Chapter 11 Part 2 - The Vestibular System Flashcards
What does the vestibular system do?
- Monitors the position and movement of our head.
- Gives us the sense of balance and equilibrium.
- Helps coordinate movements of head and eyes.
- Helps coordinate adjustments to body posture.
What are lateral line organs?
Small pits or tubes along an animal’s sides, that contain clusters of hairlike sensory cells that detect variations in temperature, electrical fields, etc.
What is the vestibular labyrinth?
A series of interconnected chambers where all hair cells are contained.
What does the vestibular labyrinth contain?
- The otolith organs, which detect the force of gravity and tilts of the head.
- The semicircular canals, which are sensitive to head rotation.
These transmit mechanical energy from head movement to the hair cells.
What are the otolith organs?
- Saccule
- Utricle
They are relatively large chambers near the center of the labyrinth. The semicircular canals that lie on approximately orthogonal planes are the three arcing structures of the labyrinth.
How do hair cells of vestibular organs relate to nerves?
Each hair cell of the vestibular organs makes an excitatory synapse with the end of a sensory axon from the vestibular nerve, a branch of the auditory-vestibular nerve (cranial nerve VIII).
There are about 20.000 vestibular nerve axons on each side of the head, and their cell bodies lie in Scarpa’s ganglion.
What are otolith organs?
The saccule and utricle, i.e., the otolith organs, detect changes of the head angle, as well as linear acceleration.
They also contain a sensory epithelium called a macula.
What is a macula?
A sensory epithelium vertically oriented within the saccule, horizontally oriented with the utricle, when the head is upright.
What does the macula contain?
Hair cells that lie among a bed of supporting cells with their cilia projecting into a gelatinous gap.
What happens when the angle of the head changes?
A force is exerted on the otoconia, and on the gelatinous gap; this causes the cilia to bend.
One especially tall cilium per hair cell, the kinocilium, is specifically important.
What happens with the kinocilium when the head is tilted?
When the hairs bend toward the kinocilium, it results in a depolarizing, excitatory receptor potential.
When the hairs bend away from the kinocilium, a hyperpolarization occurs and the cell is inhibited.
If the hairs are bent perpendicular to their preferred direction, they barely respond.
What do the semicircular canals do?
They detect movements of the head, such as shaking the head from side to side or nodding up and down.
They also detect angular acceleration.
What are the semicircular canals filled with?
Endolymph, the same fluid as the scala media.
What is an ampulla?
A bulge along the semicircular canals that contains the crista, a sheet of cells that detect the movement of the endolymph.
What causes the dizziness after spinning?
The inertia in the endolymph: After you have been rotating for some time, and suddenly stop, the inertia will keep moving the endolymph but the hairs are pushed in the opposite direction, so you feel like you’re rotating in the other direction.
