L18: posture and balance

Question 1

which type of muscles are very active in postural control

Answer 1

extensor muscles

Question 2

what brain structure is the most important for posture maintenance

Answer 2

brainstem

Question 3

3 main sensory systems for balance

Answer 3

1. somatosensory receptors
2. visual system
3. vestibular system

Question 4

4 descending tracts originating in the brainstem for controlling posture

Answer 4

• vestibulospinal tract
• tectospinal tract
• potine reticulospinal tract
• medullary reticulospinal tract

Question 5

what does ventromedial pathways control

Answer 5

axial or proximal trunk muscles

Question 6

dorsolateral pathways control

Answer 6

fine muscle control

Question 7

where are posture motor neurons innervating axial or proximal muscles located in the spinal cord

Answer 7

medially

Question 8

where are voluntary movements affecting distal musculature located in the spinal cord

Answer 8

laterally

Question 9

3 ventromedial tracts

Answer 9

• tectospinal
• vestibulospinal
• pontine reticulospinal

Question 10

2 dorsolateral tracts

Answer 10

• corticospinal

- rubicospinal

Question 11

function of vestibulospinal and tectospinal tracts

Answer 11

keep head balanced on shoulders as body moves

Question 12

where does vestibulospinal receive input from

Answer 12

vestibular labyrinth in inner ear

Question 13

where does vestibulospinal orginate from

Answer 13

vestibular nuclei in medulla

Question 14

where does tectospinal receive input from

Answer 14

• retina of eye

- auditory informaiton

Question 15

where does tectospinal originate from

Answer 15

superior colliculus (optic tectum)

Question 16

what does tectospinal response lead to

Answer 16

direction of head and eyes to a particular location in space

Question 17

where do pontine and medullar reticulospinal tracts originate from

Answer 17

reticular formation (controlled by inputs from the cerebellum and cortex)

Question 18

what does pontine reticulospinal do

Answer 18

enhances antigravity reflexes of the spinal cord –> extensors of lower limb to maintain standing

Question 19

what does medullary reticulospinal do

Answer 19

liberates antigravity muscles (opposite to pontine tract)

Question 20

what happens in humans with extensive cortical damage and why

Answer 20

increased extensor tone bc of the brainstem action

Question 21

where is the vestibular system located

Answer 21

inner ear

Question 22

what is cranial nerve 8

Answer 22

vestibulocochlear

Question 23

what do the otolith organs detect

Answer 23

force of gravity and tilts of head (linear acceleration)

Question 24

what do semicircular canals detect

Answer 24

head rotation and angular acceleration

Question 25

in both the otolith organs and semicircular canals what converts motions into neural signals

Answer 25

hair cells

Question 26

2 parts of the otolith organs

Answer 26

utricle and saccule

Question 27

what is the macula (same in utricle and saccule)

Answer 27

matrix of supporting cells and hair cells that are innervated by sensory nerve fibers

Question 28

what part of the hair cells penetrates into the gelatinous cap

Answer 28

cilia

Question 29

what do cilia sense

Answer 29

back and forth movement of the cap

Question 30

what are otoliths

Answer 30

calcium carbonate crystals that encrust the surface of the gelatinous gap

Question 31

what is the function of otoliths

Answer 31

act as weights that are sensitive to gravity and weigh down the cap

Question 32

what happens to the gelatinous cap when head is titled down

Answer 32

the cap bends the cilia downwards which can covert the signal to a neural signal

Question 33

2 types of cilia

Answer 33

- kinocilium | - stereocilia

Question 34

what happens when hair cells are bent so that the stereocilia bend towards the kinocilium

Answer 34

depolarisation (more cell firing)

Question 35

what happens when you bend the hair cells away from the kinocilium

Answer 35

hyperpolarization (less cell firing)

Question 36

difference between utricle and saccule

Answer 36

the macula is horizontal in the utricle but vertical in the saccule

Question 37

what does a horizontal macula mean (e.g in utricle)

Answer 37

orientation of hair cells towards the striola (midline)

Question 38

what does a vertical macula mean (e.g in saccule)

Answer 38

kinocilia away from striola

Question 39

firing pattern of the vestibular nerve

Answer 39

tonically (all the time)

Question 40

what type of movement does utricular macula encode

Answer 40

horizontal linear motion/ acceleration

Question 41

what type of movement does saccular macula encode

Answer 41

vertical linear motion/ acceleration

Question 42

how many semicircular canals

Answer 42

3 - anterior, posterior and horizontal

Question 43

what are semicircular canals filled with

Answer 43

endolymph

Question 44

what else is filled with endolymph

Answer 44

cochlea

Question 45

where in the canal are the main sensory structures located

Answer 45

ampulla

Question 46

what sits inside the ampulla

Answer 46

cupula

Question 47

what is embedded into the cupula

Answer 47

cilia hair cells

Question 48

what can move the cilia hair cells in the cupula

Answer 48

endolymph in the ampulla

Question 49

where does the vestibular branch of CN8 send projections to

Answer 49

vestibular nuclei in brainstem

Question 50

where does the lateral vestibular nucleus communicate with

Answer 50

cerebellum

Question 51

where does the medial vestibular nucleus communicate with

Answer 51

extraocular muscles

Question 52

what is the vestibular ocular reflex (VOR)

Answer 52

compensatory movement of the eyes in the opposite direction of head rotation

Question 53

function of VOR

Answer 53

maintains stable vision during head movements

Question 54

if head moves the the left what semicircular canal is activated

Answer 54

left horizontal

Question 55

when head moves to the left what CN and muscles does the left semicircular canal trigger (eye turns to right)

Answer 55

- right abducens flexes right lateral rectus | - left oculomotor nerve flexes left medial rectus

Question 56

does VOR work in the dark

Answer 56

yes

Question 57

what is caloric testing for

Answer 57

brainstem function

Question 58

in normal caloric testing what happens

Answer 58

ear irrigated with water means eye moves towards that ear

Question 59

in a brain stem lesion what happens with caloric testing

Answer 59

no VOR present (no eye movement)

Question 60

what does activation of the medial vestibular nucleus do

Answer 60

sends signals to cervical spinal cord --> regulates head position by reflex

Question 61

what does activation of the lateral vestibular nucleus do

Answer 61

activates proximal muscles to regulate trunk and limbs

Question 62

what happens in the positive supporting reaction

Answer 62

placing a limb on the ground will initiate a set of reflexes to stiffen the limb (extensor leg muscles)

Question 63

Meniere's syndrome=

Answer 63

increase in volume of endolymph disrupting membranous labryrinth

Question 64

symptoms of meniere's syndrome

Answer 64

temporary attacks of vertigo, deafness and tinnitus

Question 65

what does prochlorperazine do

Answer 65

relieves severe vomiting/ nausea

Question 66

what causes benighn paroxysmal positional vertigo (BPPV)

Answer 66

calcium carbonate crystals dislodged from otolith organs disrupting flow of endolymph in semicircular canals

Question 67

symptoms of BPPV

Answer 67

suddenly feeling dizzy on moving head in one direction, nausea and vomiting

Question 68

what is migraine associated vertigo

Answer 68

attack of vertigo that may be accompanied by migraine symptoms

Question 69

in VOR what tract can be damaged to cause 1 eye dysfuction

Answer 69

medial longitudinal fasiculus