Audition and Equilibrium: Understanding the Ear and Hearing

Basics of Audition

• Audition: Main sensory modality for hearing, interpreting sound waves.

• Ear Structure: Comprised of three main parts: outer ear (pinna/oracle), middle ear (tympanic membrane/eardrum), inner ear (cochlea, vestibule).

Sound Transmission Process

• Sound waves travel through the ear canal to the tympanic membrane, causing it to vibrate.

• Vibrations pass through three small bones of the middle ear (ossicles): malleus, incus, stapes.

• Stapes connects to the oval window, creating waves in the inner ear's fluid-filled ducts (scala tympani and scala vestibuli).

Cochlea and Hearing Mechanism

• Cochlea: Converts sound wave vibrations into nerve signals using the Organ of Corti.

• Frequency and Amplitude: Frequency (measured in Hz) relates to pitch; amplitude relates to volume (decibels).

• High frequency sounds stimulate hair cells at the base of the cochlea; low frequency sounds travel further in.

Mechanotransduction in Hair Cells

• Hair cells within Organ of Corti have stereocilia that bend due to fluid motion, generating tension.

• Tension in stereocilia opens mechanically gated ion channels, leading to depolarization and nerve signal generation.

Equilibrium

• Vestibule: Responsible for balance; consists of utricle and saccule (position) and semicircular canals (movement).

• Utricle and saccule contain otolithic membrane with otoliths (calcium crystals), which bend hair cells to signal head positioning.

• Semicircular canals contain fluid that moves with head rotation, stimulating hair cells for motion detection.

Vision Overview

• Vision: Sensation based on light stimuli; light enters the eye and is processed to transmit information to the brain.

• Eye Structure: Comprised of multiple layers: fibrous tunic (sclera and cornea), vascular tunic (choroid, ciliary body, iris), neural tunic (retina).

• Photoreceptors in the retina convert light into electrical signals sent to the brain.