Classification Principles
From a histological perspective, the organs of hearing, balance, and taste are classified as secondary receptor organs (secondary sense organs).
A key morphological distinction of this group lies in the nature of the receptive element. Unlike primary sensory systems, where the stimulus is captured directly by a nerve cell, reception here is carried out by specialized epithelial cells known as epitheliosensory cells (or sensoepithelial cells).
Mechanism of Sensory Signal Transmission
The processing of an incoming stimulus involves a strictly defined sequence of stages:
- Perception of the stimulus.
- Transduction (conversion of stimulus energy).
- Signal conduction.
- Impulse transmission.
At the cellular level, this mechanism unfolds as follows: the action of a specific stimulus alters the transmembrane potential of the sensitive epitheliosensory cell membrane. The signal is then transmitted via a synaptic contact to the dendrites of neurons that form the ascending pathways. Notably, this transmission step to dendrites operates similarly to primary sense organs.
Organ of Hearing and Balance: Specifics and Topography
The apparatus responsible for hearing and spatial orientation possesses a wide range of sensitivity, capable of responding to four main types of physical stimuli:
- Sound waves;
- Vibration;
- Gravitational forces;
- Angular accelerations (e.g., generated during body rotation).
Anatomical Structure and Topography
Structurally, the organ is divided into three interrelated parts: the external, middle, and internal ear.
Topographically, these parts feature different supporting frameworks. The external part, which includes the auricle (pinna) and the initial third of the external acoustic meatus, relies on a cartilaginous framework. All other deeper and more complex structures of the hearing and balance apparatus are securely protected within the petrous part of the temporal bone of the skull.