Chapter 32, Problem F32.1A

Summary Introduction

To analyze:

Major structures of the ear in thegiven diagram.

Introduction:

Ear is the sensory organ responsible for hearing in an individual. Due to differences in the air pressure of the surrounding area or even moderate level vibrations causes tympanic membrane to vibrate and thereby the waves proceed towards the inner ear, cochlea and hence enabling an organism to hear. The normal hearing range is 20 − 20000Hz andhuman beings can hear at 0 dB (decibel) frequency..

Explanation of Solution

The major structures in the ear are labeled.

  

Ear comprises three bones which are known as ear ossicles. They are malleus, incus and stapes. These bones are interconnected to each other. Malleus is the first among the three ear ossicles. Pinna is the external part of outer ear. It is responsible for the collection of vibrations in the air which produce sound.Malleus is known as hammer bone because of its shape. It is attached to incus and when sound waves reach malleus, it transmits these waves from incus to the eardrum.Incus is the second bone among the ear ossicles. It is the connecting link between malleus and stapes.Incus is shaped like an anvil. Its one part which articulates with the malleus is known as short crus and the other part which is long and articulates with stapes is known as long crus. It receives the sound waves from the malleus and transmits it to the stapes for further processing.The inner ear comprises of a vestibular apparatus which comprises of the bony labyrinth part along with these semicircular canals or semicircular ducts and otolith organs. The inner ear has fluid filled labyrinth.

The sound waves or vibrations from the stapes reach cochlea. It is surrounded by membrane and the fluid present in its surrounding known as perilymph. This cochlea possesses hair cells or stereocilia which receives the sound waves and then further these sound waves produce nerve impulse which travels to the auditory cortex of the brain and thereby on being analyzed, sound can be heard.The vestibulocochlear nerve comprises of the cochlear nerve and the vestibular nerve. The name itself suggests that this nerve carries information about hearing as well as the balance of the body with regards to the posture. Thus, it performs a dual function.

Oval window connects the three ears ossicles present in the middle ear − malleus, incus and stapes to the cochlea of the ear. Stapes is the bone which gets connected to this oval window, but since the three bones are interconnected, therefore we say that ear ossicles are connected to the cochlea through this window.The tympanic membrane is composed of connective tissue. It receives vibrations from the external meatus and transmits them towards the ossicles. Also, it sets the demarcation between the outer ear and the middle ear.The tympanic membrane is composed of connective tissue. It receives vibrations from the external meatus and transmits them towards the ossicles. Also, it sets the demarcation between the outer ear and the middle ear.

Eustachian tube connects the middle ear to the nasopharynx thereby to the upper part of the throat. Eustachian tube has a major role in maintaining the balance of the body. It helps in equalizing air pressure between the middle ear and the external surrounding.External auditory canal comprises of hair and wax secreting sebaceous glands which help in trapping any dust particles present in the surrounding air which has to be passed to the middle ear. Thus, it helps in ensuring that purified air reaches the middle ear thereby preventing any sort of infection.