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Briefly describe the structure of the following: (c) Ear

Q1.    Briefly describe the structure of the following:

                (c) Ear

Answers (1)

Ear: Ear is the sense organ for hearing and equilibrium. It consists of three portions external ear, middle ear, and internal ear. 

1. External ear: It consists of the pinna, external auditory meatus, and a tympanic membrane. Pinna is a sensitive structure that collects and directs the vibrations into the ear to produce sound. External auditory meatus is a tubular passage supported by cartilage in the external ear. The tympanic membrane is a thin membrane that lies close to the auditory canal. It separates the middle ear from the external ear. 

2. Middle ear: It is an air-filled tympanic cavity that is connected with pharynx through the eustachian tube. The eustachian tube helps to equalize air pressure in both sides of the tympanic membrane. The middle ear contains a flexible chain of three middle bones called ear ossicles. The three ear ossicles are malleus, incus, and stapes that are attached to each other. 

3. Internal ear: It is also known as the labyrinth. The labyrinth is divided into the bony labyrinth and a membranous labyrinth. The bony labyrinth is filled with perilymph while a membranous labyrinth is filled with endolymph. 

The membranous labyrinth is divided into 2 parts. 

  • Vestibular apparatus: It is a central sac-like part that is divided into utriculus and sacculus. A special group of sensory cells called macula are present in sacculus and utriculus. Vestibular apparatus also contains three semi-circular canals. The lower end of each semi-circular canal contains a projecting ridge called crista ampularis. Each ampulla has a group of sensory cells called crista. Crista and macula are responsible for maintaining the balance of body and posture. 
  • Cochlea: Cochlea is a long and coiled outgrowth of the sacculus. It is the main hearing organ. Cochlea consists of three membranes. The organ of Corti, a hearing organ, is located on the basilar membrane that has hair cells.