Module 7: Sense Organs Vocabulary

Comprehensive vocabulary flashcards covering the properties, pathways, and structures of sensory receptors, general senses, pain, taste, smell, hearing, equilibrium, and vision from Chapter 16.

Sensory receptor

Any structure specialized to detect a stimulus, ranging from simple bare nerve endings to complex sense organs.

Sense organ

A structure that combines nervous tissue with other tissues (such as epithelial, muscular, or connective tissue) that enhance its response to a specific type of stimulus.

Transduction

The fundamental purpose of any sensory receptor, defined as the conversion of one form of energy into nerve signals.

Receptor potential

A small local electrical change produced by a sensory receptor cell in response to an environmental stimulus.

Modality

The type of stimulus or perception produced by a sensory signal (e.g., vision, hearing, taste), determined by where the sensory signals terminate in the brain.

Receptive field

The specific area within which a single sensory neuron detects stimuli.

Phasic receptors

Receptors that generate a burst of action potentials when first stimulated, then quickly adapt and sharply reduce or stop signaling even if the stimulus continues.

Tonic receptors

Receptors that adapt slowly and generate nerve signals more steadily throughout the duration of a stimulus.

Thermoreceptors

Sensory receptors that respond to temperature changes (heat and cold).

Chemoreceptors

Sensory receptors that respond to chemicals, including odors, tastes, and body fluid composition.

Mechanoreceptors

Receptors that respond to physical deformation of a cell or tissue caused by vibration, touch, pressure, stretch, or tension.

Proprioceptors

Sensory receptors located in muscles, tendons, and joint capsules that sense the position and movements of the body or its parts.

Free nerve endings

Unencapsulated bare dendrites with no special association with specific accessory cells, functioning as warm receptors, cold receptors, and nociceptors.

Tactile (Merkel) discs

Unencapsulated tonic receptors for light touch that reside in the stratum basale of the epidermis and respond to skin compression.

Tactile (Meissner) corpuscles

Encapsulated phasic receptors for light touch and texture, concentrated in sensitive hairless areas such as the fingertips, palms, eyelids, lips, and genitals.

Lamellar (pacinian) corpuscles

Large encapsulated phasic receptors located deep in the dermis and viscera that respond chiefly to deep pressure, stretch, tickle, and vibration.

Fast pain

Immediate, sharp, localized pain mediated by myelinated $A\beta$ or $A\triangle$ (A-delta) nerve fibers conducting at speeds of $12$ to $30\,m/s$.

Slow pain

Delayed, burning, dull, or aching pain mediated by small unmyelinated type C nerve fibers conducting at speeds of $0.5$ to $2.0\,m/s$.

Referred pain

Pain originating in the viscera that is mistakenly perceived as arising from the skin or other superficial sites due to neural convergence in the CNS.

Substance P

The key neurotransmitter released by first-order pain neurons onto second-order neurons in the posterior horn of the spinal cord.

Endogenous opioids

Internally produced neuropeptides (enkephalins, endorphins, and dynorphins) secreted by the CNS and other organs to block pain transmission and produce euphoria.

Gustation

The sense of taste, produced by chemical stimulation of sensory taste cells clustered in taste buds by dissolved molecules (tastants).

Filiform papillae

Small spike-shaped lingual papillae without taste buds; the most abundant papillae on the human tongue, serving to provide friction and detect food texture.

Vallate papillae

Large lingual papillae arranged in a V-shape at the rear of the tongue, surrounded by a deep trench and containing up to half of all taste buds.

Olfaction

The sense of smell, triggered by airborne volatile chemicals (odorants) binding to receptors on cells in the olfactory mucosa.

Glomeruli

Spheroidal clusters in the olfactory bulb where axons of olfactory neurons synapse with the dendrites of mitral cells and tufted cells.

Pitch

The perception of a sound as high or low, determined by the vibration frequency of the sound source measured in hertz ($Hz$).

Loudness

The perception of sound energy, intensity, or vibration amplitude, expressed in decibels ($dB$).

Cerumen

Sticky earwax formed by ceruminous and sebaceous gland secretions mixed with dead skin cells, which waterproofs and protects the auditory canal.

Auditory ossicles

The three small middle-ear bones (malleus, incus, and stapes) that transfer sound vibrations from the tympanic membrane to the inner ear.

Tympanic reflex

A protective middle-ear reflex in which the tensor tympani and stapedius muscles contract to lessen the transfer of loud sound vibrations to the oval window.

Cochlea

A coiled, snail-like tube of the inner ear winding around the modiolus that contains the spiral organ for hearing.

Spiral organ

A thick epithelium resting on the basilar membrane within the cochlear duct composed of hair cells and supporting cells that converts vibrations into nerve signals.

Stereocilia

Long, stiff microvilli on the apical surface of auditory and vestibular hair cells that bend to modulate mechanically gated ion channels.

Tip link

A fine, stretchy protein filament connecting a mechanically gated $K^+$ channel at the tip of one stereocilium to the sidewall of the adjacent taller stereocilium.

Vestibular apparatus

The inner ear complex responsible for equilibrium, consisting of three semicircular ducts, a saccule, and an utricle.

Otoliths

Protein-calcium carbonate granules embedded in the otolithic membrane of the macula sacculi and macula utriculi that add inertia to enhance gravity and motion sensing.

Crista ampullaris

A mound of hair cells and supporting cells within the dilated ampulla of each semicircular duct that detects angular acceleration.

Conjunctiva

A transparent, highly vascularized mucous membrane covering the inner surface of the eyelids and the anterior white surface of the eyeball.

Cornea

The anterior, transparent region of the fibrous tunic of the eyeball specialized to admit and refract light.

Aqueous humor

A serous fluid secreted by the ciliary body into the posterior chamber that flows through the pupil into the anterior chamber before reabsorption by the scleral venous sinus.

Vitreous body

A clear jelly-like substance filling the vitreous chamber behind the lens that maintains intraocular pressure and holds the retina flat against the choroid.

Fovea centralis

A tiny pit in the center of the macula lutea containing densely packed cone cells, responsible for producing the most finely detailed visual images.

Refraction

The bending of light rays when passing obliquely from one medium to another of a different refractive index.

Emmetropia

The natural relaxed state of the eye when focused on an object more than $6\,m$ ($20\,ft$) away, allowing parallel light rays to land on the retina without muscular effort.

Accommodation

The thickening of the lens induced by ciliary muscle contraction that increases its refractive power to focus on nearby objects.

Rod cells

Photoreceptors with cylindrical outer segments containing stacked discs of rhodopsin, specialized for night (scotopic) and monochromatic vision.

Cone cells

Photoreceptors with tapering outer segments containing photopsin pigments, specialized for day (photopic), trichromatic, and high-acuity vision.

Bleaching

The photochemical reaction in which absorbed light causes cis-retinal to isomerize to trans-retinal and separate from opsin.

Duplicity theory of vision

The theory stating that a single photoreceptor system cannot provide both high sensitivity and high resolution, requiring distinct rod and cone systems.

Hemidecussation

The crossing over of exactly half of the optic nerve fibers from each eye to the opposite hemisphere at the optic chiasm.