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External Auditory Canal

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What is External Auditory Canal?

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The external auditory canal is also called the ear canal, external acoustic meatus, external auditory meatus (EAM). It is a passageway running from the outer ear to the middle ear, the size of the adult human ear can extend from the pinna to the eardrum and the length of external auditory canal is about 2.5 cm (1 in)  and 0.7 cm (0.3 in) in diameter. 

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External Auditory Canal Anatomy

The ear of the human can mainly be divided into two parts, the elastic cartilage part, which forms the outer third of the canal. Its anterior and the lower wall are cartilaginous, but its superior and back wall is fibrous. The lower wall of the ear is cartilage and continuation of the pile frame of the pinna. The cartilaginous portion of the human ear canal contains some of the small hair and also some of the specialized glands known as apocrine glands, this produce cerumen also known as ear wax.  The bony part forms the inner two thirds and the bony part is much shorter in children and is only a ring (annulus tympanicus) in the ear of the newborn babies. The epithelium encompassing layer of the bony portion of the ear canal is much thinner and more sensitive in comparison to the cartilaginous portions of the ear. 

 

The size and shape of the ear canal vary from individual to individual, the ear canal length of a human is approximately 1 inch and 0.28 inch in diameter. The human ear canal forms the sigmoid and runs from behind and above the downward and the forward and on the cross-section, it is oval. These are some of the important factors to consider while fitting the earplug in the human ear. 

 

Disorders 

As the canal of the ear is exposed to the external world, it is susceptible to various disease and disorders, some of the disorders have been mentioned below:

  • Atresia of the ear canal

  • Cerumen impaction

  • The exposure of the bone is caused by the wearing away of the skin in the canal.

  • Auditory canal osteoma which is bony outgrowths of the temporal bone. 

  • Cholesteatoma

  • Contact dermatitis of the ear canal

  • Fungal infection (otomycosis)

  • Ear mites in animals

  • Ear myiasis, an extremely rare infestation of maggots

  • Foreign body in the ear

  • Granuloma, a scar usually caused by tympanostomy tubes

  • Otitis externa is also known as the swimmer’s ear, which is a bacteria-caused inflammation of the ear canal.

  • Stenosis, a gradual closing of the canal

Ear Wax

It is also called the cerumen, which is yellowish in colour and a waxy substance is secreted in the ear canals. Ear wax plays an important role in the canal of the human ear, for assisting in cleaning and lubrication and also protecting from infections like bacteria, fungi and insects. If the ear secretes an excess amount of earwax, it can press against the eardrum and occlude the external auditory canal and impairing hearing, causing some conductive hearing loss. If these conditions of the ear are not treated on time, cerumen impaction will increase the risk of developing an infection within the human ear canal.  

Interesting Facts About Ear and Hearing

  • Our sense of balance lies in our ears: the vestibular system is located in the inner ear and is responsible for maintaining balance. The cause of most cases of vertigo lies within the hearing system.

  • The hardest bone is one of the temporal bones that protect the inner ear and is the hardest in the human body.

  • The smallest bone: the ear also has the smallest bone in the body. Cords, or “syrup,” in the middle ear, are part of the ossicles and are the smallest bone in the human body.

  • Our ears are always working: Did you know that our ears and hearing do not rest? When we sleep, our brains can ignore the sounds around us and respond only to loud or unexpected sounds as a defence mechanism that allows us to respond quickly.

  • 10 unpleasant noises in the human ear: a study by the University of Newcastle found some very unpleasant noises, including a bottle-scrubbing knife, a scratching fork on a plate, chalk on a board, a bottle in a bottle, nails on a board, a baby's cry, electric piercing, rusty jing chains, repeater and two pieces of expanded polystyrene rub together.

  • Wax is a natural protective agent: wax known as cerumen is secreted by the body to protect the middle ear from dust, dirt and infection by bacteria or fungi. However, when hidden in large numbers, it can cause formation and closure in the ears that affect our hearing.

  • The inner ear creates electrical impulses: sound waves are transmitted to different parts of the ear before they are converted into electrical energy by the cochlea and the Corti frame.

  • A small tube opens our ears: the Eustachian tube is 3.5 cm long and attached to the back of the nose. It helps to balance the pressure levels in the middle ear and creates a sense of self-opening or "explosion".

  • Hearing problems can be prevented by diet: Omega 3 fatty acids, found in fish such as salmon or tuna, strengthen the blood vessels in the inner ear. Also, antioxidants - especially folic acid - and the use of leafy green vegetables such as spinach and lettuce help to prevent hearing loss caused by noise exposure.

  • We hear better music on our left side: according to a study by the University of California and Arizona published in the journal Science, our right ear is more responsive to speech from birth, and our left side is more interested in continuous tones and musical sounds.

FAQ (Frequently Asked Questions)

Q1. What is the Shape of the External Acoustic Meatus?

Answer. The shape of the external acoustic meatus does not have a straight path, but it travels in an S-shaped curve like Initially, it travels in a superoanterior direction. Then it turns slightly to move superoposterior, and finally, It ends by running in an inferoanterior direction.

Q2. What is the External Auditory Meatus of Ear Made up of?

Answer. The external auditory meatus is made up of lateral cartilaginous and medial bony components. Infection of the EAC(External Auditory Canal) can penetrate inferomedially to the skull base and associated spaces via the fissures of Santorini (gaps in the EAC cartilage). The external ear including EAC lymphatic drainage is to the parotid nodal chain.

Q3. What is the Auditory Canal Function?

Answer. Some of the important functions of the auditory canal are to collect sound waves and guide them to the tympanic membrane. The middle ear is a narrow air-filled cavity in the temporal bone.