[Biology Class Notes] on Human Ear Pdf for EXAM

The human ear is the organ of hearing and equilibrium that detects and analyzes sound by transduction. Ear functions the conversion of sound waves into electrochemical impulses and maintains the sense of balance. The ears are not just the hearing organ but are a complex system of parts that not only allows humans to hear, but also makes it possible for humans to walk or function the whole body system.

In earth, most mammals have an external ear. The ear is the part of our Auditory system. The part of the ear that is visible from outside is called Pinna. Being mammals, humans also have ears. Ears are located on both sides of the brain within the temporal bones of the skull. 

Pinna is made up of elastic yellow cartilages and it is covered with integument and tendons and muscles attach it with surrounding parts. In the fetus, the ear derives from the first pharyngeal pouch. Each layer of ear derives from different germinal layers, inner ear from Ectoderm, middle ear from Endoderm, and outer ear from Mesenchyme. 

Structure of the Human Ear

The human ear is divided into three sections, those are the outer ear, the middle ear, and the inner ear.

The outer ear or external ear is consisting of the pinna and the ear lobe. Pinna is cartilaginous and it directs the sound wave towards the external auditory canal. The external auditory canal channels the sound to the tympanic membrane. In general, the tympanic membrane is called the eardrum. The tympanic membrane is thin and semi-transparent. 

The external ear is formed by the pinna and the external auditory canal that receives sounds and transmits them to the middle ear via the eardrum. The eardrum is very circular and flexible, and it begins to vibrate when the incoming sound waves strike it.

The middle ear consists of three tiny bones and it is filled with air. The bones are known as ossicles. The three bones of the middle ear are named malleus, incus, and stapes. Sound vibration on the tympanic membrane is transmitted further by these three bones.

These three bones form a bridge between the eardrum and the inner ear through the oval window that covers the cochlea. A narrow tube called the Eustachian tube is approximately 3.5 cm in length, connects the ear to the outer part of the nose, and acts as an equalizing valve. This valve ensures that the pressure on either side of the eardrum is balanced and that sound can be heard correctly.

The inner ear or, the labyrinth consists of two main structures. The structures are the cochlea and the vestibular system. The main function of the cochlea is to help in hearing. The vestibular system consists of 3 semi-circular canals, saccule, and utricle.

The inner ear includes the cochlea, a structure that has a spiral shape similar to a snail shell and is located in the bony labyrinth that has several membranous sections filled with fluids called endolymph. When these liquids move, they will create fluctuations in the cochlea’s which are hair-like structures called stereocilia.

 

And at last, the Organ of Corti transforms the mechanical energy of the sound waves into nerve energy by creating electric impulses and these impulses are then sent to the brain through the auditory or vestibulocochlear nerve.

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The Smallest Bone in The Body

The bones in the ear are the 3 smallest bones of the human body. The bones are malleus, incus, and stapes. Among these 3 bones, stapes is the smallest bone. 

The Function of The Human Ear

• The main function of the ear is to help in hearing. In our brain, the temporal lobe senses sound. Pinna directs the sound wave toward the eardrum through the auditory canal and the eardrum amplifies it. The vestibulocochlear nerve sends the sound wave stimulus to the temporal lobe and then we are able to hear the sound.

• The ear also helps in balancing the body. The human ear allows us to feel the effect of gravity that is known as stationary balance and it also helps to feel the acceleration that is known as dynamic balance. 

• The utricle and saccule provide a static balance.

• Dynamic balance is provided by semi-circular canals. 

• While moving eye tracking is maintained by vestibule-ocular reflex.

Human Ear Diagram

In the human ear diagram, we can distinguish between the inner ear, middle ear, and outer ear.

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Parts of Human Ear 

Different structures of the human ear help in different functions. 

The pinna of the outer ear protects the eardrum from intense sound and channels the sound to the eardrum through the auditory canal. The eardrum vibrates and transmits the sound to the inner ear.

The ossicles of the middle ear amplify the sound and pass the vibration to the oval window. The oval window is the membrane between the inner and middle ear. There is a narrow tube that connects our nose to the ear, named the Eustachian tube. This tube helps to pass air into the middle air and drains the mucus to the nasopharynx.

In the inner ear, a structure named cochlea is observed. It is filled with fluid and contains the organ of Corti. The Organ of Corti has several hairs like a sensory cell, named cilia. The waves from the middle year cause vibration in inner ear fluid and it makes cilia vibrate. This vibration of the cilia sends nerve impulses to the brain. The semicircular canals in the inner ear are situated vertically to each other. It also contains fluid and helps in movement.

Fun fact

Egg-laying mammals are called monotremes, as they are primitive mammals they don’t have pinna in their body.

This is all about the human ear, its various parts, and its functions. The human ear functions not only as a hearing sense organ but also assists us to maintain our balance. Learn more about its physiology and understand its features.