1,240 articles
Sweetness
Sweetness: a basic taste quality detected by the T1R2/T1R3 receptor, innate in human infants, lost in obligate carnivores like cats; sugars and non-sugar sweeteners differ in temporal profile and health evidence.
Sympathetic nervous system
Sympathetic nervous system (SNS): thoraco-lumbar autonomic division mediating fight-or-flight, thermoregulation, blood pressure, and skin and muscle innervation, with cholinergic preganglionic and mostly noradrenergic postganglionic neurons.
Sympathetic neuron
Sympathetic neuron: preganglionic spinal cord (T1–L3) and postganglionic neural crest-derived autonomic neurons mediating fight-or-flight responses; mostly noradrenergic, specified by BMP-driven Phox2b, Mash1, Hand2, Gata3.
Synapse
A synapse, or synaptic junction, is where a neuron passes an electrical or chemical signal to another neuron or effector cell; chemical synapses release neurotransmitters, electrical ones pass current directly.
Synapsin
Synapsins (synapsin I, II, III; SYN1, SYN2, SYN3) are neuron-specific phosphoproteins coating synaptic vesicles, regulating neurotransmitter release via phosphorylation, and modulating neuronal development, plasticity, and neurological disease.
Synaptic plasticity
Synaptic plasticity, also called Hebbian plasticity, LTP and LTD, is activity-dependent change in synaptic strength considered the main mechanism of learning and memory storage, spanning potentiation, depression, homeostatic scaling, and metaplasticity.
Synaptic Potentials
Synaptic potentials are graded voltage changes across pre- or postsynaptic membranes, chiefly EPSPs and IPSPs produced by ligand-gated ion channels, that summate temporally and spatially to decide whether a neuron fires.
Synaptic pruning
Synaptic pruning is the developmental elimination of excess neural synapses, driven by activity and executed by microglia, astrocytes, and OPCs via complement and other immune signals; dysregulation links to schizophrenia and autism.
Synaptic scaling
Synaptic scaling, or homeostatic synaptic scaling, is a slow non-Hebbian plasticity first described by Turrigiano in 1998 in which neurons globally multiply all excitatory synapse strengths up or down, via AMPA receptor trafficking, to stabilize firing.
Synaptogenesis
Synaptogenesis is the formation of synapses between neurons, via growth-cone contact and recruitment of scaffold and cell adhesion proteins such as PSD95, neurexin, and neuroligin; it peaks postnatally in rodents (P7–P14) and continues throughout life, with mutations in SHANK and SYNGAP1 linked to autism and intellectual disability.
Synaptotagmin
Synaptotagmin (SYT): a family of 17 mammalian vesicle membrane proteins with tandem C2 domains that act as Ca2+ sensors for exocytosis; Syt1/2/9 trigger fast synchronous neurotransmitter release, Syt7 asynchronous release and facilitation.
Synaptotropic hypothesis
Synaptotropic hypothesis: Vaughn's 1989 proposal that synaptic inputs direct dendritic and axonal arbor growth by selectively stabilizing filopodia on which synapses form; tested in Xenopus and zebrafish optic tectum.
Syringomyelia or syringobulbia
Syringomyelia or syringobulbia (ICD-11 8D66) is a spinal cord or brainstem fluid-filled cavity (syrinx), usually from Chiari I malformation obstructing CSF flow; diagnosed by MRI, treated by decompression or shunting.
Tachykinin family
Tachykinin family, or neurokinins: peptide neurotransmitters sharing the C-terminal Phe-X-Gly-Leu-Met-NH2 motif, including substance P, neurokinin A, and neurokinin B, acting through NK1, NK2, and NK3 GPCRs across vertebrates and invertebrates.
Tapetum lucidum
Tapetum lucidum: reflective layer behind the retina of many vertebrates and some invertebrates that boosts dim-light vision and causes eye-shine; types include retinal, guanine, cellulosum, and fibrosum tapeta; absent in primates, birds, and pigs.
Tarlov cyst
Tarlov cyst (perineural cyst): CSF-filled sac around sacral spinal nerve roots containing nerve fibers, first described by Isadore Tarlov in 1938; prevalence 1.5–13.2%, symptomatic in 10–20%, treated by surgery or fibrin-sealant aspiration.
Tarsal tunnel syndrome
Tarsal tunnel syndrome, also called posterior tibial neuralgia or tibial nerve entrapment, is compression of the posterior tibial nerve in the tarsal tunnel at the ankle, defined by Keck and Lam in 1962, causing foot pain and numbness, treated conservatively or by flexor retinaculum release.
Taste
Taste (gustation) is the chemical sense detecting sweet, sour, salty, bitter, and umami via taste bud receptor cells; also covers transduction, TAS2R38 genetics, PROP/PTC heritability, oleogustus, taste disorders, and penguin taste loss.
Taste bud
Taste bud: cluster of 50-100 neuroepithelial cells in tongue, palate, and throat papillae that transduces sweet, sour, salty, bitter, and umami stimuli; 2,000-5,000 per human oral cavity, continually renewed.
Taste receptor
Taste receptor: receptor proteins on taste receptor cells detecting bitter, sweet, umami, salty, and sour tastants. T1R and T2R GPCR families; TAS1R2+TAS1R3 sweet receptor; TAS2R14 structure solved 2024; also expressed in gut, lungs, heart, brain.
Tay–Sachs disease
Tay–Sachs disease, a fatal autosomal recessive GM2-gangliosidosis caused by HEXA gene variants on chromosome 15 lacking hexosaminidase-A; infantile form kills by age five, carriers common in Ashkenazi Jews, no cure, gene therapy in trials.
TBIDFTECWCTC trial
TBIDFTECWCTC is a registered clinical trial (NCT07451678) testing eyelid cleansing with topical chlorhexidine wipes twice daily for four weeks against Demodex folliculorum blepharitis, assessing collarettes, erythema, and dry eye.
Tears
Tears (lacrimal fluid) are secretions of the lacrimal, Meibomian, and conjunctival glands forming the tear film that lubricates, protects, and optically smooths the eye; types are basal, reflex, and emotional, and deficiency causes dry eye disease.
Temperature play
Temperature play, also called hot and cold play, is a consensual erotic or BDSM sensory practice using controlled warmth and coolness, such as ice, warm oil, or low-temperature wax, with burn and frostbite risk managed through negotiation and safewords.
Temporal lobe
Temporal lobe: one of the four cerebral lobes, below the lateral sulcus (Sylvian fissure). Handles hearing (Heschl gyri), language, emotion, and memory via the medial temporal lobe memory system; temporal lobe epilepsy is the most common focal epilepsy syndrome.
Tensor tympani muscle
Tensor tympani (musculus tensor tympani), a small middle-ear muscle innervated by CN V3, tenses the eardrum via the malleus, participates in the middle ear muscle reflex, and causes tensor tympani syndrome when it contracts involuntarily.
Terrien marginal degeneration
Terrien marginal degeneration (TMD), also called Terrien's marginal degeneration, is a rare, slowly progressive, usually non-inflammatory thinning of the peripheral cornea causing high against-the-rule astigmatism, lipid deposition, vascularization, and rare perforation.
Tethered cord syndrome
Tethered cord syndrome (TCS), abnormal fixation of the spinal cord causing traction, pain, and bladder or motor deficits; first described by Hoffman et al. 1976; treated by detethering or spinal column shortening.
Tetrachromacy
Tetrachromacy is possession of four independent color channels, usually four cone types from X-linked opsin heterozygosity in women; strong functional tetrachromacy is rare, weak forms more common, and no online tests are valid.
Tetraplegia
Tetraplegia (quadriplegia) is paralysis of all four limbs from cervical spinal cord injury, C1–T1, affecting arm and leg function, breathing, and daily living; distinguished from paraplegia by affected arm function.