Question

In twirling head, what happens to the endolymph in the canal?

1) It moves in the same direction as the head
2) It moves in the opposite direction of the head
3) It remains stationary
4) It lags behind pushing the cupula

Answer 1

The endolymph in the semicircular canals lags behind when the head turns quickly, causing the cupula (option 4) and hair cells to bend and send signals to the brain indicating rotational movement.

Step-by-step explanation:

When twirling the head, the endolymph in the semicircular canals of the vestibular system tends to remain stationary due to inertia. As a result, when the head turns quickly, the endolymph initially does not move in the same direction; instead, it lags behind. This lagging causes the cupula — a gelatinous structure that the hair cells are embedded into — to bend, which in turn bends the hair cells. The bending of the hair cells is then interpreted by the brain as rotational movement.

So, the correct answer to the student's question is that the endolymph lags behind pushing the cupula, which is option 4. This mechanism allows our brain to detect angular acceleration or deceleration, such as when turning the head. It is a part of the body's vestibular system, contributing to our sense of balance and spatial orientation.