1,240 articles
Trigeminal nerve
Trigeminal nerve (CN V), the largest cranial nerve, a mixed sensory and motor nerve with ophthalmic (V1), maxillary (V2), and mandibular (V3) branches; V3 alone carries motor fibers to the muscles of mastication; best-known disorder is trigeminal neuralgia.
Trochlear nerve
Trochlear nerve (CN IV), fourth cranial nerve, purely motor to the superior oblique muscle; smallest cranial nerve with the longest intracranial course and the only dorsal brainstem exit; palsy causes vertical diplopia and head tilt.
Tropical spastic paraparesis
Tropical spastic paraparesis, or HAM/TSP, is a chronic HTLV-1-caused inflammatory myelopathy of the lower thoracic cord with progressive spastic paraparesis and bladder dysfunction; steroids help, antiretrovirals do not, mogamulizumab is emerging.
Tubocurarine
Tubocurarine, also called d-tubocurarine, is the active alkaloid of curare that blocks neuromuscular transmission; isolated in 1935, it became the first muscle relaxant used in anesthesia in 1942.
Tumefactive multiple sclerosis
Tumefactive multiple sclerosis (TMS), also called tumefactive demyelinating lesion, is a rare MS variant with demyelinating lesions over 2 cm that mimic brain tumors on MRI.
Tunnel vision
Tunnel vision, or peripheral vision loss, narrows the visual field to central vision only. Causes include glaucoma, retinitis pigmentosa, retinal detachment, migraine, and low blood pressure; legal blindness is a field of 20 degrees or less.
Two-point discrimination
Two-point discrimination (2PD), from Weber's 1834 method, measures the minimum skin separation at which two blunt contacts feel distinct; thresholds range from 1–2 mm at the tongue tip to 20–30 mm on the hand back, but nonspatial cues inflate performance, prompting the two-point orientation discrimination alternative.
Two-streams hypothesis
Two-streams hypothesis: primate visual cortex model with a ventral "what" stream to temporal cortex for perception and a dorsal "where/how" stream to parietal cortex for action; proposed by Ungerleider and Mishkin (1982) and Goodale and Milner (1992), now revised toward interacting streams.
Tympanosclerosis
Tympanosclerosis, also called myringosclerosis when limited to the eardrum, is calcified scar plaque formation in the tympanic membrane and middle ear after infection, surgery, or injury, often causing conductive hearing loss treated with tympanoplasty or hearing aids.
Tympanostomy tube
A tympanostomy tube, also called an ear tube or grommet, is a small tube inserted through the eardrum to drain fluid and ventilate the middle ear.
Type I vestibular sensory cell
Type I vestibular sensory cell (type I hair cell): amniote-only flask-shaped vestibular hair cell enveloped by a calyx afferent terminal, with low-voltage-activated K+ currents and both quantal and non-quantal transmission, unlike bouton-innervated type II cells.
U-138MG
U-138MG, also written U138 or U-138 MG, is a human cancer cell line from a malignant brain glioma, established in 1968 and widely used in glioblastoma research.
U-373MG ATCC
U-373MG ATCC (CVCL_2219, HTB-17) is a human glioblastoma/astrocytoma cell line shown by STR profiling and sequencing to be a U-251MG derivative, not the original 1973 Uppsala U-373MG line; ICLAC-00295, ATCC distribution discontinued.
Ulceration of conjunctiva
Ulceration of conjunctiva (conjunctival ulcer, ICD-11 9A60.30; SNOMED CT 95744009) is a necrotic depressed lesion of the eye's conjunctiva, infective (tuberculosis, herpes) or non-infective (Behçet's, Crohn's, mechanical), diagnosed by fluorescein staining.
Ulnar claw
Ulnar claw, or claw hand (intrinsic-minus hand), is a deformity with MCP hyperextension and IP flexion of the ring and little fingers from ulnar nerve palsy, causing 60-80% pinch and grip strength loss; treated with splinting and tendon transfers.
Ulnar nerve
Ulnar nerve (nervus ulnaris): terminal branch of the medial cord of the brachial plexus, C8–T1, supplying forearm flexors and most intrinsic hand muscles and medial 1.5 digits; compressed at cubital tunnel or Guyon canal.
Unipolar neuron
Unipolar neuron (pseudounipolar neuron): a neuron with one process from the soma, typical of PNS sensory neurons in dorsal root and cranial nerve ganglia; develops from bipolar embryonic neurons, with axons up to 1 m or more.
Upper motor neuron
Upper motor neuron: cortical and brainstem neurons of the pyramidal (corticospinal and corticobulbar) tracts that synapse on lower motor neurons; lesions cause spasticity, hyperreflexia, clonus, and a positive Babinski sign.
Upper motor neuron lesion
Upper motor neuron lesion: damage to CNS motor neurons or the corticospinal/corticobulbar tracts above the anterior horn, causing weakness, spasticity, hyperreflexia, clonus, and the Babinski sign, distinct from lower motor neuron lesions.
Utricle (ear)
Utricle (ear): otolith organ of the vestibular labyrinth, with the saccule; its horizontal macula, striola, and otoconial membrane sense horizontal linear acceleration and head tilt, tested clinically by oVEMP and SVV.
Uveitis
Uveitis (iritis, choroiditis) is inflammation of the uvea, the eye's middle layer (iris, ciliary body, choroid). Causes include autoimmune disease, infection, injury, and lymphoma; treated with corticosteroids and steroid-sparing immunosuppressants.
Vagus nerve
Vagus nerve (cranial nerve X): longest cranial nerve, medulla to abdomen, sensory and parasympathetic fibers. Also covers vagus nerve stimulation, FDA-approved uses, and evidence quality.
Vagus nerve stimulation
Vagus nerve stimulation (VNS, taVNS) is electrical neuromodulation of the vagus nerve, FDA-approved since 1997 for drug-resistant epilepsy and later for depression, obesity, stroke rehabilitation, and rheumatoid arthritis, with about 46% of epilepsy patients achieving 50% seizure reduction.
Variant Creutzfeldt–Jakob disease
Variant Creutzfeldt–Jakob disease (vCJD), also called human mad cow disease, is a fatal prion disease from BSE-contaminated beef, first described in the UK in 1996; 233 deaths worldwide, median age 28, transmissible by blood transfusion.
Vasoproliferative tumor of the retina
Vasoproliferative tumor of the retina (RVPT), also called retinal vasoproliferative tumor, is a rare benign retinal vascular growth, typically in the peripheral retina, causing vision loss and floaters.
Ventral cochlear nucleus
Ventral cochlear nucleus (VCN), first relay of the central auditory system in the brainstem, subdivided into AVCN and PVCN; its octopus, bushy, and stellate cells run parallel timing and sound-localization pathways.
Ventricular system
Ventricular system: interconnected brain cavities (two lateral, third, fourth ventricles) that produce and circulate cerebrospinal fluid via the choroid plexus, foramina of Monro, Luschka, and Magendie; obstruction causes hydrocephalus.
Vergence
Vergence: disconjugate eye movements (convergence, divergence) rotating the eyes oppositely to fixate targets at different depths, driven by retinal disparity, cross-linked with accommodation, and disrupted in convergence insufficiency.
Vernal keratoconjunctivitis
Vernal keratoconjunctivitis (VKC) is a rare, chronic, sight-threatening allergic inflammatory eye disease of children, mainly boys in warm climates, marked by giant tarsal papillae, Horner-Trantas dots, shield ulcers, and Th2-driven inflammation.
Vertigo
Vertigo: the false sensation of spinning or motion, a subcategory of dizziness causing up to 8% of medical consultations. Key causes include BPPV, Meniere's disease, vestibular migraine, and stroke; diagnosed with Dix-Hallpike and HINTS exams.