■ Can sound be heard with an ear?

耳殻:Ear pinna、外耳道:Ear canal、鼓膜:Eardrum、鼓室:Tympanic cavity ,耳小骨:Auditory ossicle,耳管:Auditory tube,外耳:External ear,中耳:Middle ear,内耳:Internal ear,蝸牛:Cochlea、三半規管:semicircular canal

<Animator Prefectural Nichinan hospital Clinical laboratory Chief engineer Rika Yabuoshi>

The feeling to sound is hearing.

As for humans, about 20-20000 Hz, a dog, and a bat can hear the sound (ultrasonic wave) of tens of thousands of Hz.

Our "ear" consists of three structures, the external ear which collects and sends sound, the middle ear which strengthens sound, and the internal ear which sends sound to a brain.

External ear
They are an ear pinna and an external auditory canal.

Middle ear
The end of an external auditory canal has the eardrum, and the back of the eardrum is the middle ear. The inner side of the eardrum is the drum cavity which is the room currently filled by air. With the auditory tube, it leads to the pharynx portion of the nose from under the drum cavity.

Internal ear
The internal ear is, there are a cochlea which feels the sound, and semicircular canals・vestibule・otolith organ which is the organ balance.

The sound which entered from the external ear vibrates the eardrum.
This vibration is lead to a malleus, a incus, and a stapes.

Sound pressure is amplified about 22 times by the structure of these three ear bones, and the area ratio of the eardrum and the stapes. By amplification of this sound pressure, the sound transmitted to stapes transmits the inside of lymph in cochlea, and is lead to the receptor of sound. Many of cochlea of a vertebrate are straight, but the about 2.5 circumference requires mammalian cochlea like the husks of a land snail.

■Furthermore, let's investigate in detail.

<Animator Prefectural Nichinan hospital Clinical laboratory Chief engineer Rika Yabuoshi>

つち骨 :a malleus,キヌタ骨 :an incus,アブミ骨 :a stapes,外耳道 :an external auditory canal,鼓膜 : an eardrum,鼓室 : a drum cavity,内耳 : an internal ear,耳管 : an auditory tube

In the above anime, ossicula auditus is malleus, a stapes, and an incus. But it is wrong.

To be exact, it is the order of a malleus, an incus, and a stapes. We correct it.

Artificial ossicula auditus is shown in a right photograph.

They are a malleus from the left, an incus, and a stapes.

<Ear pinna>

It is made of a cartilage with the intricately bent pleat so that it may turn out that an ear pinna touches. It is useful for the collection of sound action and the sense of direction of the sound. Gather the difference in the complicated uneven and very small sound, and an earlobe makes it resonate, and sends a very small sound into an external auditory canal.
If a hand is held up after an ear pinna in order to hear sound, the sound collection action which can be heard greatly will be committed. By changing the angle of the hand, it is well audible and the directions of sound differ.

"My ear is a shell of shellfish. I miss the sound of the sea." As Jean Cocteau said, the form resembles the shell.

The lowermost part of an ear pinna has blunt consciousness, and is used for the fashion which attaches an earring and pierced earring.

Ear canal

In adults, the length is 3 cm, and it is bent into theく shape. The eardrum is at the very back.
An ear canal serves as a resonant tube. It acts as a pipe which resonates sound and leads to the eardrum.
Short Hair has grown up to about 1 cm from the entrance, and it prevents foreign substances, such as an insect, from entering. An ear wax line is there and here is the line which secretes fat and ear wax.

The end of an external auditory canal has the eardrum (ellipse form 9 mm x 10 mm and, thickness of 0.1 mm). It vibrates sensitively in response to vibration of air.
It attaches to the ear canal in the form which inclines downward about 30 degrees.

Tympanic cavity
The inner side of the eardrum is the middle ear. The inner side of the eardrum is the tympanic cavity which is the room filled by air. (Cavity of the middle ear) Why is there air ?  It is said that it is maintaining at the suitable state where the sound is transmitted. In addition, it has the work which discharges the excretions in the middle ear outside.

Auditory ossicle
In a drum cavity, three bones called a malleus (malleus) incus (incus) stapes (stapes) are connected at the joint, and are called an auditory ossicle chain. It is the mechanism which transmits vibration of the eardrum to an internal ear. That is, the one end of the malleus has stuck to the eardrum, and one end of the stapes is fitted in and crowded in the vestibular window of the land snail of an internal ear.
The sound which entered from the ear canal is reinforced by chain of the eardrum and auditory ossicle, and gets across to the liquid of an internal ear.
Auditory ossicle is the smallest (it is 207 at the whole) bone in the bone which forms the human body.
It is called auditory ossicle.

Auditory tube
It is connected with the pharynx in the inner part of a nose. Change of the atmospheric pressure in the middle ear is adjusted. Although it is closed usually, it opens, when we swallow food and yawn. By carrying out like this, pressure in the middle ear and atmospheric pressure can be adjusted uniformly.
We may think that the ears get blocked when we climb the high mountain or take an airplane.
The difference was made between the middle ear and atmospheric pressure, and the eardrum was pulled. It makes us feel that our ears are blocked.
If we swallow spit, an auditory tube will open, and the difference of pressure will be lost and we do not feel that our ears are blocked. It is because the auditory tube is working.
When we swallow the spit in order to get to know work of an auditory tube (open and close), we hear the sound like stream in the both ears. This is the sound of auditory tube.

Inner ear
It is made from the land snail which is a sense organ of sound, and the semicircular ducts and the vestibule which are the sense-of-balance mechanism of the body.

Semicircular ducts serve to maintain bodily balance. Since there are three, it is called a semicircular canal. It maintains the balance of the body, and catches how much the organ which feels the acceleration of the movement, the roll acceleration and the head and the body have moved. When the body is turned round and round repeatedly, we feel dizzy since a semicircular canal is stimulated.

There is an organ called otolith organ and it takes in the stimulus from the outside, such as a position of gravity, centrifugal force, linear acceleration, and the head.
It is an otolith organ that takes in the feeling which goes up or falls in an elevator etc.

The inside of the cochlea which takes in sound is filled with lymph.
Vibration transmitted from the middle ear changes to the wave of a liquid here.
On lymph, there are hair cells (30,000〜40,000) which take in a wave , and a wave is changed to an electrical signal, and it has become the mechanism of transmitting the signal to a cerebrum from the acoustic nerve.

Reference HP