55 Vestibular system and postural control

Question 1

The vestibular apparatus in the inner ear includes the ____________ and the ______________.

Answer 1

Semicircular canals;

otolith organs

Question 2

Semicircular canals sense _____________, otolith organs sense ____________.

Answer 2

Head rotation/ rotational accelerations;

linear accelerations/ head translations (including static head orientation relative to gravity)

Question 3

Head rotation is sensed by _____________ in the ______ of the semicircular canal adjoining the utricle.

Answer 3

Hair cells; ampulla

Question 4

In the ampulla, hairs of the hair cells are embedded within _______________

Answer 4

a gelatinous diaphragm called the cupula

Question 5

_____________transduce mechanical stimuli into neural signals in the ear

Answer 5

Hair cells

Question 6

How does a neural signal of head rotation is detected?

Answer 6

During head rotation, cupula is displaced by movement of endolymph fluid inside the semicircular canal as the result of inertia.
Displacement of cupula also deflects hairs of hair cells, thus generating neural signals

Question 7

Hair of hair cells are arranged from short to long/ long to short.

Answer 7

short to long

Question 8

When hair cells bend to long side (from short to long), it will cause _____________.

Answer 8

depolarization

Question 9

When hair cells bend to short side (long to short), it will cause ______________.

Answer 9

hyperpoloarization

Question 10

Why the semicircular canals are sensitive to rotations in 3D place?

Answer 10

They sense rotations in the 3 planes that are perpendicular to one another.

Question 11

In the ___________, hair of hair cells project to the otolithic membrane (covered by CaCO3 particles, otoconia)

Answer 11

Utricle

not in ampulla

Question 12

_______________ is detected by the movement of otoconia relative to the epithelium of the utricle. This movement ______________.

Answer 12

Translational acceleration;

bends the hairs of the cell

Question 13

Utricle and saccule contains __________, for the sensation fo translational/linear acceleration.

Answer 13

otolith organ

Question 14

Utricle and saccule are cavities that link the ____________.

Answer 14

semicircular canals

Question 15

Hair cells in utricle and saccule are arranged in ______ direction for the detection of translational acceleration.

Answer 15

all

Question 16

In VOR, when the head turns to one side, the hair cells bend to the __________ side, and the vestibular nucleus on the __________ side increases firing.

Answer 16

ipsilateral;

ipsilateral

Question 17

What is the function of vestibular-ocular reflex?

Answer 17

Maintains steady vision by both exciting and inhibiting the appropriate eye muscles

Question 18

In VOR, when the left vestibular nucleus fires, the _________ abducens nucleus and the ___________occulomotor nucleus is excited. The eye is directed to/away from the head turning direction.

Answer 18

contralateral;
ipsilateral;
away from

Question 19

How can the vestibulo-ocular reflex be modulated to adapt to different situations?

Answer 19

Gain (output of strength) of VOR is modulated by the vestibulocerebellum.
Afferents:
1. visual error signals > inferior olivary nucleus (via climbing fibers to vestibulocerebellum)
2. vestibular nucleus > mossy fibers

Question 20

When eyeglasses worn for shortsightedness, how will the VOR gain change?

Answer 20

Smaller image > smaller VOR gain

Question 21

How do you define the direction of nystagmus?

Answer 21

By the direction of quick phase

Question 22

What is slow phase of eye movement?

Answer 22

Direction of eye movement for steady vision.

Question 23

How to VOR persistent head rotation leads to nystagmus?

Answer 23

1. Slow phase (direction of eye movement for steady vision)
2. Eyes reach limit of orbital range
3. Resetting eye movement in direction of head movement = quick phase

Question 24

What happens in left-beating nystagmus?

Answer 24

1. Head turn to the left
2. Slow phase: eyes move to right
3. Quick phase: eye moves to the left

Question 25

In pathological nystagmus, quick phase moves towards the ___________ side.

Answer 25

healthy (side with more firing from vestibular nucleus)

Question 26

If there is left-beating nystagmus, which side is lesioned?

Answer 26

right side

Question 27

State the 6 causes of nystagmus.

Answer 27

1. Persistent head rotation (merry-go-round)
2. Vestibular nerve damage (e.g. vestibular neuritis)
3. Vestibular nuclei lesion
4. Semicircular canal/ otolith organ damage
5. Vestibulocerebellum lesion
6. Blindness

Question 28

Vestibular system is important in maintaining posture equilibrium other than VOR. It provides ____________to external forces acting on body, for locomotion or other tasks.

Answer 28

active resistance
e.g. dominant external force: gravity
posture control: stand on unsteady surface of small base of support

Question 29

Which are the 2 main strategies of postural response?

Answer 29

1. Bring center of mass back over base of support

2. Widen base of support

Question 30

When bringing center of mass back over base of support, what pattern of muscle activation will be activated?

Answer 30

Hip flexors activated (when standing on a narrow beam)

Question 31

When widening the base of support, what pattern of muscle activation will be activated?

Answer 31

Ankle extensors activated (when standing on platform)

Question 32

Is spinal cord along enough to produce postural control/ generate motor responses for balance, why?

Answer 32

No, brainstem nuclei are actively involved in maintaining balance.

(can generate locomotor patterns but not postural control/balance)

Question 33

Brainstem contains circuitries that organize activations of the ________ and _______ muscles for maintenance of balance and postural regulation.

Answer 33

1. axial

2. proximal

Question 34

_________ and _________ work together with the cortex to maintain balance during voluntary movement (e.g. spinocerebellum receives input from pontocerebellar tract and send efferent to vestibular nuclei and thus vestibulospinal tract)

Answer 34

Vestibular nuclei and reticular formation

Question 35

Which 2 tracts are highly involved in maintaining balance and postural regulation? What are they responsible for respectively?

Answer 35

1. Medial vestibulospinal tract
   - Bilateral terminations regulating head position by activating neck muscles in response to head rotational signals
2. Lateral vestibulospinal tract
   - Ipsilateral projections for activating proximal muscles (limb extensors for resisting gravity)

Question 36

Briefly describe the brainstem circuitry when receiving signals from the semicircular canals and otolith organs for postural control.

Answer 36

Semicircular canals > Lateral/ Medial vestibular nuclei > Lateral/ medial vestibulospinal tract > cervical spinal cord > muscles for postural/ balance control

Question 37

What is the function of reticular formation in postural maintenance? What kind of RF is involved?

Answer 37

• provides feedforward, anticipatory motor commands
  (e. g. pull handle on wall> gastrocnemius contracts before biceps)
• Pontine and medullary reticular formation (> reticulospinal tract)

Question 38

Effects of biceps contraction anticipated by the motor system is a feedforward/feedback/inhibitory control.

Answer 38

feedforward

Question 39

What are the 2 routes from the motor cortical areas to the spinal cord for movement/posture? What is the significance?

Answer 39

1. Direct: to spinal cord innervating muscles for action (distal) by corticospinal tract
2. Indirect: via brainstem reticular formation > spinal cord: muscles for posture (axial/proximal)

• when the direct route is damaged, the indirect route will compensate