The Vestibular System Flashcards
What is the basic function of the vestibular system?
Balance
Describe the basic structure of the vestibular apparatus.
There are three semicircular ducts arranged at 90º angles to one another. They are connected to the rest of the inner ear via the utricle.
Hair cells of the vestibular system are located in the ________.
ampullae (the enlarged area where the semicircular ducts attach to the utricle)
What kind of movement stimulates the saccule?
Vertical movement (the saccule is arranged vertically midway between the utricle and the cochlea)
What fluid is inside the semicircular ducts?
Endolymph –same as in the inner ear
The superior semicircular canal is also called __________.
the anterior canal
The saccule and the ampullae are collectively referred to as __________.
the maculae
The vestibular system is located in what bone?
The temporal bone
The utricle and the saccule respond to __________ accelerations, while the semicircular canals respond to __________ accelerations.
linear; angular
The vestibular system is __________ and _________ to the cochlear.
posterior; lateral
The hair cells, floating in the endolymph, are on the _________ side of the membrane.
apical
Each hair cell has about 60 to 100 stereocilia. The tallest is called the _________, and it gives the bundle __________.
kinocilium; directional sensitivity
Each macula has a gelatinous layer of hair cells covered with ____________.
otoconia (calcium carbonate crystals)
True or false: the cupula of the semicircular canals sense constant speed.
False. The cupula adapts to the movement of semicircular fluid and thus only senses accelerations and decelerations.
Pushing against the kinocilium (tallest-first direction) leads to ______________.
hyperpolarization and consequent decrease in spontaneous action potentials fired
Similar to photoreceptor cells in the eyes, hair cells conduct by _____________.
passive electrical gradient – the afferent nerves fire action potentials
Ion channels in hair cells are opened by ____________.
pushing the stereocilia in the excitatory direction, thus causing the tip links to pull open the potassium channels
What effect drives nystagmus?
When the head is rotated, one vestibular system is stimulated and the other is inhibited. These signals connect to the oculomotor system, thus promoting compensatory eye movements via the lateral rectus.
In the ____________, the axis of polarity changes direction in the middle.
utricle
Within each ampullae, there is a patch of epithelium that contains the sensory cells called the ____________.
crista
What is the cupula?
A gelatinous mass that the hair cells of the cristae projet into
The semicircular canals primarily sense changes in movement because the _____________ moves in relation to the head.
endolymph (which then stimulates the cupula)
True or false: at rest roughly 10% of the hair cell cation channels are open.
True! They have a resting firing rate
Give the inputs for each of the vestibular nuclei.
Superior and medial: semicircular canals (gaze control)
Lateral: semicircular canals and otoliths (postural reflexes)
Descending: otolith input to integrate vestibular and motor input
Describe the basis for the vestibular-ocular reflex.
The semicircular canals send efferents (from the vestibular nucleus) to the medial rectus of the ipsilateral eye and the lateral rectus of the contralateral eye; when the head rotates (sensed by the semicircular canals), the eyes rotate opposite the direction of rotation.
