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Problem #9 Balance
THE VESTIBULAR SYSTEM
● Contributes to the perception of self-motion, head position and spatial orientation relative
to gravity
● Stabilizing gaze, head and posture
● Peripheral portion → inner ear
○ Reports info about the motions and positions of the head and body to enters in the
brainstem, cerebellum and somatic sensory cortices
● Vestibular nuclei = makes connections with brainstem and cerebellar structures
○ Innervates mature neurons controlling extraocular, cervical and postural muscles
■ Stabilize eye gaze, head orientation and posture
THE VESTIBULAR LABYRINTH
● Labyrinth = main component of the vestibular system
○ Interconnected chambers
● Acceleration = a part of any motion that involves a change in speed or direction
○ Linear acceleration → when you speed up or slow down in a car that's
moving
○ Acceleration around a turn because of the change in direction
○ Without info about acceleration → you would lose balance and fall
● Motions transduce from head movement, inertial effects due to gravity, and ground-borne
vibrations
● Vestibular system = the sense organs used to produce neural signals carrying info about
balance and acceleration
○ The neural signals come from hair cells
○ Adjacent to the cochlea
● The cochlear and vestibular spaces are joined
○ Filled with fluid → endolymph
● Between the bony walls and the membranous labyrinth is another fluid → perilymph
○ Similar to cerebrospinal fluid
● Includes semicircular canals = three perpendicular hollow curves tubes in the skull
○ Signal head rotation, respond to rotational accelerations of the head
○ At the base, contains the ampulla = the vestibular hair cells are in the utricle and
saccule in three swellings called ampulla
○ The ampulla is next to the utricle
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■ The cristae contains the hair cells, with the hair cells enclosed in a
gelatinous cap called the cupula
● In each ampulla, the vestibular hair cells extend their hair bundles into the
endolymph of the membranous labyrinth
○ The endolymph selectively bathes the hair cell bundle while remaining
separate from the perilymph
Vestibular Hair Cells
● Transduce minute displacements into receptor potentials
● Movement of the stereocilia opens transduction channels at the tips of the stereocilia
○ Depolarizes the cell → causes neurotransmitter release
● Movement away from the stereocilia → closes the channels and hyperpolarizes the
hair cell
○ This reduces vestibular nerve activity
● Some transduction channels are open in the absence of stimulation
○ Hair cells release transmitter are generates activity in the vestibular nerve fibers
■ The firing rate can increase and decrease in a way that mimics receptor
potentials produced by hair cells
● The hair cell bundles have specific orientations
○ The organ is responsive to displacements in all directions
● In a given semicircular canal → hair cells in the ampulla are polarized in the same way
● Striola = divides the hair cells into two populations with opposing polarities
○ In the utricle and saccule
THE OTOLITH ORGANS
● Otolith organs = consist of the utricle and the saccule
○ Signal when the head is undergoing linear acceleration or being held in a tilted
position
○ Contain structure with hair cells called a macula = consists of hair cells and
associated supporting layers
■ In each macula → hair cells are oriented in different directions
● The hair cells are embedded in a gelatinous layer topped by tiny crystals called otoconia
○ Crystals make the membrane heavier
■ So when the head tilts, gravity causes the membrane to shift
■ The shearing motion between the macula and otolithic membrane
displaces the hair bundles and this generates an action potential
● When the head is held in a tilted position →
○ Gravity pulls on the otoconia in a different direction than when the head is upright
■ This pull causes the otoconia to drag on the gelatinous layer in the macula
Problem #9 Balance
THE VESTIBULAR SYSTEM
● Contributes to the perception of self-motion, head position and spatial orientation relative
to gravity
● Stabilizing gaze, head and posture
● Peripheral portion → inner ear
○ Reports info about the motions and positions of the head and body to enters in the
brainstem, cerebellum and somatic sensory cortices
● Vestibular nuclei = makes connections with brainstem and cerebellar structures
○ Innervates mature neurons controlling extraocular, cervical and postural muscles
■ Stabilize eye gaze, head orientation and posture
THE VESTIBULAR LABYRINTH
● Labyrinth = main component of the vestibular system
○ Interconnected chambers
● Acceleration = a part of any motion that involves a change in speed or direction
○ Linear acceleration → when you speed up or slow down in a car that's
moving
○ Acceleration around a turn because of the change in direction
○ Without info about acceleration → you would lose balance and fall
● Motions transduce from head movement, inertial effects due to gravity, and ground-borne
vibrations
● Vestibular system = the sense organs used to produce neural signals carrying info about
balance and acceleration
○ The neural signals come from hair cells
○ Adjacent to the cochlea
● The cochlear and vestibular spaces are joined
○ Filled with fluid → endolymph
● Between the bony walls and the membranous labyrinth is another fluid → perilymph
○ Similar to cerebrospinal fluid
● Includes semicircular canals = three perpendicular hollow curves tubes in the skull
○ Signal head rotation, respond to rotational accelerations of the head
○ At the base, contains the ampulla = the vestibular hair cells are in the utricle and
saccule in three swellings called ampulla
○ The ampulla is next to the utricle
, 2
■ The cristae contains the hair cells, with the hair cells enclosed in a
gelatinous cap called the cupula
● In each ampulla, the vestibular hair cells extend their hair bundles into the
endolymph of the membranous labyrinth
○ The endolymph selectively bathes the hair cell bundle while remaining
separate from the perilymph
Vestibular Hair Cells
● Transduce minute displacements into receptor potentials
● Movement of the stereocilia opens transduction channels at the tips of the stereocilia
○ Depolarizes the cell → causes neurotransmitter release
● Movement away from the stereocilia → closes the channels and hyperpolarizes the
hair cell
○ This reduces vestibular nerve activity
● Some transduction channels are open in the absence of stimulation
○ Hair cells release transmitter are generates activity in the vestibular nerve fibers
■ The firing rate can increase and decrease in a way that mimics receptor
potentials produced by hair cells
● The hair cell bundles have specific orientations
○ The organ is responsive to displacements in all directions
● In a given semicircular canal → hair cells in the ampulla are polarized in the same way
● Striola = divides the hair cells into two populations with opposing polarities
○ In the utricle and saccule
THE OTOLITH ORGANS
● Otolith organs = consist of the utricle and the saccule
○ Signal when the head is undergoing linear acceleration or being held in a tilted
position
○ Contain structure with hair cells called a macula = consists of hair cells and
associated supporting layers
■ In each macula → hair cells are oriented in different directions
● The hair cells are embedded in a gelatinous layer topped by tiny crystals called otoconia
○ Crystals make the membrane heavier
■ So when the head tilts, gravity causes the membrane to shift
■ The shearing motion between the macula and otolithic membrane
displaces the hair bundles and this generates an action potential
● When the head is held in a tilted position →
○ Gravity pulls on the otoconia in a different direction than when the head is upright
■ This pull causes the otoconia to drag on the gelatinous layer in the macula
