Vestibular System Flashcards
What three mechanisms contribute to balance and how many are essential for good balance?
Proprioceptive, vestibular, and visual systems. Two.
What are the components of the vestibular system and what do they detect?
Semicircular canals (horizontal, anterior, posterior canals): good for circular/angular movements. Utricle: connects three canals. Saccule: continuous with cochlea. Both utricle and saccule good for linear motion and gravity sensors.
Where are hair cells clustered?
In ampulla of semicircular canals. Atop of hair cells is gelatinous membrane = cupula.
What are hair cells in the vestibular system sensitive to?
Acceleration force, NOT velocity.
Describe the vestibular pathway as you turn your head left.
Movement of head pushes fluid in opposite direction. Turn head to left, fluid moves clockwise. On left side, stereocilia towards kinocilia = depolarization, increased CN VIII firing. On right side, stereocilia away from kinocilia = hyperpolarization, decreased CN VIII firing. Difference in firing of the two = velocity of motion.
Describe orientation of hair cells and semicircular canals.
Hair cells oriented in specific planes. Horizontal canals oriented toward utricle. Anterior and posterior canals oriented away from utricle.
Describe pairing of semicircular canals.
Horizontal canals are paired. Anterior canal on one side paired with posterior canal on other side. Allows for relative comparison. Matched pair needed for balance.
Describe location and function of otolithic granules.
Saccule and utricles contain otolithic granules, which have weight and, therefore, respond to gravity. Also detect position (standing, lying down, yoga pose, etc.)
What is the function of the utricle?
Detects upright position and head tilt. Primary gravity sensor. Detects horizontal linear acceleration.
What is the function of the saccule?
Detects general orientation and vertical linear acceleration.
Describe vestibular input to CNS.
Hair cell -> bipolar cell (AP’s) -> vestibular ganglion -> CN VIII -> vestibular nuclei.
What are the two divisions of the vestibular ganglion and what do they do?
1) Inferior: does posterior saccule and posterior semicircular canals.
2) Superior: does everything else.
What is the function of the MLF and where is it located?
Located on top of medial lemniscus. Connects CN 3, 4, 6 to vestibular system.
Distinguish between ascending and descending MLF functions.
Ascending MLF controls eye movements. Descending MLF controls head and neck movements.
Describe the vestibulospinal tract, its two divisions, and what they do.
Primary afferent to vestibular nuclei. Secondary to cerebellum, spinal cord, brainstem, thalamic and cortical areas. Lateral VST acts on proximal limb muscles. Medial VST (descending MLF) acts on neck muscles, maintains head erect.
