119+-+Lecture+4+-+Human+Hearing+Pt+1

Stapes: A small bone that connects to the oval window of the cochlea, part of the chain of three bones that help transmit sound.
Incus: The middle bone of the three tiny bones in the ear, also called the anvil.
Malleus: The first bone in the chain, attached to the eardrum, often called the hammer.
Cochlea: A spiral-shaped part of the inner ear that contains liquid and tiny hair cells that change vibrations into electrical signals for the brain.
Middle Ear Components: This area has the tympanic cavity, which holds the ossicles, the eustachian tube that helps equalize pressure, and the round window that allows movement of fluid in the cochlea.
Nerves: The cochlear nerve sends sound signals to the brain, and the vestibular nerve helps with balance.

Anatomy of the Human Ear: Check out the video available in the lecture folder on Canvas for more information.

Pinna (Auricle): The visible part of the ear made of cartilage and skin, consisting of three parts: the tragus, helix, and lobule.
Ear Canal: A tube that channels and shapes sound waves toward the eardrum.

Frequency Resonance: The ear canal can amplify certain sound frequencies, making them easier to hear.
Strong Resonances: Most effective within the 2 kHz to 4 kHz range, important for understanding speech and recognizing sounds like consonants and baby cries.

Also called the eardrum, this membrane vibrates when hit by sound waves, changing sound energy into mechanical energy.

Ossicles: The three bones (Malleus, Incus, Stapes) work together to make sounds louder and better transfer them to the inner ear, increasing sound pressure about twenty times.
Oval Window: A membrane that transfers vibration from the ossicles to the cochlea.

Cochlea: Contains fluid and hair cells that convert sound vibrations into electrical signals sent to the brain.
Auditory Nerve: Carries messages from the cochlea and balance organs to the brain, integrating hearing and balance functions.
Cochlea Cross-Section: Important parts include the scala vestibuli, Reissner's membrane, scala media, organ of Corti, and scala tympani.

Human Auditory Range: Healthy young adults can hear sounds from about 20 Hz to 20,000 Hz.
Ultrasonic: Sounds above 20,000 Hz; Infrasonic: Sounds below 20 Hz.
Temporal Acuity: Humans can notice timing differences as small as 10 microseconds, important for figuring out where sounds are coming from.
Transient Sounds: Quick, loud noises that are essential for detecting important sounds in the environment.

Sound can travel through the bones of the skull to the inner ear, particularly effective for low-frequency sounds.

Humans figure out where sounds come from by using:
- Differences in sound volume between ears (Intensity differences)
- Timing differences of when sounds reach each ear (Temporal differences)
- Changes in sound character based on frequency (Spectral differences)

Inter-aural Time Differences (ITD): The time gap between sound arriving at each ear helps locate the source.
Inter-aural Level Differences (ILD): The sound level difference in each ear gives spatial clues.

When sound reaches both ears at the same time, spectral cues help determine its height.
Pinna and Ear Canal: Shape and structure filter sounds, aiding in recognizing sounds coming from above or below.

Intermediate Distances: Sounds are quieter.
Great Distances: High-frequency sounds are reduced; echoed sounds become more prominent, making it harder to distinguish direct sounds from echoes.

The brain organizes sounds into understandable patterns, helping distinguish between various sound sources even in loud environments.