Question

Structure of human ear and their function

Answer 1

1. External Ear:

(i) Pinna:

The pinna is a projecting elastic cartilage covered with skin. Its most prominent outer ridge is called the helix. The lobule is the soft pliable part at its lower end composed of fibrous and adipose tissue richly supplied with blood capillaries. It is sensitive as well as effective in collecting sound waves.

Parts of Human Ear

(ii) External Auditory Meatus:

It is a tubular passage supported by cartilage in its exterior part and by bone in its inner part. The meatus (canal) is internally lined by hairy skin (stratified epithelium) and ceruminous glands (wax glands). The latter are modified sweat glands which secrete a waxy substance— the cerumen (ear wax) which prevents the foreign bodies entering the ear.

(iii) The tympanic membrane (tympanum):

Separates the tympanic cavity from the external auditory meatus. It is thin and semi-transparent, almost oval, though somewhat broader above than below. The central part of the tympanic membrane is called the umbo. The handle of the malleus is firmly attached to the membrane’s internal surface.


Functions of External Ear:

It directs sound waves towards the tympanic membrane. The sound waves produce pressure changes over the surface of the tympanic membrane. The cerumen (ear wax) prevents the entry of the foreign bodies into the ear.

2. Middle Ear:

It includes the following:

(i) The tympanic cavity, filled with air is connected with the nasopharynx through the Eustachian tube (auditory tube), which serves to equalize the air pressure in the tym­panic cavity with that on the outside.

(ii) There is a small flexible chain of three small bones called ear ossicles— the malleus (hammer shaped), the incus (anvil shaped) and the stapes (stirrup shaped). The malleus is attached to the tympanic mem­brane on one side and to the incus on the other side.

The incus in turn is connected with the stapes, which is attached to the oval membrane covering the fenestra ovalis (oval window) of the inner ear. Malleus is the largest ossicle, however, stapes is smallest ossicle. Stapes is also the smallest bone in the body.

(iii) Two skeletal muscles, the tensor tympani attached to the malleus and the stapedius attached to the stapes, are also present in the middle ear. Stapedius is the smallest muscle in the body.

(iv) 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) as mentioned above and (b) fenestra rotunda (round window).

The fenestra ovalis is covered by foot plate of the stapes. The fenestra rotunda is enclosed by a flexible secondary tympanic membrane. The latter is responsible for equalizing the pressure on either side of the tym­panic membrane.

Ear Osslicles

Functions of Middle ear:

(i) Due to the pressure changes produced by sound waves, the tympanic membrane vibrates, i.e., it moves in and out of the middle ear. Thus the tympanic membrane acts as a resonator that reproduces the vibration of sound,

(ii) It transmits sound waves from external to the internal ear through the chain of ear ossicles,

(iii) The intensity of sound waves is increased about twenty times by the ear ossicles. It may be noted that the frequency of sound does not change and

(iv) From the tympanic cavity extra sound is carried to the pharynx through Eustachian tube.

3. Internal Ear:

There is a body cavity on each side enclosed in the hard periotic bone which contains the perilymph. The later corresponds to the cerebrospinal fluid. A structure, the membranous labyrinth floats in the perilymph. The membranous labyrinth consists of three semicircular ducts, utricle, saccule, endolymphaticus and cochlea.

(i) Semicircular Ducts:

There are present three semicircular ducts; the anterior, the posterior and the lateral semicircular ducts. They arise from the utricle. The anterior and posterior semicircular ducts arise from crus commune.

Each semicircular duct is enlarged at one end to give rise to a small rounded ampulla. The anterior and lateral semicircular ducts bear ampullae at their anterior ends, while the posterior duct contains an ampulla at its posterior end.

Membranous Labyrinth, Crista, Macula

(ii) Utricle, Endolymphaticus and Saccule:

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 utriculosaccular duct. From this duct a long tube, the ductus endolymphaticus arises which ends blindly as the saccus

Both cristae and maculae are concerned with balance.

(iii) Cochlea:

It is the main hearing organ which is connected with saccule by a short ductus reuniens leading from the saccule. It is spirally coiled that resembles a snail shell in appearance. It tapers from a broad base to an almost pointed apex.

Answer 2

ᴀɴsᴡᴇʀ࿐

ᴛʜᴇ ᴇᴀʀ ᴄᴀɴ ʙᴇ ʙʀᴏᴀᴅʟʏ ᴄʟᴀssɪғɪᴇᴅ ɪɴᴛᴏ ᴛʜʀᴇᴇ ᴘᴀʀᴛs

ᴏᴜᴛᴇʀ ᴇᴀʀ:- ᴛʜᴇ ᴇᴀʀ ᴅʀᴜᴍ ᴠɪʙʀᴀᴛᴇᴅ ᴡʜᴇɴ ᴛʜᴇ ᴇᴀʀ ᴅʀᴜᴍ sᴏᴜɴᴅ ᴡᴀᴠᴇs sᴛʀɪᴋᴇ ɪᴛ ᴀɴᴅ ᴛʀᴀɴsᴍɪᴛs ᴛʜᴇ sᴏᴜɴᴅ ᴛᴏ ᴛʜᴇ ᴍɪᴅᴅʟᴇ ᴇᴀʀ.

ᴍɪᴅᴅʟᴇ ᴇᴀʀ:- ᴛʜᴇ ᴛʜᴇ ᴛʜʀᴇᴇ ʙᴏɴᴇs ᴀʀᴇ ᴘʟᴀᴄᴇᴅ ɪɴ sᴜᴄʜ ᴀ ᴡᴀʏ ᴛʜᴀᴛ ᴛʜᴇʏ ᴍᴏᴠᴇ ᴡʜᴇɴ ᴛʜᴇ ᴇᴀʀ ᴅʀᴜᴍ ᴠɪʙʀᴀᴛᴇs ᴀɴᴅ ᴛʜᴇ ᴛʜᴇʀᴇғᴏʀᴇ , ᴛʀᴀɴsᴍɪᴛs ᴛʜᴇ ᴠɪʙʀᴀᴛɪᴏɴ ᴛᴏ ᴛʜᴇ ɪɴɴᴇʀ ᴇᴀʀ.

ɪɴɴᴇʀ ᴇᴀʀ:- ᴛʜᴇ ʜᴀɪʀ ᴏғ ɪɴɴᴇʀ ʜᴀɪʀ ᴛʀᴀɴsғᴏʀᴍ ᴛʜᴇ ᴠɪʙʀᴀᴛɪᴏɴs ɪɴᴛᴏ ᴇʟᴇᴄᴛʀɪᴄᴀʟ ɪᴍᴘᴜʟsᴇs , ᴡʜɪᴄʜ ᴀʀᴇ ᴛʜᴇɴ ᴛʀᴀɴsғᴇʀʀᴇᴅ ᴛᴏ ᴛʜᴇ ʙʀᴀɪɴ ᴠɪᴀ ᴛʜᴇ ᴀᴜᴅɪᴛᴏʀʏ ɴᴇʀᴠᴇ.