
explain the different types of movement that the semicircular canals and
otolithic organs (saccule & utricle) respond to
1. semicircular ducts = angular/rotational acceleration
3 at 90 degrees = 3 axis directional info = v sensitive
ampullary crest = thickening of epithelia inside ampulla, topped with
gelatinous cupula embedded with hair cells all with axis in same direction
(towards utricle)
eg. head turns left > acceleration (not constant velocity) generates force >
shifts fluid in ducts to right > left side hair cells bend towards axis (fire) +
right side bend away (dec fire) = signals
dont detect linear as linear planes hit cupula from both sides so cancel out
otolith organs
2. utricle = static head tilt, linear acceleration
otoconia (calcium carbonate crystals) sit on top of gelatinous material =
otolith > otolithic membrane with sterocilia poking into otolith > soma of
hair cells embedded in thickened epithelium = macula (horizontal when
upright) > nerve fibres
Semester B 2
, cilia not all aligned but face TOWARDS curved landmark of striola
eg. head tilt to left/linear acceleration right > gravity drags otolithic mass
to left > shear causes left hair cells bend away from axis (dec fire) and
right side bend towards (fire)
frequent fluctuations = motion sickness
dont detect rotation as endolymph flow isnt strong enough to move heavy
mass
3. saccule = head position, vertical linear acceleration
as ^ but macula vertical when upright and cilia face AWAY from striola
list the connections of the vestibular nuclei and explain their relevance
CN8 (vestibulocochlear)
1. labyrinth > primary afferents (first axon) of bipolar vestibular ganglion >
other axon joins cochlear part to form CN8
2. CN8 through internal acoutus meatus and enters brainstem at
cerebellopontine angle
3. to ipsilateral nuclei in medulla (levels of inf cerebellar peduncle):
a) lateral vestibular nuclei = mainly from utricle(/saccule) > lateral
vestibulospinal/vestibulocerebellar to coordinate limb extensor/flexors for
balance
b) medial/superior vestibular nuclei = mainly from semicircular ducts >
medial vestibulospinal to innervate cervical (eg. neck extension on falling)
+ medial longitudinal fasciculus to CN3/4/6 nuclei to coordinate head/eye
movements (vestibuloocular reflex - head rotation rotates eyes in same
angle but opposite direction) + thalamus then motor cortex for conscious
perception of movement/space
5. also sends direct primary afferents to cerebellum (only sensory organ):
a) primary vestibulocerebellar fibres through juxtarestiform body and
medial inf cerebellar peduncle
b) to mossy fibres > fastigial nucleus
Semester B 3
, c) reciprocal connections with vestibular nuclei to regulate
head/eye/balance
provide a few examples for disorders that affect the vestibular system
assess with caloric test of warm water in ear
1. menieres disease
excess endolymph (endolymphatic hydrops) > distension of membranous
labyrinth > severe vertigo, nausea, nystagmus, progressive hearing loss,
tinnitus
2. benign positional vertigo
cupololithiasis = otoconia dislodged into posterior semicircular ducts >
movement causes abnormal fluid displacement = brief vertigo
3. acoustic neuroma/vestibular schwannoma
benign schwann cell tumour in C8 at cerebellopontine angle >
vestibular/hearing/cerebellar defects + facial palsy from CN7 compression
physics of auditory system
vibrations > pressure wave from source (sound) > transduced in ear into
neural signals > brain
frequency (Hz - cycle/s, humans 20-20000) = pitch = 1/T(period, time for
one full cycle)
amplitude (decibels, log ie. 60Db is 1millx 1Db) = volume
anatomy of external ear
elastic fibrocartilagenous pinna (helix, lobule, tragus) = collects sound and
discriminates direction
external auditory meatus (canal) = 2.5cm s shaped, air filled, first 1/3
cartilage then temporal bone, skin supplied by sensory from CN10
canal ends at concave (bulge out, shiny on light reflex test) tympanic
membrane (drum) lying at oblique angle, supplied by sensory from CN5
anatomy of middle ear
Semester B 4
