DCOM 225 – Unit 2 Study Guide: Anatomy and Physiology of Hearing and Balance

Comprehensive vocabulary flashcards covering anatomical planes, outer, middle, and inner ear structures, auditory transduction mechanisms, and vestibular balance systems from DCOM 225 Unit 2.

Anatomy

The study of the body's structures and how they are organized, focusing on what something is and where it is located.

Physiology

The study of how body structures function and work together, focusing on how mechanisms operate.

Transducer

A device or biological structure that converts one form of energy into another; in hearing, the cochlea acts as a sensory transducer where hair cells convert mechanical vibrations into electrical signals that stimulate the auditory nerve.

Sagittal plane

An anatomical plane that divides the body into left and right portions; the midsagittal plane divides the body into equal halves.

Frontal (coronal) plane

An anatomical plane that divides the body into front (anterior) and back (posterior) portions.

Transverse (horizontal) plane

An anatomical plane that divides the body into upper (superior) and lower (inferior) portions.

Pinna (auricle)

The outer ear structure that captures sound waves from the environment, directs them into the ear canal, and assists in vertical sound localization.

External auditory canal

The canal directing sound to the tympanic membrane; divided into an outer cartilaginous portion (approximately $\frac{1}{3}$) with hair follicles and ceruminous glands, and an inner bony portion (approximately $\frac{2}{3}$) lined with thin, sensitive skin.

Cerumen

Earwax; a yellow, orange, or brown secretion (wet/sticky or dry/flaky) that traps debris, lubricates the ear canal, and defends against bacteria and fungi through its protective chemical properties.

Tympanic membrane

A vibrating membrane separating the outer and middle ear composed of three tissue layers: an outer epithelial layer, a middle fibrous layer, and an inner mucosal layer.

Ossicles

The three tiny middle ear bones—the malleus (hammer), incus (anvil), and stapes (stirrup)—that mechanically transmit sound vibrations from the tympanic membrane to the oval window.

Tensor tympani muscle

A middle ear muscle innervated by cranial nerve V (trigeminal) that attaches to the malleus and increases tension on the tympanic membrane.

Stapedius muscle

A middle ear muscle innervated by cranial nerve VII (facial) that attaches to the stapes to restrict its movement during the acoustic reflex, reducing the transmission of loud, sustained sounds.

Eustachian tube

A passage connecting the middle ear cavity to the nasopharynx that equalizes air pressure across the tympanic membrane, drains secretions, and protects against pathogens; it opens briefly during swallowing and yawning.

Area ratio (hydraulic mechanism)

A middle ear mechanical advantage where sound force collected over the larger area of the tympanic membrane is concentrated onto the smaller stapes footplate, producing increased pressure at the oval window.

Ossicular lever mechanism

A mechanical advantage created by the lever action between the malleus and incus that increases force to help overcome the impedance mismatch between air and fluid in the inner ear.

Scala media (cochlear duct)

The middle chamber of the cochlea filled with potassium-rich endolymph, bounded by the vestibular membrane and basilar membrane, and housing the organ of Corti.

Perilymph

The fluid filling the scala vestibuli and scala tympani; characterized by high sodium ($Na^+$) and low potassium ($K^+$) concentrations, similar in ionic composition to extracellular fluid.

Endolymph

The fluid filling the scala media; characterized by high potassium ($K^+$) and low sodium ($Na^+$) concentrations, holding a positive electrical potential relative to perilymph.

Tonotopic organization

The spatial arrangement of frequency sensitivity along the basilar membrane, where the narrower, stiffer base responds best to high frequencies and the wider, more flexible apex responds best to low frequencies.

Helicotrema

An anatomical opening located at the cochlear apex that connects the scala vestibuli and scala tympani, allowing fluid pressure communication between the two chambers.

Organ of Corti

The sensory receptor structure for hearing located on the basilar membrane within the scala media, consisting of inner hair cells, outer hair cells, pillar cells, and the tectorial membrane.

Inner hair cells

The primary sensory receptors for hearing (approximately $3{,}500$ cells arranged in a single row along the modiolar side) that release neurotransmitter to provide most sensory input to the brain via type I afferent auditory nerve fibers.

Outer hair cells

Motile cells within the organ of Corti that act as cochlear amplifiers, altering their length to sharpen frequency tuning, improve sensitivity to soft sounds, and receiving predominant direct efferent connections from the brainstem.

Electromotility

The length-changing mechanical process in outer hair cells driven by the motor protein prestin in response to electrical stimulation, amplifying basilar membrane vibrations.

Depolarization (hair cells)

The electrical event where stereocilia bend toward the tallest stereocilia, opening mechanically gated ion channels to allow potassium ($K^+$) entry, making the interior less negative and triggering calcium influx and neurotransmitter release.

Hyperpolarization (hair cells)

The electrical event that occurs when stereocilia bend away from the tallest stereocilia, closing mechanically gated channels, reducing inward current, making the cell interior more negative, and reducing neurotransmitter release.

Traveling wave

A wave of fluid displacement moving along the basilar membrane from the base toward the apex, reaching maximum displacement at the resonant point tuned to the incoming sound's frequency.

Vestibulocochlear nerve (Cranial Nerve VIII)

The cranial nerve divided into a cochlear branch, which transmits acoustic action potentials from the cochlea to the brainstem, and a vestibular branch, which conveys equilibrium information.

Semicircular canals

Three fluid-filled bony and membranous loops (superior/anterior, horizontal/lateral, posterior) oriented at right angles to detect rotational head movement via cristae within their ampullae.

Otolith organs

Vestibular structures consisting of the utricle and saccule that contain calcium carbonate crystals (otoconia) to detect linear acceleration and gravitational head tilt.

Utricle

An otolith organ whose macula primarily detects horizontal linear acceleration (such as moving sideways or forward in a car) and head tilt relative to gravity.

Saccule

An otolith organ whose macula primarily senses vertical linear acceleration (such as riding in an elevator) and head orientation relative to gravity.

Vertigo

The false sensation of personal or environmental spinning or motion occurring in the absence of actual physical movement, frequently associated with inner ear disorders like BPPV.

Proprioception

The conscious and subconscious awareness of body position and joint/muscle movement provided by somatosensory receptors, integrated with visual and vestibular sensory inputs for balance.