Anatomy of the Ear - External

Anatomy of the Ear - External

• The anatomy of the ear can be divided into three parts: the external ear, the middle ear, and the inner ear.
• Pinna (Auricle)'s primary composition is elastic cartilage covered by a thin layer of skin.
• The pinna exhibits a (complex, irregular shape with various folds and depressions, each possessing a specific name (helix, antihelix, tragus, antitragus, concha, lobule).
• Lobule is the only part of the pinna that lacks cartilage and is made of fatty and connective tissue.
• The auricle aids in sound localization due to its shape, creating subtle differences in the timing and intensity of sound waves reaching each ear.
• Auricle acts as a funnel, collecting sound waves and directing them into the external auditory canal.
• Auricle selectively modifies sound frequencies, this contributes to the ability to perceive sound direction and quality.
• The external auditory canal is a slightly curved, tubular passage from the pinna to the tympanic membrane.
• The external auditory canal is roughly 2.5 cm long
• The canal's curvature and narrowness protect the tympanic membrane from foreign objects.
• Cerumen traps dust, debris, and insects, preventing them from reaching the eardrum.
• The outer third of the auditory canal is cartilaginous, and the inner two-thirds, is temporal bone.
• It transmits sound waves from the pinna to the tympanic membrane.
• Skin lining the canal contains ceruminous glands that produce cerumen (earwax).
• Cerumen also possesses antibacterial and antifungal properties.

Anatomy of the Ear – External/ Middle

• The tympanic membrane is a thin translucent, oval-shaped membrane separating the external auditory canal from the middle ear.
• Structure of the tympanic membrane is composed of three layers: an outer epithelial layer, a middle fibrous layer, and an inner mucous membrane layer.
• Slightly cone-shaped membrane, with the apex pointing inward (the umbo).
• In terms of function, it vibrates in response to sound waves, which then transmit vibrations to the ossicles in the middle ear.
• Furthermore, the tympanic membrane acts as a barrier, protecting the middle ear from infection and foreign objects.

Anatomy of the Ear – Middle ear

• The middle ear, (tympanic cavity) is an air-filled, mucosa-lined cavity is between the outer and inner ear.
• The middle ear connects laterally by the tympanic membrane, medially by the bony wall separating it from the inner ear, anteriorly by the Eustachian tube, posteriorly by the mastoid air cells, and superiorly by the tegmen tympani.
• Connects to the tympanic membrane on one side and to the membrane that separates the inner and middle ear (oval window) on the other.
• Bones within the middle ear consists of three of the smallest bones: malleus, incus, and stapes
• The handle of the malleus connect to the tympanic membrane and the base of the stapes connect to the oval window by a ligament.

Anatomy of the Ear – Middle ear structures and functions

• Ossicles (Malleus, Incus, Stapes) are the three smallest bones in the human body, forming a chain that transmits sound vibrations.
• The Malleus (Hammer) is attached to the inner surface of the tympanic membrane, with a head, neck, and handle (manubrium).
• The incus (anvil) connects the malleus to the stapes; a body comprised of two limbs.
• The smallest ossicle, stapes' (stirrup), footplate fits into the oval window, a membrane-covered opening leading to the inner ear.
• The ear ossicles amplify sound vibrations by acting as a lever system and by concentrating the force from the larger surface area of the tympanic membrane onto a smaller oval window.
• The ossicular chain converts the larger movements of the tympanic membrane into smaller, but more forceful movements of the stapes footplate.
• The Eustachian tube connects the middle ear to the nasopharynx .
• Eustachian tubes normally collapsed and sealed off from the middle ear.
• Their function, to open transiently to allow pressure re-equilibration.
• Pressure changes in the middle ear occur during: flying, diving, changes in altitude.
• Eustachian tubes equalize pressure to prevent painful damage to the tympanic membrane rupturing.
• Open during: yawning, chewing, swallowing
• Infections can cause swelling in Eustachian tubes.

Anatomy of the Ear – Inner ear

• The inner ear is a fluid-filled interconnected cavities and tubes, located deep within the temporal bone.
• Oval and round windows of the inner ear keep fluid separate from the air-filled middle ear
• It's responsible for both, hearing (cochlea) and balance (vestibular system).
• The 2 main parts are: the bony and membranous labyrinth
• Utricle and Saccule are the Vestibule

Anatomy of the Ear – Vestibular System and Semicircular Canals

• The vestibular system is comprised of the vestibule and semicircular canals.
• The vestibule is comprised of the utricle and saccule
• The vestibule contains maculae is, the sensory organs that detect linear acceleration and changes in head position relative to gravity.
• In the vestibule are otolithic membranes, containing(calcium carbonate crystals) that move in response to gravity and linear acceleration.
• Semicircular canals are three canals oriented in different planes (anterior, posterior, and lateral).
• The 3 canals contain ampullae at enlarged regions and at is based of each canal.
• The ampullae contain cristae ampullares, which are sensory organs that detect rotational movements of the head.
• Within the ampulla, the cupula: a gelatinous structure within the crista, that is displaced by endolymph movement.

Anatomy of the Ear – Inner ear and Cochlea

• The cochlea is a spiral canal is divided into three compartments: scala vestibuli, scala media (cochlear duct), and scala tympani.
• The scala vestibuli, is located above the cochlear duct, filled with perilymph,
• Scala media (cochlear duct), is filled with endolymph, located between the scala vestibuli and scala tympani.
• The scala tympani is filled with perilymph, located below the cochlear duct.
• Cochlea converts sound vibrations into nerve impulses, and different frequencies of sound stimulate different regions of the structure
• The Organ of Corti contains hair cells that transduce the mechanical vibrations into electrical signals.

Anatomy of the Ear – The Organ of Corti

• The Organ of Corti is an organ of the inner ear located within the cochlea that contributes to audition. The organ contains three rows of outer and one of inner hair cells.
• Vibrations caused by sound waves bend the stereocilia on these hair cells via an electromechanical force.
• The organ sits on top of the basilar membrane
• It contains over 16000 receptor cells called hair cells
• Hair cells in basilar membrane are put into vibration
• Tectorial membrane provides movement of hair cells
• Kinocilia (tallest of the stereocilia) is attached to the tectorial membrane.

Sound

• Sound waves are mechanical waves caused by air molecules put into motion.
• Air molecules transfer kinetic energy to the next molecule they bump in to.
• Sound is a travelling wave of oscillating pressure that travels best though liquid, solid, and gas material.
• There must be a certain material present, as traveling requires medium

Sound Properties

• Sound must have loudness, this is measured via amplitude and intensity (decibels)
• Sound must have pitch, that is determined by wavelength and frequency.

Perception of Sound

• Sensory systems have two primary processes sensing our environment and perception of how we interpret those signals.
• Sensation is the process of sensing, this is a physicochemical response.
• Perception is an interpretation of signals that is psychological process.
• Most sensory pathways project the thalamus in the brain
• The thalamus relays information to the (visual cortex) & is linked to cerebral cortex.
• The area acts as a translator, were inputs are processed, where is then, sensory information is relayed to the cerebral cortex.
• The human ear can hear Frequency into (Pitch).
• Our ear’s range for sounds are around (20 -20 000 Hz)
• Ears most sensitive (1500 - 4000 Hz)
• When tuning fork produces a pure tone it (i.e. produces the same frequency)
• Most sounds are mixtures of several frequencies.
• Pitch, human are can hear 12 Hz to 20,000 Hz
• The interdividual may vary, which can be linked to age
• Old age: difficultly with higher frequencies
• Young human ear with undamaged hearing (12 Hz)
• Decreases after the age of 8

Perception of Sound properties & location

• The high frequency end does not transmit far.
• It reaches its maximum displacement of basilar membrane at the oval window.
• Low frequency transmitters transmit further
• They reach maximum displacement of basilar membrane at the distal helicotrema
• Hair cells nearest the oval window are activated for highest pitch sounds
• Hair cells nearest the distal end of the vestibular duct (helicotrema) get activated by low pitches
• A combination of differential responses, hair cells to frequency of the sound(pitch) is the key, where coding occurs from most strongly activated hair cells
• Location is sensed at both ears where complex brain processing creates a 3D representation, and ultimately, Spatial interpretation occurs via the ears to send the signal to the brain
• The human ear makes multiple tones by varying the frequency, where (simultaneously) the coding is being read from the cochlear nuclei to the auditory cortex (temporal lobe) occurs.

Perception of Sound – Loudness

• Loudness goes up with greater sound intensity and when there is and increase in vibrations of membrane
• Loudness increase when the stereocilia is able to bend, where K plus channels open, raising the generator potentials and neurotransmitter release for the nervous system to interpret
• Neurotransmitters release in higher frequency allows the perception to know loudness.
• An signal with a greater frequency, due to high intensity, results in a louder sound overall.

Diseases Associated with the Ear

• Ear infections, middle ear infection otitis media, and outer ear otitis externa infections.
• Acute otitis media (AOM), otitis media with effusion (OME), and otitis externa are known as swimmer’s ear
• Ear infections can lead to Earache, fever, hearing loss, headaches, drainage from the ear, and a sense of fullness
• Furthermore, the outer ear can experience itchiness and pain.
• Medical specialists use an otoscope to better diagnose the inner ear.

List of Ear Diseases

• Noise-Induced Hearing Loss
• Tinnitus causes ringing in ears.
• Vestibular Schwannoma (Acoustic Neuroma)
• Age-Related Hearing Loss
• Ear wax
• Perforation of the ear drum
• Meniere's disease can cause dizzy spells.
• Hearing loss often occurs with Meniere's disease.
• Aural fullness occurs: sensation of pressure in ear.
• Labyrinthitis can cause feeling of movement and results in dizziness to patients and is caused by viral infections.

Otitis Externa and Otitis Media

• Otitis Externa is external ear infections.
• In the outer ear, Oto- (ear) is triggered with -itis (inflammation)
• External ear infections can be due to the outer ear canal delicate skin, due to swimmers (warm, damp) conditions are common.
• When this occurs, we can see acute infections, contact sensitivity, or seborrheic dermatitis, among other skin infections
• Causes by hearing-aids/earbuds etc are also factors
• In Otitis Media infection, is triggered with -itis (inflammation
• Causes related to E.g. colds, sore throat, Eustachian tube swells, fluid build up in middle ear that traps bacteria
• When this build up happens in the tympanic membrane, we can measure significant inflammation of the walls
• If such a buildup happens Non-infectious, it will be triggered by clear fluid due to is cause (clear fluid) build up due to food allergies
• In such causes, physicians will try a Grommet that allow to enter the middle ear - falls out after 6-12 months

Infections Leading to Hearing Loss

• Middle ear infections (conductive) leads to ('glue-ear', otitis media) such as Inflammation of middle ear & build up of fluid due to viral or bacterial transmission
• This means following repeat infections gets cholesteatoma i.e. abnormal skin growth behind the ear drum
• In this case, the middle ear bones gets damaged and invades the cochlea (sensorineural)
• Tinnitus can be broadly categorized such as whether sounds are internally produced or if they are from an external source (Vasculature problems for example)

Summary: Human Ear Function and Internal parts

• The function of the External ear to capture sound and conduct to tympanic membranes via auricle.
• The middle ear transforms sound waves from Low range vibration- to high-amplitude as they get transferred to smaller parts
• Finally the Internal ear houses: parts such as Bony labyrinths & membranous labyrinths that contains and supports utricle and saccule which create information about head position.
• Semicircular ducts provide information about movements of the head
• Cochlear duct provides information for hearing

Summary: Internal Ear and Labyrinth

• The vestibule, a central part of of the bony cavity
• Houses: utricle + saccule which belong to the membranous labyrinth
• Cochlea: important for hearing
• Semicircular provides us a sense for the body direction
• All membranous structures houses a the three semicircular canals
• The auditory and vestibular apparatuses are sensory systems that are closely tied together when we talk about labyrinths.
• The cochlea is the most important structure within the membranous labyrinths; this provides a sensing organ for hearing in our body.

Extra Content: if a tree falls with in the forest with not soul to hear

• No as energy need to be converted in sound, (not hard because no one is around)
• Vibrations has to be converted within brain.