---
title: "The Human Body"
description: "79 topics in Science, in the order they build on each other."
canonical: https://lightmysky.com/learn/science/areas/the-human-body
source: https://lightmysky.com/learn/science/areas/the-human-body.md
retrieved: 2026-10-19
---

> **Agent view.** This is the Markdown twin of the page, for tools and assistants.
> When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md
> API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md
> Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt
> Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json
> Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`.

# The Human Body

79 topics in Science, in the order they build on each other.

Page: https://lightmysky.com/learn/science/areas/the-human-body

- [Bones & Muscles](https://lightmysky.com/learn/science/bones-and-muscles-mt_SdIWVjzopp): Know that the body has a skeleton made of bones inside it that gives the body its shape and protects important organs like the brain (skull) and heart (ribcage), and that muscles attached to bones allow the body to move
- [How Breathing Works](https://lightmysky.com/learn/science/how-breathing-works-mt_tiPyEkm4cU): Know that we breathe air into our lungs through the nose and mouth, that our lungs take in oxygen from the air which our body needs to stay alive, and that we breathe out carbon dioxide as waste
- [The Brain Controls the Body](https://lightmysky.com/learn/science/the-brain-controls-the-body-mt_pJ5zsocdNx): Understand that the brain is the body’s control centre: it receives messages from the senses, thinks and makes decisions, and sends messages through nerves to tell muscles what to do
- [The Five Senses](https://lightmysky.com/learn/science/the-five-senses-mt_nwSWPTENmv): Explore the five senses in detail: sight uses eyes to detect light, hearing uses ears to detect sound, touch uses skin to feel pressure and temperature, taste uses the tongue to detect flavours, and smell uses the nose to detect odours
- [The Heart & Blood](https://lightmysky.com/learn/science/the-heart-and-blood-mt_lp1eTsQen7): Understand that the heart is a muscle that pumps blood around the body through tubes called blood vessels, and that we can feel our heartbeat by placing a hand on our chest or fingers on our wrist
- [Basic Body Needs](https://lightmysky.com/learn/science/basic-body-needs-mt_cxJRc15osy): Know that the body needs food for energy, water to stay hydrated, sleep to rest and grow, and exercise to keep muscles and the heart strong — and that these are basic needs every human body has
- [Balanced Diet & Food Groups](https://lightmysky.com/learn/science/balanced-diet-and-food-groups-mt_QhLAeAlHI0): Know the main food groups (carbohydrates, proteins, fats, vitamins, minerals, fibre, water) and understand that a balanced diet includes the right amounts from each group to keep the body healthy and provide energy, growth materials, and protection from illness
- [Cells, Tissues & Organs](https://lightmysky.com/learn/science/cells-tissues-and-organs-mt_C7FNeIDGc6): Understand that the body is organised in a hierarchy: tiny cells are the building blocks, groups of similar cells form tissues, tissues combine into organs (like the heart or stomach), and organs work together in organ systems (like the circulatory system)
- [How the Eye Works](https://lightmysky.com/learn/science/how-the-eye-works-mt_-gkJdxJUQT): Describe how the eye works: light enters through the pupil, the lens focuses it onto the retina at the back of the eye, and the retina sends signals along the optic nerve to the brain, which interprets the image
- [Naming Major Bones](https://lightmysky.com/learn/science/naming-major-bones-mt_OMmiuv9ZLH): Identify major bones of the human skeleton by name (skull, spine/vertebrae, ribcage, pelvis, femur, humerus) and explain the skeleton’s three jobs: supporting the body’s shape, protecting organs, and enabling movement with muscles
- [How Muscles Move Bones](https://lightmysky.com/learn/science/how-muscles-move-bones-mt_6N-4TqCleR): Understand that muscles work in pairs to move bones: when one muscle contracts (gets shorter and pulls), the opposite muscle relaxes, and that some muscles are voluntary (we choose to use them) while others like the heart are involuntary (they work automatically)
- [The Digestive Journey](https://lightmysky.com/learn/science/the-digestive-journey-mt_JpQUM1129q): Trace the journey of food through the digestive system: food enters the mouth where teeth break it down and saliva begins digestion, travels down the oesophagus to the stomach, passes through the small intestine where nutrients are absorbed, and waste moves through the large intestine
- [Types of Teeth](https://lightmysky.com/learn/science/types-of-teeth-mt_I047mKeeaq): Identify the four types of human teeth (incisors for cutting, canines for tearing, premolars and molars for grinding) and understand that tooth shape is linked to function, just as in other animals — herbivores have flat teeth, carnivores have sharp teeth
- [Growing Up & Puberty](https://lightmysky.com/learn/science/growing-up-and-puberty-mt_pu2mmK27UA): Describe the stages of human development from birth to old age: baby, toddler, child, adolescent (puberty), young adult, middle-aged adult, elderly — understanding the physical changes that happen at each stage, especially during puberty
- [Heart & Blood Circulation](https://lightmysky.com/learn/science/heart-and-blood-circulation-mt_g_M4Vh_pK7): Describe the circulatory system in detail: the heart has four chambers (two atria, two ventricles) that pump blood in a double loop — one to the lungs for oxygen and one to the rest of the body to deliver it — through arteries, veins, and tiny capillaries
- [How the Lungs Work](https://lightmysky.com/learn/science/how-the-lungs-work-mt_zPDDJLAl-J): Explain how the respiratory system works in detail: air travels through the nose/mouth, down the trachea, into bronchi and bronchioles, reaching tiny air sacs (alveoli) in the lungs where oxygen passes into the blood and carbon dioxide passes out
- [Circulation & Breathing Together](https://lightmysky.com/learn/science/circulation-and-breathing-together-mt_QK-ZZb7UUN): Understand how the circulatory and respiratory systems work together: the lungs oxygenate the blood, the heart pumps it around the body, cells use the oxygen and produce carbon dioxide waste, and the blood carries the waste back to the lungs to be breathed out
- [The Immune System](https://lightmysky.com/learn/science/the-immune-system-mt_4JpMXUIxeD): Know that the body has an immune system that protects against illness: the skin acts as a barrier, white blood cells identify and destroy germs (bacteria and viruses), and vaccines train the immune system to recognise specific diseases before they cause illness
- [Healthy Lifestyle Choices](https://lightmysky.com/learn/science/healthy-lifestyle-choices-mt_4k3HGahK2k): Understand how lifestyle choices affect the body’s health: a balanced diet, regular exercise, adequate sleep, and avoiding harmful substances (tobacco, alcohol, drug misuse) help body systems function well, while poor choices increase the risk of disease
- [The Nervous System](https://lightmysky.com/learn/science/the-nervous-system-mt_qzbgwaUQOA): Understand that the nervous system has two parts: the central nervous system (brain and spinal cord) and nerves that branch throughout the body. Nerve signals travel at high speed to coordinate senses, thought, and movement
- [Immunity & Vaccines](https://lightmysky.com/learn/science/immunity-and-vaccines-mt_LkOMijDvL7): Distinguish innate (non-specific, immediate) from adaptive (specific, memory-forming) immunity; explain how B cells produce antibodies that recognise specific antigens, how T cells destroy infected cells, and why immunological memory makes vaccines work; and describe the gut microbiome as a community of trillions of microbes that significantly influences immune function
- [Neurons & Brain Structure](https://lightmysky.com/learn/science/neurons-and-brain-structure-mt_okUMpHsV-P): Explain how neurons transmit signals as electrochemical impulses across chemical synapses; describe how the brain is organised (lobes and functions, limbic system for emotion); and explain neuroplasticity, why learning and practice physically change brain structure, using optical illusions as evidence that the brain constructs reality rather than passively recording it
- [DNA & Genes](https://lightmysky.com/learn/science/dna-and-genes-mt_0sELh0MYWb): Describe the double helix structure of DNA (base pairs, complementarity), explain how genes are sections of DNA that code for proteins, introduce the central dogma (DNA → mRNA → protein) conceptually, and discuss the ethical implications of CRISPR gene editing — including potential benefits (genetic disease treatment) and concerns (germline editing, 'designer babies')
- [How the Body Stays in Balance](https://lightmysky.com/learn/science/how-the-body-stays-in-balance-mt_J40cOn7VWn): Explain homeostasis as the process of maintaining a stable internal environment; describe the main feedback loop systems (negative feedback) using blood glucose regulation (insulin/glucagon) and body temperature as concrete examples; and connect the endocrine system (hormone-secreting glands) to the nervous system as two complementary communication systems with different speeds and durations
- [Cancer & Stem Cells](https://lightmysky.com/learn/science/cancer-and-stem-cells-mt_roinupb_7L): Explain that cancer occurs when mutations in DNA disable normal cell-cycle controls, causing uncontrolled cell division and tumour formation; describe how stem cells differ from specialised cells and their potential for regenerative medicine; and evaluate the ethical debates around embryonic stem cell research and genetic testing
- [The Reflex Arc and Synapses](https://lightmysky.com/learn/science/the-reflex-arc-and-synapses-mt_evlgCVxTnK): A withdrawal reflex runs receptor to sensory neurone to relay neurone to motor neurone to effector, with no decision from the conscious brain in this arc. Covers the chemical synapse gap and why that gap is the slow step.
- [Hormones and Negative Feedback](https://lightmysky.com/learn/science/hormones-and-negative-feedback-mt_OBa6BHmW29): A hormone travels in the blood, often acts more slowly and for longer than a nerve impulse, and reaches every organ, which is the opposite trade-off from a nerve impulse. Negative feedback usually holds a quantity near a set point by acting against whichever way it moved.
- [Blood Glucose Control and Diabetes](https://lightmysky.com/learn/science/blood-glucose-control-and-diabetes-mt_eOzNtiBvX2): Insulin and glucagon push blood glucose back towards its set point after a meal or a long gap without one. Type 1 and type 2 diabetes break the loop at different places, which is why the treatments differ.
- [Hormones in the Menstrual Cycle and Fertility](https://lightmysky.com/learn/science/hormones-in-the-menstrual-cycle-and-fertility-mt_DENo5Fbr1d): Four hormones run the monthly cycle: FSH and LH from the pituitary, oestrogen and progesterone from the ovaries. The same loop explains how hormonal contraception and fertility treatment work.
- [Blood Components and Blood Vessels](https://lightmysky.com/learn/science/blood-components-and-blood-vessels-mt_aWZ2sGXGMn): Plasma, red cells, white cells and platelets each carry a different job, and arteries, veins and capillaries are built for the pressures they meet. Explains why a red blood cell has no nucleus and why a capillary wall is one cell thick.
- [Heart Rate, Stroke Volume and Cardiac Output](https://lightmysky.com/learn/science/heart-rate-stroke-volume-and-cardiac-output-mt_mjrPFHgvfx): Cardiac output is stroke volume multiplied by heart rate, and breathing follows the same shape as tidal volume multiplied by breathing rate. Use both to compare a person at rest with the same person exercising.
- [How Communicable Diseases Spread](https://lightmysky.com/learn/science/how-communicable-diseases-spread-mt_o__-bF814q): Bacteria, viruses, fungi and protists spread through air, water, direct contact or a vector, and each route points at a different way to break the chain. Uses named human and plant diseases.
- [Non-Communicable Disease and What Counts as a Risk Factor](https://lightmysky.com/learn/science/non-communicable-disease-and-what-counts-as-a-risk-factor-mt_IciZ1CJn6h): Diseases that nobody catches still have causes, and those causes are usually a raised probability rather than a certainty. Separating a correlation in a population from a demonstrated mechanism in a body is the core skill here.
- [The Brain: Regions and the Evidence for What They Do](https://lightmysky.com/learn/science/the-brain-regions-and-the-evidence-for-what-they-do-mt_BA_DGCDic8): The brain is not one organ doing one job, and the map of which region does what was built from damage, stimulation and scanning rather than from looking. Knowing how that evidence was gathered is what stops the map from being a set of labels to memorise.
- [The Eye as a Receptor Organ](https://lightmysky.com/learn/science/the-eye-as-a-receptor-organ-mt_fslwsM3I7F): The eye converts light into nerve impulses, and every part of it exists to serve that conversion: the lens to focus, the iris to control intensity, the retina to transduce. The common sight defects are all failures of focus, and each correction follows from where the image lands.
- [Vaccination and Antibiotic Resistance](https://lightmysky.com/learn/science/vaccination-and-antibiotic-resistance-mt_XmDqQONako): A vaccine trains the immune system with a harmless form of a pathogen so the second response is fast enough to stop illness. Antibiotics kill bacteria and do nothing to viruses, and resistant strains spread when antibiotics are overused.
- [The Specific Immune Response: Phagocytes, T Cells and B Cells](https://lightmysky.com/learn/science/the-specific-immune-response-phagocytes-t-cells-and-b-cells-mt_hqI22Uey2k): Beyond the general defences sits a response tailored to one antigen, built by cells that recognise a shape and then divide. Memory cells are why the second exposure is faster, and they are what a vaccine is actually for.
- [Haemoglobin, the Dissociation Curve and the Bohr Shift](https://lightmysky.com/learn/science/haemoglobin-the-dissociation-curve-and-the-bohr-shift-mt_MmYJArGxrE): The oxygen dissociation curve is S-shaped because binding the first oxygen makes the next one easier. Carbon dioxide shifts the whole curve to the right, so tissue that is working hard gets unloaded first.
- [Monoclonal Antibodies and What They Are Used For](https://lightmysky.com/learn/science/monoclonal-antibodies-and-what-they-are-used-for-mt_YfxZrdvIIo): One antibody-producing cell fused to a dividing one gives an unlimited supply of a single antibody, and that single specificity is the whole point. Pregnancy tests, diagnostic stains and targeted cancer drugs are three uses of the same trick.
- [The Cardiac Cycle and Pressure in the Heart](https://lightmysky.com/learn/science/the-cardiac-cycle-and-pressure-in-the-heart-mt_iOSVyoV3Pj): Valves open and shut because of pressure differences, not because of nerve signals, and a pressure trace shows it. Reading the trace explains the order of atrial and ventricular contraction.
- [The Resting Potential and the Action Potential](https://lightmysky.com/learn/science/the-resting-potential-and-the-action-potential-mt_0sh4w30ocz): A neurone holds its inside negative by pumping sodium out and potassium in, and an impulse is that difference briefly reversing. Voltage-gated channels open in sequence and the membrane resets behind the impulse.
- [Conduction Speed: Myelination and the Refractory Period](https://lightmysky.com/learn/science/conduction-speed-myelination-and-the-refractory-period-mt_x3M0sv6oD6): Myelin makes the impulse jump between gaps, so a myelinated axon conducts far faster than a bare one of the same width. The refractory period caps the frequency and keeps the impulse travelling one way.
- [Synaptic Transmission, Summation and Inhibition](https://lightmysky.com/learn/science/synaptic-transmission-summation-and-inhibition-mt_0uM8xRV92B): Calcium entry makes vesicles release transmitter, which binds receptors on the next cell. Several small inputs can add up, and some synapses make the next cell harder to fire rather than easier.
- [The Sliding Filament Model of Muscle Contraction](https://lightmysky.com/learn/science/the-sliding-filament-model-of-muscle-contraction-mt_BsB4s4HfD8): Calcium released inside a fibre uncovers binding sites, and myosin heads pull actin filaments past each other in a repeating cycle that spends ATP. The filaments do not shorten; their overlap grows.
- [Tissue Fluid and Its Return to the Circulation](https://lightmysky.com/learn/science/tissue-fluid-and-its-return-to-the-circulation-mt_0jw7uXpK3C): Hydrostatic pressure forces fluid out of a capillary at the arteriole end, and water potential pulls most of it back at the venule end. Whatever is left returns through the lymph vessels.
- [Ultrafiltration and Selective Reabsorption in the Nephron](https://lightmysky.com/learn/science/ultrafiltration-and-selective-reabsorption-in-the-nephron-mt_vSKfoJN6zh): The glomerulus filters blood by the same pressure argument as any capillary, only harder, and the tubule then takes back what the body needs. Filtration and reabsorption are separate steps with separate mechanisms.
- [Osmoregulation and the Action of ADH](https://lightmysky.com/learn/science/osmoregulation-and-the-action-of-adh-mt_Rz_MmL-Pa-): The water potential of blood is held steady by changing how much water the collecting duct takes back. ADH is the signal and the permeability of one tubule wall is the effector.
- [Equilibrium Potentials and What Sets the Resting Voltage](https://lightmysky.com/learn/science/equilibrium-potentials-and-what-sets-the-resting-voltage-mt_mRT_5vDEO1): Each ion has a voltage at which its electrical pull balances its concentration gradient, and that value can be calculated from the two concentrations. The membrane sits near the equilibrium potential of whichever ion it is currently most permeable to.
- [Channel Kinetics and the Ionic Basis of the Spike](https://lightmysky.com/learn/science/channel-kinetics-and-the-ionic-basis-of-the-spike-mt_47-LDzgcKp): The action potential comes from two channel populations with different speeds: sodium channels that open fast and then inactivate, and potassium channels that open late. Clamping the voltage and measuring the current is what separated those two currents.
- [Cable Properties and Dendritic Integration](https://lightmysky.com/learn/science/cable-properties-and-dendritic-integration-mt_bbPl-eJUFF): A voltage change spreads along a dendrite and fades with distance, at a rate set by membrane resistance and internal resistance. Inputs arriving close together in time and space add up, and only their sum at the trigger zone decides whether a spike is fired.
- [Tissue Types and How a Body Is Organised](https://lightmysky.com/learn/science/tissue-types-and-how-a-body-is-organised-mt_dQ-glI4kdz): Every organ is built from four tissue types, and knowing which one you are looking at tells you what it can do: cover a surface, connect and support, contract, or signal. Reading a section under a microscope is a matter of matching structure to that short list.
- [Bone, Cartilage and the Mechanics of a Joint](https://lightmysky.com/learn/science/bone-cartilage-and-the-mechanics-of-a-joint-mt_1_q3aL7E5D): Bone is a living connective tissue that is constantly rebuilt in response to load, which is why it heals and why it thins when unloaded. A joint is then a mechanical problem: the shapes of the surfaces set what movements are possible, and the muscles that cross it set which ones happen.
- [Pacemaker Potentials, Conduction and Reading an ECG](https://lightmysky.com/learn/science/pacemaker-potentials-conduction-and-reading-an-ecg-mt_D-WKFc7BZm): Heart cells that drift towards threshold on their own set the rhythm, and the wave they start spreads through the muscle by a fixed route with a deliberate delay. The trace recorded at the skin is the sum of those events, so each deflection can be named.
- [Preload, Afterload and the Frank-Starling Relationship](https://lightmysky.com/learn/science/preload-afterload-and-the-frank-starling-relationship-mt_WK8o6OPZ-O): A heart that fills more stretches more and ejects more, which is how the two sides keep matched output without any signal between them. Output is set by filling, by the resistance the heart pumps against and by contractility.
- [Regional Anatomy of the Central Nervous System](https://lightmysky.com/learn/science/regional-anatomy-of-the-central-nervous-system-mt_S9f5cUS8NZ): The brain and spinal cord are organised into regions with distinct cell populations and connections, and the pathways between them run in predictable places. Knowing where a tract runs is what lets a clinician infer the site of damage from the pattern of loss.
- [From Photons to Spikes: the Retina](https://lightmysky.com/learn/science/from-photons-to-spikes-the-retina-mt_kviN7WskmP): A photoreceptor works backwards from most sensory cells: light closes channels and the cell hyperpolarises. The retina then does real processing before anything leaves the eye, subtracting a centre from its surround so that what the optic nerve carries is contrast rather than brightness.
- [Transmitter Systems and Two Kinds of Receptor](https://lightmysky.com/learn/science/transmitter-systems-and-two-kinds-of-receptor-mt_yXaSbrBxua): A transmitter can open a channel directly or act through a receptor that starts an internal cascade, which makes one effect fast and brief and the other slow and lasting. The same transmitter can do both, depending on which receptor the target cell carries.
- [Synaptic Plasticity and the Molecular Rules of Change](https://lightmysky.com/learn/science/synaptic-plasticity-and-the-molecular-rules-of-change-mt_HldevO4Lzw): A synapse strengthens when its input arrives just before the target cell fires, and weakens when the timing is reversed. Calcium entry through receptors that need both transmitter and depolarisation is what detects the coincidence.
- [Building a Visual Scene: Pathways, Maps and Receptive Fields](https://lightmysky.com/learn/science/building-a-visual-scene-pathways-maps-and-receptive-fields-mt_wOc4YpkdYL): Beyond the retina the visual system is a set of maps in which neighbouring cells look at neighbouring parts of the world, and each cell responds best to a specific feature in its own small window. What a cell prefers gets more elaborate at each stage, from edges to objects.
- [Hormone Classes and Why Their Receptors Sit in Different Places](https://lightmysky.com/learn/science/hormone-classes-and-why-their-receptors-sit-in-different-places-mt_GAg2xTiKVL): Water-soluble hormones cannot cross the membrane, so they bind receptors on the surface and act through cascades within seconds. Steroid and thyroid hormones cross, bind receptors inside and change transcription, which takes hours but lasts longer.
- [Hypothalamic and Pituitary Axes and Layered Feedback](https://lightmysky.com/learn/science/hypothalamic-and-pituitary-axes-and-layered-feedback-mt_tgRAAq3Poe): Several hormone systems run through three levels, with each level releasing a hormone that drives the next and the final product suppressing both levels above it. That arrangement gives amplification going down and stability coming back.
- [The Autonomic Nervous System and Its Two Outflows](https://lightmysky.com/learn/science/the-autonomic-nervous-system-and-its-two-outflows-mt_bnVgu4T4E9): A separate motor system runs the organs without conscious control, through two outflows that leave the cord at different levels and usually oppose each other. Because each outflow uses its own transmitters and receptors, most drugs that affect heart rate, pupils or gut motility act here.
- [Resistance, Flow and the Regulation of Blood Pressure](https://lightmysky.com/learn/science/resistance-flow-and-the-regulation-of-blood-pressure-mt_EvmGvDGNja): Flow through a vessel depends steeply on its radius, so small changes in arteriole diameter make large changes in resistance. Pressure is held within range by fast reflexes that adjust rate, contractility and diameter, and by slower control of blood volume.
- [Lung Mechanics: Compliance, Surface Tension and the Work of Breathing](https://lightmysky.com/learn/science/lung-mechanics-compliance-surface-tension-and-the-work-of-breathing-mt_vNZEKuTjYQ): Filling the lungs means overcoming both the stretch of the tissue and the surface tension of the film lining each alveolus. Surfactant lowers that tension more in small alveoli than in large ones, which stops the small ones emptying into the big ones.
- [Touch, Temperature and Pain](https://lightmysky.com/learn/science/touch-temperature-and-pain-mt_rnSuJA4-kj): Skin receptors encode mechanical, thermal and potentially damaging stimuli. Receptor density, receptive fields and central connections help explain tactile acuity and the distorted cortical body map. Spinal and descending modulation help explain why felt pain does not directly measure tissue damage.
- [Hearing and Balance: Frequency, Place and Head Motion](https://lightmysky.com/learn/science/hearing-and-balance-frequency-place-and-head-motion-mt_qzPAt9JMOZ): The cochlea sorts sound by frequency mechanically, so position along it stands for pitch before any neuron is involved. The same kind of hair cell, placed in fluid-filled loops instead, reports how the head is turning, which is why one organ serves two senses.
- [Ventilation and Perfusion Matching, and the Control of Breathing](https://lightmysky.com/learn/science/ventilation-and-perfusion-matching-and-the-control-of-breathing-mt_O89KdcN_Vv): Gas exchange only works where air and blood arrive in the right ratio, and local vessel and airway responses steer both towards the regions that need them. Breathing rate is set mainly by carbon dioxide sensed as a change in pH, not by oxygen.
- [Acid-Base Balance: The Bicarbonate System and Compensation](https://lightmysky.com/learn/science/acid-base-balance-the-bicarbonate-system-and-compensation-mt_LFLgZre62C): Blood pH is held in a narrow range by a buffer whose two components are controlled separately: carbon dioxide by the lungs and bicarbonate by the kidneys. Because one is fast and the other slow, a disturbance in one can be partly offset by the other.
- [Motor Control: From Intention to Muscle](https://lightmysky.com/learn/science/motor-control-from-intention-to-muscle-mt_hrWOuRtPDl): Movement is produced by a hierarchy: the cord holds reflex circuits and pattern generators, the brainstem handles posture, and the cortex specifies what to do rather than which muscle to use. Errors are corrected by loops through the cerebellum and basal ganglia, which is why damage there degrades movement without paralysing it.
- [Memory Systems: What Amnesia Separates](https://lightmysky.com/learn/science/memory-systems-what-amnesia-separates-mt_oNFXpEHl8b): Memory is not one store: patients who cannot form new episodes still learn skills, and that dissociation is the main evidence that different structures do different jobs. The hippocampus is needed to acquire an episode but not to keep it forever, which is why consolidation is treated as a separate process.
- [Sleep, Circadian Rhythms and the Clock in the Brain](https://lightmysky.com/learn/science/sleep-circadian-rhythms-and-the-clock-in-the-brain-mt_cXx4SaLJUM): A clock built from a gene loop inside single cells runs near a day, and light resets it through a dedicated pathway from the retina. Sleep itself is a sequence of states with distinct electrical signatures, and what is lost when it is disrupted is a way of testing what those states are for.
- [Fuel Homeostasis and the Fed to Fasted Switch](https://lightmysky.com/learn/science/fuel-homeostasis-and-the-fed-to-fasted-switch-mt_zZrXwbWqw-): After a meal insulin drives storage, and as fuel runs low glucagon and the counter-regulatory hormones release it again, with the liver switching direction between the two states. The switch is a pair of opposing signals acting on the same enzymes.
- [The Stress Response: Fast Nerves, Slow Hormones and the Cost of Staying On](https://lightmysky.com/learn/science/the-stress-response-fast-nerves-slow-hormones-and-the-cost-of-staying-on-mt_4ZxCU21ziH): A threat triggers a nerve-driven response in seconds and a hormone-driven one over minutes to hours, and the two do different jobs. The system is useful when it switches off, and much of its damage comes from staying on.
- [Innate Immunity: Pattern Recognition, Complement and Inflammation](https://lightmysky.com/learn/science/innate-immunity-pattern-recognition-complement-and-inflammation-mt_3TcgoOGI0L): The first response recognises molecular patterns shared by whole classes of microbe rather than any particular one, so it works within minutes without prior exposure. Complement proteins and the changes of inflammation both bring more defence to the site.
- [Adaptive Immunity: Antigen Presentation and T-Cell Selection](https://lightmysky.com/learn/science/adaptive-immunity-antigen-presentation-and-t-cell-selection-mt_8hTGqrnqGY): Cells display fragments of the proteins inside them on surface molecules, and T cells inspect those displays. Because the useful receptors are selected during development, the system reacts to what is foreign and normally ignores what is not.
- [Antibody Diversity, Memory and What Tolerance Failure Costs](https://lightmysky.com/learn/science/antibody-diversity-memory-and-what-tolerance-failure-costs-mt_5YXKhiOqoA): A limited set of gene segments is rearranged and mutated to give an enormous range of antibodies, and the cells that bind best are selected and kept. Memory explains why a second exposure is faster and stronger, and failures of tolerance explain autoimmunity and allergy.
- [Checkpoint Blockade: Taking a Brake Off a T Cell](https://lightmysky.com/learn/science/checkpoint-blockade-taking-a-brake-off-a-t-cell-mt_f9P4LlaBGb): Inhibitory receptors that normally limit T-cell responses are used by tumours to avoid killing, and antibodies against those receptors restore it in a minority of patients. This stop covers the mechanism, the markers that predict response, and the autoimmune cost.
- [Engineered Cell Therapy: Receptor Design, Manufacture and Toxicity](https://lightmysky.com/learn/science/engineered-cell-therapy-receptor-design-manufacture-and-toxicity-mt_e15TOnMMwL): A chimeric antigen receptor gives a patient's own T cells a new specificity that does not depend on antigen presentation. This stop follows the design choices through manufacture and into the toxicities they cause.
- [Clinical Trials: Phases, Endpoints and Why Most Candidates Fail](https://lightmysky.com/learn/science/clinical-trials-phases-endpoints-and-why-most-candidates-fail-mt_xKBKzSYxLh): Trial design decides what a result is allowed to claim: which patients, which comparator, which endpoint measured when. This stop reads a protocol and locates the point at which most candidates stop.