Lets learn abot Human ear in detail. The Phonoreceptor and Mechanism of hearing or auditory sensations and equilibrium

Also known as stato-acuostic organ. It is the receptor for balancing and hearing which is sensitive for gravity and sound waves. It is also sensitive in orientation of body. It is also known as mechano receptor because of it change mechanical energy of sound waves in to action potential.

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Structure of Human Ear
Ear of mammal is divided in to 3 parts –

(1) External ear :
It is made up of pinna and auditory meatus.
Pinna is found in only mammals.
Its upper rounded part is helix and lower is ear lobe.
It is made up of adipose connective tissue and elastic cartilage and has ear muscles which are vestigeal in case of human beings.
Pinna collect the sound waves and drive towards auditory meatus. Auditory meatus is 25 mm. long canal lined by simple columnar epithelia and made up of fibro elastic cartilage.
It possesses ceruminus gland which secrete cerumin (ear wax). Cerumin trap the dust particles and microbes.
Tympanic membrane : It is also called ear drum and present at the junction of auditory meatus and tympanic cavity.

(2) Middle ear :
The cavity of middle ear is known as tympanic cavity which is enclosed by tympanic bulla bone of skull and filled with air. Middle ear separated from external ear by ear drum and from internal ear by thin bony portion or partition with two openings known as oval and round window.

(i) Ear ossicle : A chain of three small, movable bones, the auditory or ear ossicles crosses the tympanic cavity. The outer ossicle is attached to the inner surface of the tympanic membrane.

homan ear oscicles chart
In man ear ossicles are known as H.A.S. stapes is the smallest bone of the body. In frog only stapes is present.

human ear ossicles
(ii) Joints
human ear joints
(iii) Muscles
Tenser tympani : Limits movements and increases tension on eardrum to prevent damage to inner ear from loud sound.

(iv) Eustachian tube
It is made up of elastic cartilage and it connect middle ear to nosopharynx. It maintain equilibrium in and out side of the tympanic membrane. Blocking of eustachian tube impairs hearing due to imperfect vibrations of drum. Eustachian tube is normally closed, it opens during swallowing and yawning.

(v) Fenestrae
Between middle ear and internal ear a thin bony membrane is present which possess two apertures (Windows).
(a) Fenestra ovalis : It is upper window, connect middle ear to internal ear and guarded by membrane. End of stapes is fit on the upper window. It is towards vestibule so it is also known as F. vestibuli.
(b) Fenestra rotundus : It is ventral window, connect middle ear to internal ear and guarded by membrane.It is towards scala tympani so it is also known as F. Tympani (also known as F. cochleae).

(3) Internal ear (Membranous labyrinth) :
Internal ear is also known as membranous labyrinth and enclosed by bony labyrinth. Bony labyrinth is formed by periotic bone or petrous. A cavity is present between membranous labyrinth and bony labyrinth known as perilymphatic space. It is filled with perilymph and endolymph is found in membranous labyrinth. The membranus labyrinth consists of 2 parts – Vestibule and Cochlea.

human ear inner ear
(i) Vestibule : (Human Ear)
The vestibule is a central sac like part. It further consists of 2 chambers large – Utriculus(Upper) and smaller – sacculus (lower).

(a) Semicircular canal :
From utriculus 3 semicircular canals arise these are –
Anterior semicircular canal (Superior)
Posterior semicircular canal (Inferior)
Horizontal semicircular canal (External)
They are perpendicular to each other.

Crus commune : A common part of anterior and posterior semicircular canal arise from dorsal region of utriculus is known as crus commune.
Ampulla : Terminal part of the each semicircular canal is enlarged to form an ampulla.
Crista : Each ampulla has a sensory spot called crista ampullaris or simply crista, for equilibrium.

semicircular canals
Credit@Tortora
cristae and ampulla internal ear
(b) Sacculus :
It is a lower chamber of vestibule. From the lower part of the sacculus arises a short tube,the ductus reuniens, that joins the cochlear duct.
Ductus endolymphaticus : It is filled with endolymph and arises from the junction of utriculus and sacculus.
Macula : are present in utriculus and sacculus. it is a group of sensory cells. In man (Rabbit) 2 maculas are present. (A crista resembles a macula in structure except that lies on an elevation, the acoustic ridge,its sensory cells have longer “hair”, and its gelatinous mass is dome shaped, lacks otoliths and is called cupula).

Otolith : Also known as otoconia made up of protein and calcium carbonate and present in endolymph.

inner human ear
(ii) Cochlear duct and Cochlea :(Human Ear)
It is a spirally coiled tube (2 – 3 coiling) which is connected to sacculus by a short duct. It is divided into 3 chambers by 2 membranes.
(a) Scala vestibuli : Upper chamber filled with – perilymph – connect with middle ear by F. ovalis, or oral window.
(b) Scala media (Real cochlear duct) : Middle chamber filled with – endolymph.
(c) Scala tympani : Lower chamber filled with – perilymph connect with middle ear by F. Tympani or round window.
(d) Reissner’s membrane : Present at the roof of scala media, it separate Scala Media from Scala Vestibule.

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section of cochlea
(e) Basilear membrane : Present at the base of S.M. It is thicker than Reissner’s membrane and it separates S.M. to S.T.
(f) Modiolus : A bony core around which bony spiral canal of cochlea make2 (3/4) turns or coils in man.
(g) Helicotrema : A aperture present in scala media which connect scala vestibuli to scala tympani is known as helicotrema.
(h) Tectorial membrane : Tectorial membrane is a leaf like gelatinous structure present at the dorsal side of organ of corti.
(i) Organ of corti : Discovered by Italian anatomist Alfanso-Corti. Also known as ridges of corti which are present in basiler membrane. Organ of Corti contains a variety of cells.