114 articles
Midbrain
Midbrain (mesencephalon): the rostral brainstem segment between diencephalon and pons, divided into tectum and tegmentum, containing the substantia nigra, VTA, colliculi, and cerebral aqueduct; central to Parkinson's disease research and organoid models.
Motor cortex
Motor cortex: frontal lobe region for voluntary movement, comprising primary motor cortex (M1, Brodmann area 4), premotor cortex, and supplementary motor area; somatotopic map, Betz cells, corticospinal output, discovered by Fritsch and Hitzig in 1870.
Myotome
Myotome: the group of skeletal muscles innervated by one spinal nerve ventral root, and the somite compartment forming skeletal muscle; used clinically to localize radiculopathy, though maps vary between patients.
Neck
The neck (cervical spine): seven vertebrae C1–C7, atlas and axis, eight cervical nerves, discs and facet joints, supporting the head, enabling motion, and protecting the spinal cord.
Neocortex
Neocortex (isocortex): the six-layered outer cerebral cortex found only in mammals, part of the dorsal pallium, up to about 80% of the human brain, expanded in human prefrontal and language areas.
Neural plate
Neural plate: thickened columnar ectoderm induced by notochord signals during neurulation; folds into the neural tube (brain and spinal cord precursor). BMP antagonism induces it; failure of closure causes neural tube defects like spina bifida.
Nigrostriatal pathway
Nigrostriatal pathway: dopaminergic tract from the substantia nigra pars compacta (A9) to the dorsal striatum (caudate and putamen), governing motor control and associative learning; its degeneration causes Parkinson's disease, and it also contributes to reward.
Oculomotor nerve
Oculomotor nerve (cranial nerve III): midbrain motor nerve supplying four extraocular muscles, levator palpebrae, and pupil constriction via Edinger-Westphal fibers; palsy causes ptosis, diplopia, down-and-out eye, pupil-involving from aneurysm or herniation.
Olfactory bulb
Olfactory bulb: first central processing station for smell in the forebrain, receiving olfactory nerve input in glomeruli (100-200 um) and relaying via mitral and tufted cells to piriform cortex; site of adult neurogenesis and a marker in neurodegenerative disease.
Olfactory nerve
The olfactory nerve, or CN I, is the first cranial nerve, carrying smell signals from the roof of the nasal cavity to the olfactory bulbs of the brain.
Optic chiasm
Optic chiasm: brain-base structure where optic nerves partially decussate, nasal retinal fibers crossing (about 53:47 crossed-to-uncrossed), enabling binocular vision; pituitary tumor compression causes bitemporal hemianopia.
Optic disc
Optic disc (optic nerve head): retinal site where ganglion cell axons exit as the optic nerve; no photoreceptors, so it forms the blind spot; central retinal vessels pass through it; key glaucoma and papilledema landmark.
Optic nerve
Optic nerve (cranial nerve II, nervus opticus): the CNS white-matter tract of about 1.2 million retinal ganglion cell axons carrying vision from retina to chiasm and brain; myelinated by oligodendrocytes, afferent limb of the light reflex, limited regeneration.
Parasympathetic nervous system
Parasympathetic nervous system, the craniosacral division of the autonomic nervous system coined by Langley. Outflow via cranial nerves III, VII, IX, X and S2–S4; long preganglionic fibers, acetylcholine, ganglia near target organs, rest-and-digest function.
Parasympathetic neuron
Parasympathetic neuron: cholinergic motor neuron of the parasympathetic (craniosacral) autonomic division; preganglionic cells in brainstem nuclei and S2–S4, postganglionic cells in ganglia near target organs, vagus carrying 75% of fibers.
Parietal lobe
The parietal lobe, bounded by the central and parieto-occipital sulci, contains primary somatosensory cortex and posterior association areas for spatial attention, reaching, language, and number; damage causes neglect, apraxia, Gerstmann and Bálint syndromes.
Pelvic splanchnic nerves
Pelvic splanchnic nerves (nervi erigentes) are preganglionic parasympathetic nerves from S2-S4 anterior rami supplying the bladder, hindgut, ureter, prostate, urethra, and erectile tissue via the inferior hypogastric plexus.
Phrenic nerve
Phrenic nerve (nervus phrenicus): bilateral mixed nerve from C3-C5 (mainly C4) that is the sole motor supply of the diaphragm and sensory nerve of its center, pericardium, and mediastinal pleura; injury causes hemidiaphragm paralysis.
Primary motor cortex
Primary motor cortex (M1), Brodmann area 4, in the precentral gyrus; the cortical output area for voluntary movement. Contains Betz cells, somatotopic motor homunculus (Penfield and Boldrey, 1937), corticospinal and corticobulbar tracts, contralateral control.
Pudendal nerve
Pudendal nerve (Alcock's canal nerve), paired S2–S4 sacral plexus nerve supplying perineum, genital sensation, and anal and urethral sphincters; compression causes pudendal neuralgia, diagnosed by Nantes criteria and treated with blocks, stimulation, or decompression.
Pyramidal tracts
Pyramidal tracts: cortical motor fiber systems (corticospinal and corticobulbar tracts) passing through the medullary pyramids; about 75-90% decussate, controlling voluntary movement, with lesions causing contralateral weakness.
Radial nerve
Radial nerve: C5–T1 terminal branch of the brachial plexus posterior cord, supplying arm and forearm extensors and dorsal hand sensation; injuries cause wrist drop, Saturday night palsy, and Wartenberg's syndrome.
Recurrent laryngeal nerve
Recurrent laryngeal nerve (RLN, nervus laryngeus recurrens): vagus nerve branch supplying the larynx's intrinsic muscles; right loops under the subclavian artery, left under the aortic arch; injury is a key thyroidectomy complication.
Reflex arc
A reflex arc, or reflex circuit, is the neural pathway that produces an automatic, involuntary response to a stimulus, integrating it in the spinal cord or brainstem without conscious involvement.
Renshaw cell
Renshaw cell: spinal inhibitory interneuron (named for Birdsey Renshaw, 1941) in the ventral horn's lamina VII/IX; excited cholinergically by α-motoneuron collaterals, it inhibits motoneurons glycinergically, mediating recurrent inhibition.
Sacral and coccygeal spinal nerves
The sacral and coccygeal spinal nerves are five pairs of sacral nerves (S1–S5) and one coccygeal nerve, the lowest spinal nerves, supplying the pelvis and lower limb.
Sacral plexus
Sacral plexus (plexus sacralis): pelvic nerve network formed by the lumbosacral trunk (L4, L5) and S1–S4, anterior to piriformis; gives the sciatic, gluteal, posterior femoral cutaneous, perforating cutaneous, and pudendal nerves and the S2–S3 parasympathetic outflow.
Sciatic nerve
Sciatic nerve: largest human nerve, from L4–S3 roots, exiting the pelvis below piriformis and dividing into tibial and common peroneal nerves near the knee; supplies posterior thigh and most leg and foot motor and sensory function.
Smell
Smell, or olfaction, is the chemical sense by which gaseous odorant molecules are detected and identified, mediated by the olfactory nerve and closely coupled to taste in flavor perception.
Soft palate
Soft palate (velum, palatum molle): mobile muscular posterior third of the palate ending in the uvula, with five muscles innervated by the vagus via the pharyngeal plexus except tensor veli palatini (V3); central to swallowing, speech, and sleep apnea.