[Physics Class Notes] on Sound and Anatomy of Human Ear Pdf for Exam

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). 

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. 

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: