Lecture 11 - Structure of Ear | Animal Physiology and Functional Histology- I - MBBS PDF Download

 Page 1


 Structure of Ear 
 
 
Institute of Life Long Learning, University of Delhi  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Lesson Name : Structure of Ear 
Lesson Developer : Dr Mahtab Zarin and Dr. Zubeda 
College/Department : Department of Zoology 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Page 2


 Structure of Ear 
 
 
Institute of Life Long Learning, University of Delhi  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Lesson Name : Structure of Ear 
Lesson Developer : Dr Mahtab Zarin and Dr. Zubeda 
College/Department : Department of Zoology 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Structure of Ear 
 
 
Institute of Life Long Learning, University of Delhi  
Table of Contents 
• Introduction 
• Structures of Ear 
1. External (outer) ear 
• Auricle 
• Ear canal 
• Tympanic membrane 
2. Middle Ear 
• Auditory ossicles 
• Skeletal muscles 
• Eustachian tube 
3. Inner (Internal) Ear 
• Bony labyrinth 
• Membranous labyrinth 
• Cochlea 
• Organ of Corti  
• Semicircular Canals 
• Utricle and Saccule 
• Structures of Neural Pathways  
1. Structure of auditory nerve pathways  
2. Structure of equilibrium (vestibular) nerve pathways  
• Summary 
• Exercises 
• Glossary 
• References 
 
 
 
 
 
 
 
 
 
 
 
Page 3


 Structure of Ear 
 
 
Institute of Life Long Learning, University of Delhi  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Lesson Name : Structure of Ear 
Lesson Developer : Dr Mahtab Zarin and Dr. Zubeda 
College/Department : Department of Zoology 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Structure of Ear 
 
 
Institute of Life Long Learning, University of Delhi  
Table of Contents 
• Introduction 
• Structures of Ear 
1. External (outer) ear 
• Auricle 
• Ear canal 
• Tympanic membrane 
2. Middle Ear 
• Auditory ossicles 
• Skeletal muscles 
• Eustachian tube 
3. Inner (Internal) Ear 
• Bony labyrinth 
• Membranous labyrinth 
• Cochlea 
• Organ of Corti  
• Semicircular Canals 
• Utricle and Saccule 
• Structures of Neural Pathways  
1. Structure of auditory nerve pathways  
2. Structure of equilibrium (vestibular) nerve pathways  
• Summary 
• Exercises 
• Glossary 
• References 
 
 
 
 
 
 
 
 
 
 
 
 Structure of Ear 
 
 
Institute of Life Long Learning, University of Delhi  
 
 
 
Learning objectives 
•  Explain the structures of the ear; 
• Understanding the functions of each part of the ear; 
• Describe structures and function of receptor organs for equilibrium  
• To discuss neural pathways/parts of ear. 
Introduction 
Hearing is among the five senses in our body that is vision, taste, smell, and 
touch. The ears collect sound and transmit it to brain, where it is construed, so 
that speech, music, and other signals can be listened. So, the auditory system 
needs a source of sound, mechanism for detecting this sound, mechanisms for 
transmitted sounds to the central nervous system, and pathways of central 
nervous systems in order to send this sensory information to the brain where it 
can be processed, interpreted and accumulated. 
Structure of Ear 
The ear is the part of auditory system, which perceives sound and helps in 
maintenance of balance and body position.  
Ear is partitioned into three major parts (Fig. 1): 
1. External ear or outer ear 
• It collects sound waves and channels them inside of the ear. 
• It is the most outer part of the ear. 
• It is subdivided into the auricle, ear canal and tympanic membrane. 
2. Middle ear 
• It is cavity filled with airin the temporal bone, which opens through the 
eustachian tube into nasopharynx and from nasopharynx to the external.   
• Three auditory ossicles: the mallaeus, incus and stapes are placed in 
the middle ear.  
• Manubrium or handle of the malleus is connected to backside of the 
tympanic membrane. 
• The head of the malleus is connected to wall of middle ear and is attached 
to the incus. 
• Incus articulates with the head of the stapes. 
• The foot plate of stapes is connected through an annular ligament to the 
walls of the oval window. 
Page 4


 Structure of Ear 
 
 
Institute of Life Long Learning, University of Delhi  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Lesson Name : Structure of Ear 
Lesson Developer : Dr Mahtab Zarin and Dr. Zubeda 
College/Department : Department of Zoology 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Structure of Ear 
 
 
Institute of Life Long Learning, University of Delhi  
Table of Contents 
• Introduction 
• Structures of Ear 
1. External (outer) ear 
• Auricle 
• Ear canal 
• Tympanic membrane 
2. Middle Ear 
• Auditory ossicles 
• Skeletal muscles 
• Eustachian tube 
3. Inner (Internal) Ear 
• Bony labyrinth 
• Membranous labyrinth 
• Cochlea 
• Organ of Corti  
• Semicircular Canals 
• Utricle and Saccule 
• Structures of Neural Pathways  
1. Structure of auditory nerve pathways  
2. Structure of equilibrium (vestibular) nerve pathways  
• Summary 
• Exercises 
• Glossary 
• References 
 
 
 
 
 
 
 
 
 
 
 
 Structure of Ear 
 
 
Institute of Life Long Learning, University of Delhi  
 
 
 
Learning objectives 
•  Explain the structures of the ear; 
• Understanding the functions of each part of the ear; 
• Describe structures and function of receptor organs for equilibrium  
• To discuss neural pathways/parts of ear. 
Introduction 
Hearing is among the five senses in our body that is vision, taste, smell, and 
touch. The ears collect sound and transmit it to brain, where it is construed, so 
that speech, music, and other signals can be listened. So, the auditory system 
needs a source of sound, mechanism for detecting this sound, mechanisms for 
transmitted sounds to the central nervous system, and pathways of central 
nervous systems in order to send this sensory information to the brain where it 
can be processed, interpreted and accumulated. 
Structure of Ear 
The ear is the part of auditory system, which perceives sound and helps in 
maintenance of balance and body position.  
Ear is partitioned into three major parts (Fig. 1): 
1. External ear or outer ear 
• It collects sound waves and channels them inside of the ear. 
• It is the most outer part of the ear. 
• It is subdivided into the auricle, ear canal and tympanic membrane. 
2. Middle ear 
• It is cavity filled with airin the temporal bone, which opens through the 
eustachian tube into nasopharynx and from nasopharynx to the external.   
• Three auditory ossicles: the mallaeus, incus and stapes are placed in 
the middle ear.  
• Manubrium or handle of the malleus is connected to backside of the 
tympanic membrane. 
• The head of the malleus is connected to wall of middle ear and is attached 
to the incus. 
• Incus articulates with the head of the stapes. 
• The foot plate of stapes is connected through an annular ligament to the 
walls of the oval window. 
 Structure of Ear 
 
 
Institute of Life Long Learning, University of Delhi  
• The middle ear also contains two small skeletal muscles named as tensor 
tympani and the stapedius. These muscles control the vibrations of the 
tympanic membrane.  
• It pass on the sound waves to the oval window. 
3. Internal ear or inner ear 
• It is also known as labyrinth and consists of two parts i.e. bony and 
membranous labyrinth, placed one within the other. 
• Bony labyrinth is a sequence of channels in petrous portion of the 
temporal bone of the skull. Inside these channels, enclosed by a fluid 
known as perilymph, is the membranous labyrinth. 
• Membranous labyrinth encloses a fluid called endolymph. 
• Labyrinth is provided with a system of passages includes two chief 
functional divisions that is the cochlea and vestibular system. 
• Cochlea is a coiled tube, which is 35mm long and makes 2.5 in humans 
and devoted to hearing. 
• Vestibular system comprises of three semicircular canals and saccule and 
utricle. These vestibular apparatus are dedicated to maintain the balance 
or equilibrium.  
• The sensory receptors involved are hair cells. There are six groups of hair 
cells in each inner ear i.e. in the cochlea, each of 3 semicircular canals, 
saccule and utricle. 
 
Page 5


 Structure of Ear 
 
 
Institute of Life Long Learning, University of Delhi  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Lesson Name : Structure of Ear 
Lesson Developer : Dr Mahtab Zarin and Dr. Zubeda 
College/Department : Department of Zoology 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Structure of Ear 
 
 
Institute of Life Long Learning, University of Delhi  
Table of Contents 
• Introduction 
• Structures of Ear 
1. External (outer) ear 
• Auricle 
• Ear canal 
• Tympanic membrane 
2. Middle Ear 
• Auditory ossicles 
• Skeletal muscles 
• Eustachian tube 
3. Inner (Internal) Ear 
• Bony labyrinth 
• Membranous labyrinth 
• Cochlea 
• Organ of Corti  
• Semicircular Canals 
• Utricle and Saccule 
• Structures of Neural Pathways  
1. Structure of auditory nerve pathways  
2. Structure of equilibrium (vestibular) nerve pathways  
• Summary 
• Exercises 
• Glossary 
• References 
 
 
 
 
 
 
 
 
 
 
 
 Structure of Ear 
 
 
Institute of Life Long Learning, University of Delhi  
 
 
 
Learning objectives 
•  Explain the structures of the ear; 
• Understanding the functions of each part of the ear; 
• Describe structures and function of receptor organs for equilibrium  
• To discuss neural pathways/parts of ear. 
Introduction 
Hearing is among the five senses in our body that is vision, taste, smell, and 
touch. The ears collect sound and transmit it to brain, where it is construed, so 
that speech, music, and other signals can be listened. So, the auditory system 
needs a source of sound, mechanism for detecting this sound, mechanisms for 
transmitted sounds to the central nervous system, and pathways of central 
nervous systems in order to send this sensory information to the brain where it 
can be processed, interpreted and accumulated. 
Structure of Ear 
The ear is the part of auditory system, which perceives sound and helps in 
maintenance of balance and body position.  
Ear is partitioned into three major parts (Fig. 1): 
1. External ear or outer ear 
• It collects sound waves and channels them inside of the ear. 
• It is the most outer part of the ear. 
• It is subdivided into the auricle, ear canal and tympanic membrane. 
2. Middle ear 
• It is cavity filled with airin the temporal bone, which opens through the 
eustachian tube into nasopharynx and from nasopharynx to the external.   
• Three auditory ossicles: the mallaeus, incus and stapes are placed in 
the middle ear.  
• Manubrium or handle of the malleus is connected to backside of the 
tympanic membrane. 
• The head of the malleus is connected to wall of middle ear and is attached 
to the incus. 
• Incus articulates with the head of the stapes. 
• The foot plate of stapes is connected through an annular ligament to the 
walls of the oval window. 
 Structure of Ear 
 
 
Institute of Life Long Learning, University of Delhi  
• The middle ear also contains two small skeletal muscles named as tensor 
tympani and the stapedius. These muscles control the vibrations of the 
tympanic membrane.  
• It pass on the sound waves to the oval window. 
3. Internal ear or inner ear 
• It is also known as labyrinth and consists of two parts i.e. bony and 
membranous labyrinth, placed one within the other. 
• Bony labyrinth is a sequence of channels in petrous portion of the 
temporal bone of the skull. Inside these channels, enclosed by a fluid 
known as perilymph, is the membranous labyrinth. 
• Membranous labyrinth encloses a fluid called endolymph. 
• Labyrinth is provided with a system of passages includes two chief 
functional divisions that is the cochlea and vestibular system. 
• Cochlea is a coiled tube, which is 35mm long and makes 2.5 in humans 
and devoted to hearing. 
• Vestibular system comprises of three semicircular canals and saccule and 
utricle. These vestibular apparatus are dedicated to maintain the balance 
or equilibrium.  
• The sensory receptors involved are hair cells. There are six groups of hair 
cells in each inner ear i.e. in the cochlea, each of 3 semicircular canals, 
saccule and utricle. 
 
 Structure of Ear 
 
 
Institute of Life Long Learning, University of Delhi  
 
Fig. 1.  Cross-section of ear consists of outer, middle and 
inner ear. 
Source: http://cnx.org/contents/b375ea7d-22d5-4f47-b10a-41dd93637896@4 
CC 
 
External ear 
The external ear is the outer part of the ear. It contains the fleshy noticeable 
outer ear termed as auricle, ear canal, and the tympanic membrane. 
a) Auricle 
The visible and flap like part is called the auricle or 
(Fig. 2) 
pinna. It is composed of a fine 
sheet of yellow elastic cartilage, enclosed by skin. It isconnected to the 
neighboring parts through ligaments and muscles and leading to external acoustic 
meatus through fibrous tissue. 
Auricle consists of the curved rim, the helix and it is extended up to the ear canal 
known as the external acoustic meatus. The inferior portion of the auricle is 
lobule. Ligaments and muscles connect the auricle to the head. The center of 
the pinna named as the concha that leads to the external auditory 
canal.