Intro to Anatomy, Histology, Brain and ANS, Nervous Tissue & Cerebral Blood Flow, Spinal Cord & Sensory Receptors, and Peripheral/Cranial Nerves, condensed to the highest-yield facts.
| Topic | One-glance facts |
|---|---|
| Levels of organization | Chemical → cellular → tissue → organ → organ system → organism, each level built on the one below. Systemic anatomy studies by functional system; regional anatomy studies all structures in one area together. |
| Terms of relationship & laterality | Anterior/ventral vs. posterior/dorsal; superior/cranial vs. inferior/caudal; medial vs. lateral; proximal vs. distal; superficial vs. deep; ipsilateral vs. contralateral — all referenced to standard anatomical position. |
| Anatomical planes | Sagittal = left/right (midsagittal splits exactly in half; parasagittal = any other sagittal cut). Frontal/coronal = anterior/posterior. Transverse/horizontal/axial = superior/inferior. |
| Terms of movement | Flexion (↓ joint angle) vs. extension (↑); abduction (away from midline) vs. adduction (toward); medial/lateral rotation; pronation (palm down) vs. supination (palm up); inversion (sole medial) vs. eversion (sole lateral); elevation/depression, protraction/retraction. |
| Body cavities | Dorsal cavity = cranial cavity (brain) + vertebral canal (spinal cord), continuous. Ventral cavity = thoracic (paired pleural cavities + mediastinum with pericardial cavity, great vessels, trachea, esophagus) + abdominopelvic (no wall dividing abdominal/pelvic portions). |
| Serous membranes | Parietal layer lines the cavity wall, visceral layer covers the organ, with serous fluid between reducing friction. Named by site: pleura (lungs), pericardium (heart), peritoneum (abdominal organs). |
| Nine abdominal regions | Superior row: right hypochondriac, epigastric, left hypochondriac. Middle row: right lumbar, umbilical, left lumbar. Inferior row: right iliac, hypogastric, left iliac — set by two horizontal and two vertical lines. |
| Topic | One-glance facts |
|---|---|
| Four primary tissue types | Epithelial, connective, muscle, and nervous tissue — all body structures are built from these four. |
| Epithelial tissue classification | Classified by cell shape (squamous/cuboidal/columnar) × layering (simple/stratified/pseudostratified). Transitional epithelium is a special stretchy stratified type (bladder). Functions: protection (stratified squamous), secretion (glandular), absorption (simple columnar w/ microvilli), filtration (simple squamous). |
| Connective tissue composition & types | Ground substance + fibers (collagen = tensile strength, elastic = stretch/recoil, reticular = supportive mesh), made by fibroblasts. Categories: loose (areolar, adipose, reticular), dense (regular = tendons/ligaments, irregular = dermis, elastic = large arteries), supportive (cartilage, bone), fluid (blood — plasma matrix). |
| Muscle tissue types | Skeletal (striated, voluntary, multinucleate); cardiac (striated, involuntary, branching, intercalated discs); smooth (non-striated, involuntary, spindle-shaped uninucleate, hollow organs/vessels). |
| Cartilage types | Hyaline (most common, glassy — articular surfaces, respiratory rings); fibrocartilage (highest tensile strength — intervertebral discs, menisci); elastic (flexible — external ear, epiglottis). All avascular. |
| Bone tissue & osteon histology | Compact bone = dense outer shell; spongy/trabecular bone = marrow-filled lattice at long-bone ends. Osteon: central Haversian canal (vessels/nerves) surrounded by concentric lamellae, osteocytes in lacunae connected by canaliculi; perforating (Volkmann's) canals run perpendicular, linking osteons to periosteum. |
| Epiphyseal growth plate zones | Resting (anchors plate) → proliferative (rapid division) → hypertrophic (chondrocytes enlarge, matrix calcifies) → calcification (cells die, replaced by bone). Ossifies fully at growth's end, leaving the epiphyseal line. |
| Topic | One-glance facts |
|---|---|
| Cerebral lobes | Frontal (voluntary motor, executive function, personality), parietal (somatosensory, spatial awareness), temporal (auditory, memory, language), occipital (vision) — divided by the central and lateral sulci; gyri (ridges)/sulci (grooves) increase cortical surface area. |
| Gray/white matter & basal nuclei | Gray matter (unmyelinated cell bodies) forms the outer cortex; white matter (myelinated axons) fills the interior. Basal nuclei (caudate, putamen, globus pallidus) = gray-matter islands modulating voluntary movement. Limbic system (hippocampus, amygdala, cingulate gyrus) governs emotion and memory. |
| Diencephalon | Thalamus = sensory relay to cortex (except smell). Hypothalamus = homeostasis master regulator (temperature, hunger, thirst, circadian rhythm) plus controls the pituitary. Epithalamus = pineal gland (melatonin). |
| Brainstem & cerebellum | Midbrain (cerebral peduncles, superior/inferior colliculi); pons (relays cerebrum ↔ cerebellum, respiratory rhythm); medulla (cardiovascular/respiratory centers, decussation of the pyramids). Cerebellum coordinates fine motor movement, posture, and balance. |
| Cranial meninges | Dura mater (outer, periosteal + meningeal layers form dural venous sinuses; folds = falx cerebri, tentorium cerebelli) → arachnoid mater (web-like, defines subarachnoid space) → pia mater (innermost, follows every gyrus/sulcus). |
| Ventricles, CSF & blood-brain barrier | CSF path: lateral ventricles → interventricular foramina (of Monro) → third ventricle → cerebral aqueduct → fourth ventricle → subarachnoid space; made by choroid plexus, reabsorbed via arachnoid granulations into dural sinuses. BBB = endothelial tight junctions + astrocyte end-feet, blocking large/hydrophilic molecules. |
| Autonomic nervous system | Sympathetic: thoracolumbar (T1–L2) outflow, short preganglionic/long postganglionic fibers (chain ganglia) — rapid, widespread. Parasympathetic: craniosacral (cranial nerve nuclei + S2–S4) outflow, long preganglionic/short postganglionic — localized. Enteric NS (myenteric = motility, submucosal = secretion) self-coordinates; sympathetic inhibits GI activity, parasympathetic (vagal) stimulates it. |
| Topic | One-glance facts |
|---|---|
| Neuron structure | Cell body (soma, nucleus) → dendrites (receive input) → axon (arises from axon hillock, the action-potential trigger zone) → axon terminals; often myelin-insulated. CNS = brain + spinal cord; PNS = nerves/ganglia outside the CNS. |
| Neuron classification | Functional: sensory/afferent (toward CNS), motor/efferent (away from CNS), interneuron (within CNS). Structural: multipolar (1 axon, many dendrites — most CNS/motor neurons), bipolar (1 axon, 1 dendrite — retina), unipolar/pseudounipolar (1 process splits into peripheral/central branches — sensory, dorsal root ganglia). |
| CNS neuroglia | Astrocytes (most abundant — support neurons, help form the BBB, regulate extracellular environment); oligodendrocytes (myelinate segments of multiple CNS axons); microglia (CNS's resident immune cells); ependymal cells (line ventricles, help produce/circulate CSF). |
| PNS neuroglia & conduction | Schwann cells (each myelinates one segment of one PNS axon) and satellite cells (support ganglion cell bodies). Nodes of Ranvier interrupt myelin, enabling saltatory conduction (faster than unmyelinated conduction). At a synapse, the presynaptic terminal releases neurotransmitter across the cleft to excite/inhibit the postsynaptic cell. |
| Cerebral arterial supply | Internal carotid arteries → anterior circulation (most of the cerebrum). Paired vertebral arteries ascend and join → single basilar artery → posterior circulation (brainstem, cerebellum, occipital lobes). |
| Circle of Willis | Internal carotids give rise to anterior cerebral arteries (linked by the anterior communicating artery) and middle cerebral arteries (largest, most of the lateral cerebral surface); basilar artery terminates in posterior cerebral arteries, each linked to its carotid by a posterior communicating artery — a collateral loop preserving perfusion. |
| Venous drainage | Cerebral veins empty into dural venous sinuses (between the two dura layers): superior sagittal, inferior sagittal, straight, and paired transverse/sigmoid sinuses → drain into the internal jugular veins. |
| Topic | One-glance facts |
|---|---|
| Spinal cord terminal anatomy | Cord runs foramen magnum → about L1–L2, tapering into the conus medullaris; the filum terminale anchors it to the coccyx, surrounded by descending lumbar/sacral roots = cauda equina. Cervical enlargement (upper limb) and lumbosacral enlargement (lower limb) mark thicker regions. |
| Gray matter organization | Dorsal (posterior) horns = sensory input; ventral (anterior) horns = motor neuron cell bodies; lateral horns (only at T1–L2) = intermediolateral gray horn, sympathetic preganglionic cell bodies. Rami communicantes: white ramus (myelinated preganglionic, to chain ganglion) and gray ramus (unmyelinated postganglionic, rejoins spinal nerve). |
| Ascending (sensory) tracts | Dorsal columns (fasciculus gracilis/cuneatus) — fine touch, vibration, conscious proprioception, ipsilateral until the medulla. Spinothalamic tracts — pain, temperature, crude touch, cross near entry level. Spinocerebellar tracts — unconscious proprioception to the cerebellum. |
| Descending (motor) tracts | Corticospinal tracts carry voluntary motor commands: lateral corticospinal tract (majority, already crossed at the medulla's pyramidal decussation) controls limb muscles; anterior corticospinal tract (crosses at its level of exit) controls axial/trunk muscles. |
| Spinal cord blood supply | One anterior spinal artery plus paired posterior spinal arteries, reinforced by segmental radicular arteries — the largest, the artery of Adamkiewicz, is clinically important in aortic surgery. |
| General sense receptor categories | Mechanoreceptors (physical deformation), thermoreceptors (warm/cool, free nerve endings), nociceptors (tissue damage/pain, mostly free nerve endings), chemoreceptors (chemical concentration — carotid/aortic bodies; also underlie olfaction/CN I and gustation/CN VII, IX, X). |
| Mechanoreceptor subtypes | Meissner corpuscles (light touch, fine discrimination — fingertips); Pacinian corpuscles (deep pressure/vibration — deep dermis/hypodermis); Merkel discs (sustained light touch/pressure); Ruffini endings (skin stretch). |
| Topic | One-glance facts |
|---|---|
| Spinal nerve formation | 31 pairs (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal): dorsal root (sensory, cell bodies in the dorsal root ganglion) + ventral root (motor) unite, then split into a dorsal ramus (deep back) and a larger ventral ramus (body wall/limbs). |
| Nerve plexuses | Cervical (C1–C4, phrenic nerve); brachial (C5–T1 → median, ulnar, radial, musculocutaneous, axillary nerves); lumbar (L1–L4 → femoral, obturator); sacral (L4–S4 → sciatic, the body's largest nerve) — lumbar and sacral often grouped as the lumbosacral plexus. |
| Reflex arc | Receptor → sensory neuron → integration center (spinal cord) → (± interneuron) → motor neuron → effector. Monosynaptic (patellar/stretch reflex) = sensory neuron synapses directly on the motor neuron, fastest. Polysynaptic (withdrawal reflex) = one or more interneurons, can recruit the opposite limb. |
| Cranial nerves I–IV | I Olfactory (cribriform plate — smell); II Optic (optic canal — vision); III Oculomotor (superior orbital fissure — most eye movements, eyelid elevation, pupillary constriction/lens accommodation); IV Trochlear (superior orbital fissure — superior oblique). |
| Cranial nerves V–VIII | V Trigeminal (V1/V2: superior orbital fissure/foramen rotundum, V3: foramen ovale — facial sensation, mastication muscles via V3); VI Abducens (superior orbital fissure — lateral rectus); VII Facial (internal acoustic meatus → stylomastoid foramen — facial expression, anterior 2/3 tongue taste, lacrimal/salivary glands); VIII Vestibulocochlear (internal acoustic meatus — hearing & balance). |
| Cranial nerves IX–XII | IX Glossopharyngeal (jugular foramen — posterior tongue/pharynx taste-sensation, stylopharyngeus, carotid body/sinus reflex input); X Vagus (jugular foramen — parasympathetic to thoracic/abdominal viscera, pharyngeal/laryngeal muscles); XI Accessory (jugular foramen — sternocleidomastoid & trapezius); XII Hypoglossal (hypoglossal canal — tongue muscles). |
| CN III & IX clinical highlights | CN III carries parasympathetic fibers via the ciliary ganglion for pupillary constriction and lens accommodation, beyond its motor role. CN IX gives a carotid sinus/carotid body branch carrying baroreceptor/chemoreceptor input for blood pressure and breathing reflexes, beyond its taste/motor roles. |