PS231 Exam 2

Sensory Transduction

The process of converting energy from an external stimulus into electrical signals in a sensory receptor cell.

Receptive Field

The sensory space in which a stimulus alters a particular neuron’s firing rate.

Labeled Lines

A coding system in which specific receptors and neural pathways transmit specific types of sensory information to dedicated brain areas. The idea that each photoreceptor type sends signals along separate pathways to the brain (basis of trichromatic theory).

Primary Sensory Area

The first cortical region that receives sensory input from a particular modality.

Association Areas

Brain regions that further process sensory information after it reaches primary sensory cortex.

Combinatorial (Pattern) Coding

A coding system in which receptors respond to multiple stimuli, and the brain decodes patterns of activation.

Bottom-Up Processing

Perception driven directly by incoming sensory input.

Top-Down Processing

Perception influenced by prior knowledge, expectations, or context.

Law of Continuity

The perceptual tendency to perceive partial stimuli as complete or continuous.

Perceptual Completion

The brain’s ability to “fill in” missing sensory information.

Blind Spot

Area of the retina lacking photoreceptors where the optic nerve exits the eye.

Multisensory Integration

The process by which the brain combines information from multiple sensory systems.

McGurk Effect

A perceptual illusion in which visual information alters auditory perception.

Sound

Air vibrations between 20–20,000 Hz perceived by the auditory system.

Hertz

Unit of frequency; cycles per second.

Amplitude

Physical intensity of a sound wave; related to loudness.

Decibel

Unit measuring sound intensity.

Frequency

Number of sound wave cycles per second; related to pitch.

Wavelength

Physical distance between sound wave peaks; inversely related to frequency.

Pitch

Perceptual correlate of frequency.

Loudness

Perceptual correlate of amplitude.

Timbre

The perceived quality or “complexity” of a sound; determined by fundamental frequency plus overtones.

Fundamental Frequency

The lowest frequency of a sound.

Overtones

Frequencies above the fundamental; harmonics are integer multiples of the fundamental.

Audiogram

A graph showing the lowest intensity (dB) at which different frequencies can be detected.

Tuning Curve

A graph showing a sensory system’s sensitivity to different frequencies.

Pinna

The external ear structure that collects and directs sound into the auditory canal.

Auditory Canal

Tube that channels sound toward the tympanic membrane.

Tympanic Membrane (Eardrum)

Membrane that vibrates in response to sound waves.

Ossicles

Three small bones (malleus, incus, stapes) that amplify vibrations.

Malleus

First ossicle attached to the tympanic membrane.

Incus

Middle ossicle.

Stapes

Final ossicle; its footplate contacts the oval window.

Oval Window

Membrane-covered opening where stapes transfers vibrations to the cochlea.

Amplification (Middle Ear)

Lever action of ossicles increases vibration amplitude ~20× to compensate for air-to-fluid transition.

Cochlea

Fluid-filled, coiled structure containing auditory receptor cells.

Scala Vestibuli

Upper cochlear chamber filled with perilymph.

Scala Tympani

Lower cochlear chamber filled with perilymph.

Scala Media

Middle chamber filled with endolymph.

Perilymph

Cochlear fluid low in potassium (K⁺).

Endolymph

Cochlear fluid high in potassium (K⁺).

Round Window

Membrane at end of cochlea that relieves pressure.

Helicotrema

Opening at the apex connecting scala vestibuli and scala tympani.

Basilar Membrane

Flexible membrane running along cochlea; vibrates in response to sound.

Organ of Corti

Structure resting on the basilar membrane where auditory transduction occurs.

Mechanotransduction

Conversion of mechanical movement into electrical signals.

Hair Cells

Auditory receptor cells that convert basilar membrane motion into neural signals.

Inner Hair Cells

Single row (~3500); essential for hearing and perception of pitch and timbre.

Outer Hair Cells

Three rows (~12,000); amplify and fine-tune cochlear responses.

Stereocilia

Hair-like projections on hair cells where transduction occurs.

Tectorial Membrane

Structure contacting stereocilia; movement causes bending.

Cochlear Nerve (Auditory Nerve)

Nerve carrying signals from hair cells to the brain.

Place Code

Frequency coding mechanism where different frequencies stimulate different locations along the basilar membrane.

High frequencies → base (narrow, stiff)

Low frequencies → apex (wide, flexible)

Temporal Code

Frequency coding mechanism (<4000 Hz) based on timing and rate of action potentials.

Traveling Wave

Movement of fluid along the basilar membrane in response to stapes motion.

Tonotopic Organization

Spatial arrangement of frequency tuning along the basilar membrane (and preserved in auditory cortex).

Tip Links

Fine filament connections between adjacent stereocilia that mechanically open ion channels when stretched.

Insertional Plaques

Structures where tip links anchor to stereocilia.

Mechanically Gated Channels

Ion channels opened directly by physical stretching of tip links.

Depolarization (Hair Cell)

Occurs when K⁺ and Ca²⁺ enter the hair cell from endolymph, causing neurotransmitter release.

Hyperpolarization (Hair Cell)

Occurs when stereocilia bend in the opposite direction, closing channels and reducing neurotransmitter release.

Afferent Fibers

Nerve fibers that carry sensory information from hair cells to the brain.

Efferent Fibers

Nerve fibers from the brain that modulate hair cell activity (especially outer hair cells).

Bipolar Cells (Cochlear Nerve Neurons)

Neurons whose dendrites synapse with hair cells and whose axons form the cochlear nerve.

Glutamate (IHCs)

Neurotransmitter released by inner hair cells to excite auditory nerve fibers (≈95% of input).

Acetylcholine (OHCs)

Neurotransmitter released by outer hair cells; involved in modulatory control.

Vestibulocochlear Nerve (Cranial Nerve VIII)

Nerve carrying auditory (cochlear) and balance (vestibular) information to the brain.

Cochlear Amplifier

The process by which outer hair cells enhance basilar membrane vibrations to increase sensitivity.

Electromotility

Property of outer hair cells where depolarization causes shortening and hyperpolarization causes lengthening.

Gain Control

Brain-mediated adjustment of outer hair cell amplification via efferent input.

Sound Localization

The process of determining the spatial origin of sound.

Spectral Filtering

Frequency-dependent modification of sound caused by reflections off the pinna.

Vertical Localization

Determining sound elevation using pinna reflections and spectral cues.

Interaural Time Difference (ITD)

Difference in arrival time of sound at each ear; strongest cue for abrupt sounds.

Phase Disparity

Low-frequency cue based on differences in compressions and rarefactions reaching each ear.

Interaural Intensity Difference (IID)

Difference in sound intensity between ears; strongest cue for high frequencies.

Head Shadow Effect

Reduction in sound intensity at the ear farther from the source due to head blocking high-frequency waves.

Diffraction

Bending of long-wavelength (low-frequency) sounds around the head, reducing IID effectiveness.

Cochlear Nucleus

First brainstem relay receiving input from auditory nerve.

Superior Olivary Nucleus

Brainstem structure involved in computing interaural differences (localization).

Inferior Colliculus

Midbrain auditory center integrating localization and frequency information.

Medial Geniculate Nucleus (MGN)

Thalamic relay nucleus projecting to auditory cortex.

Primary Auditory Cortex

First cortical region receiving auditory input (Brodmann areas 41 & 42).

Auditory Association Cortex

Higher cortical regions involved in interpretation and meaning of sounds.

Tonotopy

Spatial organization of frequency mapping preserved from cochlea through auditory cortex.

Characteristic Frequency

The specific frequency to which a neuron is most responsive.

Anteroventral Stream

(“What”) Auditory pathway decoding sound identity (pitch, recognition, meaning).

Posterodorsal Stream

(“Where”) Auditory pathway decoding spatial location of sounds.

Brodmann Area 41

Primary auditory cortex (Heschl’s gyrus).

Brodmann Area 42

Secondary auditory cortex adjacent to area 41.

Wernicke’s Area

Auditory association region involved in language comprehension (dominant hemisphere).

Subcortical Auditory Processing

Brainstem-level processing that can support reflexes even after cortical damage.

Conductive Hearing Loss

Hearing impairment due to middle ear problems preventing sound transmission to cochlea.

Sensorineural Hearing Loss

Hearing impairment due to cochlear (hair cell) damage.

Central Deafness

Hearing impairment due to damage in auditory brain structures.

Acoustic Trauma

Hearing damage caused by exposure to intense sound (e.g., ≥120 dB).

Stereocilia Damage

Structural destruction of hair cell projections leading to permanent hearing loss.

Electromagnetic Radiation

Energy that travels in waves across the electromagnetic spectrum.

Visible Light

The portion of electromagnetic radiation detectable by humans, with wavelengths between 380–760 nm.

Nanometer

A unit of wavelength equal to one-billionth of a meter.