Describe the various parts of the human ear and their functions.

(N/A) The ears perform two primary sensory functions: hearing and the maintenance of body balance. Hence,they are also called phonoreceptors.
Anatomically,the ear can be divided into three main regions:
$(a)$ Outer ear $(b)$ Middle ear $(c)$ Inner ear
$(a)$ Outer ear: Consists of the pinna and the external auditory canal.
The pinna is a funnel-shaped structure that collects vibrations in the air,which produce sound. The auditory canal is '$S$'-shaped and extends up to the tympanic membrane (eardrum).
There are very fine hairs and wax-secreting glands (ceruminous glands) in the auditory canal. These glands secrete a brown-coloured fatty substance known as earwax,which protects and lubricates the inner lining of the auditory canal.
$(b)$ Middle ear: The tympanic membrane is a thin,double-layered epithelial partition between the external auditory canal and the middle ear. It is made of fibrous connective tissue.
The middle ear contains three ossicles: Malleus,Incus,and Stapes,attached 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. These ossicles increase the efficiency of sound wave transmission to the inner ear.
An Eustachian tube connects the middle ear cavity with the pharynx,helping to equalize the pressure on both sides of the eardrum.
$(c)$ Inner ear: The fluid-filled inner ear,called the labyrinth,consists of two parts: the bony and the membranous labyrinths.
The bony labyrinth is a series of channels containing the membranous labyrinth,which is surrounded by a fluid called perilymph. The membranous labyrinth is filled with a fluid called endolymph.
$(i)$ The coiled portion of the labyrinth is called the cochlea. The Reissner's membrane and basilar membrane divide the perilymph-filled bony labyrinth into an upper Scala Vestibuli and a lower Scala Tympani. The space within the cochlea,called the Scala Media,is filled with endolymph.
The Organ of Corti is a structure located on the basilar membrane that contains hair cells,which act as auditory receptors. Above the rows of hair cells is a thin elastic membrane called the tectorial membrane.
$(ii)$ The inner ear also contains a vestibular apparatus located above the cochlea. It is composed of three semi-circular canals and the otolith organ (saccule and utricle). The crista ampullaris (in the ampulla of the canals) and the macula (in the saccule and utricle) are the specific receptors responsible for the maintenance of body balance and posture.