Flashcards in Posture and Balance Deck (47):
What systems contribute to posture and balance? (3)
-Somatosensory system (proprioception)
What are the structural features of the vestibular system involved in posture and balance? (2)
-Semicircular canals (x3)
-Vestibule (contains utricle and saccule)
What nerve is involved with balance in the vestibular system?
Vestibular branch of the vestibulocochlear nerve (VIII).
What nerves is the vestibular branch composed of? (3)
How many degrees of freedom are there in vestibular navigation?
6 degrees of freedom.
-3 translational, 3 rotational
What are the translation degrees of freedom? (3)
X, y and z.
What is translational motion and linear acceleration detected by?
Utricle and saccule.
What are the rotational degrees of freedom? (3)
-Roll (around x)
-Pitch (around y)
-Yaw (around z)
What is rotational motion and angular acceleration detected by?
What are the main sensory detectors of the utricle and saccule?
What does the macula contain?
Matrix of cells surrounding hair cells innervated by utricular and saccular nerves.
What structures do the hair cells contain that provide information about movement?
What do the cilia penetrate into?
The otolithic membrane.
-gelatinous calcium carbonate crystals
What is the effect of bending of the cilia and kinocilium?
Bending of cilia towards kinocilium >> increased firing in nerve >> DEPOLARISATION.
Bending of cilia away from kinocilium >> decreased firing in nerve >> HYPERPOLARISATION.
What sort of ion channels do hair cells contain?
What happens when the K+ channels are distorted?
K+ channels become activated
>> activation of VG Ca channels
>> glutamate release.
What is the macula activated by?
What does the macula provide information about? (2)
What is static equilibrium?
Position of head relative to horizontal.
What is dynamic equilibrium?
Linear acceleration / deceleration.
What planes are the maculae orientated in?
UTRICLE – horizontal.
SACCULE – vertical.
Opposing directions >> better sensitivity.
What are the utricle and saccule also known as collectively?
What do the otolith organs provide information about? (3)
What are the main functional features of the semicircular canals?
-Main sensory structure is localised to AMPULLA
-Canal on both sides of head work in pairs
What do the semicircular canals provide information about? (2)
What are the semicircular canals filled with?
What is an ampulla?
Bulge at base of semicircular canal.
-location of main sensory structures
What is a cupula?
Gelatinous membrane in ampulla containing sensory processes.
-hair cells and cilia
-forms barrier against endolymph flow
What nerve innervate hair cells in the semicircular canals?
How does head rotation lead to nerve impulses?
>> endolymph inertia (lags behind)
>> cupula bends in opposite direction to rotation
>> distortion of cilia
>> excites / inhibits sensory nerves.
Why are the semicircular canals arranged in pairs?
Allows for comparison (pull-push mechanism).
-1 side depolarised, 1 side hyperpolarised
What nerve do sensory afferents of the vestibular pathways run in?
Vestibulocochlear nerve (CNVIII).
Where do sensory afferents from the otolith organs (utricle and saccule) project to?
Where do the efferents from the otolith organs (utricle and saccule) project to?
From lateral nucleus >> cerebellum and limb motor neurons.
-maintain upright body posture
Where do sensory afferents from the semicircular canals project to?
Where do the efferents from the semicircular canals project to?
From medial nucleus >> neck motor neurons and extraocular nerves (III, IV, VI).
-orientate head and stabilise retinal image
What is a major function of the vestibular system?
To maintain forward vision during head movements.
What enables you to maintain forward vision during head movements?
Vestibulo-ocular reflex (VOR).
-involves semicircular canals and extraocular muscles
What is nystagmus?
Rapid involuntary eye movements.
-travel slowly in one direction then rapidly flick in opposite direction
-e.g. when spinning
What is rightwards nystagmus?
Eyes track slowly to the left then rapidly flick to the right.
What is caloric testing?
Lie patient down and irrigate ear with warm / cold water >> convection currents in endolymph.
-WARM >> increased firing
-COLD >> decreased firing
What diseases affect the vestibular system? (5)
-Benign paroxysmal positional vertigo
-Vestibular neuritis / brainstem carcinoma / infarction / haemorrhage
What is Meniere’s syndrome?
Increased endolymph volume and membranous labyrinth rupture.
>> earache, tinnitus, dizziness, falls
What is benign paroxysmal positional vertigo?
Calcium carbonate crystals dislodged from otoliths.
-movement in canal >> illusion of movement and dizziness
What is ototoxicity?
Damage due to drugs / chemicals.
>> damage of vestibulocochlear nerve
What is medulloblastoma?
Childhood tumour growth in cerebellum.
-unable to use lateral vestibular information from otoliths
>> postural instability