Chapter 18: Sensory Systems

Vocabulary practice flashcards covering Chapter 18 on sensory systems, including general sensory receptors, olfaction, gustation, ear and vestibular anatomy, cochlear sound transduction, eye structure, and visual pathways.

Sensation

Sensory information arriving at the central nervous system (CNS).

Perception

The conscious awareness of a sensation.

Receptive Field

The specific area monitored by a single receptor cell or process.

Tonic Receptors

Sensory receptors that are always active.

Phasic Receptors

Sensory receptors that are normally inactive and become active only when a change occurs in the conditions being monitored.

Peripheral Adaptation

A reduction in sensitivity that occurs when sensory receptors or sensory neurons alter their levels of activity; characteristic of phasic receptors.

Central Adaptation

A reduction in sensitivity that occurs when sensory neurons remain active, but neurons along the sensory pathway are inhibited.

Nociceptors

Free nerve endings with large receptive fields that respond to extreme temperatures, physical damage, and dissolved chemicals such as histamine and capsaicin.

Referred Pain

A phenomenon where visceral pain is felt far from the site of the stimulus because multiple first-order sensory neurons converge on the same second-order neurons.

Thermoreceptors

Fast-acting phasic free nerve endings located in the dermis, skeletal muscles, liver, and hypothalamus; cold receptors are $3\text{–}4$ times more abundant than warm receptors.

Mechanoreceptors

Sensory receptors sensitive to stimuli that stretch, compress, twist, or distort their cell membranes; divided into tactile receptors, baroreceptors, and proprioceptors.

Root Hair Plexus

An unencapsulated tactile receptor consisting of sensory nerve endings wrapped around the base of a hair follicle to monitor hair displacement.

Tactile Discs

Unencapsulated tactile receptors composed of Merkel cells associated with sensory nerve terminals that detect fine touch and pressure.

Tactile Corpuscles

Encapsulated sensory receptors located in the dermal papillae that detect light touch, pressure, and low-frequency vibration.

Bulbous Corpuscles

Encapsulated receptors situated in the dermis that are sensitive to continuous pressure and skin distortion.

Lamellar Corpuscles

Large encapsulated sensory receptors composed of concentric layers of collagen fibers around a central dendritic process that detect deep pressure, pulsation, and vibration.

Baroreceptors

Stretch receptors that monitor pressure changes by detecting the stretch of hollow organ walls, such as the carotid sinus, aortic sinus, lungs, digestive tract, and bladder.

Muscle Spindles

Proprioceptors consisting of intrafusal fibers monitored by sensory neurons and innervated by gamma motor neurons that detect muscle length and rate of stretch.

Golgi Tendon Organs

Proprioceptors located at the junction of skeletal muscle and tendon that monitor tension during muscle contraction.

Chemoreceptors

Specialized receptors that detect small changes in the concentrations of dissolved chemicals, including blood $pH$, $P_{CO_2}$, and $P_{O_2}$ in carotid/aortic bodies, and CSF $pH$ and $P_{CO_2}$ in the medulla oblongata.

Carpal Tunnel Syndrome

A compression neuropathy caused by compression of the median nerve beneath the transverse carpal ligament, commonly presenting with paresthesia in the hand.

Olfactory Sensory Neurons

Specialized bipolar neurons in the olfactory epithelium with 20 or more cilia containing receptor proteins that detect air-borne odorants.

Olfactory Glands

Mucus-secreting glands located in the lamina propria beneath the olfactory epithelium that dissolve incoming odorants.

Taste Buds

Sensory organs found along the sides of lingual papillae containing gustatory epithelial cells with microvilli, basal epithelial stem cells, and sensory nerve endings from CN VII, IX, and X.

Lingual Papillae

Epithelial projections on the tongue surface, classified as vallate, foliate, fungiform, and filiform papillae.

Umami

A pleasant, savory taste sensation triggered by amino acids such as glutamate and aspartate.

T2R38 Receptors

Bitter taste receptors located on ciliated nasal epithelial cells that detect bacterial acyl-homoserine lactones (AHL) and stimulate the rapid production of antibacterial nitric oxide.

Ceruminous Glands

Integumentary glands along the external acoustic meatus that secrete cerumen (earwax) to help prevent foreign matter from entering the ear canal.

Auditory Ossicles

The three tiny bones in the middle ear—the malleus, incus, and stapes—that transmit mechanical sound energy from the tympanic membrane to the oval window.

Otitis Media

Middle ear infection and inflammation characterized by undrained fluid accumulation in the tympanic cavity behind the tympanic membrane.

Bony Labyrinth

The shell of dense bone in the temporal bone consisting of the vestibule, semicircular canals, and cochlea, surrounding and protecting the membranous labyrinth and filled with perilymph.

Membranous Labyrinth

The fluid-filled collection of membranous tubes and chambers containing endolymph, comprising the utricle, saccule, semicircular ducts, and cochlear duct.

Maculae

Oval sensory structures in the utricle and saccule containing hair cells whose cilia are embedded in a gelatinous otolithic membrane covered by calcium carbonate crystals called otoliths.

Utricle

A chamber within the vestibule containing a macula horizontally oriented to detect horizontal acceleration and head tilt.

Saccule

A chamber within the vestibule containing a macula vertically oriented to detect vertical acceleration and gravity.

Ampullary Crest

The elevated sensory ridge inside the ampulla of each semicircular duct containing hair cells whose kinocilia and stereocilia are embedded in an ampullary cupula to detect angular acceleration.

Spiral Organ

The receptor organ for hearing inside the cochlear duct, where hair cells resting on the basilar membrane bend against the tectorial membrane to transduce sound waves into nerve impulses.

Basilar Membrane

The membrane supporting the spiral organ that exhibits frequency tuning: high-frequency sounds deflect the stiff base near the oval window, and low-frequency sounds deflect the flexible apex near the helicotrema.

Palpebrae

The eyelids, composed of skin, the orbicularis oculi and levator palpebrae superioris muscles, the tarsal plate, and the palpebral conjunctiva.

Lacrimal Apparatus

The anatomical structures that produce, distribute, and remove tears, consisting of the lacrimal gland, excretory ducts, lacrimal puncta, lacrimal canaliculi, lacrimal sac, and nasolacrimal duct.

Superior Oblique Muscle

An extra-ocular eye muscle innervated by CN IV (trochlear) that passes through the pulley-like trochlea to roll the eye and direct gaze inferiorly and laterally.

Cornea

The transparent anterior portion of the fibrous layer of the eye, made of precisely aligned collagen fibers; it is avascular and densely supplied with free nerve endings.

Choroid

The heavily vascularized posterior five-sixths of the middle layer (uvea) of the eye that delivers oxygen and nutrients to the retina.

Ciliary Body

A thickened ring of vascular tunic tissue surrounding the lens that secretes aqueous humor and contains the ciliary muscle, which alters lens shape through ciliary zonule fibers.

Pupillary Constrictor and Dilator

Two smooth muscle layers of the iris: the circular sphincter pupillae, which constricts the pupil, and the radial dilator pupillae, which enlarges the pupil.

Cataract

An opacity or clouding of the crystalline lens of the eye that impedes light transmission and causes blurred vision.

Presbyopia

The age-related loss of lens elasticity that impairs accommodation, making focusing on near objects increasingly difficult.

Fovea Centralis

A tiny central pit within the retinal macula containing exclusively cones, functioning as the site of highest visual resolution and sharpest color vision.

Optic Disc

The anatomical region on the retina where ganglion cell axons converge and exit as the optic nerve (CN II); contains no photoreceptors and is known as the blind spot.

Aqueous Humor

A clear fluid resembling CSF produced by the ciliary body in the posterior chamber that flows into the anterior chamber to nourish the cornea and lens before exiting via the scleral venous sinus.

Optic Chiasm

The anatomical junction where medial/nasal axons from each retina decussate to the contralateral optic tract, ensuring information from each visual field half projects to the opposite cerebral hemisphere.