耳の解剖学

The human ear consists of the external ear, middle ear, and internal ear. The external ear includes the auricle and auditory canal, which direct sound waves to the tympanic membrane. The middle ear contains three ossicles that transmit vibrations, while the internal ear houses structures for hearing and balance.

The three auditory ossicles—malleus, incus, and stapes—form a connected chain in the middle ear. The malleus attaches to the eardrum and meets the incus, which connects to the stapes. The stapes links with the inner ear, transmitting vibrations from the eardrum through this mechanical chain to the fluid-filled cochlea.

The Eustachian tube, also called the auditory tube, connects the middle ear to the nasopharynx and equalizes air pressure on both sides of the tympanic membrane. It remains closed but opens briefly during swallowing or yawning, allowing pressure to balance and preventing eardrum damage from pressure differences.

The cochlea, a spiral structure in the inner ear, contains fluid-filled chambers called the scala vestibuli and scala tympani that surround the cochlear duct. Vibrations from the ossicles cause fluid waves within these chambers, stimulating sensory neurons in the organ of Corti, which converts mechanical vibrations into neural impulses transmitted via the vestibulocochlear nerve.

The vestibule, a central oval-shaped structure in the inner ear, and the three semicircular canals projecting from it detect changes in head position and maintain body equilibrium. These structures work together to sense rotational and linear movements, providing the brain with information necessary for balance and spatial orientation.

The tympanic membrane, or eardrum, is a thin, transparent tissue that separates the external ear from the middle ear. It vibrates when struck by sound waves traveling through the auditory canal, converting acoustic energy into mechanical vibrations that are then transmitted to the ossicles for further amplification and processing.

The oval window, where the stapes connects to the inner ear, marks the beginning of the scala vestibuli, a fluid-filled chamber within the cochlea. Vibrations from the stapes push against the oval window, creating pressure waves in the cochlear fluid that travel through the scala vestibuli and scala tympani, ultimately stimulating hearing receptors.