Touch, Hearing, Vestibular

Sensory Transduction

The process where the energy of a stimulus is converted into an electrical signal

Generator (or receptor) potential

A depolarizing current generated in afferent nerve endings by a stimulus altering the permeability of cation channels

Stimulus Strength Encoding

The process where stimulus strength is encoded by the amplitude of the generator potential and the frequency of action potentials

Tonic Receptor

A sensory receptor that adapts slowly to a stimulus

Phasic Receptor

A sensory receptor that adapts rapidly to a stimulus

Dermatome

A region of skin innervated by the spinal nerve of a single dorsal root ganglion (DRG)

Receptive field

The area of the skin surface over which stimulation results in a significant change in the rate of action potentials

2-point discrimination

The ability to distinguish two simultaneously applied stimuli as distinct, which serves as a measure of spatial acuity

Primary somatosensory cortex

An area located in the postcentral gyrus containing a highly disproportionate map of the body's periphery

Dorsal Column-Medial Lemniscal System

A neural pathway carrying tactile information from the body to the somatosensory cortex

Trigeminothalamic System

A neural pathway transmitting tactile information from the face via the thalamus

Glabrous skin

Hairless skin involved in discriminative touch

Merkel's Disks

Superficial, slow-adapting (SA) mechanoreceptors with high spatial acuity that detect edges, points, curves, shape, and texture

Meissner's Corpuscles

Superficial, fast-adapting (FA) encapsulated mechanoreceptors with high spatial acuity responsible for detecting skin motion and aiding in grip control

Pacinian Corpuscles

Deep, fast-adapting (FA) encapsulated mechanoreceptors with low spatial acuity that detect vibration

Ruffini's Corpuscles

Deep, slow-adapting (SA) spindle-shaped mechanoreceptors with low spatial acuity that detect skin stretch, hand shape, and finger position

PIEZO

A mechanosensitive ion channel that converts touch into electrical signals

Gracile Nucleus

A neural structure in the dorsal column-medial lemniscal system conveying mechanosensory pathways from the lower body

Cuneate Nucleus

A neural structure in the dorsal column-medial lemniscal system conveying mechanosensory pathways from the upper bod

Hearing

The ability to detect and interpret sound

Tone

The frequency of the sound wave, ranging from 20-20,000Hz in humans and 20-200KHz in bats

Loudness

The amplitude of the sound wave

Outer Ear

The region of the ear that amplifies sound pressure for frequencies between 2-5KhZ and aids in the localization of a sound source's elevation

Middle Ear

The region of the ear important for amplifying the sound wave by focusing the force of the large tympanic membrane down onto the much smaller oval window via the lever action of the malleus and incus

Inner Ear

The region of the ear containing specialized sensory cells called hair cells

Organ of Corti

A structure containing 16,000 hair cells, comprising 4,000 inner and 12,000 outer hair cells

Basilar membrane

A tapered structure that is narrow at one end and progressively wider along its length, featuring a tonotopic organization of frequency that allows the distinction of different pitches

Hair cells

Specialized sensory cells whose mechanical movement transduces the vibrational energy in the basilar membrane into an electrical signal

Inner hair cells

Sensory receptors that send afferent signals back to the central nervous system and conduct signals to the brainstem

Outer hair cells

Cells that receive efferent signals from the central nervous system, actively contract and expand in response to electrical currents (electromotility), and amplify the motion of the basilar membrane

Sensorineural hearing loss

A peripheral hearing insult caused by damage to the inner ear, typically the cochlear hair cells or the auditory nerve, which manifests as a raised hearing threshold on the affected side

Cochlear implants

An effective treatment to restore hearing to people with hair cell damage

Endocochlear potential

The ionic basis of hair cell activity where stereocilia are bathed in high K+ endolymph while the base is bathed in low K+ perilymph

Biphasic response

The condition where both the depolarization and hyperpolarization of hair cells are K+ dependent

Labelled Line Coding

A coding mechanism exemplified by the tonotopic organization of the basilar membrane, where a single hair cell provides information about a particular frequency

Characteristic frequency

The specific sound frequency to which an individual auditory neurone is most sensitive, requiring the lowest sound intensity to increase its electrical activity

Cochlear amplifiers

Mechanisms that enhance the amplitude and sharpness of sound signals

Spiral ganglion

The anatomical location containing the cell bodies of bipolar auditory nerves

Superior olive

The location in the auditory pathway where information from each ear reaches both sides of the system

Interaural time differences

The sound timing differences between the two ears that enable the localization of a sound source in the horizontal plane

Delay line model

A model of auditory integration incorporating an anatomical method of producing a time delay to convert sound information into a place code via coincidence detectors tuned to different time delays

Vestibular System

Located in the ear, it provides information about head position, self-motion, spatial orientation, and is important for reflexive movements and balance

Proprioception

Sensory information regarding limb position

Otolith organs

Comprising the utricle and saccule, these primarily detect translational movements and static head tilts

Semi-circular canals

Three structures in each ear that detect rotational movements of the head

Hair cells

Specialized sensory cells located in the utricle, saccule, and the ampullae of the semi-circular canals that depolarize via mechanogated K+ channels to release glutamate

Macula

The sensory epithelium of the otolith organs

Otolithic membrane

A gelatinous layer containing calcium carbonate crystals known as otoconia

Striola

An axis of symmetry in the macula where hair bundles on either side have opposing morphological polarization, setting up a differential pattern of excitability

Utricle

An otolith organ with a horizontally orientated macula that detects translational movements in the horizontal plane and side-ways head tilts

Saccule

An otolith organ with a vertically orientated macula that detects vertical translational movements and upward or downward head tilts

Scarpa’s ganglion

The location of the cell bodies of vestibular nerves

Cranial nerve VIII

The cranial nerve whose vestibular branch conveys signals from the vestibular system to the central nervous system

Ampulla

The structure within the semicircular canals that houses the sensory epithelium

Vestibulo-ocular Reflex (VOR)

A fast, automatic reflex that stabilizes gaze by moving the eyes in the opposite direction of head movement

Oscillopsia

A condition featuring bouncing vision caused by damage to the vestibular system

Vestibulospinal Reflex (VSR)

A descending pathway coordinated by the lateral and medial vestibular nuclei that is important for postural adjustments of the body

Vestibulocervical Reflex (VCR)

A descending pathway coordinated by the medial vestibular nucleus that controls neck muscles for postural adjustments of the head

Vestibular nuclei

Brainstem structures that integrate sensory information including visual, cutaneous, proprioceptive, and vestibular signals

Ascending pathways

Neural pathways that carry vestibular information via the thalamus to the cortex, allowing perception of the body in space