Lecture 5 Flashcards
Vestibular System
The vestibular system is a sensory
system located in:
the inner ear
The vestibular system processes sensory information underlying (3):
➢ Motion
➢ Head position
➢ Spatial orientation relative to gravity
The vestibular system is responsible for
the body’s equilibrium
The vestibular system is responsible for
the body’s equilibrium; It helps to
stabilize
gaze, head, and postur
vestibular system uses specialized sensory neurons __ to transduce physical motion into
neural impulses.
hair cells
The vestibular labyrinth composed of two organs:
(1) Otolith organs (Utricle & Saccule)
(2) Semicircular canals (Superior, Posterior & Horizontal)
Otolith organs:
Utricle & Saccule
Semicircular canals:
Superior, Posterior & Horizontal
Vestibular hair cells:
Flask-shaped epithelial cells with a
bundle of hair-like processes
(STEROCILLIA) attached between each
other by a TIP LINK.
Vestibular hair cells: kinocillum:
the longest process
Hair cell is very sensible to
movement
Hair cell is very sensible to movement.
The movement changes
its membrane
potential
When the hairs (sterocillia) move toward
Kinocillum =
depolarization (excitation)
When the hairs (sterocillia) move far from the
Kinocillum =
hyperpolarization (inhibition)
When the sterocillia (hair bundle) is deflected toward
the kinocilium,
tip links are stretched and directly
open K+
-selective channels near the tips of the
stereocilia, allowing K+ to flow into the hair cell and
depolarize the hair cell.
The resulting depolarization of the hair cell
opens Ca2+
channels in the cell body, allowing Ca2+ entry and
release of neurotransmitter to excite the post–synaptic
neuron (vestibular nerve) and the electrical signal is
sent to the brain.
the hair cell (receptor) is ___ to
the nerve.
not directly attached
2 otolith organs:
(1) utricle and
(2) saccule
Each otolith organ contains (3) :
(1) Macula
(2) Gelatinous layer
(3) Otolithic membrane
Macula:
sensory epithelia containing
the soma (cell body) of hair cells and
supporting cells,
Gelatinous layer:
containing hair
bundles
Otolithic membrane
Fibrous layer
embedding ‘Otoconia’: crystals of
calcium carbonate (ear rocks, stones).
Otoconia
crystals of
calcium carbonate (ear rocks, stones)
Otolith organs detect __ movements
linear
Otolith organs detect linear movements:
(1) Translational movements of the head (i.e., forward & backward movements)
(2) Static head movement relative to the gravitational axis (i.e., head tilts)
The otoconia (ear rocks) make
the otolithic membrane heavier than the
structures and fluids surrounding it.
When the head tilts or moves, gravity causes the otolithic membrane to
shift relative to the macula. The hairs in the gelatinous layer are
displaced and a receptor potential is generated.
The utricle is positioned
horizontally
The utricle detects:
the horizontal translational movements of the head
(i.e., moving forward or backward = moving in X axe):
➢ e.g., walking, being in a moving car.
The saccule is positioned
vertically
The saccule detects
the vertical translational movements of the head
(i.e., moving up & down = moving in Y axe):
➢ e.g., being in a moving elevator.
Semicircular canals
Fluid-filled tubes specialized for
responding to rotations of the
head.
3 semicircular canals:
(1) Horizontal
(2) Superior
(3) Posterior
Horizontal semicircular canal:
turning left & right (No sign)
superior semicircular canal:
nodding up & down (Yes sign)
posterior semicircular canal:
tilting to a side (towards the shoulders)
Semicircular canals: AMPULLA:
an enlargement at the base of each
semicircular canal. It houses the hair cells.
Semicircular canals: the hair bundles extend out into a gelatinous mass,
the cupula
semicircular canals: endolymph fluid:
circulates in the
semicircular canal.
semicircular canals: the rotation of the head causes the movement of the:
endolymph fluid in the
opposite direction of the head movement,
which pushes the cupula and displaces the
hair bundles. As a result, the hair cell is
depolarized and receptor potential is
generated, the electrical signal sent to the
brain.
Each semicircular canal works in
opposite manner with its pair
located on the other side of the
head
A tilt of the head to one side
(e.g. right) activates the hair
cells in the
right horizontal
canal but inhibits the hair cells
in the left horizontal canal
slide 14 15
The Vestibulo-Ocular
Reflex (VOR) produces
eye
movements that counter
head movements (i.e.,
moving the eyes in opposing
direction to the head), thus
permitting the gaze to
remain fixed on a particular
point:
