Posture and Balance

Question 1

What systems contribute to posture and balance? (3)

Answer 1

• Vestibular system
• Visual system
• Somatosensory system (proprioception)

Question 2

What are the structural features of the vestibular system involved in posture and balance? (2)

Answer 2

• Semicircular canals (x3)

- Vestibule (contains utricle and saccule)

Question 3

What nerve is involved with balance in the vestibular system?

Answer 3

Vestibular branch of the vestibulocochlear nerve (VIII).

Question 4

What nerves is the vestibular branch composed of? (3)

Answer 4

• Utricular nerve
• Saccular nerve
• Ampullary nerve

Question 5

How many degrees of freedom are there in vestibular navigation?

Answer 5

6 degrees of freedom.

-3 translational, 3 rotational

Question 6

What are the translation degrees of freedom? (3)

Answer 6

X, y and z.

Question 7

What is translational motion and linear acceleration detected by?

Answer 7

Utricle and saccule.

Question 8

What are the rotational degrees of freedom? (3)

Answer 8

• Roll (around x)
• Pitch (around y)
• Yaw (around z)

Question 9

What is rotational motion and angular acceleration detected by?

Answer 9

Semicircular canals.

Question 10

What are the main sensory detectors of the utricle and saccule?

Answer 10

Maculae.

Question 11

What does the macula contain?

Answer 11

Matrix of cells surrounding hair cells innervated by utricular and saccular nerves.

Question 12

What structures do the hair cells contain that provide information about movement?

Answer 12

• Multiple cilia

- 1 kinocilium

Question 13

What do the cilia penetrate into?

Answer 13

The otolithic membrane.

-gelatinous calcium carbonate crystals

Question 14

What is the effect of bending of the cilia and kinocilium?

Answer 14

Bending of cilia towards kinocilium&raquo_space; increased firing in nerve&raquo_space; DEPOLARISATION.
Bending of cilia away from kinocilium&raquo_space; decreased firing in nerve&raquo_space; HYPERPOLARISATION.

Question 15

What sort of ion channels do hair cells contain?

Answer 15

K+ channels.

-mechanoreceptors

Question 16

What happens when the K+ channels are distorted?

Answer 16

K+ channels become activated
» activation of VG Ca channels
» glutamate release.

Question 17

What is the macula activated by?

Answer 17

Head tilting.

Question 18

What does the macula provide information about? (2)

Answer 18

• Static equilibrium

- Dynamic equilibrium

Question 19

What is static equilibrium?

Answer 19

Position of head relative to horizontal.

-sensitivity

Question 20

What is dynamic equilibrium?

Answer 20

Linear acceleration / deceleration.

Question 21

What planes are the maculae orientated in?

Answer 21

UTRICLE – horizontal.
SACCULE – vertical.

Opposing directions&raquo_space; better sensitivity.

Question 22

What are the utricle and saccule also known as collectively?

Answer 22

Otolith organs.

Question 23

What do the otolith organs provide information about? (3)

Answer 23

• Head tilting
• Gravity
• Linear acceleration

Question 24

What are the main functional features of the semicircular canals?

Answer 24

• Main sensory structure is localised to AMPULLA

- Canal on both sides of head work in pairs

Question 25

What do the semicircular canals provide information about? (2)

Answer 25

- Rotational movements | - Angular acceleration

Question 26

What are the semicircular canals filled with?

Answer 26

Endolymph.

Question 27

What is an ampulla?

Answer 27

Bulge at base of semicircular canal. | -location of main sensory structures

Question 28

What is a cupula?

Answer 28

Gelatinous membrane in ampulla containing sensory processes. - hair cells and cilia - forms barrier against endolymph flow

Question 29

What nerve innervate hair cells in the semicircular canals?

Answer 29

Ampullary nerve. | -from CNVIII

Question 30

How does head rotation lead to nerve impulses?

Answer 30

``` Head rotation >> endolymph inertia (lags behind) >> cupula bends in opposite direction to rotation >> distortion of cilia >> excites / inhibits sensory nerves. ```

Question 31

Why are the semicircular canals arranged in pairs?

Answer 31

Allows for comparison (pull-push mechanism). - 1 side depolarised, 1 side hyperpolarised - greater sensitivity

Question 32

What nerve do sensory afferents of the vestibular pathways run in?

Answer 32

Vestibulocochlear nerve (CNVIII).

Question 33

Where do sensory afferents from the otolith organs (utricle and saccule) project to?

Answer 33

Lateral nucleus.

Question 34

Where do the efferents from the otolith organs (utricle and saccule) project to?

Answer 34

From lateral nucleus >> cerebellum and limb motor neurons. | -maintain upright body posture

Question 35

Where do sensory afferents from the semicircular canals project to?

Answer 35

Medial nucleus.

Question 36

Where do the efferents from the semicircular canals project to?

Answer 36

From medial nucleus >> neck motor neurons and extraocular nerves (III, IV, VI). -orientate head and stabilise retinal image

Question 37

What is a major function of the vestibular system?

Answer 37

To maintain forward vision during head movements.

Question 38

What enables you to maintain forward vision during head movements?

Answer 38

Vestibulo-ocular reflex (VOR). | -involves semicircular canals and extraocular muscles

Question 39

What is nystagmus?

Answer 39

Rapid involuntary eye movements. - travel slowly in one direction then rapidly flick in opposite direction - e.g. when spinning

Question 40

What is rightwards nystagmus?

Answer 40

Eyes track slowly to the left then rapidly flick to the right.

Question 41

What is caloric testing?

Answer 41

Lie patient down and irrigate ear with warm / cold water >> convection currents in endolymph. - WARM >> increased firing - COLD >> decreased firing

Question 42

What diseases affect the vestibular system? (5)

Answer 42

- Meniere’s syndrome - Benign paroxysmal positional vertigo - Ototoxicity - Vestibular neuritis / brainstem carcinoma / infarction / haemorrhage - Medulloblastoma

Question 43

What is Meniere’s syndrome?

Answer 43

Increased endolymph volume and membranous labyrinth rupture. | >> earache, tinnitus, dizziness, falls

Question 44

What is benign paroxysmal positional vertigo?

Answer 44

Calcium carbonate crystals dislodged from otoliths. | -movement in canal >> illusion of movement and dizziness

Question 45

What is ototoxicity?

Answer 45

Damage due to drugs / chemicals. | >> damage of vestibulocochlear nerve

Question 46

What is medulloblastoma?

Answer 46

Childhood tumour growth in cerebellum. -unable to use lateral vestibular information from otoliths >> postural instability

Question 47

What do vestibular neuritis / brainstem carcinoma / infarction / haemorrhage lead to?

Answer 47

Disrupted postural control secondary to vestibular system damage.