Sound and music are intricately linked with our everyday lives. We can perceive different sounds due to the elaborate human ear anatomy and specific characteristics of the sound itself (such as pitch and frequency). The external ear consisting of the pinna, the auditory canal, and the tympanic membrane, the ossicles of the middle ear, and the inner ear comprising of the cochlea, the semicircular canals, and the vestibule constitute the structure of the human ear. So, let us learn about the nature of sound waves and how the anatomy of the human ear enables the detection of sound.
Nature of Sound Waves
Sound waves as mechanical waves: Sound is a disturbance that is transmitted through a medium via particle-to-particle interaction. Hence, sound waves are mechanical.
Sound waves as longitudinal waves: Sound waves are longitudinal, meaning that the direction of propagating sound waves is the same as the vibration of the medium particles.
Sound waves as pressure waves: The vibrating particles of the medium interact with the air particles. Hence, there are regions of high pressure (compressions) and areas of low pressure (rarefactions).
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Frequency, Pitch, and Human Perception of Sound
Frequency: It indicates the rate of vibration of medium particles when a wave passes through it. Its unit is Hertz, where 1 Hertz = 1 vibration/second.
Pitch: It is the sensation of frequency. High pitch corresponds to high-frequency sounds, whereas low pitch relates to sounds of low frequency.
The human ear is capable of perceiving sound waves ranging between 20 Hz to 20,000 Hz.
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Anatomy of The Human Ear
The human ear performs the functions of perception and interpretation of sound waves. The ear is divided into three parts:
External ear
Middle ear
Inner ear
The External Ear
The external ear consists of the following parts:
Pinna: It is a flap of cartilage located on the side of the head. Its peculiar shape, made up of thick folded cartilage, is well-suited for gathering the sound waves and directing them towards the auditory canal.
Auditory Canal: It is an inch long tunnel that ends at the tympanic membrane or the eardrum. The channel contains hairs and glands for secreting earwax.
Tympanic Membrane: It is a thin membrane, stretched tight like a drum head, located between the middle and the outer ear. When sound waves strike the membrane, it vibrates to produce sound.
The Middle Ear
The middle ear is an air-filled hollow cavity and is separated from the outer ear by the tympanum. The middle ear's anterior wall contains an opening that leads directly into the Eustachian tube; this tube connects the middle ear to the throat and equalizes the air pressure on either side of the eardrum.
Ear ossicles: The air space of the middle ear has an arch of three small bones - the malleus, the incus, and the stapes. These three bones are collectively termed as ear ossicles. The vibrating eardrum transmits the vibration to the ear ossicles, which relay the vibration to the inner ear.
The Inner Ear
The inner ear or the labyrinth is composed of the cochlea, the semicircular canals, and the vestibule. The bony labyrinth is filled with a fluid called the perilymph.
Cochlea: It is a bony canal with two-and-a-half spirals connected to the middle ear via the oval window. The cochlea is internally separated by membranes into three canals. The upper canal and the lower canal are filled with perilymph, while the central canal has endolymph.
The central canal also possesses sound receptors called organs of Corti; its hair cells transform sound vibrations to nerve impulses and are suited for the interpretation of sounds of different frequencies.
Semicircular canals: It is a set of three fluid-filled channels arranged perpendicular to each other and are responsible for the maintenance of body balance in motion.
Vestibule: The central portion of the labyrinth consists of two sacs - the utricle and the saccule. The vestibule has receptors for the maintenance of the body's static equilibrium.
Diagram Showing The Internal Structure of The Human Ear
Given below is a simple human ear diagram for class 9:
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FAQs on Sound and Anatomy of Human Ear
1. What are the three main parts of the human ear and what do they do?
The human ear is divided into three main sections, each with a specific role in hearing:
- The Outer Ear: This includes the pinna (the visible part of the ear) and the ear canal. The pinna collects sound waves from the environment and funnels them through the ear canal to the eardrum.
- The Middle Ear: This part contains the eardrum and three tiny bones called the ossicles (malleus, incus, and stapes). When sound waves hit the eardrum, it vibrates. These vibrations are then amplified by the ossicles.
- The Inner Ear: This contains the cochlea, a snail-shaped, fluid-filled tube. The amplified vibrations from the middle ear create waves in this fluid, which are detected by tiny hair cells and converted into electrical signals for the brain.
2. How does the ear turn sound waves into something we can actually hear?
The process of hearing involves several steps where sound energy is converted into nerve impulses:
- First, sound waves are collected by the outer ear and travel to the eardrum, causing it to vibrate.
- These vibrations are passed to the three small bones in the middle ear, known as ossicles, which amplify the vibrations significantly.
- The last of these bones pushes on the cochlea in the inner ear, creating waves in the fluid inside it.
- Tiny sensory hair cells inside the cochlea move in response to these fluid waves and convert this movement into electrical signals.
- Finally, the auditory nerve carries these signals to the brain, which interprets them as the sounds we recognise.
3. What is the normal hearing range for a healthy human?
For a young, healthy person, the audible range of sound frequency is typically between 20 Hertz (Hz) and 20,000 Hertz (20 kHz). Frequencies below this range are called infrasound, and those above it are called ultrasound. This range can decrease with age or due to damage to the ear.
4. How do simple hearing aids work to help people hear better?
A hearing aid is a small electronic device designed to make sounds louder. It has three basic parts: a microphone to pick up sound, an amplifier to increase the sound's power, and a speaker to send the amplified sound into the ear. This helps people whose inner ear hair cells are damaged, as the louder sound can better stimulate the remaining healthy cells.
5. Why do my ears sometimes feel blocked or 'pop' when I'm in an airplane or going up a hill?
This feeling is caused by a change in air pressure. The middle ear is an air-filled space that is connected to the back of your throat by a small passage called the Eustachian tube. This tube's job is to equalise the pressure in your middle ear with the pressure outside. When you go up or down quickly, the pressure changes faster than the tube can adjust, causing the eardrum to bulge in or out. Swallowing or yawning helps open the Eustachian tube, allowing the pressure to equalise, which causes the 'popping' sound.
6. Why are the tiny bones in the middle ear so important for hearing?
The three tiny bones in the middle ear, the ossicles, are crucial because they act as an amplifier. The vibrations from the large eardrum are concentrated onto a much smaller area of the inner ear's oval window. This lever-like action significantly increases the force of the vibrations, making them strong enough to move the fluid inside the cochlea. Without this amplification, most sound energy would be too weak to be detected properly.
7. What causes the ringing sound in the ears that some people experience?
This condition is known as tinnitus. It's the perception of sound, like ringing or buzzing, without any actual external source. It's not a disease but a symptom, often caused by damage to the tiny sensory hair cells in the cochlea of the inner ear. This can happen due to exposure to loud noise, age, or other medical conditions. The brain misinterprets the abnormal signals from these damaged cells as sound.
