2,701 articles
Superior limbic keratoconjunctivitis
Superior limbic keratoconjunctivitis (SLK, Theodore's syndrome) is a chronic relapsing inflammation of the superior bulbar and tarsal conjunctiva and superior limbus, mainly in women aged 30–55, linked to thyroid eye disease and dry eye.
Superior mesenteric artery
Superior mesenteric artery (SMA): second anterior branch of the abdominal aorta at L1, supplying the midgut from duodenum to splenic flexure via jejunal, ileal, ileocolic, right colic, and middle colic branches; linked to mesenteric ischemia, SMA syndrome, and nutcracker syndrome.
Superior mesenteric artery syndrome
Superior mesenteric artery syndrome, or Wilkie's syndrome, is rare duodenal obstruction from compression of the third duodenum between the aorta and superior mesenteric artery, usually after rapid weight loss; treated first with nutrition and positioning, then duodenojejunostomy.
Superior mesenteric vein
Superior mesenteric vein (SMV): large abdominal vein draining the small intestine, right colon, pancreas, stomach, and appendix; runs right of the superior mesenteric artery and joins the splenic vein behind the pancreas to form the portal vein.
Superior olivary complex
Superior olivary complex (SOC), or superior olive: cluster of auditory nuclei in the caudal pontine tegmentum, first site of binaural convergence; MSO computes interaural time differences, LSO level differences, for sound localization.
Superior orbital fissure
The superior orbital fissure is a cleft in the sphenoid bone connecting the orbit to the middle cranial fossa and transmitting cranial nerves III, IV, V1, and VI.
Superior vena cava
Superior vena cava (SVC): the largest central systemic vein, draining upper-body blood to the right atrium; formed by brachiocephalic veins, joined by the azygos vein; obstruction causes SVC syndrome, treated by stenting.
Supination
Supination: rotation turning the palm forward or upward at the forearm (radius around ulna, 80–90° range; supinator and biceps), or adduction plus inversion raising the foot's arch; opposite of pronation.
Supine position
Supine position: lying flat on the back, face up (decúbito supino). The most common surgical position; highest cardiac output and lowest vascular resistance of compared body positions; arms kept under 90 degrees abduction.
Suprachiasmatic nucleus
Suprachiasmatic nucleus (SCN), hypothalamic master circadian pacemaker above the optic chiasm, ~20,000 neurons, intrinsic period ~24.2 h, light-entrained via the retinohypothalamic tract, synchronizes peripheral clocks and melatonin rhythms.
Supraclavicular lymph nodes
Supraclavicular lymph nodes (nodi lymphoidei supraclaviculares): 4-12 nodes above the clavicle draining breast, lung, esophagus, and abdomen; the left Virchow node (Troisier sign) signals metastatic cancer in 54-85% of enlargements.
Supraspinatus muscle
Supraspinatus muscle: rotator cuff muscle of the shoulder, originating in the supraspinous fossa of the scapula and inserting on the greater tubercle of the humerus; initiates 0-15 degrees of arm abduction, innervated by the suprascapular nerve (C5, C6), and the cuff tendon most prone to tears.
Supratrochlear lymph nodes
Supratrochlear (epitrochlear, cubital) lymph nodes: 1–2 superficial nodes 4–5 cm above the medial epicondyle draining the medial fingers and forearm to the axilla; palpable nodes over 0.5 cm are abnormal.
Supravalvular aortic stenosis
Supravalvular aortic stenosis (SVAS), also called supravalvar aortic stenosis or elastin arteriopathy, is congenital narrowing of the ascending aorta above the aortic valve, caused by ELN gene mutation or deletion at 7q11.23, alone or in Williams-Beuren syndrome.
Sural nerve
Sural nerve: purely sensory lower-leg cutaneous nerve formed mainly by union of the medial sural cutaneous and peroneal communicating nerves; standard site for nerve conduction studies, nerve biopsy, and graft harvesting.
Surface chemistry of neural implants
Surface chemistry of neural implants: coatings (Pt, IrOx, PEDOT, graphene, hydrogels, drug-releasing layers) on neural electrodes that lower impedance, raise charge capacity, and suppress glial scar formation at the electrode–tissue interface.
Suspensory ligament of ovary
Suspensory ligament of ovary (infundibulopelvic ligament, ligamentum suspensorium ovarii): a peritoneal fold from ovary to pelvic sidewall carrying the ovarian vessels, nerves, and lymphatics; not a true ligament, distinct from the proper ovarian ligament.
Swallowing
Swallowing (deglutition) moves food and liquid from mouth to stomach in four phases using six cranial nerves and over 30 muscles; its disorder, dysphagia, affects up to 68% of long-term care residents and is assessed by VFSS and FEES.
Swartz Prize for Theoretical and Computational Neuroscience
The Swartz Prize for Theoretical and Computational Neuroscience is an annual award by the Society for Neuroscience, first given in 2008 to Wilfrid Rall and supported by the Swartz Foundation.
Sweat gland
Sweat gland (sudoriferous gland): exocrine skin gland in two forms, eccrine (thermoregulatory, 2–4 million, up to 4 L sweat/hour) and apocrine (hair follicles, puberty-onset, body odor via bacterial breakdown).
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.