Hearing Anatomy + Physiology Flashcards
Another word for hearing is?
Audition
Purpose of the ear?
To conduct energy
The ear will convert acoustic energy into electrochemical energy so that the brain can process the information
What are the 3 main parts of the ear?
Outer Ear
Middle Ear
Inner Ear
Outer Ear Parts
Pinna or Auricle - outermost portion of the outer ear
Pinna Transmits sound to the middle and inner ears, and to localize sound
You can hear without the pinna
Lobe or lobule
Concha Cava - entrance to the ear
Outer Ear - air filled
The entire outer ear is comprised of ?
Cartilage
Except for the lobule - composed of fat and connective tissue
Medial to the concha cava is the ?
EAM
External Auditory Meatus or ear canal
Together, the concha cava + EAM help with what?
Transmission of sound to the middle and inner ear
External Auditory Meatus
Later 1/3 is made of cartilage
Medial 2/3 forms the bony meatus of the temporal bone
Terminates @ Tympanic Membrane
Contains cilia (small hairs) + cerumen (ear wax)
Cerumen
Protects the ear from dryness + intrusion of bugs/other foreign bodies
Tympanic Membrane
Boundary b/w the outer and middle ears
Transmits sound to the 3 ossicles or bones (AKA ossicular chain) of the middle ear.
These bones are medial to the TM
Sound enters the Outer Ear and then reaches the TM, setting it into vibration
3 ossicles or bones of the middle ear
Malleus, incus, stapes
Ossicular Chain
Delivers vibrations to inner ear + helps protect the inner ear from excessively loud vibrations
Middle ear is filled with what
Air
Middle Ear Bones: malleus
Most lateral point of attachment for the tympanic membrane
middle ear bones: incus (anvil)
lies medial
in between the malleus and stapes
Stapes
Most medial of the 3 bones - the smallest
Articulation of middle ear bones
Malleus + incus articulate by means of saddle joint
will move as 1 unit when the TM vibrates/moves
Stapes - it’s footplate fills the oval window which is a part of the inner ear
2 muscles of the inner ear
Stapedius + Tensor Tympani
Both are attached to the ossicular chain
Purpose of the middle ear muscles
to damp or reduce the vibration of the ossicular chain
Stapedius (middle ear muscle)
O: Bone of the posterior wall of the middle ear
C: Anterior
I: posterior crus of stapes
F: pulls stapes posteriorly to damp/reduce the vibration of the ossicular chain
Tensor tympani (middle ear muscle)
O: embedded in the anterior wall of the middle ear
C: posteriorly
I: malleus
F: pulls malleus anteromedially to stiffen the entire ossicular chain (damps or reduces vibration)
Middle Ear Landmarks - Medial wall
Medial wall of the middle ear
1) Oval Window: part of the inner ear. articulates with the footplate of the stapes. allows fluid in inner ear to move
2)round window: inferior to oval window. allows fluid in inner ear to move
Middle Ear Landmarks: anterior wall of middle ear
Eustachian Tube - brings O2 to middle ear to maintain balance/equilibrium and to balance the pressure in the middle ear with atmospheric pressure
Middle Ear Landmarks: posterior wall + floor of the middle ear
Mastoid Air Cells: irregularly shaped, hollowed out spaces in the temporal bone. They lighten the weight of the skull + are important in the conduction of sound through bone
Inner Ear
Unlike the outer/middle ears, the inner ear is filled with different types of fluids
At this point, the acoustic signal is transported through fluid to CN VIII, the Auditory Cranial Nerve, for processing by the barin
It is embedded within the petrous portion of the TEMPORAL BONE
Inner Ear Landmarks: oval + round windows
Oval + Round Windows - lateral wall of the inner ear. Oval window will vibrate when stapes moves - this action will cause the fluid of the inner ear to be set into motion
Semicircular Canals - important for balance/equilibrium. Fluid-filled, line with cilia
Inner Ear: Cochlea
Looks like a coiled snail shell
Primary organ of hearing
What lies within the cochlea?
Scala Vestibuli and Scala Tympani - form two incomplete chambers in the cochlea. They are separated by a bony shelf called the SPIRAL LAMINA
The spiral lamina serves as a point of attachment for the scale media which houses the sensory organ for hearing - the organ of Corti
Scala Media
Lies within the cochlea
separates the scala vestibuli and scala tympani
Helicotrema
Within the cochlea (inner ear)
Point where the scala tympani and scala vestibuli meet. The scala tympani and scala vestibuli communicate with each other via the helicotrema
Basilar Membrane
Lies within the cochlea
Forms the floor of the scala media
The organ of Corti rests on the basilar membrane
Cochlea is filled with fluid
Inner Ear - Scala Vestibuli + Scala Tympani, scala media
Scala Vestibuli + Scala Tympani - the type of fluid found in these chambers is PERILYMPH
Scala Media - the type of fluid found here is endolymph
Acoustic energy moves through the outer/middle ears and is transmitted through these fluids
Inner Ear - Organ of Corti
Within the cochlea
Housed in the scala media and rests on the basilar membrane
contains inner and outer hair cells
Inner + Outer Hair Cells
Inner hair cells (IHC) and outer hair cells (OHC) respond to different aspects of the acoustic signal
Frequency range for the human auditory mechanism
10 octaves, from about 20 to 20,000 Hz
Auditory stimuli can range from whisper to rock concert
Frequency
psychological correlate of pitch
Recorded in Hz
Loudness
psychological correlate of intensity
Recorded in decibels
Hearing Physiology - audiogram
During an audiological evaluation, the audiologist presents tons of different frequencies and loudness levels
The results - that is, how the patient responds - is recorded on an audiogram
Hearing Physiology
Cochlea is the organ of audition in the inner ear
Recall that the outer and middle ear will funnel in sound
Sound travels through air in these two parts of the inner
Sound travels through fluid-filled inner ear
Cochlea changes the auditory signal into neural impulses that are transmitted to the brain for proessing, via CN VII (Auditory Nerve)
Being aware that you heard something, and interpreting what you heard, are both processed by the brain - your ear has nothing to do with this!
Hearing Physiology IHC + OHC
The organ of Corti contains inner hair cells (IHC) and outer hair cells (OHC). These functioning differently from one another
ICH Inner Hair Cells (Organ of Corti)
Respond to different frequencies of an incoming auditory signal. They help the cochlea process complex sound for frequency, intensity, and other temporal aspects
OHC Outer Hair Cells (Organ of Corti)
Help regulate hearing sensitivity for less intense (softer) sounds. They will amplify softer sounds that aids in awareness of interpretation
Damage to Hair Cells Results in
Permanent sensory hearing loss
The most common cause of this loss is from excessive noise exposure
- concerts, NASCAR, NFL games and other sporting arenas, hunting, etc.
The cochlea is unable to generate new hair cells; therefore, once these cells are damaged, damage is irreversible as the cells cannot regenerate
Auditory Signal Traveling to Brain
Auditory information is transmitted from the organ of Corti to the CN VIII
Along CN VIII, there are several areas or processing stations that are important in the processing of auditory information
- Superior Olivary Nucleus
- Lateral Lemniscus
- Inferior Colliculus
- Primary Auditory Cortex
Heschel’s gyrus and Wernicke’s Area
Superior Olivary Nucleus
Integrates information received from both ears. This is the first place the auditory system where binaural processing (stereo hearing) is possible
Lateral Lemniscus
Important in sound localization
Inferior Colliculus
Located in the brainstem.
Important in the integration and localization of sound
Primary Auditory Cortex
Located in the temporal lobe
Usually the left for most people who are right-handed.
