114 articles
Solitary nucleus
Solitary nucleus (nucleus tractus solitarii, NTS): dorsomedial medulla gray matter receiving visceral and taste afferents via cranial nerves VII, IX, X; first relay for baroreflex, respiration, and gut reflexes, using glutamatergic vagal input.
Somatic nervous system
Somatic nervous system (SoNS): PNS division for voluntary movement and sensory input via skeletal muscles; 12 cranial and 31 spinal nerve pairs, single-neuron efferent path releasing acetylcholine, distinct from the two-neuron autonomic system.
Spinal cord
Spinal cord: the CNS cylinder of gray and white matter with 31 segments (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal), ascending sensory and descending motor tracts, reflex function, and regeneration failure after injury.
Spinal cord segments and vertebral levels
Spinal cord segments and vertebral levels do not align: the adult cord ends at L1–L2, so its 31 nerve segments sit higher than the vertebrae of the same name.
Spinal grey matter
Spinal gray matter is the central, butterfly- or H-shaped region of the spinal cord containing neuronal cell bodies, organized into ten Rexed laminae and surrounded by white matter.
Spinal nerve
Spinal nerve: one of 31 paired mixed nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal) formed by ventral and dorsal roots, exiting via intervertebral foramina as part of the peripheral nervous system.
Stretch reflex
Stretch (myotatic, deep tendon) reflex: involuntary muscle contraction on rapid stretch, via monosynaptic Ia afferent–alpha motor neuron spinal connections; basis of knee jerk, ~20 ms upper-limb latency, delayed 14 ms in older adults.
Suboccipital nerve
The suboccipital nerve is the dorsal ramus of the C1 spinal nerve, a mainly motor nerve supplying the four suboccipital muscles and semispinalis capitis within the suboccipital triangle alongside the vertebral artery.
Substantia gelatinosa of Rolando
Substantia gelatinosa of Rolando (SGR), or substantia gelatinosa, is the translucent lamina II of the spinal dorsal horn, described by Rolando in 1824, that receives C and Aδ fiber input and modulates nociception via gate control circuitry.
Substantia nigra
The substantia nigra, Latin for "black substance", is a nucleus of the midbrain that supplies dopamine to the basal ganglia and helps modulate motor movement and reward.
Superior laryngeal nerve
Superior laryngeal nerve (nervus laryngeus superior), a vagus nerve branch dividing into an internal sensory branch to the supraglottic larynx and an external motor branch to the cricothyroid muscle; injury causes pitch-range loss and dysphagia.
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.
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.
Thalamus
Thalamus: paired ovoid gray-matter nuclei at the top of the brainstem relaying all sensory information except smell to cortex; also gates consciousness, sleep rhythms, cognition, and is a target for DBS in tremor and epilepsy.
Thecal sac
Thecal sac (dural sac, saccus durae matris spinalis): the dural sheath in the spinal canal enclosing the spinal cord, cauda equina, and cerebrospinal fluid; key MRI stenosis marker, lumbar puncture target, and SBRT contour.
Tibial nerve
Tibial nerve: terminal branch of the sciatic nerve (L4–S3) supplying motor and sensory innervation to the posterior leg and plantar foot; passes through the tarsal tunnel, dividing into medial and lateral plantar nerves; tarsal tunnel syndrome is its main entrapment.
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.
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.
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.
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.
Vestibulocochlear nerve
Vestibulocochlear nerve (CN VIII, acoustic nerve): purely sensory eighth cranial nerve carrying hearing from the cochlea and balance from the vestibular organs through the internal auditory canal to brainstem nuclei.
Vocal cord paresis
Vocal cord paresis, or vocal fold paresis, is partial weakness of a vocal fold from incomplete laryngeal nerve denervation, between normal function and full paralysis; it causes glottic insufficiency, breathy voice, and is diagnosed with laryngoscopy plus laryngeal EMG.