L18: posture and balance Flashcards
which type of muscles are very active in postural control
extensor muscles
what brain structure is the most important for posture maintenance
brainstem
3 main sensory systems for balance
- somatosensory receptors
- visual system
- vestibular system
4 descending tracts originating in the brainstem for controlling posture
- vestibulospinal tract
- tectospinal tract
- potine reticulospinal tract
- medullary reticulospinal tract
what does ventromedial pathways control
axial or proximal trunk muscles
dorsolateral pathways control
fine muscle control
where are posture motor neurons innervating axial or proximal muscles located in the spinal cord
medially
where are voluntary movements affecting distal musculature located in the spinal cord
laterally
3 ventromedial tracts
- tectospinal
- vestibulospinal
- pontine reticulospinal
2 dorsolateral tracts
- corticospinal
- rubicospinal
function of vestibulospinal and tectospinal tracts
keep head balanced on shoulders as body moves
where does vestibulospinal receive input from
vestibular labyrinth in inner ear
where does vestibulospinal orginate from
vestibular nuclei in medulla
where does tectospinal receive input from
- retina of eye
- auditory informaiton
where does tectospinal originate from
superior colliculus (optic tectum)
what does tectospinal response lead to
direction of head and eyes to a particular location in space
where do pontine and medullar reticulospinal tracts originate from
reticular formation (controlled by inputs from the cerebellum and cortex)
what does pontine reticulospinal do
enhances antigravity reflexes of the spinal cord –> extensors of lower limb to maintain standing
what does medullary reticulospinal do
liberates antigravity muscles (opposite to pontine tract)
what happens in humans with extensive cortical damage and why
increased extensor tone bc of the brainstem action
where is the vestibular system located
inner ear
what is cranial nerve 8
vestibulocochlear
what do the otolith organs detect
force of gravity and tilts of head (linear acceleration)
what do semicircular canals detect
head rotation and angular acceleration
in both the otolith organs and semicircular canals what converts motions into neural signals
hair cells
2 parts of the otolith organs
utricle and saccule
what is the macula (same in utricle and saccule)
matrix of supporting cells and hair cells that are innervated by sensory nerve fibers
what part of the hair cells penetrates into the gelatinous cap
cilia
what do cilia sense
back and forth movement of the cap
what are otoliths
calcium carbonate crystals that encrust the surface of the gelatinous gap
what is the function of otoliths
act as weights that are sensitive to gravity and weigh down the cap
what happens to the gelatinous cap when head is titled down
the cap bends the cilia downwards which can covert the signal to a neural signal
2 types of cilia
- kinocilium
- stereocilia
what happens when hair cells are bent so that the stereocilia bend towards the kinocilium
depolarisation (more cell firing)
what happens when you bend the hair cells away from the kinocilium
hyperpolarization (less cell firing)
difference between utricle and saccule
the macula is horizontal in the utricle but vertical in the saccule
what does a horizontal macula mean (e.g in utricle)
orientation of hair cells towards the striola (midline)
what does a vertical macula mean (e.g in saccule)
kinocilia away from striola
firing pattern of the vestibular nerve
tonically (all the time)
what type of movement does utricular macula encode
horizontal linear motion/ acceleration
what type of movement does saccular macula encode
vertical linear motion/ acceleration
how many semicircular canals
3 - anterior, posterior and horizontal
what are semicircular canals filled with
endolymph
what else is filled with endolymph
cochlea
where in the canal are the main sensory structures located
ampulla
what sits inside the ampulla
cupula
what is embedded into the cupula
cilia hair cells
what can move the cilia hair cells in the cupula
endolymph in the ampulla
where does the vestibular branch of CN8 send projections to
vestibular nuclei in brainstem
where does the lateral vestibular nucleus communicate with
cerebellum
where does the medial vestibular nucleus communicate with
extraocular muscles
what is the vestibular ocular reflex (VOR)
compensatory movement of the eyes in the opposite direction of head rotation
function of VOR
maintains stable vision during head movements
if head moves the the left what semicircular canal is activated
left horizontal
when head moves to the left what CN and muscles does the left semicircular canal trigger (eye turns to right)
- right abducens flexes right lateral rectus
- left oculomotor nerve flexes left medial rectus
does VOR work in the dark
yes
what is caloric testing for
brainstem function
in normal caloric testing what happens
ear irrigated with water means eye moves towards that ear
in a brain stem lesion what happens with caloric testing
no VOR present (no eye movement)
what does activation of the medial vestibular nucleus do
sends signals to cervical spinal cord –> regulates head position by reflex
what does activation of the lateral vestibular nucleus do
activates proximal muscles to regulate trunk and limbs
what happens in the positive supporting reaction
placing a limb on the ground will initiate a set of reflexes to stiffen the limb (extensor leg muscles)
Meniere’s syndrome=
increase in volume of endolymph disrupting membranous labryrinth
symptoms of meniere’s syndrome
temporary attacks of vertigo, deafness and tinnitus
what does prochlorperazine do
relieves severe vomiting/ nausea
what causes benighn paroxysmal positional vertigo (BPPV)
calcium carbonate crystals dislodged from otolith organs disrupting flow of endolymph in semicircular canals
symptoms of BPPV
suddenly feeling dizzy on moving head in one direction, nausea and vomiting
what is migraine associated vertigo
attack of vertigo that may be accompanied by migraine symptoms
in VOR what tract can be damaged to cause 1 eye dysfuction
medial longitudinal fasiculus
