Ear consists of three parts namely external ear, middle ear and internal ear. External ear is fan shaped fixed part projects out from the head. It is called pinna. It collects sound waves and direct them into the ear. It cannot move but in animals it can move around and can be directed in the direction of sound waves. The external auditory meatus connects the middle ear. This canal is lined by glands that secretes cerumen (ear wax) which protects from infection and external agents like insects. The ear is lodged in boney cavity and protected by temporal bone fromall sides.
Middle ear the external ear is separated from the middle ear by tympanic membrane. The membrane is exposed to the outside atmospheric pressure through external meatus. The membrane is also connected internally by Eustachian tube to the external atmospheric pressure in the pharynx. Thus on either side, the tympanic membrane is exposed to equal atmospheric pressure. This membrane is connected internally to a set of 3 ossciles a)malleus b) incus and c) stapes. They are connected serially to one another and to the tympanic membrane (outside) and to oval window (inside).
Inner ear: The entire structure is safely lodged, in temporal bone. This enables us to hear and also maintains the equilibrium of the body position. The inner ear extends from oval window to cochlea. The different parts of inner ear are bony labyrinth, membranous labyrinth , cochlea , vestibular and semi circular canals.
Bony labyrinth is a cavity within the temporal bone lined with periosteum. It has perilymph. Within the membranous labyrinth there is a fluid called endolymph. Vestibule is the expanded part of the middle ear. It contains oval and round windows. Semicircular canals – there are three tubes arranged in three different planes in spaces. They are in continuity with the vestibule.