Structure of the Human Ear MCQ - Practice Questions with Answers

• The ears perform two sensory functions, hearing and maintenance of body balance.
• Anatomically, the ear can be divided into three major sections called the outer ear, the middle ear and the inner ear. 

External Ear:

• It comprises a pinna, external auditory meatus (canal) & tympanic membrane.
• Pinna:
  • The pinna collects the vibrations in the air which produce sound. 
  • It is made of elastic cartilage covered with skin.
• External Auditory Meatus:
  • It is a tubular passage supported by cartilage in its exterior part and by bone in its inner part.
  • Along the length of the auditory canal are ceruminous glands that contribute to the production of cerumen (earwax). 
  • Because cerumen is sticky it can help prevent small particles from finding their way to the tympanic membrane. 
  • Cerumen also helps prevent bacterial growth, waterproofs the auditory canal and tympanic membrane, and maybe a deterrent to small insects.
  • The external auditory meatus leads inwards and extends up to the tympanic membrane.
• The tympanic membrane (tympanum):
  • The tympanic membrane is composed of connective tissues covered with skin outside and with mucus membrane inside.
    

• There is a tympanic cavity that is filled with air.
• It is connected with the nasopharynx through the Eustachian tube (auditory tube) 
• The eustachian tube serves to equalize the air pressure in the tym­panic cavity with that on the outside.
• The middle ear contains three ossicles called malleus, incus and stapes which are attached to one another in a chain-like fashion. 
• The malleus is attached to the tympanic membrane and the stapes is attached to the oval window of the cochlea. 
• The ear ossicles increase the efficiency of transmission of sound waves to the inner ear. 
• The middle ear is connected with the inner ear through two small openings closed by the membranes.
• These openings are:
  • (a) fenestra ovalis (oval window) 
  • (b) fenestra rotunda (round window)
• The fenestra ovalis is covered by footplate of the stapes. 
• The fenestra rotunda is enclosed by a flexible secondary tympanic membrane. 
• The fenestra rotunda is responsible for equalizing the pressure on either side of the tym­panic membrane.
   

• The fluid-filled inner ear called labyrinth consists of two parts, the bony and membranous labyrinths. 
• The bony labyrinth is a series of channels. 
• Inside these channels lies the membranous labyrinth, which is surrounded by a fluid called perilymph. 
• The membranous labyrinth is filled with a fluid called endolymph
• It consists of Cochlea and Vestibular Apparatus
• Cochlea is the main organ of hearing and Vestibular apparatus helps in balancing 

Cochlea: 

• The coiled portion of the labyrinth is called cochlea. 
• The membranes constituting cochlea, the reissner’s and basilar, divide the surrounding perilymph filled bony labyrinth into an upper scala vestibuli and a lower scala tympani 
• The space within cochlea in the middle is called scala media and it is filled with endolymph. 
• At the base of the cochlea, the scala vestibuli ends at the oval window, while the scala tympani terminates at the round window which opens to the middle ear.
• The organ of Corti is a structure located on the basilar membrane which contains hair cells that act as auditory receptors. A large number of processes called stereocilia are projected from the apical part of each hair cell.
• The sensory hairs project from the outer ends of the hair cells into the scala media, while from the inner end of the cells nerve fibres arise, which unite to form the cochlear nerve. 
• The tectorial membrane overhangs the sensory hair in the scala media. 
• Its properties are to determine the patterns of vibration of sound waves.
  

• The inner ear also contains a complex system called the vestibular apparatus, located above the cochlea. 
• The vestibular apparatus is composed of three semicircular canals and the otolith
• This is concerned with the balance of the body 
• The vestibular apparatus is connected to Cochlea by ductus reuniens

Semicircular Canals:

• There are present three semicircular canals; the anterior, posterior and lateral
• The three canals are orthogonal to each other (at 90 degree) . 
• Each semicircular duct is enlarged at one end to give rise to a small rounded ampulla.
• Each ampulla contains a sensory patch of cells, the crista ampullaris
• Each crista consists of two kinds of cells, the sensory and supporting cells. 
• The sensory cells bear long sensory hairs at their free ends and nerve fibres at the other end. 
• The sensory hairs are partly embedded in a gelatinous mass, the cupula. 
• The cristae are concerned with the dynamic balance of the body.

The Otolith

• It consists of Utricle (bag like) and Saccule (sac like)
• The utricle is a dorsally placed structure to which all the three semicircular ducts are connected. 
• The saccule is a ventrally situated structure which is joined with the utricle by a narrow utricular saccular duct.
• Both utricle and saccule contain sensory patches, the maculae.
• A macula comprises sensory and supporting cells similar to those of the crista. 
• The hair is not actually motile and is embedded in a gelatinous membrane called the otolith membrane.
• The otolith membrane also has very small crystals of calcium carbonate called the otolith. 
• The cristae and maculae are the receptors of static balance.

Thus Crista Ampullaris and Maculae are concerned with balance