Three parts of the ear are involved in the hearing process: the outer ear, the middle ear and the inner ear.
Hearing begins when sound waves enter the outer ear and travel through the ear canal to the eardrum, causing it to vibrate. These vibrations travel through three tiny bones in the middle ear, called the ossicles. The ossicles cause the sound to be amplified before it enters the inner ear.
The inner ear contains a fluid-filled cochlea that is lined with thousands of tiny hair cells. As the fluid moves in waves along the cochlea, approximately 12,000 hair cells bend. The frequency and intensity of the sound is determined by which hair cells bend.
The action causes nerve impulses to travel up the auditory nerve to the brain for processing. These nerve impulses are the “language” that the brain understands and converts into meaningful sounds.
How We Hear : A complex Process
How We Hear
The ear is a complex organ of hearing and balance. It is capable of perceiving an incredible range from the tiniest audible sound, which would be 1 trillion times weaker than that of a sound that would cause pain. This range is about 130 decibels Besides loudness, the human ear can detect pitch. This relates to the sound vibrations per second or the frequency, which is measured in Hertz. The higher the frequency, the higher the pitch. This range is incredible, from about 20 to 20,000 Hertz.Finally, the human ear can detect tone. This allows us to tell the difference between flute and a clarinet when both instruments play the same note.
Parts of the Ear
How We Hear : Parts of the Ear
In order for the ear to perform these extraordinary functions, it must detect, decipher and analyse the sounds. The ear is divided into four different parts:
- The outer ear
- The middle ear
- The inner ear
- Auditory nerve leading to the brain
Pathway of Sound
How We Hear : Pathway of Sound
The outer ear is a funnel that directs waves from the air to the ear drum, sending vibrations that cause the three bones in the middle ear to move mechanically. These mechanical vibrations move to the inner ear, where they are turned into electrical energy by the tiny hair cell of the cochlea. These impulses travel the auditory nerve to the b rain, where they are translated into useful sound information that we understand.
The Outer Ear
How We Hear : The Outer Ear
The outer ear is composed of 2 parts: the pinna, which is the visible part of the ear and the ear canal, or the external auditory meatus.
The pinna is composed mainly of skin and cartilage. It collects and funnels sound into the external auditory canal to the eardrum.
The ear canal is a twisted passageway that connects the pinna to the ear drum. It is about 2 to 3 cm in length. Since it is not straight, it makes it difficult for foreign objects or insects to enter. Also, there are cerumen glands(earwax) in the ear canal that help keep the dust, dirt and bugs from entering.
The Middle Ear
How We Hear : The Middle Ear
The middle ear space is filled with air and is located between the outer ear canal and the inner ear. It is composed of the ear drum, the ossicles(bones), Eustachian tube, muscles and ligaments.
The ear drum (tympanic membrane) is an opaque conical shaped tissue located at the end of the ear canal and strike the ear drum that causes it to vibrate.
The sound is transferred to the middle ear bones. These bones are the smallest bones in our body. They are held in place by muscles and ligaments that also allow then to rock back and forth with the sound.
The first bone in the chain is the malleus (hammer). It is attached to ear drum.
The second bone is the incuss (anvil).
The third bone in the chain is the smallest bone in our body and is called the stapes (stirrup). This bone is attached to the oval window, which is a membrane that covers the opening to the inner ear.
The Inner Ear
How We Hear : The Inner Ear
The inner ear is a structure that contains the cochlea (hearing apparatus) and the labyrinth(organ of balance). It is a capsule filled with fluid. The cochlea is a bony tube that resembles a snail, having 2-5 turns. It is a complex organ tat is partitioned into 3 parts.
The fluid moves as a wave sets along the entire length of the cochlea. As the fluid moves, approximately 12,000 hair cells will bend. The frequency and intensity of the sound is determined by which hair cells bend. This action causes nerve impulses to travel up the auditory nerve to the brain for processing. Any damage to the hair cells will affect our hearing.
The Auditory Nerve
How We Hear : The Auditory Nerve
Once the hair cells move in the inner ear, electrical signals are sent to the auditory nerve, which is connected to the auditory center of the brain (temporal lobe). Input from each ear will end up in the brain on each side of the brain. The brain will translate the electrical energy into sounds that we can recognize.