POSTURE AND BALANCE Flashcards
what is posture?
the relative position of the various parts of the body with respect to one another, the environment and to gravity
what is postural equilibrium?
a state in which all forces acting on the body are balanced
outline the postural system?
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
what are the 4 main descending tracts that maintain postural control?
vestibuluspinal tract
tectospinal tract
pontine reticulospinal tract
medullary reticulispinal tract
whats the function of the vestibulospinal tract?
to keep the head balanced on the shoulders as the body moves
outline the course of the vestibulospinal tract?
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
whats the function of the tectospinal tract?
turning head towards visual stmulus
outlien the course of the tectospinal tract?
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
whats the function of the reticulospinal tract?
preparatory and movement-related activities, postural control, and modulation of some sensory and autonomic functions.
whats the difference in function between pontine and medullary reticulospinal tracts?
pontine - inhibits limb flexors and stimulates extensors
medullary - inhibits limb extensors and stimulates flexors
what is decerebrate rigidity?
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
whats the fucntion of the vestibular system?
sense of ballance
allows us to detect motion
provides information about head orientation
what is within the vestibular system?
vestibule and semicircular canals
whats within the vestibule of the ear?
otolith organs
whats the function of the otolith organs?
to detect force of gravity and tilts of the head
whats the function of semicircular canals?
detecting head rotation - helps balance you
what are the 2 otolith organs?
utricle and saccule
what do the utricle and saccule detect?
linear acceleration and whether or not your head is in its proper orientation
how do the utricle and saccule work?
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
whats the function of semicircular canals?
providing information about rotational and angular movements to maintain balance
what are the 3 semicircular canals?
anterior, posterior and horizontal semicircular canals
what pushes the hair cells within the semicircular canals?
endolymph flows with rotation of the head
what haooens when hair cells depolarise?
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
whats the difference in function between medial and lateral vestibular nuclei?
medial - sends info to extraocular motor neurones and neck motor neurones
lateral - sends info to cerebellum and limb motor neurones
what is the vestibulo-occular reflex?
ensures best vision during head motion by moving the eyes contrary to the head to stabilize the line of sight in space.
outline how the vestibulo-ocular reflex works?
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
why does the vestibule-ocular reflex work even in the dark or when your eyes are closed?
it doesnt require visual input because its vestibular system based
what happens if the vestibulo-ocular reflex doesnt work?
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.
why do we test the vestibulo-ocular reflex?
it checks for brainstem function in patient
how do we test for the vestibulo-ocular nerve?
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
what would you see in caloric testing if the brainstem is intact?
eye movement
what would you see in caloric testing if there was a bilateral medial longitudinal fasciculus lesion?
movement in only 1 eye
what would you see in caloric testing if there is a low brainstem lesion?
no eye movement
outline the reflexes that occur when you trip?
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
what is anticipatory postural control?
the activation of postural muscles in a feedforward manner before a voluntary movement begins, in anticipation of the destabilizing forces caused by the movement.
what is vestibular plasticity?
postural reflexes adapt in order to optimise performance
what is menieres syndrome?
a sudden increase in volume of endolymph which disupts the function in the membranous labyrinth of inner ear
what are the symptoms of menieres syndrome?
temporary attacks of vertigo, deafness and tinnitus, sense of fullness in ear
what causes benign paroxysmal positional vertigo?
calcium carbonate crystals dislodging from otolith organs, disrupting the flow of endolymph which stimulates hair cells and causes dizziness
what are the symptoms of benign paroxysmal positional vertigo?
suddenly feeling dizzy on moving head in certain direction, nausea, vomiting
whats the treatment for benign paroxysmal positional vertigo?
epley or semont maneouvre to reposition the calcium carbonate crystals
what is migraine associated vertigo?
attacks of vertigo that may or may not be accompanied with usual migraine symptoms such as headaches and photosensitivity
