Spatial Orientation and the Vestibular System

Question 1

Vestibular system:

Answer 1

The set of five organs—three semicircular canals
and two otolith organs—located in each inner ear that sense head motion
and head orientation with respect to gravity.

Question 2

Vestibular system is also called the:

Answer 2

“vestibular labyrinth”

Question 3

Why do we say that vestibular system is often an overlooked sense?

Answer 3

An often overlooked sense:
* Evolutionarily very old
* Not one of the “five senses”

Question 4

Spatial orientation:

Answer 4

A sense comprised of three interacting sensory modalities: Our senses of linear motion, angular motion, and tilt

Question 5

Why considered different “modalities”? In regards to spatial orientation

Answer 5

Sensing linear motion, angular motion, and tilt involves
different receptors and/or different stimulation energy

Question 6

Otolith organs:

Answer 6

The mechanical structures in the vestibular system
that sense both linear acceleration and gravity

Question 7

Semicircular canals:

Answer 7

The three toroidal tubes in the vestibular system
that sense angular motion

Question 8

The three spatial orientation modalities:

Answer 8

1. Angular motion: Can be sensed when rotating head from side
   to side as if to say “no”.
2. Linear motion: Sensed when accelerating or decelerating in a
   car
3. Tilt: Can be sensed when nodding head up and down as if to
   say “yes”

Question 9

x-axis:

Answer 9

Points forward, in the direction the person is facing

Question 10

y-axis:

Answer 10

Points laterally, out of the person’s left ear

Question 11

z-axis:

Answer 11

Points vertically, out of the top of the head

Question 12

Axes are defined relative to:

Answer 12

the person, not relative to gravity

Question 13

Three directions for sense of rotation:

Answer 13

Roll, Pitch, Yaw

Question 14

Roll:

Answer 14

Rotation around x-axis.

Question 15

Pitch:

Answer 15

Rotation around y-axis.

Question 16

Yaw:

Answer 16

Rotation around z-axis.

Question 17

Linear motion

Answer 17

Movements represented in terms of changes in the x-, y-, and z-axes

Question 18

Any arbitrary linear motion can be represented as

Answer 18

a change along these
three axes

Question 19

Hair cells:

Answer 19

Support the stereocilia that transduce mechanical movement in the
vestibular labyrinth into neural activity sent to the brain stem. Act as
mechanoreceptors (pressure, vibration, movement

Question 20

Head motion causes hair cell stereocilia to

Answer 20

deflect, causing a change in hair cell
voltage and altering neurotransmitter release

Question 21

In the absence of stimulation, hair cells release neurotransmitter at

Answer 21

a constant
rate

Question 22

When hair cell bundles bend, change in hair cell voltage is proportional to:

Answer 22

the amount of deflection

Question 23

When hair cell bundles bend, change in hair cell voltage is proportional to the
amount of deflection, bending toward tallest stereocilia:

Answer 23

Depolarization

Question 24

When hair cell bundles bend, change in hair cell voltage is proportional to the
amount of deflection, Bending away from tallest stereocilia

Answer 24

Hyperpolarization

Question 25

each semicurcular canal is about

Answer 25

three-
fourths of a toroid (donut)
shape, measuring 15 mm long
and 1.5 mm in diameter

Question 26

semicircular canals are filled with a fluid called

Answer 26

perilymph

Question 27

A second __ is found inside the __ measuring 0.3 mm in diameter

Answer 27

A second, smaller toroid is
found inside the larger toroid,
measuring 0.3 mm in diameter

Question 28

smaller toroid is formed by a:

Answer 28

membrane filled with fluid called endolymph

Question 29

Cross section of each canal
swells substantially near where
the canals join the vestibule:

Answer 29

Ampulla

Question 30

Within the endolymph space of each ampulla is

Answer 30

the crista

Question 31

Cristae:

Answer 31

The specialized detectors of angular motion located in each
semicircular canal in a swelling called the ampulla.

Question 32

Each crista has about

Answer 32

7000 hair cells and associated
supporting cells and nerve fibers.

Question 33

Cilia of hair cells project into

Answer 33

a jellylike cupula that forms an
elastic dam extending to the opposite wall of the ampulla, with
endolymph on both sides of the dam

Question 34

When the head rotates, the inertia of the endolymph causes it to

Answer 34

lag behind, leading to tiny deflections of the hair cells

Question 35

__ semicircular canals in each ear

Answer 35

three

Question 36

each canal is oriented in:

Answer 36

a different plane

Question 37

Each canal is maximally sensitive to:

Answer 37

rotations perpendicular to the canal plane

Question 38

Hair cells in opposite ears respond in

Answer 38

a complementary fashion to each
other

Question 39

When hair cells in the left ear depolarize, those in the analogous structure
in the right ear

Answer 39

hyperpolarize

Question 40

In the absence of any rotation, many afferent neurons from the
semicircular canals have a resting firing rate of about

Answer 40

100 spikes/s.

Question 41

afferent neurons from the
semicircular canals have a _ firing rate relative to nerve fivers in other sensory systems

Answer 41

high

Question 42

Changes in firing rate are proportional to:

Answer 42

angular velocity of the head
aligned with the canal the neuron is in.

Question 43

Neural activity in semicircular canals is sensitive to

Answer 43

changes in rotation
velocity

Question 44

Constant rotation leads to __ from the canal neurons after a few seconds

Answer 44

decreased

Question 45

Canal afferent neurons are also
sensitive to

Answer 45

back and forth rotations
of the head

Question 46

Canal afferent neurons greates sensitivity to rotations at:

Answer 46

1 Hz or less (faster rotation than 1 Hz would be dangerous)

Question 47

firing rate (canal afferent neurons) goes ___ as the head rotates back and forth

Answer 47

up and down

Question 48

__ otolith organs in each ear

Answer 48

two

Question 49

Utricle contains about

Answer 49

30,000
hair cells.

Question 50

Saccule contains about

Answer 50

16,000 hair cells

Question 51

each otolith organ contains a

Answer 51

macula

Question 52

macula:

Answer 52

detector of linear acceleration and
gravity, sensitive primarily shear
forces.

Question 53

Hair cells are encased in a
gelatinous structure that contains
calcium carbonate crystals called

Answer 53

otoconia.

Question 54

Forces acting on the head result in
displacement of

Answer 54

the otoconia

Question 55

Larger accelerations (or larger
gravitational shear forces) move the
otolith organ’s otoconia __, this leads to

Answer 55

• Larger accelerations (or larger
  gravitational shear forces) move the
  otolith organ’s otoconia more.
• This leads to greater deflection of the hair
  cell bundles.

Question 56

(Coding of amplitude in the otolith organs)
Change in receptor potential is proportional to:

Answer 56

magnitude of linear
acceleration or gravitational shear

Question 57

At first, constant rotation (in the dark) is perceived

Answer 57

accurately

Question 58

Humans are so sensitive to ___ that we can detect movements of
less than _ degree per second.

Answer 58

Humans are so sensitive to yaw rotation that we can detect movements of
less than 1 degree per second.

Question 59

As yaw rotation frequency decreases, it takes ___ movement to be
detected.

Answer 59

faster

Question 60

• When people are passively translated in the dark, they are able to

Answer 60

use a
joystick to reproduce the distance they traveled quite accurately.