Vertigo Flashcards
When does Syncope occur?
When cardiac output falls
True vertigo is a disease of
the vestibular system
The clinical sign of vertigo
Nystagmus- fast ans slow phase. Fast phase consists of corrective saccades from the frontal eye field of the contralateral hemisphere. Person is blind during the fast phase because the brain suppresses the visual info. During the slow phase the person feels dizzy.
How many degrees of freedom are there and what detects positional change in these six degrees of freedom in humans?
The Vestibular apparatus
Translational motion
linear along x,y,z
Rotational Motion
angular around x,y, z
Linear motion and the effects of gravity are sensed by two specialized organs called
Sacculus and Utricle
What detects angular movements
The semicircular canals, detect rotational acceleration or deceleration within the plane of the canal
A specialized organ called a corpula located inside the amupulla transduces this info
Cellular structure of the utricle and saccule
Sensory Hair cells with Cilia are embedded in a gelatinous matrix. On top of this matrix filled with hair cells, tiny crystals of calcium carb called otoiths are stuck to the membrane and are sufficiently heavy to distort the matrix by a linear force during movement and gravitational pull.
The nerve fibers whose cell bodies lie in Scarpa’s ganglion have afferent and efferent sides
The Efferent axons project to the brainstem via the vestibular nerve
Remember that each vestibular apparatus acts as a pushing muscle…that is, if you turn your head suddenly to the left but want to keep your eyes fixed on a point, the left semicircular canal is stimulated while the right is inhibited
ok….This is the vestibulo-occular reflex
How would you reveal a centrally compensated vestibular dysfunction
Frenzel lenses ….keep the eyes from focusing on distant objects
Head Thrust maneuver does what
can detect a decrease in the vestibular-ocular reflex by the presence of a catch up saccade
Semi-circular canals work in a push-pull manner
when head rotation stimulates one the other part is inhibited
BPPV
Benign Paroxysmal Positional Vertigo-
Caused when otoliths break off with age or trauma and enter the semi-circular canals. They tend to collect in the posterior semi-circular canals due to head dependency during sleep. THey can form a sludge which produces greater pressure in the affected canal and send signals to the brain via the ampulla that the head has rotated posteriorly much quicker and to a greater extent that it really has. Vertigo occurs 5-10 seconds after head movement and lasts about 45 secs
