[Biology Class Notes] on Labelled Diagram of Human Ear Pdf for EXAM

The ear is the organ of hearing and equilibrium in the mammalian body. Mammalian ears convert soundwaves into electrochemical impulses and maintain a sense of balance. In all vertebrates including humans, a pair of ears are there.

The outer part of the ear receives sound waves and transmit them down the ear canal and ultimately to the eardrum. The travelling sound starts a vibration in the eardrum and as a result, sound is produced.

The ear diagram is one of the important topics for Class 10 and 12 students of the CBSE board and in this article, we will briefly explain the structure of the ear, its different parts and their functions.

Parts of the Human Ear

The human ear consists of three different parts. These are:

1. The outer ear.

2. The middle ear

3. The inner ear

Here, we will discuss all parts of the ear.

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The Outer Ear:

The outer ear collects sounds from the environment and funnels them across the auditory system. It is composed of :

• Pinna: These are flap-like structures and are skin-coloured cartilage which makes them flexible. The lowest part of the pinna is called the lobe or lobule. These structures cannot be moved by humans but can be moved by cats and dogs.

• External Auditory Canal: It is a passageway to the temporal lobe of the skull and is approximately 2.5 cms long. The outer one-third of this canal is lined with ceruminous and hair cells. Cerumen and hair trap foreign bodies and dirt and protects the eardrum; it also keeps the canal moist.

• Tympanic Membrane: The tympanic membrane or the eardrum is a thin and concave membrane that is stretched across the inner end of the external auditory canal. It’s 63 sq mm in length and consists of three layers which help the membrane to vibrate on sound conduction whilst maintaining a protective thickness.

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Middle Ear

The middle ear acts as a transport hub of sound from the outer ear to the inner ear. It is an air-filled space and has a volume space of 2 cubic cm.  The back wall which separates this part from the inner ear has an oval and around window. The middle ear consists of the Eustachian tube, bones or ossicles and muscles.

• Eustachian Tube: This part connects the middle ear to the nasopharynx. The tube is generally closed and opens only because of muscle movement during yawning, swallowing or sneezing.  The main function of the Eustachian tube is to equalise the air pressure in the middle ear to match the air pressure in the outer ear.

• Bones and Muscles: Middle ear bones are also called ossicles and they form a chain which assists in the conduction of sound waves from the eardrum to the oval window. These bones are the malleus, incus and stirrup. The vibration on the eardrum sets up the vibration of these bones which amplifies the sound and transmits it to the inner ear via the oval window.

The two muscles in the middle ear are the stapedius and the tensor tympani. They respond flexibly, i.e. without conscious control.

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Inner Ear

The sound which travels from the outer and the middle parts of the ear is interpreted by the inner ear. These parts have various interconnecting chambers and are compared to a labyrinth. The inner ear consists of:

• Vestibule: It is a round space that accesses numerous passageways and is the central structure of the inner ear. The outer wall of the vestibule consists of  the oval and round windows. It has two membranous sacs which are the utricle and the saccule. They are attached to nerve fibres and function as vestibular sense organs.

• Semicircular Canals: The canals are attached in the vestibular part of the inner ear. There are three of them and all canals are loop-shaped and fluid-filled. The semicircular canals are named according to their location which is lateral, superior and posterior and all canals are attached perpendicularly to each other. The main function of the canals is maintaining balance when the body or the head rotates.

• Cochlea: The cochlea is the primary sensory organ of hearing. It consists of a bony shell that contains three fluid-filled canals. The scala vestibuli or the upper canal, which begins at the oval window, the scala tympani or the lower canal which begins at the round window and the scala media, the middle canal which is located between the two canals.

Reissner’s membrane separates the scala media from the scala vestibuli whilst the basilar membrane separates it from the scala tympani. A part called the organ of Corti is located in the scala media and it lies along the entire length of the basilar membrane. In this organ, sound waves are converted to nerve impulses which are sent to the brain to the cranial nerve VII or the auditory nerve.

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