How the Ear Keeps Us Balanced
Semicircular canals, ampulla, utriculus and sacculus
Follow a head movement through the balance organs of the inner ear.
You turn or tilt your head. The three semicircular canals are set at right angles to one another in three different planes, one horizontal and two vertical, so any movement disturbs at least one of them.
A brief turn barely disturbs the fluid, so balance is restored at once.
Free play — step through the process at your own pace, and move the slider to see what changes. Switch to when you're ready to test yourself.
What this lesson covers
What you do
- Name the widened end of each semicircular canal and say what it contains.
- State which nerve carries both hearing and balance impulses to the brain.
- Explain why the canals are arranged in three different planes rather than one.
Challenges to clear
- Step through every stage of the balance pathway.
- Reach the stage that explains balance while you are standing perfectly still.
- Spin long enough to make yourself thoroughly dizzy.
The task
Follow a head movement through the balance organs of the inner ear.
What this lesson covers
- Head turns — You turn or tilt your head. The three semicircular canals are set at right angles to one another in three different planes, one horizontal and two vertical, so any movement disturbs at least one of them.
- Fluid is shaken — The fluid inside the semicircular canals is shaken as the head moves, and it keeps moving for a moment after the head itself stops.
- Hair cells respond — The moving fluid pushes against the sensory hair cells in the ampulla, the widened end of each canal, which register dynamic balance while the body is in motion.
- Impulse to the brain — Nerve fibres attached to the hair cells join the auditory nerve and carry the impulse to the brain, which corrects your posture.
- Standing still — The utriculus and sacculus, the short stem joining the canals to the cochlea and together called the vestibule, hold similar sensory patches that register static or positional balance with respect to gravity.
- Dizziness after spinning — If you spin and then stop, the fluid in the canals goes on swirling for a short time, so you feel dizzy and your eyes flick back and forth. The same disruption causes sea-sickness, air-sickness and car-sickness.
- A brief turn barely disturbs the fluid, so balance is restored at once.
- Long spinning keeps the fluid swirling after you stop, so the brain is still being told that you are turning.
Hint
Cochlea does hearing; semicircular canals do dynamic balance while you move; utriculus and sacculus (the vestibule) do static balance when you are still. All three lie in the INNER ear — never place the semicircular canals in the middle ear.