Introduction

The human ear is the organ of hearing and helps in maintaining posture. The outer ear is responsible for collecting the sound heard and amplifying it by adding strength to it. The middle ear performs the same function as the outer ear but at a granular level and maintains air pressure with the help of an eustachian tube . The inner ear acts by converting the sound waves to messages and sends the message to the brain cells. 

Parts of human ear

The human ear is divided into three major parts:

• The outer ear
• The middle ear
• The inner ear

Internal Structure of Human Ear

The three parts of the human ear differ in their structural details:

• Outer ear: It consists of ear pinna and external auditory canal
• Pinna : The external ear is composed of cartilage. Hair follicles are present in the thin lining of cartilage. A curved cartridge is developed parallel to the helix or outer rim of the ear. A protruded ear is developed with lobule and triangular fossa. Pinna consists of the helix, antihelix cartridge, tragus, earlobes, concha, triangular fossa, anterior notch and antitragus 
• External auditory canal – This external auditory canal is cylindrical in structure protected by bones and cartilages. The inner layer is lined with a thin layer of skin which holds wax-producing glands. These glands are a group of ceruminous and sebaceous glands. The sebaceous glands secrete sebum which is an oily substance into the hair follicles of the auditory canal. The ceruminous glands produce a moist white secretion that becomes sticky, dark, and thick when dried

Middle ear

The middle ear has no regular shape and varies from individual to individual. It is lined with mucosa. The middle ear is filled with nitrogen-rich gas. It has the following parts:

• Tympanic membrane , eustachian tube and ear ossicles
• The tympanic membrane – It facilitates dividing the external ear from the middle ear. It consists of three layers – external ear canal, fibrous middle layer, and mucosal layer
• The pars tensa comprise the major portion of this membrane and occupy themselves at the lower part of the tympanic membrane. Below the pars tensa, the pars flaccida is present, which is a triangular area. This area lacks a fibrous layer
• Ear disease can be caused when the dead skin gets accumulated in the middle ear. This leads to hearing loss when the complexity increases. The annulus is the thick membrane at the outer rim
• Tegmen tympani is present on the roof of the middle ear. It separated the middle ear from the meninges and temporal lobe of the brain. Due to the proximity of the vein and artery in the middle ear, people can sense the pumping of blood in the ear. The anterior wall of the middle ear has an opening for the eustachian tube. This tube is made of bone and cartilage. Air entry is allowed by the eustachian tube. Air pressure is equalized because of this air entry. The eustachian tube contracts when the individual is chewing, swallowing and yawning. The air passes into the middle ear as the tube is opened. Along with the growth of the head and as the skull enlarges, the eustachian tube turns to be more vertical. This improves the equalization of air pressure in the middle ear
• Ear ossicles-These are three named malleus (hammer), incus (anvil)  and stapes (stirrup). Out of this stapes is the smallest bone in the human body
• Malleus is in contact with the tympanic membrane and receives the auditory vibrations from it. The vibrations are passed to the second ear ossicle, the incus and thereafter to the stapes. The third ear ossicle, stapes is connected to the membrane of the oval window. Through the oval window the vibrations generated by sound are passed to the internal ear.

Inner Ear

The inner ear consists of  semicircular canals, the vestibule and the cochlea. These organs facilitate hearing capacity and provide balance to the body.

• Semicircular canals are three and are called horizontal, superior and posterior semicircular canals. These are filled with a fluid called endolymph. These are helpful in maintaining the posture particularly during different types of head movements
• The vestibule is oval and slightly flat in structure. It is present between semicircular canals and cochlea. It is filled with endolymph.It keeps on sending signals to the brain which in turn help in maintaining postural  equilibrium
• The cochlea is a snail-like structure that houses the organ Corti (organ of hearing). It is a spiral canal and varies in length from individual to individual. Bones and membranes divide them into three compartments – upper component (scala tympani), middle compartment (scala media) and lower component (scala vestibuli)
• Fluid filled in the scala tympani and scala vestibuli is called perilymph and in scala media it is called endolymph
• Hair-like projections are present in the lower membrane and are connected to the auditory nerves. High, base, and low frequencies are responded to by these projections. The canal bulges into the middle ear forming the organ of the promontory

Process of Hearing

Holistically, the parts of the human ear put in efforts together to help an individual here and remain balanced. The functions of the human ear include:

• Sound waves around the ear are collected by the external ear 
• Sound waves reach the eardrum through the ear canal
• When the sound waves travel through the eardrum, it vibrates. Hence, the bones of the middle ear reflect to be in motion
• The mastoid bone surrounds the middle ear
• The sound waves are transmitted to the inner ear through the bones present in the middle ear
• Air pressure remains in the middle ear. It is regulated by a eustachian tube. A healthy ear facilitates maintaining the air pressure balanced in the middle ear
• Sound waves are converted into messages and signals are carried over to the brain cells by the vestibular nerve
• The semicircular canals present in the inner ear facilitate balance to an individual
• The cochlea present in the inner ear reacts to the sound waves and converts them to nerve signals 
• The sound signals reach the brain cells through auditory nerves

Conclusion

Human ear is a complicated sense organ of the human body. Its anatomy is helpful in understanding the structural details of each part along with the function. The skin and cartilage present in the outer ear and the ear canal are protective in nature. The eardrum separates the middle ear from the outer ear and is helpful in amplifying the sound signals. The inner ear is not only meant for sending signals to the brain to facilitate hearing but has a crucial role in balancing an individual in every type of movement.