Medical terms, defined.

The long thoracic nerve (C5, C6, C7) arises directly from the roots of the brachial plexus and innervates the serratus anterior. Injury (e.g., during mastectomy/axillary lymph node dissection or from a blow to the lateral chest wall) cau...

The foramen magnum is the large opening in the occipital bone (posterior cranial fossa) through which the medulla oblongata becomes the spinal cord. It lies at approximately the C1 level and transmits the spinal cord, meninges, vertebral...

Reichert cartilage is the cartilage of the 2nd pharyngeal (hyoid) arch. It gives rise to the stapes, styloid process, stylohyoid ligament, lesser horn of the hyoid, and upper part of the body of the hyoid. Its nerve is CN VII (facial), a...

The thoracodorsal nerve (middle subscapular nerve, C6–C8) is a branch of the posterior cord of the brachial plexus that innervates the latissimus dorsi. It is at risk during axillary lymph node dissection (e.g., breast cancer surgery), a...

The posterior cricoarytenoid (PCA) is the ONLY intrinsic laryngeal muscle that abducts the vocal cords (opens the glottis). It is innervated by the recurrent laryngeal nerve (branch of CN X). Mnemonic: "PCA = Position for Climbing Air" –...

The motor end plate is the specialized region of the skeletal muscle fiber membrane (sarcolemma) at the neuromuscular junction (NMJ) that contains a high density of nicotinic acetylcholine receptors (nAChR) and is folded into junctional...

The musculocutaneous nerve (C5–C7) is a terminal branch of the lateral cord of the brachial plexus. It innervates the anterior arm compartment muscles (coracobrachialis, biceps brachii, brachialis) and continues as the lateral antebrachi...

The axillary nerve (C5–C6) is a terminal branch of the posterior cord of the brachial plexus. It innervates the deltoid (shoulder abduction 15–90°) and teres minor (lateral rotation), and supplies sensation over the lateral shoulder (sup...

The lateral femoral cutaneous nerve (LFCN, L2–L3) is a purely sensory nerve supplying the anterolateral thigh. Its entrapment under or through the inguinal ligament near the ASIS causes meralgia paresthetica: burning pain, tingling, and...

The common peroneal (fibular) nerve is a terminal branch of the sciatic nerve (L4–S2) that wraps around the fibular neck, where it is highly vulnerable to injury. Damage causes foot drop (loss of dorsiflexion and eversion) with a high-st...

The median nerve (C5–T1; lateral and medial cords of the brachial plexus) innervates most forearm flexors, the thenar muscles, and the first two lumbricals. It supplies sensation to the palmar lateral 3½ digits. Key clinical correlates a...

The obturator nerve (L2–L4, anterior divisions of lumbar plexus) exits the pelvis via the obturator canal to innervate the medial (adductor) compartment of the thigh and a patch of medial thigh skin. Injury causes weakened thigh adductio...

The cisterna chyli is a dilated lymphatic sac at the origin of the thoracic duct, lying anterior to L1–L2 vertebrae in the retroperitoneum. It receives lymph from the right and left lumbar (lumbar trunks) and intestinal lymphatic trunks,...

Hesselbach triangle (inguinal triangle) is an anterior abdominal wall region bounded by the inferior epigastric vessels (lateral), lateral border of the rectus abdominis (medial), and the inguinal ligament (inferior). Hernias that protru...

Intercostal nerves are the anterior rami of thoracic spinal nerves T1–T11 (T12 is the subcostal nerve). They run in the intercostal spaces between the innermost and internal intercostal muscles, supplying intercostal muscles, overlying s...

Retroperitoneal organs lie posterior to the peritoneum and are covered by peritoneum only on their anterior surface. They are classified as primary retroperitoneal (always retroperitoneal) or secondary retroperitoneal (initially intraper...

The porta hepatis is the deep transverse fissure on the visceral (inferior) surface of the liver where the portal vein, hepatic artery proper, and bile ducts (common hepatic duct) enter/exit. It is also the site where lymphatics and nerv...

The ligamentum venosum is the fibrous remnant of the fetal ductus venosus, which shunted oxygenated blood from the umbilical vein (left portal vein) directly to the IVC, bypassing the liver. It lies in the fissure for the ligamentum veno...

The splenic artery is the largest branch of the celiac trunk (T12 level). It runs along the superior border of the pancreas in the splenorenal ligament to supply the spleen, and also gives branches to the pancreas and stomach. It is the...

The occipital lobe is the posterior-most cerebral lobe and houses the primary visual cortex (V1, Brodmann area 17) along the calcarine sulcus. It receives visual input from the lateral geniculate nucleus via the optic radiations and is s...

The retroperitoneal space is the compartment posterior to the peritoneal cavity (behind the posterior parietal peritoneum) containing organs that lie against the posterior abdominal wall. Mnemonic SADPUCKER: Suprarenal (adrenal) glands,...

The common iliac arteries are the paired terminal branches of the abdominal aorta, arising at the L4 vertebral level (aortic bifurcation, roughly at the umbilicus/iliac crest). Each divides at the pelvic brim (sacroiliac joint, ~L5-S1) i...

The parietal lobe is the cerebral lobe between the central sulcus (anterior) and the parieto-occipital sulcus (posterior). It houses the primary somatosensory cortex (postcentral gyrus) and association areas for spatial processing, praxi...

The greater omentum is a large, apron-like fold of peritoneum (4 layers) that hangs from the greater curvature of the stomach and proximal duodenum, draping over the transverse colon and small intestines. Often called the "policeman of t...

The cingulate gyrus is a medial cortical gyrus above the corpus callosum and a core part of the limbic system (Papez circuit). It mediates emotion, pain affect, motivation, and attention/error monitoring. Lesions cause apathy and akineti...

The postcentral gyrus is the primary somatosensory cortex (Brodmann areas 3, 1, 2) in the parietal lobe, located just posterior to the central sulcus. It receives somatotopically organized sensory input (touch, vibration, proprioception,...

The insular cortex (insula) is a cortical region buried deep within the lateral sulcus (Sylvian fissure), covered by the frontal, parietal, and temporal opercula. It integrates interoception, taste (primary gustatory cortex), visceral/au...

The precentral gyrus is the primary motor cortex (Brodmann area 4) located in the posterior frontal lobe, just anterior to the central sulcus. It contains upper motor neurons (including Betz cells) that initiate contralateral voluntary m...

Broca area is the motor speech area located in the posterior inferior frontal gyrus (Brodmann areas 44 and 45) of the dominant (usually left) hemisphere. Lesions cause Broca (expressive/nonfluent) aphasia: impaired fluency and repetition...

Wernicke area is the receptive language (comprehension) center located in the posterior superior temporal gyrus (Brodmann area 22) of the dominant hemisphere (usually left). Lesions cause Wernicke (receptive/fluent) aphasia: fluent but m...

The arcuate fasciculus is a white matter association tract connecting Wernicke's area (posterior superior temporal gyrus, Brodmann 22) with Broca's area (inferior frontal gyrus, BA 44/45). Lesions cause conduction aphasia: fluent speech...

The external capsule is a thin lamina of white matter in the cerebrum, lying between the putamen (medially) and the claustrum (laterally). It carries cholinergic fibers from the basal forebrain (nucleus basalis of Meynert) to the cortex...

The nucleus accumbens (NAc) is part of the ventral striatum and is the core of the brain's mesolimbic reward circuit. It receives dopaminergic input from the ventral tegmental area (VTA) and mediates reward, motivation, reinforcement, an...

The ventral posterolateral (VPL) nucleus is a thalamic relay nucleus that transmits somatosensory information from the body (trunk and limbs) to the primary somatosensory cortex (postcentral gyrus, areas 3, 1, 2). It receives the dorsal...

The medial geniculate nucleus (MGN) is the thalamic relay nucleus for auditory information, located in the metathalamus. It receives input from the inferior colliculus via the brachium of the inferior colliculus and projects via the acou...

The inferior olivary nucleus is a fold-shaped nucleus in the rostral (open) medulla that gives rise to climbing fibers. These fibers cross the midline via the olivocerebellar tract and enter the contralateral cerebellum through the infer...

The raphe nuclei are a set of midline serotonergic (5-HT) nuclei running through the brainstem reticular formation (midbrain, pons, medulla). They are the main source of CNS serotonin and regulate mood, sleep-wake cycles, pain modulation...

The mammillary bodies are paired hypothalamic nuclei at the posterior floor of the hypothalamus that are part of the limbic system (Papez circuit) and are critical for recollective memory. Damage, classically from thiamine (B1) deficienc...

The ventral posteromedial (VPM) nucleus is a thalamic relay nucleus that transmits somatosensory information (touch, pain, temperature, proprioception) from the face and oral cavity, as well as taste, to the cerebral cortex. It receives...

The lateral geniculate nucleus (LGN) is the thalamic relay nucleus for the visual pathway. It receives input from retinal ganglion cells via the optic tract and projects via the geniculocalcarine tract (optic radiations) to the primary v...

The fornix is a C-shaped white matter tract of the limbic system that carries efferent fibers from the hippocampus to the mammillary bodies (part of the Papez circuit) and septal nuclei. Damage causes anterograde amnesia and impaired mem...

The anterior commissure is a small white matter tract crossing the midline at the lamina terminalis, just anterior to the columns of the fornix. It connects the temporal lobes (amygdalae, inferior/middle temporal cortex) and olfactory st...

The posterior commissure is a white matter tract crossing the midline at the junction of the midbrain and diencephalon, just superior to the cerebral aqueduct and at the base of the pineal gland. It carries fibers of the bilateral pupill...

The ventral tegmental area (VTA) is a midbrain nucleus containing dopaminergic neurons that give rise to the mesolimbic and mesocortical pathways. It is central to reward, motivation, reinforcement, and addiction. Dysfunction is implicat...

Arachnoid granulations (villi) are protrusions of arachnoid mater through the dura into the dural venous sinuses, especially the superior sagittal sinus. They act as one-way valves that reabsorb CSF from the subarachnoid space into venou...

The third ventricle is a narrow, midline, slit-like CSF-filled cavity of the diencephalon, lying between the two thalami and hypothalamus. It receives CSF from the lateral ventricles via the interventricular foramina of Monro and drains...

The lateral ventricles are paired, C-shaped CSF-filled cavities within the cerebral hemispheres, each communicating with the third ventricle via the interventricular foramen of Monro. They contain choroid plexus, which produces CSF, and...

Arachnoid villi (granulations when enlarged) are projections of arachnoid mater through the dura into the dural venous sinuses, mainly the superior sagittal sinus. They reabsorb CSF from the subarachnoid space into venous blood via one-w...

Dural venous sinuses are endothelial-lined venous channels between the periosteal and meningeal layers of the dura mater that drain blood from the brain, meninges, skull, and orbits, ultimately into the internal jugular veins. They lack...

The falx cerebri is a sickle-shaped fold of dura mater (meningeal layer) that descends in the longitudinal fissure between the two cerebral hemispheres. It anchors anteriorly to the crista galli and blends posteriorly with the tentorium...