HUMAN BODY: EARS

 The ears: 

    Hearing allows us to communicate through speech, to listen to music and other sounds, to be warned of approaching danger. Sound sources vibrate and emit sound waves that exert pressure on the air as they move. These waves are channeled inside the ear where they are detected by an area filled with cells with "eyelashes", the cochlea. When these eyelashes are pushed, pulled or pressed by the vibrations of the liquid surrounding them, the hair cells send the brain electrical signals that it transforms into sounds. The human ear perceives the pitch and strength of the sounds, and their orientation (one ear picking up the sound before the other).
The ears also play an essential role in balance. The other hair cells of the ear constantly monitor the position and movements of the body.

Eardrum: 

    Doctors use an otoscope to look inside the ear. Below we see a eardrum. It is a thin, almost transparent membrane, clogging the end of the ear canal that separates it from the middle ear. It vibrates as sound waves pass through the ear canal.

The stirrup:

     No longer than a grain of rice, the stirrup is the smallest bone of the body, and the last in the series of the three ossicles of the middle ear. The other two bones are called the hammer and the anvil. The ossicles capture the vibrations of the eardrum and transmit them to the oval window, the membrane covering the opening of the inner ear. It then passes them into the liquid of the tick mark.

Sound detector:

     The ear detects sounds in the organ of Corti, located in the center of the cochlea full of fluid. Snail-shaped, it consists of more than 15,000 hair cells that stand on four rows, each with up to 100 lashes at its tip. When it arrives from the middle ear, the sound moves the fluid, causing the eyelashes to bend, triggering the nerve impulses that the cells send along the cochlear nerve to the area of the brain that "hears" the sounds.

Auditory acuity:

     From dull growls to loud cries, the human ear detects a range of sounds. Their height depends on their frequency, which is the number of sound waves received per second, measured in hertz ( Hz ). Children hear sounds between 20 Hz ( bass ) and 20,000 Hz ( high ) . The upper threshold decreases with age. Some animals, such as bats, hear ultra-high sounds, ultrasound ( N > 20,000 Hz ). >> N: frequency

Balance:

     With balance, we stand and walk without falling. The balance sensors of the inner ear and those of the eyes, muscles, joints and skin of the feet transmit information to the brain which "knows" the position of the body and can send messages to the muscles to control it. In the inner ear, the hair cells of the utricle and saccula ( below ) monitor the position of the head while those of the three semi-circular channels detect its movements.