Chapter 14 - The Vestibular System Flashcards
The major structure in the Vestibular System is the ..
Labyrinth.
The Labyrinth is buried deep in the temporal bone and consists of the …
otolith organs and the semicircular canals.
What are the constituents of the otolith organs?
The utricle and the saccule.
How many semicircular canals do we have?
Three.
The utricle and saccule are specialised primarily to respond to …
linear accelerations of the head and static head position relative to the gravitational axis.
The utricle and saccule are specialised primarily to respond to linear accelerations of the head and static head position relative to the gravitational axis, whereas the semicircular canals are specialized for responding to …
Rotational accelerations, as their shapes suggests.
What rotation is a Pitch?
Pitch is a rotation around the y-axis. This means it’s a nod.
What rotation is a Roll?
Roll is a rotation around the x-axis. This means it’s a tilt of the head.
What rotation is a Yaw?
Yaw is a rotation around the z-axis. This means it’s a head shake.
The vestibular hair cells are located …
in the utricle and saccule, as well as three jug like swellings called ampullae, located at the base of the semicircular canals next to the utricle.
Vestibular hair cells are very much alike auditory hair cells. How do they differ?
In the utricle and saccule, a specialised area called the stroll divides the hair cells into two populations having opposing polarities.
Overlaing the hair cells and their hair bunnies is a what?
A gelatinous layer, and above this layer is a fibrous structure, the otolithic membrane, in which are embedded crystals of calcium carbonate called otoconia.
What is the function of the otoconia?
They make the otolithic membrane heavier than the structures and fluids surrounding it; thus, when the head tilts, gravity causes the membrane to shift relative to the sensory epithelium. The resulting heading motion between the otolithic membrane aunt eh macula displaces the hair bundles, which generates a receptor potential in the hair cells.
When the head tilts, gravity causes the membrane to shift relative to the sensory epithelium. The resulting heading motion between the otolithic membrane aunt eh macula displaces the hair bundles, which generates a receptor potential in the hair cells. Explain why this also happens during acceleration.
When the head undergoes linear accelerations; the greater relative mass of the otolithic membrane causes it to lag behind the macula temporarily, leading to transient displacement of the hair bundle.
How does the otolith organs convey the difference between linear accelerations and head tilts?
They don’t. They cannot distinguish between those two stimuli. However, together with the information from the semicircular canals the brain is able to distinguish between the two. (no vision needed)
Each of the three semicircular canals has at its base what?
A bulbous expansion - the ampulla.
The ampulla is structured how?
The ampulla houses the sensory epithelium, or crista, that contains the hair cells. The hair bundles extend out of the crista into a gelatinous mass, the cupula.
What is the cupula?
The cupula is a gelatinous mass in the ampulla in which the hair bundles lie. The cupula bridges the width of the ampulla, forming a viscous barrier through which endolymph cannot circulate. As a result, the relatively compliant cupula is distorted by movements of the endolymphatic fluid.
How are the hair cells in the cupula organised?
They all have the kinocilia in the same direction.
The vestibular system is a special sensory system. What makes it so special?
- It is multi sensory. Many neurons in the vestibular nuclei - the earliest point in the processing - receive visual input
- Many neurons in the vestibular nuclei function as premotor neurons it addition to giving rise to ascending sensory projections.
The information from the vestibular system is projected centrally, first coming to the …
Vestibular nucleus of the medulla.
The central projections of the vestibular system participate in two major classes of reflexes:
- Those responsible for maintaining equilibrium and gaze during movement
- Those responsible for maintaining posture.
Mention one important reflex mediated by the vestibular system.
The vestibulo-ocular reflex (VOR) which is responsible for producing eye movements that counter head movements, thus permitting the gaze to remain fixed on a particular point.
What is oscillopsia?
A condition in which patients find it impossible or difficult to fixate on visual targets while the head is moving. This is probably caused by vestibular damage, which causes the vestibulo-ocular reflex (VOR) to fail. If the damage is unilateral the patient can often regain the ability to fixate, but bilateral damage has the persistent and disturbing sense that the world is moving when the head moves.
