Cochlear Fluid Velocity
In this case, we start with some survey data and then move into the mechanistic stuff: the why questions. Source material comes from
Is N, Shimizu T., and Sugata K. (2001) Mechanics of Coriolis stimulus and including factors of motion sickness in Biol.Sci.Space 15(4): 414-419.
Cheung B, Heskin R, Hofer K, Gagnon M. J. Vestib. Res. (2001). The menstrual cycle and susceptibility to Coriolis -induced sickness.112:129-136.
Your eyes tell you something about motions of your environment. Your inner ear may tell you something else about motions. Normally your brain tries to make sense of the two information streams. When the two information streams can’t be reconciled motion sickness may occur. Motion sickness progression: feeling of restlessness to a cold sweat, to dizziness, and to vomiting and diarrhea.
As a card carrying male it does not surprise me that mothers very-soon-to-be are prone to motion sickness. Mother want-a-bees exhibit motion sickness on ovulation days during the “round-the-world” yacht race. The race was apparently an opportunity to test their theory Carioles brings on motion sickness. The Coriolis parameter is a function of sine of the latitude and is 0 at the equator. The Coriolis acceleration is the product of the Coriolis times the velocity of the cochlear fluid in question. If the fluid in motion were cross equatorial inner ear fluid velocities would go to infinity. That does not sound like a healthy-yacht race circumstance.
The technical personnel, or flight crew members, are responsible for the operation of the .... Motion sickness (dizziness, malaise and vomiting) due to abnormal ...Coriolis accelerations, which, for horizontal transit, are greatest near the equator and decreases at the higher latitudes.
The Vestibular Apparatus
The Inner Ear consists of auditory and non-auditory portions. The latter is
Primarily associated with equilibrium and contains the three semicircular canals. The semicircular canals are filled with a thick fluid and each canal lies at an approximate 90-degree angle to the other. One end of each canal is enlarged and in this area is a mound of sensory hair cells. Angular acceleration, or rotation, of the body along the yaw, pitch, or roll axis will move the fluid in a respective canal.
This movement displaces the sensory hairs and an impulse is sent to the brain to be interpreted as motion about a known axis. The hairs project into the fluid and are extremely fine, light, and sensitive to motions of the cochlear fluid of the inner ear. Any acceleration greater than 2 degrees per second will cause the hairs to displace and an impulse is sent to the brain that indicates which way the hairs are bent, the brain then figures out the plane of rotation. Since the canals lie in different planes, they can report movement in all three dimensions (yaw, pitch, and roll).
This system works fine for sudden, short turns, but, if the turn continues at a constant rate for a period of time, (approximately 25 seconds) the motion of the fluid catches up to the speed of the canal walls, and the hairs are no longer bent. In this scenario, a pilot would initially feel a turn to the right, but, after 25 seconds, as long as the rate of the turn is constant, the pilot would feel as though the turn has stopped, when in actuality, this pilot is still turning to the right.
Once the turn to the right is detected, and the turn is stopped, the fluid in the canal
Will continue to move. In this situation, the hairs that were straight because the fluid and canals were moving at the same rate would suddenly bend in the opposite direction. This would cause an opposite sensation as though one was now turning hard to the left. An untrained pilot in this situation would, more than likely, turn the aircraft back to the right to compensate for the perceived left turn. As a result, a pilot would try to counteract this imaginary motion by turning back into the original turn or spin. This is the physiology behind the classic Graveyard Spin or Spiral. “ (From FAA)
I must admit that in working up this blog I thought “no way”. As I read on, I ran into NASA and the FAA! and their due consideration.
In the mathematical derivation the equation of motion you get to the sticky point where you need to “take the determinant” so that up-down, East-west and north-south components of the Coriolis term are included. In the classroom, we can say we are only concerned with horizontal motion. In doing so set terms to zero or held constant and then talk about the rest of the equation. Well, the NASA and the FAA have the substantial responsibility of bringing the Astronauts and Aeronauts back to earth. They dare not be permitted to leave out parts of the equations.
So we have a thick fluid in the cochlea of each of the ear. When the cochlear fluid tells a story at odds with other senses spinning and discomfort may emerge. But what about the sail boat? It is horizontal in its motions. It does not have a passenger list of Astronauts and Aeronauts.
Photo: Bilby (Creative Commons Attribution 3.0 Unported)