The human ear and balance

Each person has two set of balance receptors one set found on each side of the skull in the ears. Each set can be found next to the cochlea and is composed of 5 fluid filled chambers, three semicircular canals and just underneath these canals are two chambers known as the utricle and saccule.

The three semicircular canals, shown on the right, are aligned along the three axis of 3 dimensional space so that they can detect movement in all directions.

A swelling at the base of each canal contains sensors that can determine the speed of rotation of the head.

The sensors at the base of each canal contain clusters of nerve cells with hair like projections (cilia) protruding into a gelatinous substance known as the copula.

When rotating your head the copula becomes distorted and bends the cilia. The faster the head is rotated the more the cilia bend.

When the head is upright, as shown on the right, the nerve cells fire at a constant frequency sending a constant stream of signal to the brain.

As the head is rotated, the cilia bend. Depending in which direction the head is rotated the firing of nerve impulses to the brain increase or decrease, as compared to when we a standing.

As shown on the right, when the long cilia bend towards the shorter ones increased firing occurs.
As the cilia bend the other way a slower firing occurs.
If you rotate your head at a constant slow speed the fluid in the canals does not apply a significant pressure on the copula to bend the cilia. However a fast rotation will distort the copula and bend the cilia. If you rotate quickly and then stops the fluid in the canals continues to move and apply pressure to the copula thus causing the person to feel dizzy.
The other two fluid filled chambers, the utricle and saccule, detect the position of the head relative to gravity. Hair like projections (cilia) protrude into a thick gelatinous substance covered by calcium carbonate crystals (otoconia), as shown on the right.
When you tilt your head, tiny crystals of calcium carbonate, otoconia, in the thick gelatinous fluid are pulled by gravity and cause the cilia to bend. This causes the rate of firing of the nerve cells to alter and the brain interprets the new position of the head according to the rate of impulses it receives.
These receptors provide the brain with information to determine the relative position of the body and coordinate the appropriate muscle response.
Explain how we can sense the direction and speed of head rotation?
Why do we feel dizzy when we rotate quickly and stop suddenly?
Why are the semicircular canals each aligned along one of the three axis of 3-dimensional space?