POSTURE AND BALANCE

Question 1

what is posture?

Answer 1

the relative position of the various parts of the body with respect to one another, the environment and to gravity

Question 2

what is postural equilibrium?

Answer 2

a state in which all forces acting on the body are balanced

Question 3

outline the postural system?

Answer 3

visual system, vestibular system and somatosensory system all feed information to the cerebral cortex, cerebellum, brain stem and spinal cord which then send outputs via motor neurones which maintain posture and balance

Question 4

what are the 4 main descending tracts that maintain postural control?

Answer 4

vestibuluspinal tract
tectospinal tract
pontine reticulospinal tract
medullary reticulispinal tract

Question 5

whats the function of the vestibulospinal tract?

Answer 5

to keep the head balanced on the shoulders as the body moves

Question 6

outline the course of the vestibulospinal tract?

Answer 6

sensory input comes from the vestibular labyrinth in the inner ear
tracts then originate from vestibular nuclei in medulla and remain ipsilateral in the spinal cord , with the medial tract stopping at cervical region and lateral tract extending throughout the length of the spinal cord. The LMN the go on to innervate anti-gravity to muscles to help control balance and posture

Question 7

whats the function of the tectospinal tract?

Answer 7

turning head towards visual stmulus

Question 8

outlien the course of the tectospinal tract?

Answer 8

sensory input comes from the retina of the eye
tracts originate from superior colliculus in the midbrain and quicjly decussate and enter the spinal cord where it terminates at cervical levels. LMN innervate head, eye and neck muscles

Question 9

whats the function of the reticulospinal tract?

Answer 9

preparatory and movement-related activities, postural control, and modulation of some sensory and autonomic functions.

Question 10

whats the difference in function between pontine and medullary reticulospinal tracts?

Answer 10

pontine - inhibits limb flexors and stimulates extensors

medullary - inhibits limb extensors and stimulates flexors

Question 11

what is decerebrate rigidity?

Answer 11

a massive increase in the tone of extensor muscles caused by the disinhibition of brainstem nuclei e.g. in trauma or disease when there is extensive cortcal damage like cerebral malaria

Question 12

whats the fucntion of the vestibular system?

Answer 12

sense of ballance
allows us to detect motion
provides information about head orientation

Question 13

what is within the vestibular system?

Answer 13

vestibule and semicircular canals

Question 14

whats within the vestibule of the ear?

Answer 14

otolith organs

Question 15

whats the function of the otolith organs?

Answer 15

to detect force of gravity and tilts of the head

Question 16

whats the function of semicircular canals?

Answer 16

detecting head rotation - helps balance you

Question 17

what are the 2 otolith organs?

Answer 17

utricle and saccule

Question 18

what do the utricle and saccule detect?

Answer 18

linear acceleration and whether or not your head is in its proper orientation

Question 19

how do the utricle and saccule work?

Answer 19

they contains hair cells and these hairs sit within the otolithic membrane which has otoliths on top (these are calcium carbonate crystals that encrust the surface of the gelatinous cap, acting as a weight). if you change equilibirum, the otoliths can move back and forth which pulls the hairs. depending on which direction the hair moves, they will send different signals to your brain - if the stereocilia are bent towards the kinocilium we get depolarisaton and if they bend the other way we get hyperpolarisation

Question 20

whats the function of semicircular canals?

Answer 20

providing information about rotational and angular movements to maintain balance

Question 21

what are the 3 semicircular canals?

Answer 21

anterior, posterior and horizontal semicircular canals

Question 22

what pushes the hair cells within the semicircular canals?

Answer 22

endolymph flows with rotation of the head

Question 23

what haooens when hair cells depolarise?

Answer 23

the neurones fire and send information down the vestibular branch of the vestibular cochlear nerve to the vestibular nuclei in the brain stem and then send information to the cerebellum

Question 24

whats the difference in function between medial and lateral vestibular nuclei?

Answer 24

medial - sends info to extraocular motor neurones and neck motor neurones
lateral - sends info to cerebellum and limb motor neurones

Question 25

what is the vestibulo-occular reflex?

Answer 25

ensures best vision during head motion by moving the eyes contrary to the head to stabilize the line of sight in space.

Question 26

outline how the vestibulo-ocular reflex works?

Answer 26

the person rotates their head and endolymph moves in the opposite direction which deflects the cupula and hair cells, triggering an action potential. These axons form the vestibular branch of vestibulo-cochlear nerve. This cause info to be sent to vestibular nuclei in the brain stem which stimulates occullomotor nuclei which control extraoccular muscles via CN3 = moves eyes at the same time it sends a branch to the abducens nerve which turns the opposing eye the other way

Question 27

why does the vestibule-ocular reflex work even in the dark or when your eyes are closed?

Answer 27

it doesnt require visual input because its vestibular system based

Question 28

what happens if the vestibulo-ocular reflex doesnt work?

Answer 28

corrective eye movements are not made which gives a disconcerting feeling that the world is moving as the head moves which can make standing, walking, maintaining posture etc very difficult.

Question 29

why do we test the vestibulo-ocular reflex?

Answer 29

it checks for brainstem function in patient

Question 30

how do we test for the vestibulo-ocular nerve?

Answer 30

caloric testing - irrigating the ear with warm water which causes convection currents in the endolymph which distorts the capula and hair cells which increases firing and causes the reflex

Question 31

what would you see in caloric testing if the brainstem is intact?

Answer 31

eye movement

Question 32

what would you see in caloric testing if there was a bilateral medial longitudinal fasciculus lesion?

Answer 32

movement in only 1 eye

Question 33

what would you see in caloric testing if there is a low brainstem lesion?

Answer 33

no eye movement

Question 34

outline the reflexes that occur when you trip?

Answer 34

as you trip, semicircular canals and otolith organs sense a change in balance and actvate the medial vestibular nucleus causing dorsal flexion of the neck, pulling the head up. axons from the lateral vestibular nucleus activates proximal muscles which regulates the trunk and limbs

Question 35

what is anticipatory postural control?

Answer 35

the activation of postural muscles in a feedforward manner before a voluntary movement begins, in anticipation of the destabilizing forces caused by the movement.

Question 36

what is vestibular plasticity?

Answer 36

postural reflexes adapt in order to optimise performance

Question 37

what is menieres syndrome?

Answer 37

a sudden increase in volume of endolymph which disupts the function in the membranous labyrinth of inner ear

Question 38

what are the symptoms of menieres syndrome?

Answer 38

temporary attacks of vertigo, deafness and tinnitus, sense of fullness in ear

Question 39

what causes benign paroxysmal positional vertigo?

Answer 39

calcium carbonate crystals dislodging from otolith organs, disrupting the flow of endolymph which stimulates hair cells and causes dizziness

Question 40

what are the symptoms of benign paroxysmal positional vertigo?

Answer 40

suddenly feeling dizzy on moving head in certain direction, nausea, vomiting

Question 41

whats the treatment for benign paroxysmal positional vertigo?

Answer 41

epley or semont maneouvre to reposition the calcium carbonate crystals

Question 42

what is migraine associated vertigo?

Answer 42

attacks of vertigo that may or may not be accompanied with usual migraine symptoms such as headaches and photosensitivity