Human Ear and Hearing

Overview

This lecture explains how we perceive sound and maintain equilibrium, focusing on the anatomy and function of the human ear.

Sound is created by vibrations in the air that move the eardrum.
Vibrations trigger a chain reaction through bones, membranes, and hair cells to create neural signals.
Frequency determines pitch; higher frequencies produce higher-pitched sounds.
Amplitude determines loudness; greater amplitude means a louder sound.

The ear consists of three areas: external, middle, and inner ear.
The outer ear (pinna and auditory canal) captures sound waves and funnels them to the eardrum.
The eardrum (tympanic membrane) vibrates in response to sound waves and marks the boundary to the middle ear.
The middle ear amplifies sound using three tiny bones: malleus (hammer), incus (anvil), and stapes (stirrup).
These bones transmit vibrations to the oval window of the inner ear.

The inner ear contains the bony and membranous labyrinth; the cochlea is responsible for hearing.
The cochlea consists of fluid-filled chambers separated by membranes; the basilar membrane is key for detecting sound.
The basilar membrane has fibers of varying lengths that resonate with specific sound frequencies.
The organ of Corti, sitting atop the basilar membrane, contains hair cells that convert mechanical vibrations into electrical signals.
Hair cells open sodium channels, creating action potentials sent via the cochlear nerve to the brain.
The brain interprets sound pitch based on which hair cells are activated and volume based on action potential frequency.

The vestibular apparatus in the inner ear maintains balance using fluid-filled semicircular canals and sacs (utricle and saccule).
Semicircular canals detect head rotation in different planes using fluid and hair cells.
Hair cells sense movement and send signals to the brain about head position and acceleration.
Conflicting sensory information can cause motion sickness.

Sound Wave — Vibration that travels through air and can be heard when it reaches the ear.
Frequency — Number of sound waves passing a point per second; determines pitch.
Amplitude — Height of the sound wave; determines loudness.
Pinna (Auricle) — External part of the ear that gathers sound.
Tympanic Membrane — Also known as the eardrum; vibrates in response to sound.
Ossicles — Three small bones (malleus, incus, stapes) in the middle ear that amplify sound.
Cochlea — Spiral-shaped, fluid-filled structure in the inner ear for hearing.
Basilar Membrane — Membrane within the cochlea that detects sound frequencies.
Organ of Corti — Structure in the cochlea containing hair cells for sound transduction.
Vestibular Apparatus — Structures in the inner ear responsible for balance.
Action Potential — Electrical signal sent by neurons to communicate information.

Review diagrams of the ear and label key structures.
Summarize the process of sound transmission and equilibrium in your own words.
Prepare for questions on how different ear parts contribute to hearing and balance.