Ear and Hearing Mechanism

Overview

This lecture explains how sound is detected and processed by the ear and how the inner ear maintains body balance (equilibrium).

Sound is caused by vibrations in the air that create pressure waves.
Vibrations hit the eardrum, which triggers a chain reaction leading to nerve signals interpreted as sound by the brain.
The frequency of sound waves determines pitch; higher frequency means higher pitch.
The amplitude of sound waves determines loudness; larger amplitude means louder sound.

The ear has three main parts: external, middle, and inner ear.
The external ear (pinna/auricle) catches sound waves and funnels them into the auditory canal.
The tympanic membrane (eardrum) separates the external and middle ear, vibrating in response to sound.
The middle ear amplifies sound using three bones (ossicles): malleus (hammer), incus (anvil), and stapes (stirrup).
The stapes transmits vibrations to the inner ear’s oval window, setting inner ear fluid in motion.

The inner ear (labyrinth) contains the cochlea, responsible for hearing, and structures for balance.
The cochlea has three fluid-filled chambers and a key structure called the basilar membrane.
The basilar membrane vibrates at specific locations based on the sound frequency.
The organ of corti, sitting on the basilar membrane, contains hair cells that convert mechanical vibrations into electrical impulses.
Hair cells open sodium channels when stimulated, generating action potentials sent to the brain via the cochlear nerve.
The brain identifies pitch by the location of activated hair cells and loudness by the frequency of action potentials.

The inner ear’s vestibular apparatus maintains balance using three semicircular canals positioned in different planes.
Movement of fluid in these canals stimulates hair cells, detecting head movement and acceleration.
Utricle and saccule sacs within the vestibular apparatus sense linear motion.
Sensory conflicts between the vestibular system and other sensory input can cause motion sickness.

Sound Wave — Vibration that travels through air, creating areas of high and low pressure.
Frequency — Number of sound waves passing a point per second; determines pitch.
Amplitude — Height of a sound wave; determines loudness.
Tympanic Membrane (Eardrum) — Tissue that vibrates in response to sound, marking the border between outer and middle ear.
Ossicles — Three small bones (malleus, incus, stapes) that amplify sound in the middle ear.
Cochlea — Spiral-shaped organ in the inner ear responsible for hearing.
Basilar Membrane — Structure in the cochlea that vibrates at specific locations for different sound frequencies.
Organ of Corti — Structure containing sensory hair cells that convert vibrations to nerve signals.
Vestibular Apparatus — Inner ear structures responsible for sensing balance and head movement.

Review the anatomy and function of each ear component.
Study how the cochlea and vestibular apparatus work to process sound and maintain equilibrium.