Hearing By Jack & Tori
3 Main Components of the Human Ear. Outer Ear. Middle Ear. Inner Ear
Outer Ear Pinna: >Visible part of ear and ear canal -Acts as a funnel to direct sound Eardrum: >Airtight membrane *The asymmetrical shape of the outer ear allows us to localize sound vertically
Middle Ear: Small air filled chamber medial to eardrum Ossicles: 3 smallest bones in human body, never stop moving >malleus, incus, stapes - Aid in transmission & amplification of vibrations from eardrum to inner ear >Stapedius & tensor tympani muscles: - Dampen sounds through stiffening reflex (ex: chewing sound) - Stapedius contracts when loud sounds are detected >Malleus articulates with tympanic membrane ( which converts acoustical energy of sound to mechanical energy)
Middle Ear Continued: >Incus receives mechanical vibrations from malleus and sends to stapes > Stapes Bone: - Sends sound waves through oval window - (separates air filled middle ear from fluid filled inner ear) > The Round Window: - Smooth displacement of inner ear fluid caused by entering sound waves *This complex construction prevents the mixing of air and water between the middle ear and inner ear
Inner Ear: >Cochlea: - Spiral shaped, fluid filled tube divided lengthwise by corti - (main organ of mechanical to neural transduction) >Basilar membrane: located in corti - Contains over 10,000 hair cells - Hair cells release neurotransmitters at synapses with fibers of auditory nerve - Patterns of oscillations on basilar membrane are converted into spatiotemporal patterns, which are then sent about the brain stem
Inner ear continued: 2 Divisions #1: Hearing >Organ of Corti: - Hydraulic energy of cochlear fluid activates hair cells to release chemical messengers - Messengers stimulate nerves of hearing and carries the sound stimuli to the brain
Inner Ear Continued: #2: Balance >Vestibular System: - Detect angular movements, direction, and velocity of head - This info is sent to the brain via vestibular nerves
Central Auditory Pathways: - Nerve of hearing enters brainstem, neural pathway goes to cerebral cortex and temporal lobe > Left Brain: - Processes speech and complex language functions > Right Brain: - Tonal stimuli and music deciphered
Process of Hearing = Converting Energy - Tympanic membrane transforms sound into mechanical stimulus, then goes through ossicular chain to stapes footplate - Code is transformed into hydraulic and through fluid filled cochlea, cochlea s hair cells are stimulated
Primary Auditory Pathway: > Brain Stem > Thalamus (essential for vocal response) >Auditory cortex - Leads to memorization and potentially a response
6 Basic Steps of Hearing 1. Sound waves arrive at tympanic membrane 2. Movement of eardrum causes displacement of ossicles 3. Movement of stapes at oval window establishes pressure waves 4. Pressure waves distort basilar membrane on way to round window 5. Vibration of basilar membrane causes vibration of hair cells 6. Info about region/intensity of stimuli is relayed to CNS over cochlear branch on cranial nerve VIII a. Goes to cochlear nuclei of medulla
Homeostatic Imbalances:. Myringitis. Otitis Externa. Meniere s Disease
Myringitis: Inflammation of the ear drum - Common in children 6 months-5 year - Tympanic membrane (eardrum) looks red and begins to bulge - Can be caused by bacteria or viral infection - Treated with antibiotics or antiviral drugs - Caused by exposure such as a public pool or playground
Otitis Externa: Dermatitis of epithelium of outer ear - Irritated inflamed tissues of outer ear and ear canal - Possible in all ages - Can cause severe hearing loss if left untreated - Patients feel incredible pressure, and often have discharge coming out of ear - Often very itchy, and extremely painful
Activity: Who has the best hearing? The smallest hair cells are closest to the outside of your ear. These cells pick up the slightest vibrations (higher frequencies) These cells are also the most easily destroyed Examples: Live concerts, Loud machines like construction vehicles, listening to your headphones too loud
Meniere s Disease: - Disorder of the inner ear that affects hearing, balance, and thought - No one is exactly sure what the cause or what exactly is happening - Major theory is that increased pressure in the cochlea and semicircular canals causes the symptoms - Symptoms and effects include dizziness and spinning, hearing loss, and nausea - Chromic with no specific treatment