Anatomy and Function of the Human Ear

Function of the Human Ear

• The human ear facilitates hearing, balance, and spatial orientation.
• It has three sections: outer, middle, and inner ear.
• The outer ear gathers sound waves, directing them to the eardrum.
• The eardrum then vibrates, which sends signals to the middle ear.
• The middle ear contains the malleus, incus, and stapes, which amplify sound vibrations into electrical impulses.
• These impulses are then sent to the brain via the auditory nerve.
• The semicircular canals in the inner ear help maintain balance.

Structure and Functions of The Ear

• The outer ear captures and guides sound waves into the ear.

Pinna (Auricle)

• The pinna is the visible part of the outer ear, made of cartilage covered by skin.
• It collects sound waves and directs them into the ear canal.
• The shape helps in determining the direction and source of sounds, aiding in vertical sound localization by altering sound wave frequencies.
• The pinna offers minor protection to the ear canal and eardrum from physical damage.

External Auditory Canal (Ear Canal)

• The ear canal is a narrow tube from the pinna to the eardrum.
• It transmits sound waves from the pinna to the eardrum, amplifying particular sound frequencies for speech.
• Hairs and ceruminous glands in the ear canal produce earwax (cerumen) that traps dust and microorganisms to protect the middle and inner ear.
• The ear canal regulates temperature and humidity to maintain optimal conditions for the eardrum.

Eardrum (Tympanic Membrane)

• The eardrum separates the outer and middle ear, vibrating when sound waves enter.
• These vibrations transmit to the ossicles, converting sound waves into mechanical energy.
• The eardrum acts as a barrier, safeguarding the middle ear from external contaminants.

Structure and Functions of the Middle Ear

• The middle ear acts as a bridge between the outer and inner ear.

Ossicles

• The middle ear contains three tiny bones known as ossicles which are the the smallest bones in the human body:
• Malleus (Hammer): Transfers eardrum vibrations to the incus.
• Incus (Anvil): Passes vibrations from the malleus to the stapes.
• Stapes (Stirrup): Connects to the oval window of the inner ear, transmitting vibrations.

Eustachian Tube

• The Eustachian tube connects the middle ear to the nasopharynx.
• It equalizes pressure on both sides of the eardrum for proper hearing, opening during swallowing and yawning.
• It drains fluids from the middle ear into the throat, preventing fluid buildup and infections.

Middle Ear Muscles

• Tensor Tympani: Dampens eardrum and ossicle vibrations to protect the inner ear from loud sounds.
• Stapedius: Controls stapes movement and stabilizes it.

Oval Window

• It receives vibrations from the stapes and transmits them to the cochlea in the inner ear.
• The process converts sound waves into fluid movements for sensory cells to interpret.

Round Window

• As the oval window transmits vibrations into the cochlea, the round window allows for displacement of fluid for sound wave transmission.

Middle Ear Cavity (Tympanic Cavity)

• The middle ear cavity amplifies sound vibrations, enhancing energy transfer from the outer to the inner ear.
• The Mucous membrane protects the middle ear from infections to supporting the health of the ossicles

Structure and Functions of The Inner Ear

• Cochlea, vestibule, and semicircular canals are all components of the inner ear.

Cochlea

• The cochlea is a spiral-shaped organ divided into the scala vestibuli, scala media, and scala tympani.
• Scala Vestibuli and Scala Tympani: Contain perilymph fluid, vibrations from the ossicles enter through the oval window and exit through the round window.
• Scala Media: Contains endolymph fluid and houses the organ of Corti, the sensory part for hearing.

Organ of Corti

• The organ of Corti contains inner and outer hair cells.
• Inner hair cells convert sound vibrations into electrical signals.
• Outer hair cells amplify vibrations and enhance sensitivity of inner hair cells.
• Tectorial Membrane: Causes hair cells to bend when fluid waves move through the cochlea.
• Basilar Membrane: Different regions vibrate to different sound frequencies with high-frequency sounds peaking near the base, and low-frequency sounds near the apex.

Sound Transduction

• Sound waves vibrate the tympanic membrane.
• These vibrations transmit through the ossicles to the oval window.
• The movement of the oval window creates pressure waves in the perilymph of the scala vestibuli that are transferred to the endolymph of the scala.
• Hair Cell Activation: The pressure waves causes the basilar membrane to move, bending the hair cells allowing potassium ions to enter and depolarize the cells.
• Neurotransmitter Release: Depolarization of hair cells generate nerve impulses in the auditory nerve fibers

Vestibule

• The vestibule contains the utricle and saccule.

Utricle and Saccule

• Otolith Membrane: A gelatinous layer contains otoliths overlaying the hair cells.
• Macula: The sensory region containing hair cells extends into the otolith membrane.
• Function of Utricle and Saccule: When the head moves or tilts, the otoliths cause the otolith membrane to shift, bending the hair cells' stereocilia. This bending generates nerve impulses providing head position and linear acceleration.
• Utricle responds to horizontal movements.
• Saccule responds to the vertical movements.

Semicircular Canals

• The semicircular canals are three looped structures oriented at right angles correlating to motion.

Ampulla

• Crista Ampullaris: The sensory organ containing hair cells with stereocilia embedded in the cupula.
• Cupula: A gelatinous structure which moves with the endolymph flow.

Function of Semicircular Canals

• Endolymph lags due to inertia when yourhead rotates , causing the cupula to bend. The cupula bends the stereocilia generating nerve impulses.
• Nerve impulses sent to the brain provide equilibrium and balances which is essential for spatial orientations.

Overall Summary

• Cochlea converts sound waves into electrical signals for hearing.
• Vestibule detects linear acceleration and head position.
• Semicircular Canals senses rotational movements of the head contributing to the balance.

Common Ear Disorders

• Ear infections, tinnitus, Meniere's disease, ear barotrauma, otosclerosis, earwax blockage, vestibular neuronitis, otomycosis, perichondritis, and ear tumors are all examples of ear disorders

Ear Infections

• Otitis Media: Infection of the middle is common in kids and can cause ear pain, fever, and hearing problems.
• Otitis Externa (Swimmer's Ear): Outer ear canal infection from water , causes inflammation and pain.

Tinnitus

• A condition involving ringing, buzzing, or hissing sounds, arising from noise exposure, infections, or medications.

Meniere's Disease

• Inner ear disorder causing vertigo, tinnitus, hearing loss, and ear fullness, possibly related to fluid buildup.

Ear Barotrauma

• Injury from air/water pressure changes during travel or diving, leading to pain, dizziness, and hearing loss.

Otosclerosis

• Abnormal bone growth interferes with ossicle movement, causing hearing loss, generally hereditary

Earwax Blockage

• Excessive earwax can block the ear canal, causing hearing loss or fullness that can be treated by earwax removal.

Vestibular Neuronitis

• Inflammation of the vestibular nerve causes vertigo, dizziness, and balance issues, commonly viral.

Otomycosis

• Fungal infection of the outer ear canal leads to itching, pain, and discharge that is common humid climates.

Perichondritis

• Cartilage infection of the the outer ear from injury or piercing, results in redness, swelling, and pain.

Ear Tumors

• Abnormal growths that can be benign or malignant causes hearing loss, ear pain, and discharge.