The vestibular system can be divided into two parts:
a. the parts that detect linear acceleration (utricle and saccule); also called static movements
b. the parts that detect rotational acceleration (the three semi circular canals); also called dynamic movements.
A. The Utricle and the Saccule:
1. The Utricle and the Saccule:
The utricle and the saccule are fluid-filled spaces. They contain a macula which is oriented in the horizontal direction ( = utricle) or in the vertical direction (= saccule). These two organs therefore detect movements in the horizontal or in the vertical direction.
2. The Macula:
The macula is the sensor in these two organs. It essentially consists of a row of hair cells. The hairs are connected to a gelatinous mass called the otholithic membrane. The other side of the hair cell is connected to a nerve. This is the beginning of the vestibular nerve.