Thirty-six foundational ideas — six per subject — explained the way a good tutor would explain them over coffee. Skim them, don't memorize them. Each one links to an authoritative source (NCBI Bookshelf or OpenStax) so you can go deeper wherever your curiosity pulls you.
Unofficial. Independent guide; not affiliated with the AAMC, NBME, USMLE, LCME, or NRMP. External links open the source's own site. Plain-language summaries are our own synthesis of the linked sources.
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The language first, then the map. If these six feel familiar, the first weeks of anatomy lab will feel like review instead of a foreign language.
Anatomy describes the body as if it were standing in "anatomical position" — facing forward, palms forward. From there, three planes slice it: sagittal (left-right), coronal or frontal (front-back), and transverse (top-bottom). Directional words like superior, inferior, medial, lateral, proximal, and distal then tell you exactly where one structure sits relative to another.
Source: OpenStax Anatomy and Physiology 2e — Anatomical Terminology
The brachial plexus is the network of nerves — roots, trunks, divisions, cords, and branches — that carries signals between the spinal cord and the arm. Clinicians love it because an injury at one point in the network produces a predictable pattern of weakness downstream, so it becomes a favorite exam puzzle. Our read: don't memorize it cold this summer; just learn that it exists and why its organization matters, and the details will stick when you dissect it.
Source: NCBI Bookshelf (StatPearls) — Anatomy, Head and Neck: Brachial Plexus
The heart is a muscle, and like any muscle it needs its own blood supply — that is the job of the left and right coronary arteries, which branch off the aorta just above the aortic valve and wrap around the heart's surface. When a coronary artery is blocked, the heart muscle downstream is starved of oxygen: that is a heart attack. Knowing which artery feeds which wall of the heart is the anatomical key to reading ECGs later.
Source: NCBI Bookshelf (StatPearls) — Physiology, Coronary Circulation
The nephron is the kidney's functional unit — about a million per kidney — and it does one job in stages: filter blood at the glomerulus, then reclaim water and useful solutes as the filtrate travels through the tubule. Each segment of the tubule specializes: the proximal tubule reabsorbs the bulk, the loop of Henle builds the concentration gradient, and the distal segments fine-tune under hormonal control. Nearly all of renal physiology is just following fluid through this tube.
Twelve pairs of nerves exit the brain directly (rather than through the spinal cord), numbered I through XII, and they handle most of what your head does: smell, vision, eye movement, facial sensation and expression, hearing, taste, swallowing, and more. The classic student feat is reciting all twelve in order with a mnemonic — fun, but the clinical payoff is bigger: each nerve's territory tells you exactly where a lesion sits. Skim the list now; master it when neuroanatomy arrives.
Source: OpenStax Anatomy and Physiology 2e — The Peripheral Nervous System
The front of the abdomen is built in layers — skin, fat, three flat muscles (external oblique, internal oblique, transversus abdominis) plus the rectus abdominis running vertically, then the lining of the abdominal cavity. Surgeons cut through these layers in order and close them in reverse, and hernias happen where the layers are weakest. Learning the layers now gives you a mental "stack" that makes every abdominal diagram readable.
Source: OpenStax Anatomy and Physiology 2e — Axial Muscles of the Abdominal Wall, and Thorax
Biochemistry rewards big-picture thinking: learn what each pathway is for before you learn its steps, and the steps start to make sense on their own.
The central dogma is biology's core workflow: DNA is transcribed into RNA, and RNA is translated into protein. DNA is the archive, RNA the working copy, protein the machine that does the work. Almost every genetics and biochemistry question in M1 traces back to this flow — when something goes wrong at any step, you get disease.
Enzymes are protein catalysts: they speed up chemical reactions enormously by lowering the activation energy — the energetic "hill" a reaction must climb — without being consumed themselves. They are exquisitely specific, each fitting its substrate like a lock fits a key, and the cell regulates them to control every metabolic pathway. Our read: if you understand "enzymes lower activation energy and are regulated," you already understand half of what biochemistry exams ask about them.
Source: OpenStax Biology 2e — Enzymes
Glycolysis splits one glucose molecule into two pyruvates in the cytoplasm, netting a small amount of ATP — and it runs without oxygen, which is why red blood cells and sprinting muscles depend on it. It is the entry point to the rest of energy metabolism: with oxygen available, pyruvate feeds the citric acid cycle; without it, pyruvate becomes lactate. Learn the inputs, outputs, and regulation points first; the ten individual steps come later.
Source: NCBI Bookshelf (StatPearls) — Biochemistry, Glycolysis
Also called the Krebs cycle or TCA cycle, this mitochondrial loop takes the breakdown products of carbs, fats, and proteins and strips them of high-energy electrons (carried by NADH and FADH2). It doesn't make much ATP directly — its real job is feeding those electron carriers to the electron transport chain. Think of it as the hub where all fuels converge before the final payoff.
Source: NCBI Bookshelf (StatPearls) — Biochemistry, Citric Acid Cycle
The electron transport chain is a series of protein complexes in the inner mitochondrial membrane that passes electrons down an energy staircase, using the released energy to pump protons across the membrane. The resulting proton gradient then drives ATP synthase — the cell's turbine — to mass-produce ATP. This is oxidative phosphorylation, and it produces the vast majority of the cell's energy; poisons like cyanide kill by jamming this chain.
Source: NCBI Bookshelf (StatPearls) — Biochemistry, Electron Transport Chain
Twenty amino acids are the building blocks of proteins, and each protein's function comes from its shape — which comes from its amino acid sequence folding into helices, sheets, and a precise 3D form. Change one key amino acid and the shape can collapse: sickle cell disease is a single amino acid substitution in hemoglobin. Our read: M1 biochemistry keeps returning to this theme — sequence determines structure, structure determines function.
Source: NCBI Bookshelf (StatPearls) — Biochemistry, Primary Protein Structure
Physiology is the subject of "what happens next?" — learn each system as a story of disturbance and compensation, and exam questions start to solve themselves.
Homeostasis is the body's maintenance of stable internal conditions — temperature, blood sugar, blood pressure, pH — despite a changing outside world. Negative feedback loops do most of the work: a sensor detects a deviation, and the response pushes the value back toward normal (like a thermostat). Positive feedback, rarer, amplifies a change instead — childbirth contractions and blood clotting are the classic examples.
Source: NCBI Bookshelf (StatPearls) — Physiology, Homeostasis
The cardiac cycle is the repeating sequence of the heartbeat: the atria contract (filling the ventricles), the ventricles contract (ejecting blood to the lungs and body), then everything relaxes and refills. Valves snap shut between phases, producing the "lub-dub" heart sounds — and murmurs when they leak. If you can narrate one full cycle — what contracts, what the valves do, where blood goes — you own the foundation of cardiology.
Source: NCBI Bookshelf (StatPearls) — Physiology, Cardiac Cycle
The Frank-Starling law says the heart pumps out what it takes in: the more the ventricle fills during diastole (more stretch on the muscle fibers), the more forcefully it contracts. It is the heart's built-in way of matching output to venous return, beat by beat, with no nervous system input required. Our read: this single principle explains an outsized share of heart-failure questions — when the mechanism fails, fluid backs up.
Source: NCBI Bookshelf (StatPearls) — Physiology, Frank Starling Law
An action potential is the electrical spike that travels down a neuron (or muscle cell): sodium rushes in to depolarize the membrane, then potassium flows out to repolarize it. It is all-or-none — a neuron either fires fully or not at all — and its speed depends on axon diameter and myelin insulation. Everything the nervous system does, from reflexes to thought, is built from these spikes.
Source: NCBI Bookshelf (StatPearls) — Physiology, Action Potential
Glomerular filtration is the first step of urine formation: blood pressure forces water and small solutes out of the glomerular capillaries and into the nephron, while cells and large proteins stay in the blood. The glomerular filtration rate (GFR) — how much fluid is filtered per minute — is the single best measure of kidney function, and it is what clinicians estimate with creatinine-based equations. When GFR falls, waste accumulates: that is kidney failure in one sentence.
Source: NCBI Bookshelf (StatPearls) — Physiology, Glomerular Filtration Rate
For gas exchange to work, air reaching the alveoli (ventilation, V) must match blood reaching the capillaries (perfusion, Q). A V/Q mismatch — air without blood (like a pulmonary embolism) or blood without air (like pneumonia filling alveoli) — means oxygen can't get into the blood efficiently. Our read: nearly every respiratory failure question is secretly a V/Q question; learn the ratio and the two mismatch patterns and you're most of the way there.
Source: NCBI Bookshelf (StatPearls) — Physiology, Pulmonary Ventilation and Perfusion
Histology looks intimidating until you learn the visual vocabulary. These six give you the words to describe what you're seeing — and description comes before identification.
Epithelia are the body's coverings and linings — skin, gut lining, airways — classified by cell shape (squamous/flat, cuboidal, columnar) and layering (simple/single, stratified/multiple). The shape tells you the job: flat squamous cells suit diffusion in the lung, tall columnar cells suit absorption in the intestine. When you can name the shape and the layers, you can usually name the tissue.
Source: NCBI Bookshelf (StatPearls) — Histology, Epithelial Cell
Connective tissue is the body's packing material and scaffolding — everything from loose areolar tissue under the skin to dense tendons, cartilage, and bone — and what unites it is abundant extracellular matrix with relatively few cells. The matrix determines the function: collagen for tensile strength, elastin for stretch, ground substance for cushioning. Blood is even classified as a connective tissue, since its cells float in a fluid matrix.
Source: OpenStax Anatomy and Physiology 2e — Connective Tissue Supports and Protects
Three muscle types, three jobs: skeletal muscle (striated, voluntary — moves the skeleton), cardiac muscle (striated, involuntary, branched cells joined by intercalated discs — pumps the heart), and smooth muscle (non-striated, involuntary — squeezes hollow organs like the gut and blood vessels). On a slide, striations plus multiple peripheral nuclei means skeletal; striations plus a single central nucleus means cardiac; no striations means smooth.
Hematoxylin and eosin (H&E) is the standard stain behind the classic pink-and-purple slides: hematoxylin dyes nuclei blue-purple, eosin dyes cytoplasm and extracellular proteins pink. Pathologists read disease in these two colors — a darker, crowded nucleus can signal cancer; pink deposits can signal amyloid. Learning what each color marks is the first step to reading any slide.
Under the microscope, blood is mostly red cells — small, round, pink discs with a pale center and no nucleus — plus far fewer white cells with purple nuclei, each type with a signature look: neutrophils with multi-lobed nuclei, lymphocytes with a big round nucleus and thin blue rim, and so on. The differential count — the proportion of each white cell type — is one of medicine's most-used lab tests, and it starts with recognizing these shapes.
Source: NCBI Bookshelf (StatPearls) — Histology, Red Blood Cell
Bone is living tissue in constant turnover: osteoclasts dissolve old bone, osteoblasts lay down new bone, and the balance — remodeling — keeps the skeleton strong and repairs microdamage. Hormones like parathyroid hormone and vitamin D tune the process, which is why calcium disorders show up as bone disease. Our read: "resorption vs. formation" is the axis every bone question turns on.
Source: NCBI Bookshelf (StatPearls) — Physiology, Bone Remodeling
Genetics in M1 is equal parts molecular mechanism and pedigree puzzle. The mechanism half is below; the puzzles get fun once the vocabulary is in place.
Mendel's laws describe how traits pass from parents to children: each person carries two copies of each gene, one from each parent, and dominant alleles mask recessive ones. Autosomal dominant conditions appear in every generation; autosomal recessive ones can skip generations and cluster in consanguineous families. Drawing and reading pedigrees — the family-tree diagrams — is the skill exams actually test.
Before a cell divides, it copies its DNA so each daughter cell gets a complete genome: the double helix unzips, and each strand serves as a template for a new complementary strand (semi-conservative replication). DNA polymerase builds the new strands, proofreading as it goes — but mistakes slip through, and those mistakes are mutations. Fidelity matters because errors here become permanent.
Transcription is the first half of the central dogma: RNA polymerase reads a gene's DNA and synthesizes a messenger RNA copy. In eukaryotes the raw transcript is then processed — introns spliced out, a cap and tail added — before it leaves the nucleus for translation. Regulation mostly happens here: which genes get transcribed, and how much, is what makes a neuron different from a liver cell despite identical DNA.
Mutations range from single-letter swaps (point mutations — silent, missense, or nonsense depending on the effect on the protein) to insertions, deletions, and larger chromosomal rearrangements. Frameshift insertions or deletions scramble every codon downstream and are usually the most damaging. Cells run constant DNA repair to catch these errors; when repair fails, mutations accumulate — the first step toward cancer.
Source: OpenStax Biology 2e — DNA Repair
Hardy-Weinberg is the "null hypothesis" of population genetics: in an idealized population (large, random mating, no selection or migration), allele frequencies stay constant from generation to generation, following p² + 2pq + q² = 1. Exam questions use it to calculate carrier frequencies from disease prevalence — the classic being cystic fibrosis. Our read: memorize the equation and what each term counts, and these questions become free points.
Genes on the X chromosome show a distinctive pattern: males (XY) express whatever allele their single X carries, so X-linked recessive conditions like hemophilia and Duchenne muscular dystrophy affect males far more often. An affected father passes his X to all his daughters (making them carriers) but to none of his sons. When a pedigree shows mostly affected males connected through unaffected carrier females, think X-linked.
Source: NCBI Bookshelf (StatPearls) — Genetics, X-Linked Inheritance
The most human of the M1 subjects — and the one that quietly teaches you how your own studying works.
Classical conditioning pairs a neutral stimulus with a meaningful one until the neutral stimulus alone triggers the response (Pavlov's dogs salivating at a bell). Operant conditioning shapes voluntary behavior through consequences: reinforcement makes a behavior more likely, punishment makes it less so. Our read: notice that spaced repetition and practice questions are operant conditioning applied to yourself — you are already using this chapter.
Defense mechanisms are the ego's unconscious strategies for managing anxiety: denial (refusing to accept reality), projection (attributing your feelings to others), rationalization (inventing logical excuses), displacement, sublimation, and others. Exams love vignettes — "a man diagnosed with cancer insists the lab mixed up his results" — where the task is simply naming the mechanism. Learn the definitions with one example each and these questions answer themselves.
Source: OpenStax Psychology 2e — Freud and the Psychodynamic Perspective
The Kübler-Ross model describes common responses to loss — denial, anger, bargaining, depression, acceptance — originally observed in terminally ill patients and later applied to grief generally. Modern teaching stresses these are not a fixed sequence everyone passes through; people move between them, skip them, and revisit them. For the wards, the takeaway is simpler: recognize grief as normal, don't pathologize it, and don't rush it.
Sleep cycles through NREM stages (N1 light, N2 with sleep spindles and K-complexes, N3 deep slow-wave sleep) and REM sleep, where dreaming is vivid and the brain looks almost awake. Deep NREM dominates the first half of the night and consolidates declarative memory; REM dominates toward morning. Our read: this is the scientific case for not pulling all-nighters — the sleep you skip is the sleep that files what you studied.
Source: NCBI Bookshelf (StatPearls) — Physiology, Sleep Stages
Memory runs in three stages: encoding (getting information in — deepest when you process meaning, not just appearance), storage (holding it, from fleeting sensory memory to durable long-term memory), and retrieval (getting it back out). Every effective study technique maps onto this model: elaborative encoding, spaced retrieval practice, and cues at test time. Understanding the model turns "study tips" from folklore into engineering.
The biopsychosocial model holds that health and illness emerge from the interaction of biological, psychological, and social factors — not biology alone. A patient's back pain involves the disc (bio), their fear of movement (psycho), and their job demands (social); treating only one leg of the tripod often fails. It is the philosophical backbone of modern patient-centered care, and it shows up across behavioral science exams as the "most complete" framing.
Source: NCBI Bookshelf — The Biopsychosocial Model (SAMHSA exhibit)
Want to see these ideas in question form? The M1 foundations practice asks gentle, untimed questions on exactly this material — every answer explained. Or build a summer plan that works through them week by week.